Climate (Ex) Change – Eco-engineering in the Dollart
1
2010
J.J. Punter, C.A. Gerbers, J.M Luursema
Hanze University of Applied Sciences
Groningen
7-6-2010
Eco-engineering in the Dollart
Climate (Ex) Change – Eco-engineering in the Dollart
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Title: Eco-Engineering in the Dollart
Authors: J.J. Punter 296441
C.A. Gerbers 294255
J.M. Luursema 292262
Date: 07-06-2010, Groningen
Teachers & Lecturers:
O.M. Akkerman
D. Krol
J. Postma
H. Revier
T. Van de Maarel
Cooperating companies
and institutes: Waterschap Hunze en Aa’s
Jade Hochschule
Ingenieurs- en adviesbureau Tauw
Waterschap Noorderzijlvest
Deichacht Rheiderland
Provincie Groningen
Hogeschool Van Hall Larenstein
Stenden Hogeschool
Internationaal Waddenzee
Secretariaat
Waddenacademie
Openbaar Lichaam Eems Dollart
Regio
Groninger Landschap
National Wattenmeer
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Foreword
The report “Eco-engineering in the Dollart” that lies in front of you is the results of five months
graduation by three 4th year students at the Hanze University of applied sciences in Groningen, at
the faculty of Civil Engineering. During the research, that took place between February 2010 and June
2010, we attempted to find solutions for the coastal defense in the Dollart region. The solutions
should give a new vision how to change the current embankment to improve safety and also increase
the value for nature development and recreation.
We would like to thank the following people who helped with our investigation. Ton van de Maarel
and Hans Revier from “Kenniscentrum Gebiedsontwikkeling Noorderruimte”; Olof Akkerman,
Doutzen Krol and Jaap Postma as supervisors and assessors and finally Kampe Lentz from
“Waterboard Hunze en Aa’s”. Besides that we would like to thank the following institutes:
Waterboard Hunze en Aa’s, Province Groningen, Ministery of Transport, Public works and Water
management and “Technische Adviescommissie voor de Waterkeringen”
We hope that the results will give a good vision of the alternative dike revetments and -designs
available today and the applicability for the Dollart region.
Jelmer Punter
Christiaan Gerbers
Jeroen Luursema
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Summary
After reading this report, you will get to know more about ecological engineering in the Dollart
region. An investigation is performed on how to combine the safety of dikes with nature
development. The main question of the research:
What are the possibilities of applying ecological dike concepts in the Ems Dollart region?
This question is divided in five sub-questions.
• What are the properties of the current coastline in the Dollart?
• In what way are the dikes constructed?
• What are the loads on the dikes at this moment and in 2100?
• Do the existing dikes meet the current safety requirements and what are the safety
requirements in 2100?
• Which new ecological concepts are available on the market?
Properties of the Dollart coast
The coast is homogeneous in its properties besides the trajectory along polder Breebaart. This is the
only part of the Dollart coast without marshes in front of the coast. The embankment is designed at
10,20 m +NAP, but the current crest height is lower everywhere along the coast. On the West side
the crest height is lowest, with a minimum of 7,3 m + NAP. This could be contributed to gas
extraction and local subsidence but this is not investigated.
Dike construction
The current dikes are constructed with a sand core, and an outer layer of 0,8 m with clay and a grass
revetment. The old clay dike is used on the land side of the dike and incorporated in the core. The
crest height is determined using the following steps:
Determining a reference level with an exceedance probability corresponding to the legal standards.
Adding the sea level rise during the design period
Adding the soil subsidence during the design period
Adding additions for shower oscillations, storm blows, seiches1 and local storm surges
Adding the expected crest subsidence due to settlement of the embankment and its foundation
during the design period.
Adding the height for wave run up or wave overtopping.
Loads
The loads on the current dikes are determined in 1960. The highest wave height is 1,25 m and the
review level deviates between 6,5 and 6,7 m +NAP. Since then there has been no research
publication about the hydraulic boundaries. In this research the calculation for the crest height is
made manually and with computer software CRESS. This resulted in needed crest heights Cx for three
normative profiles (x) in the future with the expected sea level rise of 1,20 m:
C4 = 10,84 m
C10 = 10,17 m
C14= 10,15 m
1 A seiche is a standing wave in an enclosed or partially enclosed body of water
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Safety requirements
The Dollart region is an estuary with specific properties. During this research it became clear that
during a storm the water level can increase dramatically. Were the normal high tide is 1.5 m +NAP
do the hydraulic conditions say that a water level can be as high as 6.8 meter + NAP at Nieuwe
Statenzijl. This extreme high water level is caused by the fact that storm surges occur in the Dollart.
The fact that the Dollart is a bay also contributes to the extreme high water, water is enclosed and
the only way is up. Waves in the Dollart a relative low when compared to the Dutch and German
coast. The waves are according the hydraulic condition on the Dutch Dollart coast 0.9 meter at Punt
van Reide and up to 1.25 meter at Nieuwe Statenzijl. The wave height at the German dikes is
unknown but is to be expected be higher than 1.25 meter.
Ecological concepts
The ecological concepts that are most interesting are those without the use of ecological hard
revetments. The revetments aren’t useful because the Dollart dikes aren’t wet. Changing the shape
of the dike could be interesting because slope changes can result in decreased wave run-up and
overtopping. Raising the crest height has similar results. The Dollart coast is divided in four sections
and for each section this research gives a recommended concept. These concepts are not final
designs, they have to be worked out further.
Conclusion
The use of ecological materials only doesn’t contribute to nature development. Other ways have to
be found to combine nature development with coastal safety.
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Index
1 INTRODUCTION 10
1.1 MOTIVATION 10
1.2 PROBLEM DEFINITION AND RESEARCH QUESTIONS 11
1.2.1 MAIN RESEARCH QUESTION 12
1.2.2 SUB-QUESTIONS 12
1.2.3 RESEARCH GOALS 12
1.2.4 RESEARCH RESULTS 12
1.2.5 RESEARCH AREA 13
1.2.6 REPORT STRUCTURE 14
2 ANALYSIS OF THE DOLLART COAST 15
2.1 ANALYSIS FORESHORE 17
2.2 ANALYSIS EMBANKMENT 17
2.2.1 THE REVETMENT OF THE CURRENT DIKES 18
2.2.2 CREST HEIGHT 18
2.2.3 MANUAL CALCULATION WAVE OVERTOPPING 22
2.2.4 CREST HEIGHT CALCULATION WITH COMPUTER PROGRAM CRESS 30
2.2.5 REVIEW LEVEL AND ALLOWANCE 33
2.2.6 ROAD TYPES AND MANAGEMENT 35
2.2.7 DUTCH DIKE STRUCTURE 35
2.2.8 LOADS , SIGNIFICANT WAVE HEIGHT & TIDES 36
2.2.9 GERMAN DOLLART DIKES 36
2.3 CONCLUSIONS CHAPTER 2 ANALYSIS OF THE DOLLART COAST 37
3 ECO ENGINEERING 39
3.1 INTRODUCTION 39
3.2 OVERVIEW INVESTIGATED ECO MATERIALS & METHODS 39
3.2.1 EVALUATION CRITERIA 40
3.3 ECO MATERIALS 41
3.3.1 PILE BUNDLES 41
3.3.2 ECO XBLOC’S 42
3.3.3 ARMORFLEX 44
3.3.4 C-STAR® COASTAL ELEMENTS 45
3.3.5 VETIVER 47
3.3.6 ELASTOCOAST 49
3.3.7 HYDROTEX 50
3.3.8 SMART GRASS REINFORCEMENT 52
3.3.9 ROAD SURFACING MATERIALS 53
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3.4 ECO METHODS 56
3.4.1 INCREASED OVERTOPPING 56
3.4.2 ADJUSTMENTS OF DIKE SLOPE 58
3.5 MULTI-CRITERIA ANALYSIS 59
3.5.1 CONCLUSIONS MCA’S 62
3.6 CONCLUSIONS CHAPTER 3 ECO ENGINEERING 63
4 CONCEPTS 64
5 CONCLUSIONS 71
6 RECOMMENDATIONS 73
7 DEFINITIONS 74
8 BIBLIOGRAPHY 76
APPENDIX 1: HYDRAULIC CONDITIONS EMS-DOLLART REGION 78
APPENDIX 2: TIDE TABLE NIEUWE STATENZIJL 79
APPENDIX 3: CALCULATION OF THE OVERTOPPING CAPACITY OF THE RETENTION BASIN 80
APPENDIX 4: OVERTOPPING CALCULATIONS WITH CRESS 82
CALCULATION DIKE PROFILE 4 CURRENT HYDRAULIC CONDITIONS 82
CALCULATION DIKE PROFILE 10 CURRENT HYDRAULIC CONDITIONS 83
CALCULATION DIKE PROFILE 10 FUTURE HYDRAULIC CONDITIONS 84
CALCULATION DIKE PROFILE 14 CURRENT HYDRAULIC CONDITIONS 85
CALCULATION DIKE PROFILE 14 FUTURE HYDRAULIC CONDITIONS 86
CALCULATION DIKE PROFILE 14 FUTURE HYDRAULIC CONDITIONS WITH SLOPE 1:6 87
CALCULATION DIKE PROFILE 14 FUTURE HYDRAULIC CONDITIONS WITH SLOPE 1:8 88
APPENDIX 5: CALCULATION WAVE PERIODS 89
APPENDIX 6: MANUAL CALCULATION WAVE OVERTOPPING 91
APPENDIX 7: MULTI CRITERIA ANALYSIS 99
APPENDIX 8: DRAWINGS CROSS-SECTION 4, 10, 14 103
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Figures
Figure 1: Overview of the research area, red line shows dike trajectory ________________________________ 13
Figure 2: Overview of cross sections of the Dutch Dollart coast ______________________________________ 15
Figure 3: Additions to the reference level to determine the height of the dikes __________________________ 19
Figure 4: Relation between crest height and overtopping after sea level rise of 1,20m ____________________ 22
Figure 5: Relation between the volume of wave overtopping and the crest height _______________________ 24
Figure 6: Determination of the characteristic slope for a cross section consisting of different slopes _________ 25
Figure 7: Relation between wave run-up and length of the “average” slope of the dike ___________________ 25
Figure 8: Relation between the volume of overtopping waves and the length of the “average”slope ________ 26
Figure 9: Relation between the wave run-up and the bermwidth _____________________________________ 26
Figure 10: Relation between the volume of overtopping waves and the bermwidth ______________________ 27
Figure 11: Relation between the angle of wave attack and volume of overtopping waves _________________ 28
Figure 12: Relation between SWL and the wave run-up ____________________________________________ 29
Figure 13: Relation between the volume of overtopping waves and review level ________________________ 29
Figure 14: Relation between the volume of overtopping waves and the significant wave height ____________ 30
Figure 15: Crest height and review level of the Dutch embankment ___________________________________ 33
Figure 16: Soil subsidence in the North of Groningen (‘Daling’ means subsidence in Dutch) ________________ 34
Figure 17: Freeboard (distance between the review level and the crest) _______________________________ 34
Figure 18: Dutch Dollart dike structure with seaside on the right. ____________________________________ 35
Figure 19: German construction methods _______________________________________________________ 37
Figure 20: Current German dike structure _______________________________________________________ 37
Figure 21: pile bundles _______________________________________________________________________ 41
Figure 22: Eco Xbloc's _______________________________________________________________________ 42
Figure 23: Revetment of Armorflex _____________________________________________________________ 44
Figure 24: A revetment of C-star elements _______________________________________________________ 45
Figure 25: Vetiver used as slope protection in Vietnam _____________________________________________ 47
Figure 26: Mixing ingridients, application and final result of an Elastocoast revetment ___________________ 49
Figure 27: Hydrotex Enviromat Lining (left) and Hydrotex Articulating Blocks ___________________________ 50
Figure 28: Picture of the smart grass reinforcement _______________________________________________ 52
Figure 29: Drawing of grass concrete blocks _____________________________________________________ 54
Figure 30: Baked clinkers made from clay _______________________________________________________ 54
Figure 31: Plastic grass stones, type slimblock ____________________________________________________ 55
Figure 32: Schematic overview of the wave overtopping simulator ___________________________________ 56
Figure 33: Test results from simulator test; left picture is the dike without reinforced grass and the right with
reinforcement _____________________________________________________________________________ 57
Figure 34: Influence of a gentle slope on the crest height ___________________________________________ 58
Figure 35: The Dollart coast divided in different sections ___________________________________________ 60
Figure 36: MCA for the materials and methods applied in section 1 ___________________________________ 61
Figure 37: MCA for the materials and methods applied in section 2 ___________________________________ 62
Figure 38: MCA for the materials and methods applied in section 3 ___________________________________ 62
Figure 39: MCA for the materials and methods applied in section 4 ___________________________________ 62
Figure 40: Concept 1.1: A gentle slope and raised crest height in combination with a Elastocoast revetment on
the berm. _________________________________________________________________________________ 65
Figure 41: Concept 2.1: No other material used, slope changes and increased overtopping ________________ 66
Figure 42: Cross section of the dike, SGR is installed under the grass revetment _________________________ 67
Figure 43: Cross section of the dike with retention basin installed in the crest ___________________________ 68
Figure 44: Top view of the Ems Dollart estuary, red line indicates the estuary ___________________________ 75
Figure 45: Top view, red line indicates The Ems Dollart region _______________________________________ 75
Figure 46: Picture were the freeboard is indicated (free crest height for wave overtopping) _______________ 91
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Figure 47: Definition angle of wave attack, red line indicated the angle of attack ________________________ 92
Figure 48: Left picture; determination of the characteristic slope for a cross section, right picture; The situation
for the manual calculation of the Dollart dikes ___________________________________________________ 95
Tables
Table 1: Analysis of the cross sections __________________________________________________________ 16
Table 2: Legend ____________________________________________________________________________ 16
Table 3: Results for the relation between crest height, materials and the volume of wave overtopping ______ 24
Table 4: Results calculation profile 4 with current hydraulic conditions ________________________________ 31
Table 5: Results calculation profile 10 with current hydraulic conditions _______________________________ 31
Table 6: Results calculation profile 10 with future hydraulic conditions ________________________________ 32
Table 7: Results calculation profile 14 with current hydraulic conditions _______________________________ 32
Table 8: Results calculation profile 14 with future hydraulic conditions ________________________________ 32
Table 9: Overview with possible combinations for the discharge pipes. ________________________________ 69
Climate (Ex) Change – Eco-engineering in the Dollart
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1 Introduction
This research is part of the project Climate (ex)change, initiated by water board Hunze and Aa’s,
Hanze University Groningen and Jade Hochschule Oldenburg. The project focuses on the Ems Dollart
region, the estuary of the river Ems in the North of the Netherlands and Germany.
Climate (ex)change is initiated to find solutions for the reinforcement of the coastal zone in
combination with nature development. An issue that’s getting more complex due to a rising sea level,
soil subsidence and changing views on nature development and protection. Several researches in the
area are conducted, looking at possibilities to apply progressive dike designs and the development of
marshes and sand flats. All with one goal:
Integrating a reinforcement of coastal protection with nature development in an international
environment.
Fresh meets salt water in this transition zone between a river and the Wadden Sea environment. The
Ems Dollart provides a habitat for a lot of endangered animals and plants. It acts as a stoppage point
for birds from the North during their winter travel to the South. They find food and shelter on the
marshes and sand flats. This research focuses on different materials that can be used on the outer
layer of the dike. Manufacturers of dike covering are developing new materials in order to meet the
demand for nature friendly dike design.
This trend is a result of the increasing human intervention in the coastal zone, which started in the
second half of the 50’s after the storm flood of February 1953. The Delta plan was initiated. For the
first time, a real statistical risk analysis was carried out to establish an acceptable small chance of a
new major flood disaster. The reaction time of the natural system to large-scale projects like the
closing of the Zuiderzee and the Delta project is in the order of decades (50-100 years). This means
we begin to see the influences of our interventions 50 years ago. With other words: it takes almost
50 years for an ecosystem to totally adjust to human intervention. This time can be shortened when
more nature friendly designs are used. The interventions like the Delta works show that it is
important for nature development to be combined with coastal engineering and that is why building
method’s are adjusted to combine nature development with coastal protection. This is called eco-
engineering (or ecological engineering).
Ecology is the interdisciplinary scientific study of the interactions between organisms and their
environment.2
K. R. Barrett from the State University of New Jersey defined eco-engineering as follows: ‘‘Eco-
engineering is the design, construction, operation and management (that is, engineering) of
landscape/aquatic structures and associated plant and animal communities (that is, ecosystems) to
benefit humanity and, often, nature.’’
1.1 Motivation
Because the Ems Dollart is a Natura2000 area3 and part of the National Ecological Network (NEN)
reinforcement of the coast has to be combined with nature development. This combination could
2 Begon, M.; Townsend, C. R., Harper, J. L. (2006). Ecology: From individuals to ecosystems. (4th ed.). Blackwell.
Climate (Ex) Change – Eco-engineering in the Dollart
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also contribute to a rising economic value, provided that the increased natural values attract
significantly more visitors and there are enough facilities to accommodate those visitors. One could
think of parking facilities and restaurants. According to Elles Bulder with the homonymous
investigation bureau, a way to attract more visitors could be accomplished by organizing large events
in the region to place the Dollart on the map.
Nature development can be developed by using new materials on the embankment. These so called
“eco-materials” can be defined as materials that are used in eco-engineering. They are designed to
fulfill multiple purposes and serve nature as well as humanity. The manufacturers thought of the
response of nature on new (civil) works and the best way to make these civil works fit in the natural
environment.
Which materials can be used best has to be investigated. There are different eco-materials available.
Before this report goes into detail, a definition of the word eco-material has to be given. Eco, derived
from ecology, tells us something about the properties of the material.
The Coastal zone of the Ems Dollart estuary forms a sharp boundary between agricultural land and a
Natura2000 area. It also forms a zone were three types of policy and law apply: the German, the
Dutch and the European law. The estuary forms a transition zone between a river environment, the
Wadden Sea and the North Sea. These three aspects are a motivation to apply eco engineering in the
Ems Dollart estuary.
The dikes are a form of human intervention. They are build to keep the ocean from our land and out
of our houses. The primary role of the dikes is coastal protection. Secondly, the dikes can fulfill the
role of transition zone between different environments. A coastal environment has a lot of potential
for nature development, especially in a transition zone like an estuary. That is why it is important to
investigate in which ways eco-engineering can help us unite these different elements in our coastal
defenses. And that is where eco-materials can be used. The different laws that apply are out of the
scope of this research.
New insights makes the society want to combine the reinforcement of coastal defenses with nature
development to create recreation and nature on and around the dikes. So, every environment asks
for different solutions, the best way to do this in the Ems Dollart region is yet unknown and has to be
investigated. Eco-engineering and eco- materials could provide solutions for this complicated
problem.
1.2 Problem definition and research questions
Due to a rising sea level all dikes in the Netherlands have to be reinforced. The Ems Dollart estuary
faces higher water levels at high tide compared to normal coastal area’s because of its shape, which
result in water level set up to fifty centimeter. When flood-control dam in the Ems is closed during a
storm, the water gets a second set up and rises another 10 centimeters4. The Netherlands assume
the sea level to rise 120 centimeters over the next 100 years. This has unknown negative effects on
the water set up due to the estuary shape and the Emsperwerk. Besides the rising water level the
surface level will locally decrease with 35 centimeter due to gas extraction.
3 Natura2000: An EUwide network of nature protection areas established under the 1992 habitats directive.
4 F.J. Sytsma, 2006, Evaluation of the German Emssperwerk: The value of more scale levels
Climate (Ex) Change – Eco-engineering in the Dollart
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1.2.1 Main research question
What are the possibilities of applying ecological dike concepts in the Ems Dollart region?
The definition of the ecological dike concept can be described as follows: A conceptual design of the
considered cross section of the dike. The considered area includes the foreshore or marshes, the dike
body and the seepage zone, which is assumed to run to the seepage ditch on the land side.
1.2.2 Sub-questions
These sub questions are answered in different chapters in this report. The chapters in which the sub
questions can be found are listed below. The sub questions can be found in the conclusion of the
chapter.
• What are the properties of the current coastline in the Dollart? Chapter 2
• In what way are the dikes constructed? Chapter 2
• What are the loads on the dikes at this moment and in 2100? Chapter 2
• Do the existing dikes meet the current safety requirements
and what are the safety requirements in 2100? Chapter 3
• Which new ecological concepts are available on the market? Chapter 4
1.2.3 Research goals
• Creating design requirements by determining the loads on the dikes at this moment and in
2100 and the way the existing dikes are constructed.
• Determine if the existing dikes meet the current safety requirements and determining the
safety requirements for the situation in 2100.
• Determine what type of ecosystem exists in the Ems Dollart estuary and what habitats exist
in the region.
• Investigating which eco materials are on the market and which of them are suited for the
Ems Dollart region.
• Defining the eco-engineering philosophies and their applicability in the Dollart region.
1.2.4 Research results
• Analysis of the fotreshore, embankment and hinterland, to get an idea of the situation in
which the ecological dike concepts (the subject of this report) have to be applied.
• Hydraulic conditions in the Dollart, because every cross section has slightly different
hydraulic conditions.
• A investigation about wave overtopping with CRESS software, because wave overtopping is
very important for the choice of ecological materials
• A sensitivity analysis of the manual calculation method for wave overtopping to investigate
the importance of all variables in the formulae.
• A multi criteria anaylsis of all investigated ecological materials.
• Several ecological dike concepts based on the outcome of the research.
• A conclusion in which the different ecological dike concepts are applied on certain cross
sections in the Dollart.
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1.2.5 Research area
The research is focused on the dike trajectory of the Dollart. This includes the dikes on the Dutch and
German part of the Dollart. The Dutch dikes start in Punt van Reide to Nieuwe Statenzijl and the
German dikes from Nieuwe Statenzijl to Pogum, see red line in Figure 1 . The total length of the dike
trajectory is 26 kilometers. The investigated trajectory is in a way unilateral. The conditions of the
sea, presence of marshes, crest height, width and the use of the hinterland differ only slightly. This
makes the results of the research applicable on similar trajectories elsewhere. This research focuses
on the Dutch calculation and design methods, which are also applicable on the German dikes.
The research area is the dike trajectory annotated with the red line. This line is chosen due to a
presence of marshes along the coast. In the West at the Punt van Reide the end of the marshes
define the end of the research area. In the East the mouth of the river Ems defines the end of the
research area. The trajectory is chosen because it is the same as in the foundation of Dutch water
boards, see Figure 1.
Figure 1: Overview of the research area, red line shows dike trajectory
Climate (Ex) Change – Eco-engineering in the Dollart
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1.2.6 Report structure
Chapter 2 � Analysis of the Dollart coast. This chapter includes a description of the Dollart
coast, the hinterland and the embankment. The major part of this chapter is
about wave overtopping and includes a sensitivity analysis, the current crest
heights and a calculation for the crest height
Chapter 3 � This chapter contains the investigation of materials. This aren’t all available
materials, but the selection gives a overview of the different kinds of
available materials. The selection is based on availability only, so the
suitability and/or applicability are not in this selection.
Chapter 4 � This chapter describes ecological concepts. The results of chapter 2 and 3
are used in combination with specific locations on which the ecological
concepts can be used best. The concepts include a location and a design
adjusted to the local conditions.
Chapter 5 � This chapter contains conclusions.
Chapter 6 � This chapter gives recommendations
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2 Analysis of the Dollart coast
This analysis is focused on the Dutch part of the Dollart coast. The analysis is made of nineteen cross
sections of the embankments, satellite images of the geographical situation and additional
information derived from literature. The cross sections form a representative image of the Dutch
Dollart coast. The emphasis in the analysis lies on safety and design of the embankment.
The method of using the cross sections for the analysis is chosen because the information from the
waterboard is also in this form. The cross sections have a distance of approximately 700 m between
them. The position of the cross sections is determined by the distance between them and the line of
cross sections runs along the research area.
Figure 2: Overview of cross sections of the Dutch Dollart coast
Figure 2 shows the nineteen cross sections that are considered for the analysis. They also mark the
research area for the Dutch part of the Dollart. The German part will be treated at the end of this
chapter. The comparison of the cross sections is made in Table 1. The foreshore, embankment and
hinterland is taken into account. Table 2 shows the legend properties and used symbols of Table 1.
Information about the German part is difficult to obtain. Therefore the Dutch part is analyzed
thoroughly and the German part needs to be investigated further. A comparison is made in
Paragraph 2.2.9 which gives a conclusion about the Dollart coast as a whole.
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1 Foreshore 2
Seaside
1.1 1.2 1.3 2.1 2.2 2.3 2.4 2.6 2.7 2.8 2.9 3.1
Cross section
1 0 m N,C PP GC, CS 7,25 6,5 0,75 G As SH 1,00 N
2 0 m N,C PP GC, CS 7,32 6,5 0,82 G As SH 1,00 N
3 0 m N,C PP GC, CS 8,17 6,5 1,67 G As SH 0,90 N
4 100 m N,C PP GC, CS 7,50 6,5 1,00 G As SH 0,90 A
5 200 m N,C PP GC, CS 8,15 6,5 1,65 G As SH 0,90 A
6 400 m N,C PP GC, CS 7,81 6,5 1,31 G As SH 0,90 A
7 400 m N,C PP GC, CS 7,95 6,6 1,35 G As SH 0,90 A
8 500 m N,C PP GC, CS 7,86 6,6 1,26 G As SH 0,95 A
9 450 m N,C PP GC, CS 7,87 6,6 1,27 G As SH 0,95 A
10 550 m N,C PP GC, CS 8,63 6,6 2,03 G As SH 0,95 A
11 850 m N,C PP GC, CS 8,52 6,6 1,92 G As SH 0,95 A
12 1100 m N,C SHGL GC, CS 8,04 6,6 1,44 G As SH 1,00 A
13 900 m N,C SHGL GC, CS 8,34 6,7 1,64 G As SH 1,10 A
14 1000 m N,C SHGL GC, CS 9,37 6,7 2,67 G As SH 1,10 A
15 1000 m N,C SHGL GC, CS 9,09 6,7 2,39 G As SH 1,10 A
16 900 m N,C SHGL GC, CS 9,04 6,7 2,34 G As SH 1,10 A
17 800 m N,C SHGL GC, CS 9,04 6,7 2,34 G As SH 1,10 A
18 450 m N,C SHGL GC, CS 9,22 6,7 2,52 G As SH 1,15 A
19 0 m N,C SHGL GC, CS 9,22 6,7 2,52 G As SH 1,15 A
Table 1: Analysis of the cross sections
Legend properties
1. Foreshore
1.1 Width of marshes, measured
right angled from cross
section
1.2 Utilization foreshore
1.3 Management
2. Embankment
2.1 Revetment materials
2.2 Crest height
2.3 Review level
2.4 Allowance: distance between
crest height and review level
2.6 Vegetation
2.7 Road types on the
embankment
2.8 Management type
2.9 Significant wave height Hs [m]
Ag Agriculture
As Asphalt
C Cattle breeding
CS Copper Slag
G Grass
GC Grass Concrete Blocks
N Nature development
PP Private property
SH Sheep
SHGL Stichting Het Groninger
Landschap
Table 2: Legend
Climate (Ex) Change – Eco-engineering in the Dollart
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2.1 Analysis foreshore
The investigated properties:
• Width of the marshes
• Utilization of the land
• Management
These three properties are chosen because they are necessary for the ecological dike concepts.
Different concepts can be used in different locations and the width of marshes, utilization of the
marshes and the owners determine the characteristics of the foreshore and the cross section at a
certain point.
The latter two are logically related. The utilization of the marshes in the Dollart goes with
management. Strangely this cannot be seen in the utilization alone, because the whole area is used
for agriculture and cattle breeding without regard of the owner. The part where Stichting het
Groninger Landschap (SHGL) is the owner, the cattle is present, but with another cause, namely to
maintain the vegetation instead of reproduction.
The factor safety is missing and that is because recent research5 shows that the influence of marshes
on coastal safety is negligible. The research concluded that wave period and height are relatively
small because of the bowl shaped estuary. Because of the same reason water boost occurs, resulting
in water level rises up to circa 5,00 m +NAP while mean high water is about 1,50 m +NAP. The ratio
between the level of the marshes and the water depth is too high. Entire breaking of waves6 does not
occur. The width of the marshes is an unimportant factor when it comes to safety, but gives an idea
of the surface of land that stretches along the coast. The role of marshes in safety is not further
addressed in this research.
An important fact that becomes clear when the foreshore is considered, is the fact that a large area
in front of the sea side of the revetment stays dry during regular weather conditions. This means the
water doesn’t reach the toe of the dike, not even at high tide. It doesn’t even come close to the dike.
The marshes flood a couple of times a year in the winter season when the storms are most powerful.
The storm season is between October and April.
2.2 Analysis embankment
The embankment forms the primary sea defense and is important for coastal protection. Tests point
out that the embankment or dike in the Dollart doesn’t meet the new safety requirements because
the outer layer which is build out of grass at this moment, is insufficient to counter wave attacks. The
conclusion that the outer layer wouldn’t suffice can be contradicted by the Waterboard, because the
standards with which the embankments are tested assume a rectangular wave and wind direction on
the dikes. In practice, this never occurs in the Dollart, making the tests too heavy. Nonetheless new
ways have to be found to protect the embankment from the rising sea level and combine this
increased protection with nature development and safety. Chapter 3 treats the different ecological
concepts available. This chapter focuses on the current situation. In this paragraph the following
properties are investigated:
5 G. Drijfhout, 2010, Grensoverschrijdende kansen voor kwelders in de Dollart
6 Entire breaking of waves is defined here as the breaking of waves higher or equal to the average wave height
(not significant wave height)
Climate (Ex) Change – Eco-engineering in the Dollart
18
• Revetment
• Crest height
• Review level
• Allowance
• Significant wave height (Hs)
• Road types
• Management
• Dike structure
• Overtopping
• Wave run up
This information is needed to determine the needed crest heights in the future and to determine
which ecological materials can be used on the dike.
2.2.1 The revetment of the current dikes
The revetment of the embankment in the Dollart is very constant. The dikes are mainly covered with
a mixture of grass. Copper slag is used at the point where the waves strike during storm surges. Grass
concrete blocks are used above the copper slag, under the first meters of grass to increase stability.
The revetments have to withstand wave attacks with a significant wave height between Hs=0,90 m
and Hs=1,25 m. As mentioned above, new tests indicate that the current revetments are insufficient
to withstand the expected wave attacks when the sea level rises. Grass is a good way of protection
against medium and small wave attacks like those in the Dollart. Because of shallow waters the
waves won’t be higher than 1,25 m. Also overtopping can be resisted as recent tests show7. These
tests, conducted on a couple of other Wadden Sea dikes showed that the force a grass revetment
can withstand is higher than assumed. The result of these tests is that the permissible amount of 0,1
l/m/s overtopping will be changed to 1 l/m/s and probably to 5 l/m/s, an increase of 5000%. This is
the same for all cross sections.
2.2.2 Crest height
This paragraph calculates the needed crest height for three different profiles in the Dollart. Wave run
up and overtopping are important criteria for new ecological concepts, especially when the criteria
for these two parameters are changed. To investigate the differences in crest height, the wave run
up and wave overtopping will be calculated manually and tested to the hydraulic boundaries. To
make sure a representing part of the dikes is investigated, profiles 4 (low crest height), 10 (medium
crest height) and 14 (high crest height) are investigated. The crest height is taken as criterion because
the height of the dike determines for the most part the amount of overtopping waves. The wind
direction is taken into account. Profile 4 is situated in the lee and profile 10 and 14 are situated in a
trajectory with the highest significant wave heights. The location of these three profiles can be seen
in Figure 2 and the drawings can be found in Appendix 8: Drawings cross-section 4, 10, 14
7 Van der Meer, Schrijver, Hardeman, Van Hoven, Verheij and Steendam, 2010, Guidance on erosion resistance of inner slopes
of dikes
Climate (Ex) Change – Eco-engineering in the Dollart
19
The crest height C is defined as C=a+b+c+d+e+f8. variable e and f can be influenced, a through d
cannot be influenced and depend on hydraulic and geographic conditions.
Figure 3: Additions to the reference level to determine the height of the dikes
The variables a through f can be seen in Figure 3 and are defined as follows:
a. A reference level with an exceedance probability corresponding to the legal standards.
The review level is given by the hydraulic preconditions and are composed by the Ministry of
Transport, Public Works and Water Management. The review level is almost constant in the Dollart
as can be seen in Figure 11. The Dollart dikes are part of the primary water retaining structures
category A and according to the legal standards the exceedance probability is 1/40009.
Profile 4: a=6,5 m +NAP
Profile 10: a=6,6 m +NAP
Profile 14: a=6,7 m +NAP
b. The sea level rise during the design period
The sea level rise is difficult to predict. The Delta commission predicts a sea level rise of 0,65 to 1,30
meter in 2100 and 2 to 4 meter in 2200. Because these predictions are based on a lot of uncertainties
they have to be used with precision. Because insight in sea level rise and other loads like wave
attacks change every year, the design period of embankments is mostly 50 years. The current dikes
are designed on a level of 10,20 m +NAP10
. In that time it was believed to be high enough to
withstand the highest water levels and storm surges. At this moment we use the expected sea level
rise of 1,20 m.
Profile 4: b=1,20 m
Profile 10: b=1,20 m
Profile 14: b=1,20 m
c. The soil subsidence during the design period
Due to gas extraction, the soil will subside locally with 18 centimeters in 2050. In this figure, a safety
margin of 1,25 is added because of uncertainties; the embankment is situated on the edge of the gas
extraction fields. In Figure 16 can be seen that the Dollart area is only partly influenced by gas
8 Technical Advice committee on Flood defense, Delft, 2002, Technical report wave Run-up and overtopping at
dikes 9 Ministry of transport, public Works and Water management, 2006, Hydraulic boundaries 2006
10 Kampe Lentz, Waterboard Hunze en Aa’s
Climate (Ex) Change – Eco-engineering in the Dollart
20
extraction. That is why an average of 18 centimeters is used to calculate the crest height of cross
section 1 to 12 and an average of 3 centimeter for cross sections 13 to 19. The Delta commission
calculated the soil subsidence in the sea level rise.
Profile 4: c= 0,18
Profile 10: c=0,18 m
Profile 14: c=0,03 m
d. Additions for shower oscillations, storm blows, seiches11
and local storm surges
The Emssperwerk in the River Ems results in water boost at high tides in combination with storms.
Dutch calculations show a boost of 8 cm at Delfzijl, at Nieuwe Statenzijl this figure is higher. Recent
German calculations show a boost of 20 centimeters at Delfzijl.12
It means the addition for water
boost due to the Emssperwerk will be higher than expected and calculations concerning this subject
have to be investigated again. In this report we apply the worst case and in this case that is the
German figure of 0,20 m. The calculation is made for the whole Dollart so different additions for
variable f can’t be used.
Profile 4: d= 0,20 m
Profile 10: d=0,20 m
Profile 14: d=0,20 m
e. the expected crest subsidence due to settlement of the embankment and its foundation
during the design period.
The embankments are build out of clay and have a sand core. The subsidence of this type of
embankments is difficult to calculate. In a design period of 50 years, the subsidence can reach 1
meter. When the crest heights at the West side of the Dollart are contemplated again, the
subsidence can be estimated on 2 meters for profile 4 and 1 meter for profile 10 and 14. These
values are based on the current crest heights and differences between them. Profile 4 has subsided
the most (2m) profiles 10 and 14 have subsided less, around 1m.
Profile 4: e= 2,00 m
Profile 10: e=1,00 m
Profile 14: e=1,00 m
f. The height for wave run up or wave overtopping.
According to the Technical Advice Committee on Flood Defence (TAW) this can be calculated using
the following procedure:
1. Determine wave conditions at toe of dike: Hm0, Tm-1,0
2. Calculate influence factor for angle of wave attack γβ
3. Adjust wave conditions if ß>80°
4. Calculate average slope, tan α
5. Calculate z2%,smooth (smooth: for γb=1 and γf=1)
6. Calculate influence factor for roughness on slope γf
7. Calculate z2%,rough (rough for: γb=1)
8. Calculate influence factor for berms γb
11
A seiche is a standing wave in an enclosed or partially enclosed body of water 12
Berekening hoogte zeedijken Groningen klopt niet meer, Heijbrock F., 08-04-2010, Cobouw
Climate (Ex) Change – Eco-engineering in the Dollart
21
9. Calculate 2% wave run-up
10. Calculate γβ for wave overtopping
11. Calculate wave overtopping with above γb and γf
12. Calculate overtopping volumes per wave
Symbols:
Hm0= significant wave height at the toe of the dike
Tm= average wave period
Tm-1,0= Tspectral= spectral wave period
ß= angle of wave attack
γβ= influence for the angle of wave attack
tan α= (1,5Hm0 + z2%) / (Lslope-B) with B=broad of berm
γb= influence of a berm
γf= influence factor for roughness elements on slope
Another method is the computer program CRESS (Coastal and River Engineering Support System).
More information about this program can be found on www.cress.nl.
The calculation is done manually and with the computer program CRESS. The manual calculation and
an analysis of the different factors can be found in paragraph 2.2.3. The calculation of variable (f)
with the computing program CRESS can be found in paragraph . In the calculation of the crest height
the values from CRESS are used for (f).
Values of (f) with an overtopping flow rate of 0,1 l/m/s (Current standard)
f4=1.461 m
f10=1.87 m
f14=1.83 m
Resulting crest heights at current standard:
C4= a+b+c+d+e+f =6,5+1,20+0,18+0,20+2,00+1.461=11,54 m
C10= a+b+c+d+e+f =6,6+1,20+0,18+0,20+1,00+1.87=11.05 m
C14= a+b+c+d+e+f =6,7+.1,20+0,03+0,20+1,00+1.83=11.00 m
Values of (f) with an overtopping flow rate of 5 l/m/s (future standard)
f4=0,76 m
f10=0,99 m
f14=0,98 m
Resulting crest heights at future standard:
C4= a+b+c+d+e+f =6,5+1,20+0,18+0,20+2,00+0,76=10,84 m
C10= a+b+c+d+e+f =6,6+1,20+0,18+0,20+1,00+0,99=10,17 m
C14= a+b+c+d+e+f =6,7+1,20+0,03+0,20+1,00+0,98=10,15 m
The value for overtopping (variable f) is lowest at profile 4. This is odd because profile 4 has the
lowest crest height. The reason for this deviation can be found in the shape of profile 4, which has a
gentler slope. Another reason is the fact that the waves at profile 4 are the lowest.
Climate (Ex) Change
Figure 4: Relation between crest height and overtopping after sea level rise of 1,20m
Figure 4 shows the relation between the calculated crest height and the overtopping flow rates for
the three considered cross sections. The graph clarifi
rates. The current standard of 0,1 l/m/s gives much higher needed crest heights in comparison with a
flow rate of 5 l/m/s. The difference is almost a meter. Tests which investigated the effect of
increased overtopping on a grass revetment show that flow rates of up to 50 l/m/s cause no
problems for the current revetments so this graph gives an indication of the needed crest height at a
certain overtopping flow rate and a sea level rise of 1,20 m.
Note: the crest height is calculated using assumptions for the sea level rise, settlements of the dike
body and settlement due to gas extraction.
2.2.3 Manual calculation wave overtopping
In this part an explanation will be given about the wave
investigation is done to get a better
region. This information is relevant because the crest height of the dikes
overtopping (see Figure 3 and Figure
influence factors that cause overtopping need to be investigated.
The manual calculation is done to make an approach and to get view of the input paramet
results will be analyzed and compared. The
wave overtopping the most.
Climate (Ex) Change – Eco-engineering in the Dollart
: Relation between crest height and overtopping after sea level rise of 1,20m
shows the relation between the calculated crest height and the overtopping flow rates for
the three considered cross sections. The graph clarifies the influence of increases overtopping flow
rates. The current standard of 0,1 l/m/s gives much higher needed crest heights in comparison with a
flow rate of 5 l/m/s. The difference is almost a meter. Tests which investigated the effect of
rtopping on a grass revetment show that flow rates of up to 50 l/m/s cause no
problems for the current revetments so this graph gives an indication of the needed crest height at a
certain overtopping flow rate and a sea level rise of 1,20 m.
t height is calculated using assumptions for the sea level rise, settlements of the dike
body and settlement due to gas extraction.
Manual calculation wave overtopping
In this part an explanation will be given about the wave overtopping in the Ems Dollart
investigation is done to get a better image of the overtopping volume of the waves in the Dollart
region. This information is relevant because the crest height of the dikes depends
Figure 4). The current loads on the inner slope are important and the
overtopping need to be investigated.
The manual calculation is done to make an approach and to get view of the input paramet
and compared. The analysis should make clear which parameters influence
22
shows the relation between the calculated crest height and the overtopping flow rates for
es the influence of increases overtopping flow
rates. The current standard of 0,1 l/m/s gives much higher needed crest heights in comparison with a
flow rate of 5 l/m/s. The difference is almost a meter. Tests which investigated the effect of
rtopping on a grass revetment show that flow rates of up to 50 l/m/s cause no
problems for the current revetments so this graph gives an indication of the needed crest height at a
t height is calculated using assumptions for the sea level rise, settlements of the dike
overtopping in the Ems Dollart region. The
image of the overtopping volume of the waves in the Dollart
depends on the wave
he current loads on the inner slope are important and the
The manual calculation is done to make an approach and to get view of the input parameters. The
r which parameters influence
Climate (Ex) Change – Eco-engineering in the Dollart
23
For the calculation the three profiles mentioned in paragraph 2.2.2 are worked out:
• Profile 4 � Crest height 7.51m
• Profile 10 � Crest height 8.35m
• Profile 14 � Crest height 9.37m
The results can be seen in Table 3. For the fourth calculation an average profile is used in with an
average crest height and that calculation is used to analyze the variables. It can be found in Appendix
6: Manual calculation wave overtopping. This chapter gives a summary of the calculation in the
appendix and consists mostly out of tables and graphs with explanations.
For the calculation of the wave overtopping the following things need to be determined:
1. The wave conditions at the toe of the dike � Tm-1,0, Hm0
2. Influence factor for the angle of wave attack � γβ
3. The average slope of the dike � tan(α)
4. The 2% wave run-up � z2%
5. Influence factor for berms � γb
6. The average wave overtopping discharge � q
7. The volume of overtopping waves per meter � V
The following results were found (The average height of all the 19 profiles is used with a slope of 1:3
and the dike is covered in grass):
1. The highest significant wave height was found on Hm0=1,25m and the spectral period of the
waves on Tm-1,0=3,25s
2. The influence factor for the angle of wave attack γβ=1, This is because the angle for the wave
attack needs to be zero. So all waves strike the dike perpendicular. This is set in the test
(Voorschrift Toetsen op veiligheid primaire waterkeringen). In reality the waves strike the
dikes under an angle.
3. The representative angle of the dike is tan(α)=0,4 with a slope of 1:3 and an estimate of the
wave run-up because this was not yet determined. In this case the wave run-up was set on
1,5x Hm0=1.9m. The calculated wave run-up should be put back in the equation for the
calculation of tan(α) for a better idea of the average slope. In this case the z2% > 1,5x Hm0.
If the wave run-up is bigger than the freeboard between the crest height and the SWL, the
freeboard height needs to be used instead of the z2% or the 1,5x Hm0.
4. The final wave run-up z2%=2,5m, see that the run-up is bigger than 1,5 the significant wave
height and so also bigger as the freeboard from crest to SWL (Crest height-SWL=1.7m, hk <
z2%).
5. The influence factor for the berm of the dike γb=1. So the berm has no effect on the wave
run-up of the waves. In this calculation is assumed that the influence of the dike is negligible.
Normally this need to be taken into account. The influence by the width of the berm and the
position of the berm in respect to the waterline is important.
6. The average overtopping discharge for a grass revetment, q=0,04m2/s. Also said as m
3 / m
per second. This average wave overtopping discharge is above the current requirements for
wave overtopping (current requirement is set on q=0,0001m2/s also written as q=0,1 l/s/m ).
Research is ongoing to get a better view on the relationship between wave overtopping and
Climate (Ex) Change
the capacity of the inner slope. The requirements for wave overtopping change, because of
the already performed research
7. Volume of overtopping wave per linear meter of the crest V=4,77m
that goes over the crest per meter during a storm event. Therefore the total amount of
waves that strike against the dike during a storm event and the ac
need to be determined. In the calculation, the storm event was estimated on 5 hours. This is
similar to 358 waves that go over the dikes.
At first the relationship between the use of different revetments, the crest height and the v
wave overtopping will be explained. In
and volume can be seen.
Profile Hcrest
[m]
Grass
q
[m2/s]
V
[m3/m]
4 7,51 0,16 10,65
10 8,35 0,0088 4,49
14 9,37 0,00535 1,11
Table 3: Results for the relation between crest height, materi
Figure 5: Relation between the volume of wave overtopping and the crest height
0
2
4
6
8
10
12
7 7,5
V [
m3
/m]
-->
Relation between the volume of wave overtopping and the crest height
Climate (Ex) Change – Eco-engineering in the Dollart
the capacity of the inner slope. The requirements for wave overtopping change, because of
ed research.
Volume of overtopping wave per linear meter of the crest V=4,77m3/m. So the total volume
that goes over the crest per meter during a storm event. Therefore the total amount of
waves that strike against the dike during a storm event and the actual overtopping waves
need to be determined. In the calculation, the storm event was estimated on 5 hours. This is
similar to 358 waves that go over the dikes.
At first the relationship between the use of different revetments, the crest height and the v
wave overtopping will be explained. In Table 3 and Figure 5 the results for the overtopping discharge
Armorflex Elastocoast
V
[m3/m]
q
[m2/s]
V
[m3/m] q [m2/s]
V
[m3/m]
10,65 0,136 10,38 0,08 9,6
4,49 0,005 3,95 0,024 2,67
1,11 0,00304 0,83 0,000603 0,34
Results for the relation between crest height, materials and the volume of wave overtopping
: Relation between the volume of wave overtopping and the crest height
8 8,5 9 9,5
Hcrest [m] -->
Relation between the volume of wave overtopping and the crest height
24
the capacity of the inner slope. The requirements for wave overtopping change, because of
/m. So the total volume
that goes over the crest per meter during a storm event. Therefore the total amount of
tual overtopping waves
need to be determined. In the calculation, the storm event was estimated on 5 hours. This is
At first the relationship between the use of different revetments, the crest height and the volume of
the results for the overtopping discharge
als and the volume of wave overtopping
9,5
Relation between the volume of wave overtopping and the crest height
Grass
Armorflex
Elastocoast
Climate (Ex) Change
• If the height of the crest increases, the volume o
height is sensitive for the outcome of the overtopping.
• The volume of overtopping waves is less for Armorflex and Elastocoast compared to the
grass revetment. This is because the
revetments. Grass has a smooth surface whi
• So in this case, Elastocoast would be the best option for the top layer of the dike
• Other revetments are not worked out. The roughness factor for these revetments are
unknown. But the outcome for other revetments w
• The yellow line indicates the average height of the dikes in the Dollart region. The
intersection between the yellow line and the green is at 4,77 m3 / m.
• By this calculation (for an average profile) the discharge of water is ab
The current requirement for the discharge of water is 0,1 l/m/s.
In this part the relation between the length of the slope and the bermwidth are investigated. Both
factors are needed to determine the average slope of the dikes. The
The average slope is needed to determine the wave run
overtopping. The formula is an approach of the characteristic slope of the dike. The outcome for the
volume of wave overtopping can be seen in
Figure 6: Determination of the characteristic slope
Figure 7: Relation between wave run-up and length of the “average” slope of the dike
12,47
3,86
0
2
4
6
8
10
12
14
0 5 10
Z2
% [
m]
-->
Relation between wave run
"average" slope of the dike
Climate (Ex) Change – Eco-engineering in the Dollart
If the height of the crest increases, the volume of overtopping waves decreases. The crest
ive for the outcome of the overtopping.
The volume of overtopping waves is less for Armorflex and Elastocoast compared to the
grass revetment. This is because the surface roughness of grass is less than the other
revetments. Grass has a smooth surface while Elastocoast has an open rough surface.
So in this case, Elastocoast would be the best option for the top layer of the dike
Other revetments are not worked out. The roughness factor for these revetments are
unknown. But the outcome for other revetments would not deviate as much.
The yellow line indicates the average height of the dikes in the Dollart region. The
intersection between the yellow line and the green is at 4,77 m3 / m.
By this calculation (for an average profile) the discharge of water is above the requirements.
The current requirement for the discharge of water is 0,1 l/m/s.
In this part the relation between the length of the slope and the bermwidth are investigated. Both
factors are needed to determine the average slope of the dikes. The formula can be seen in
The average slope is needed to determine the wave run-up and eventually the volume of wave
overtopping. The formula is an approach of the characteristic slope of the dike. The outcome for the
e of wave overtopping can be seen in Figure 7 until Figure 10.
: Determination of the characteristic slope for a cross section consisting of different slopes
up and length of the “average” slope of the dike
3,86
2,05 1,34 0,98
15 20 25 30
L slope [m] -->
Relation between wave run-up and length of the
"average" slope of the dike
25
f overtopping waves decreases. The crest
The volume of overtopping waves is less for Armorflex and Elastocoast compared to the
surface roughness of grass is less than the other
le Elastocoast has an open rough surface.
So in this case, Elastocoast would be the best option for the top layer of the dike
Other revetments are not worked out. The roughness factor for these revetments are
ould not deviate as much.
The yellow line indicates the average height of the dikes in the Dollart region. The
ove the requirements.
In this part the relation between the length of the slope and the bermwidth are investigated. Both
formula can be seen in Figure 6.
up and eventually the volume of wave
overtopping. The formula is an approach of the characteristic slope of the dike. The outcome for the
for a cross section consisting of different slopes
Climate (Ex) Change
• If the length of the slope increases the wave run
• The slope of the dike decreases when the length of the slope increases. In other words the
slope becomes gentler.
Figure 8: Relation between the volume of overtopping waves and the length of the “average”slope
• If the length of the average slope increases also the volume of wave overtopping decreases.
In other words, when the dike slope becomes more gentle the volume of overtopping
increases.
• The volume increases exponential when the length of the slope increases. In other words,
the more gentle the slope, the more water will flow
• The relation between the length of the slope and the overtopping discharge is not shown in a
graph. This is because for the determination of the overtopping discharge, the shape of the
dike is not taken into account, only the freeboard between the crest and the SW
Figure 9: Relation between the wave run
• If the bermwidth increases the wave run
• The increase of the wave run
• This is the opposite compared to the length of
1,47 3,77
0
10
20
30
40
50
0 5 10
V [
m3
/m]
-->
L slope [m]
Relation between the volume of overtopping waves
and the length of the "average" slope of the dike
3,18 3,694,35
5,24
0
2
4
6
8
10
12
14
16
18
0 2
Z2
% [
m]
-->
B [m]
Relation between the wave run
bermwidth
Climate (Ex) Change – Eco-engineering in the Dollart
If the length of the slope increases the wave run-up decreases
The slope of the dike decreases when the length of the slope increases. In other words the
: Relation between the volume of overtopping waves and the length of the “average”slope
If the length of the average slope increases also the volume of wave overtopping decreases.
when the dike slope becomes more gentle the volume of overtopping
The volume increases exponential when the length of the slope increases. In other words,
slope, the more water will flow over the crest of the dike.
tion between the length of the slope and the overtopping discharge is not shown in a
graph. This is because for the determination of the overtopping discharge, the shape of the
dike is not taken into account, only the freeboard between the crest and the SW
: Relation between the wave run-up and the bermwidth
If the bermwidth increases the wave run-up increases as well.
The increase of the wave run-up increases exponential.
This is the opposite compared to the length of the slope.
3,77
9,18
20,76
41,28
15 20 25 30
L slope [m] -->
Relation between the volume of overtopping waves
and the length of the "average" slope of the dike
5,246,49
8,35
11,26
16,3
4 6 8
B [m] -->
Relation between the wave run-up and the
bermwidth
26
The slope of the dike decreases when the length of the slope increases. In other words the
: Relation between the volume of overtopping waves and the length of the “average”slope
If the length of the average slope increases also the volume of wave overtopping decreases.
when the dike slope becomes more gentle the volume of overtopping
The volume increases exponential when the length of the slope increases. In other words,
over the crest of the dike.
tion between the length of the slope and the overtopping discharge is not shown in a
graph. This is because for the determination of the overtopping discharge, the shape of the
dike is not taken into account, only the freeboard between the crest and the SWL.
Climate (Ex) Change
Figure 10: Relation between the volume of overtopping waves and the bermwidth
• When the width of the berm increases the influence on the wave overtopping decreases.
• The line shows a sharp drop in the beginning. So the
volume of overtopping is
• In the equations the influences of the berm itself is neglected because the berm of the dikes
in the Dollart are under the SWL. Therefore we say the berm has no influence on the
overtopping. In fact this needs to be investigated. The position of the berm and the
bermwidth are important for determination of the influence factor.
The volume of wave overtopping i
decreases. It can be explained by the formula in
significant wave height is divided by the difference between the length and the width (L
slope and berm. If L gets larger and B st
therefore the angle tan(α) will decrease. If the tan(α) decreases, the volume of wave overtopping will
increase and the wave run-up decrease. If L has the same value and B is increased, the height
divided by a smaller number and therefore the tan(α) will increase.
It is hard to explain why the volume of overtopping waves increases when the slope becomes gentler
or the berm smaller and the crest height of the dikes is the same. If
for wave run-up it could be logical. The berm is almost horizontally and therefor
transfer its kinetic energy as much to the level energy. However
influences the water as well. This influence
Based on this calculation the length of the slope shows opposite results for the volume of wave
overtopping. If the slope of the dike becomes gentler, the volume of wave overtopping increases.
This observation sounds so unlikely that more research need
mistake has been made in the manual calculation. Therefore the calculation has to be done with the
program of PC-overtopping.
4,773,98
3,31
2,75
0
1
2
3
4
5
6
0 2
V [
m3
/m]
-->
B [m]
Relation between the volume of overtopping waves
and the bermwidth
Climate (Ex) Change – Eco-engineering in the Dollart
: Relation between the volume of overtopping waves and the bermwidth
When the width of the berm increases the influence on the wave overtopping decreases.
The line shows a sharp drop in the beginning. So the influence of the berm width on the
volume of overtopping is significantly.
In the equations the influences of the berm itself is neglected because the berm of the dikes
in the Dollart are under the SWL. Therefore we say the berm has no influence on the
ertopping. In fact this needs to be investigated. The position of the berm and the
bermwidth are important for determination of the influence factor.
The volume of wave overtopping increases when the slope length increases and the bermwidth
can be explained by the formula in Figure 6. The height between the wave run
significant wave height is divided by the difference between the length and the width (L
slope and berm. If L gets larger and B stays the same, the height is divided to a bigger number and
therefore the angle tan(α) will decrease. If the tan(α) decreases, the volume of wave overtopping will
up decrease. If L has the same value and B is increased, the height
divided by a smaller number and therefore the tan(α) will increase.
It is hard to explain why the volume of overtopping waves increases when the slope becomes gentler
or the berm smaller and the crest height of the dikes is the same. If the width of the berm accounts
logical. The berm is almost horizontally and therefore the water won’t
kinetic energy as much to the level energy. However the roughness of the berm
influences the water as well. This influence is so big that the volume of overtopping waves decreases.
Based on this calculation the length of the slope shows opposite results for the volume of wave
overtopping. If the slope of the dike becomes gentler, the volume of wave overtopping increases.
s observation sounds so unlikely that more research needs to be performed. It
mistake has been made in the manual calculation. Therefore the calculation has to be done with the
2,752,28
1,891,56 1,29
4 6 8
B [m] -->
Relation between the volume of overtopping waves
and the bermwidth
27
When the width of the berm increases the influence on the wave overtopping decreases.
influence of the berm width on the
In the equations the influences of the berm itself is neglected because the berm of the dikes
in the Dollart are under the SWL. Therefore we say the berm has no influence on the
ertopping. In fact this needs to be investigated. The position of the berm and the
increases and the bermwidth
. The height between the wave run-up and
significant wave height is divided by the difference between the length and the width (Lslope-B) of the
ays the same, the height is divided to a bigger number and
therefore the angle tan(α) will decrease. If the tan(α) decreases, the volume of wave overtopping will
up decrease. If L has the same value and B is increased, the height will be
It is hard to explain why the volume of overtopping waves increases when the slope becomes gentler
of the berm accounts
e the water won’t
the roughness of the berm
is so big that the volume of overtopping waves decreases.
Based on this calculation the length of the slope shows opposite results for the volume of wave
overtopping. If the slope of the dike becomes gentler, the volume of wave overtopping increases.
to be performed. It is possible that a
mistake has been made in the manual calculation. Therefore the calculation has to be done with the
Climate (Ex) Change – Eco-engineering in the Dollart
28
But it can be said (if the outcome is correct), that the idea of using a wider berm on the dikes is a
good option for decreasing the volume of wave overtopping. The problem for using a wider berm is
the location. The berm needs to be at the right level of the dike to influence the volume of
overtopping water. The top of the berm comes probability very high. So a lot of soil is needed and
the consequences for nature development should also be investigated. In most cases, the slopes
under and above the berm of the dike are sharp.
Figure 11: Relation between the angle of wave attack and volume of overtopping waves
• In Figure 11 the relation between the angle of wave attack (direction of the waves) and the
volume of overtopping water can be seen
• The volume of wave overtopping decreases linear to the increase of the β. So in other words,
V will become the largest when the wave direction is perpendicular to the dike. Therefore
the angle of wave attack is set to 0 degrees
• The angle of wave attack stops when the angle reaches 80degrees. After the wave direction
becomes 80 degrees from the perpendicular, the wave run-up and overtopping almost
become zero. But in the Dollart region this can mean that the waves can strike the
surrounding dikes in a straight line. The fetch will be less compared to the main wind
direction.
• The determination of β would not influence the outcome of the volume of wave overtopping
as much. Even if β changes for 80 degrees away from the dike, the V will only be reduced
with 1 m3/m of water. So β is not very sensitive in this calculation.
0
1
2
3
4
5
6
0 20 40 60 80 100
V [
m3
/m]
-->
β -->
Relation between the angle of wave attack and
volume of overtopping waves
Climate (Ex) Change
Figure 12: Relation between SWL and the wave run
• Figure 12 shows the relation between the SWL and the wave run
• When the SWL increases the wave run
• It can be concluded that the wave run
Note: for the result of this graph the fact that the wave run
calculation of the average slope is left out of consideration. Also, the increase of the significant wave
height [Hs ] is neglected.
Figure 13: Relation between the volume of overtopping waves and review level
0
0,5
1
1,5
2
2,5
3
3,5
5 5,5 6
Z2
% [
m]
-->
Relation between SWL and the wave run
0
2
4
6
8
10
12
14
16
4 5
V [
m3
/m]
-->
Relation between the volume of overtopping waves and review
Climate (Ex) Change – Eco-engineering in the Dollart
: Relation between SWL and the wave run-up
shows the relation between the SWL and the wave run-up
When the SWL increases the wave run-up stays constant
It can be concluded that the wave run-up is not depending on the SWL.
Note: for the result of this graph the fact that the wave run-up exceeds the freeboard for the
calculation of the average slope is left out of consideration. Also, the increase of the significant wave
: Relation between the volume of overtopping waves and review level
6 6,5 7 7,5 8
SWL [m] -->
Relation between SWL and the wave run-up
6 7 8 9
SWL [m] -->
Relation between the volume of overtopping waves and review
level
29
up exceeds the freeboard for the
calculation of the average slope is left out of consideration. Also, the increase of the significant wave
Climate (Ex) Change – Eco-engineering in the Dollart
30
• Figure 13 shows the relation between the review level and V. The yellow line indicates the
average review level that fluctuates from 6,5m until 6,7.
• The graph has an odd shape. In the beginning the graph is quite flat, then it increases
exponential and after the SWL comes above the 7m it will flatten. So if the freeboard
between the crest and the review level becomes bigger, the V will eventually be zero.
If the freeboard becomes almost zero, the influence of the dike becomes less, and the water
will just flow over the dike. The volume of overtopping will increase linear. But it can be sad
that the determination of the review level is important. Therefore it is important to predict
the right hydraulic boundaries by measurements.
Figure 14: Relation between the volume of overtopping waves and the significant wave height
• In Figure 14 the relation between the volume of wave overtopping and the significant wave
height is given. The yellow line indicates the normative value of the significant wave height in
the Dutch region of the Dollart.
• The significant wave height is very sensitive for the outcome of the V
2.2.4 Crest height calculation with computer program CRESS
In this part the input and outcome for the calculation of wave overtopping with computer program
CRESS is given.
The first calculation is made with the current hydraulic conditions and dike profiles and the second
with hydraulic conditions that can be expected in 100 years. The assumption is made that the review
level in 100 Years will be 120 cm higher than in the current situation. The location of the profiles can
be seen in Figure 2.
This program calculates the overtopping height needed for a required overtopping discharge. This
height is used to determine the final crest height of the dike. In the manual calculation this height
wasn’t found. Therefore the outcome of this calculation is used to determine the crest height. The
results are given bold.
0
5
10
15
20
25
30
35
0 0,5 1 1,5 2 2,5 3 3,5
V [
m3
/m]
-->
Hm0 [m] -->
Relation between the volume of overtopping waves and the
significant wave height
Climate (Ex) Change – Eco-engineering in the Dollart
31
Profile 4
Current hydraulic conditions
Input Result
Hm0 :0,9 m
Requirement
q [l/s/m]
Required
height f [m] z2%
[m]
Tp :3,1 s 0.1 1.461
1,35
β :0o 1.0 1.046
SWL :6,5 m 5.0 0.756
10 0.632
100 0.217
Table 4: Results calculation profile 4 with current hydraulic conditions
Note: The 2%-wave run-up is higher than the dike freeboard.
Future hydraulic conditions
The hydraulic condition contain several values. The main values are the wave height and the review
level. In the future will the wave height be the same, however because of the sea level rise will the
review level also need to rise. That fore a calculation with future review level will be conducted. The
future review level is the current review level +1,20 m sea level rise.
However this part of the dike is lower than the future review level. The dike has a crest height of
7,51+NAP and the future review level has a height of 7,7 +NAP. In this case was it not possible to
make the calculation. The future review level is too high for the dike. This means that the dike
according the future review level must be heightened to protect the land behind the dike, or other
innovative measures must conducted.
Profile 10
Current hydraulic conditions
This dike profile is the south side of the Ems Dollart region. Figure 2 is a schematic drawing of the
dike profile used for the calculation. The main input data are:
Input Result
Hm0 :1,0 m
Requirement
q [l/s/m]
Required
height f [m] z2%
[m]
Tp :3,3 s 0.1 1,87
1,7
β :0o 1.0 0,99
SWL :6,6 m 5.0 1
10 0,84
100 0,32
Table 5: Results calculation profile 10 with current hydraulic conditions
Climate (Ex) Change – Eco-engineering in the Dollart
32
Future hydraulic conditions
Input Result
Hm0 :1,0 m
Requirement
q [l/s/m]
Needed
height f [m] z2%
[m]
Tp :3,3 s 0.1 1,87
1,7
β :0o 1.0 1,35
SWL :7,8 m 5.0 0,99
10 0,84
100 0,32
Table 6: Results calculation profile 10 with future hydraulic conditions
Note: The 2%-wave run-up is higher than the dike.
Profile 14
Current hydraulic conditions
This dike profile is the south side of the Ems Dollart region. Figure 2 is a schematic drawing of the
dike profile used for the calculation.
Input Result
m0 :1,1 m
Requirement
[l/s/m]
Needed
height [m] z2%
[m]
Tp :3,4 s 0.1 1,83
1,64
β :0o 1.0 1,33
SWL :6,7 m 5.0 0,98
10 0,83
100 0,33
Table 7: Results calculation profile 14 with current hydraulic conditions
Future hydraulic conditions
Input Result
Hm0 :1,1 m
Requirement
[l/s/m]
Needed
height [m] z2%
[m]
Tp :3,4 s 0.1 1,83
1,64
β :0o 5.0 1,33
SWL :7,9 m 1.0 0,98
10 0,83
100 0,33
Table 8: Results calculation profile 14 with future hydraulic conditions
Note: The 2%-wave run-up is higher than the dike.
Climate (Ex) Change
2.2.5 Review level and allowance
Figure 15: Crest height and review level of the Dutch embankment
The figure above shows the crest height and the review level derived from the Hydraulic Boundaries
2006 (HR2006). The numbers 1 till 1
the Dollart. Big differences can be seen in crest height. In the 70’s when the current embankments
were build, the height of the crest was the same along the coast: 10,20m +NAP
the embankments body subsided
could be concluded that at the West side of the Dollart
dike body has settled the most. In the South, set
with 1 to 2 meters in 40 years. The soil subsidence can be seen in
13
K. Lentz, 2010, Waterboard Hunze en Aa’s
Climate (Ex) Change – Eco-engineering in the Dollart
Review level and allowance
: Crest height and review level of the Dutch embankment
he figure above shows the crest height and the review level derived from the Hydraulic Boundaries
2006 (HR2006). The numbers 1 till 19 represent the 19 considered cross sections
differences can be seen in crest height. In the 70’s when the current embankments
were build, the height of the crest was the same along the coast: 10,20m +NAP13
subsided with different speeds, resulting in the different crest heights. It
at the West side of the Dollart, where wind and wave attacks are lowest, the
dike body has settled the most. In the South, settlements are less, but still the crest height lowered
The soil subsidence can be seen in Figure 16.
K. Lentz, 2010, Waterboard Hunze en Aa’s
33
he figure above shows the crest height and the review level derived from the Hydraulic Boundaries
9 represent the 19 considered cross sections in the Dutch part of
differences can be seen in crest height. In the 70’s when the current embankments 13
. Due to settlement,
with different speeds, resulting in the different crest heights. It
, where wind and wave attacks are lowest, the
tlements are less, but still the crest height lowered
Climate (Ex) Change
Figure 16: Soil subsidence in the North of Groningen (‘Daling’ means su
Another factor that plays a role in the settlement of the dikes is gas extraction, of which the center is
situated Southwest of the Dollart
Dollart, which is situated in the range of influence of the gas extraction point, where t
parts of the Dollart are just outside that range. The exact settlement due to g
Dollart region is difficult to predict, but ranges between 5 and 20 centimeters.
the settlement stops in the year 2050. They assume the ground structure will be strong enough
around that time.14
The review level and allowance can be seen in the graph below. The
between the review level and the crest height. The graph shows big differences in allowance but the
review level is almost the same, differing between 6,5 m +NAP and 6,7 m +NAP. This graph clearly
shows the influence of gas extraction and settlements
cross section 1 till 10 (horizontal).
Figure 17: Freeboard (distance between the review level and the crest)
14
J.E. Pôttgens, 1991, Land Subsidence Due to Gas Extraction in the Northern
,00
,500
1,00
1,500
2,00
2,500
3,00
0 2 4
Fre
eb
oa
rd [
m]
-->
Freeboard (distance between the review level and the crest of the dike)
Climate (Ex) Change – Eco-engineering in the Dollart
: Soil subsidence in the North of Groningen (‘Daling’ means subsidence in Dutch)
Another factor that plays a role in the settlement of the dikes is gas extraction, of which the center is
lart. This also clarifies the increase in settlement on the Westside of the
d in the range of influence of the gas extraction point, where t
are just outside that range. The exact settlement due to gas extraction in the
region is difficult to predict, but ranges between 5 and 20 centimeters. Expectations are that
the settlement stops in the year 2050. They assume the ground structure will be strong enough
The review level and allowance can be seen in the graph below. The allowance is the difference
and the crest height. The graph shows big differences in allowance but the
review level is almost the same, differing between 6,5 m +NAP and 6,7 m +NAP. This graph clearly
shows the influence of gas extraction and settlements on the West side of the Dolla
cross section 1 till 10 (horizontal).
: Freeboard (distance between the review level and the crest)
ôttgens, 1991, Land Subsidence Due to Gas Extraction in the Northern Part of The Netherlands
4 6 8 10 12 14
Profiles -->
Freeboard (distance between the review level and the crest of the dike)
34
Another factor that plays a role in the settlement of the dikes is gas extraction, of which the center is
t on the Westside of the
d in the range of influence of the gas extraction point, where the Southern
as extraction in the
Expectations are that
the settlement stops in the year 2050. They assume the ground structure will be strong enough
llowance is the difference
and the crest height. The graph shows big differences in allowance but the
review level is almost the same, differing between 6,5 m +NAP and 6,7 m +NAP. This graph clearly
on the West side of the Dollart, which covers
Part of The Netherlands
16 18 20
Freeboard (distance between the review level and the crest of the dike)
Climate (Ex) Change – Eco-engineering in the Dollart
35
2.2.6 Road types and management
The roads form a large surface along the Dollart coast. This surface can be optimized by using
ecological materials. The roads on the dikes are made of tarmac and don’t have a long design period.
They need a lot of maintenance because tarmac has a relatively short design period and don’t offer a
lot of chances for vegetation or water retention. The material of which the roads are constructed
could be changed to increase nature development and decrease maintenance costs. Possibilities are
an element surfacing with concrete blocks or baked clinkers.
The management of the embankment is in hands of Waterboard Hunze en Aa’s with head office in
Veendam. They are responsible for the trajectory along the Dollart. Sheep and mowing machines
maintain the grass revetment.
When a storm threats the embankment and the water level at Delfzijl reaches a certain point a
special guard force starts patrols along the Dollart to inspect the dike body on possible failure
mechanisms.
2.2.7 Dutch Dike structure
After 1953, the Delta commission decided that al dikes had to be raised. The Dollart dikes were
initially raised with a small wall that was build on the crest. It took another 20 years before the dike
got to its current height. In the 70’s the dikes where raised to 10,20 m +NAP. The old dike which was
totally made of clay, was used in the construction of the current dikes. The contractor dumped a new
sand core against the sea side of the old dike. A new clay layer with a thickness of 0,8 m was
constructed to protect the core. This thickness was needed because the outer layer is almost always
dry. That means small cracks can form in the outer clay layer because of drought.
On the landside the old clay dike acts as a strong outer layer and the crest wall is incorporated in the
outer layer as well. The dike is constructed with a norm frequency of 1/4000 years. More details
about loads can be found in paragraph 2.2.8. The picture below shows the dike structure, with the
old clay dike, the new outer clay layer and a grass revetment. This is the same for all cross sections.
Figure 18: Dutch Dollart dike structure with seaside on the right.
Climate (Ex) Change – Eco-engineering in the Dollart
36
2.2.8 Loads , significant wave height & tides
The norm frequency of 1/4000 means the review level probably will be exceeded once in 4000 years.
The rising water level caused by onshore blowing storms and low atmospheric pressure is called a
positive storm surge. The tides and high water levels caused by storm surges are recorded by the
ministry of transport, public works and Water management (Rijkswaterstaat). The top 5 water
heights in Nieuwe Statenzijl since 1900 are given below:
483 cm +NAP 01 November 2006
453 cm +NAP 28 January 1901
451 cm +NAP 13 March 1906
448 cm +NAP 04 February 1944
446 cm +NAP 16 February 1962
These high water levels are used to determine the review levels. The significant wave height in the
Dutch Dollart fluctuates between 0,90 m and 1,25 m. The highest waves on the Dutch side of the
Dollart can be found at Nieuwe Statenzijl, where the fetch is longest. Higher waves cannot exist
because the water is rather shallow. At high tide the water is only a couple of meters deep, which
isn’t enough for waves to develop. They reach the bottom and stop growing in size. Even when the
sealevel rises the average wave height will not increase dramatically.
The Dutch dikes are tested with the average wave heights rectangular on the dike. This test is
theoretical, because in a worst case, the highest waves will always reach the dikes under an angle
when the wind comes from the Northeast and the Dollart is blown full with water from the Wadden
Sea. With other wind directions, the worst case won’t occur because the highest water doesn’t occur.
An important load is wave attack. Wave attacks are characterized by the following factors
• The Ems-Dollart region is relative shallow, this restricts the development of wave height
• The Ems-Dollart is sheltered, big waves from the North Sea can’t enter the area directly
• The fetch distance in the Ems-Dollart is restricted
In Appendix 1: Hydraulic conditions Ems-Dollart region, hydraulic conditions for the Ems-Dollart
region can be found. The most important factors for the design are the review level (based on the
highest water levels) and the significant wave height.
2.2.9 German Dollart dikes
The German Dollart dikes are constructed with slightly different hydraulic boundaries. As can be seen
in the overview of the Dollart, the German dikes are situated on the Eastside and suffer from a bigger
fetch and thus higher water set up. The construction has a different shape: the dikes are lower, with
an average crest height of 8 m +NAP. The slopes on the seaside are more gentle. The Dutch dikes are
build with outer slopes of 1:4. The German ones with a slope of 1:6. On the landside the dikes are the
same with a slope of 1:3. The gentle slope in Germany causes a reduction in wave run up and
overtopping. Because of that reduction the crest height can be lower. In the beginning of the 60’s
the German dikes were raised to the current level. Figure 19 shows the method used by the Germans
to increase the crest height. Figure 20 shows the current German dike design with an average crest
height of 8 m +NAP.
Climate (Ex) Change
Figure 19: German construction methods
Figure 20: Current German dike structure
2.3 Conclusions Chapter 2
Conclusion 2.1: The coastline is homogeneous in its properties.
A lot of them don’t change. The ones that do change are related to the position of the
embankments. Some parts of the embankment suffer from greater settlement or higher swell due to
soil properties and wind directions with a deviating crest height as result.
• The Embankment has a broad foreshore, water doesn’t reach the dike often
• The crest height deviates al
• The embankment is uniform in design.
• The Western shoreline is more subsided because its situated closer to the center of gas
extraction
Climate (Ex) Change – Eco-engineering in the Dollart
: German construction methods
Current German dike structure
Conclusions Chapter 2 analysis of the Dollart Coast
The coastline is homogeneous in its properties.
A lot of them don’t change. The ones that do change are related to the position of the
arts of the embankment suffer from greater settlement or higher swell due to
soil properties and wind directions with a deviating crest height as result.
The Embankment has a broad foreshore, water doesn’t reach the dike often
The crest height deviates along the coast.
The embankment is uniform in design.
The Western shoreline is more subsided because its situated closer to the center of gas
37
A lot of them don’t change. The ones that do change are related to the position of the
arts of the embankment suffer from greater settlement or higher swell due to
The Embankment has a broad foreshore, water doesn’t reach the dike often
The Western shoreline is more subsided because its situated closer to the center of gas
Climate (Ex) Change – Eco-engineering in the Dollart
38
• The review level is almost uniform along the coastline
• The significant wave height deviates between 0,95 m and 1,20 meter
Conclusion 2.2: The seaside of the dike can be considered dry.
Because of the marshes in front of the embankment, the water doesn’t reach the embankment very
often, only a couple of times in the storm season from October till April. Especially the dike trajectory
rectangular to the wind and dominant wave direction has a broad foreshore (up to 1100 m).
The only place where the water reaches the dike is along polder Breebaart. This trajectory of 2500 m
is potential for the use of hard ecological materials.
Conclusion 2.3: The West side of the Dollart is subjected to high subsidence.
The embankment is designed with a review level deviating from 6,5 to 6,7 m +NAP, a difference of
0,2 meter. The crest height deviates between 7,25 and 9,37 m +NAP, a difference of 2,12 m. This is a
factor 10 and implicates local subsidence. According to K. Lentz from waterboard Hunze en Aa’s, the
crest heights where designed to be equal along the Dollart coast, with an average height of 10,20 m
+NAP.
The influential zone of gas extraction can partly clarify this subsidence. This means that the
subsidence locally amounts to almost 3 meters. According to the NAM, the maximum subsidence
that can be attributed to gas extraction is 0,20 m on the Westside of the Dollart. This means that the
amount of subsidence due to settlement of the dike body is 2,80 m in the last 40 years.
Conclusion 2.4: Conclusion of the manual calculation of overtopping
• The review level and the significant wave height are important values for the outcome of the
volume of wave overtopping
• The angle of wave attack is not sensitive for the outcome of the volume of overtopping
• Using rougher revetments decreases the volume of overtopping.
• If the berm of the dike becomes wider, the wave run-up increases and the volume of
overtopping decreases.
• If the length of the slope increases the wave run-up and the volume of overtopping
decreases.
Recommendations
• The soil structure has to be investigated further by comparing CPT’s taken from the Westside
and from the Southside. This to determine the cause of settlements and subsidence.
• The use of ecological materials with a high roughness factor like Elastocoast is
recommended.
• The outcome for the influence factors of the bermwidth and the length of the slope need
further investigation.
Climate (Ex) Change – Eco-engineering in the Dollart
39
3 Eco engineering
3.1 Introduction
The use of eco-materials and methods is becoming more and more popular. The society realizes that
it has to “live” with nature and everyone has to be careful with it. When the modern dikes were built
nobody realized the important role of those dikes in nature development. Especially in wet areas at
sea sides of dikes with a hard revetment a lot of nature developed. Small plants and animals found a
new habitat created by men.
This chapter investigates the possibilities of ecological dike concepts in the Dollart. An ecological dike
concepts is defined here as the combination of a material, a method and a location.
• Material tells something about the revetment of the dike.
• Method tells something about the shape of the dike.
• Location tells something about the dike trajectory on which the concept is recommended to
use.
Paragraph 3.2 and Paragraph 3.3
These paragraphs treat the eco materials and methods that are available today to create a ecological
dike concept. It can be seen as an inventory of the possibilities in the field of eco engineering. The
materials are divided in a part for the seaside (paragraph 4.2) and the landside (paragraph 4.3) of the
dike.
Paragraph 3.4
This paragraph treats the different methods that can be combined with a material and used to create
a ecological dike concept.
The different ecological dike concepts are given in chapter 4.
3.2 Overview investigated eco materials & methods
Because the dikes need to be adapted to the sea level rise in the future and nature becomes a more
and more important factor, new ecological materials and methods are being developed. These
materials and methods have a positive influence on specific plants and animals and still protect the
dikes against incoming waves. The materials/methods which will investigated in this chapter are
listed below. These materials are mainly suitable for the use at the seaside to protect the dikes
against incoming waves. The armor layers at the seaside protect the dikes against erosion caused by
the motion of water. Besides the land side revetment, a couple of materials for the roads on the
dikes is treated as well. The chapter covers the following materials:
Materials
• Bundle of piles (palenbos) � Piles in front of the coast to break waves
• Eco-Xblocks® Large concrete armor units
• Armorflex® � Concrete mats
• C-star® coastal elements � Small C-fix elements that can be used as
revetment
• Vetiver � Tropical grass
• Elastocoast � Gravel bound together with polyurethane.
Climate (Ex) Change – Eco-engineering in the Dollart
40
• Increased overtopping � The flow rate of water that is allowed to overtop the
crest of the dike.
• Smart grass reinforcement � A reinforcing mat beneath the grass to give
the roots more strength.
• Road surfacing materials � The material of which the roads are
constructed can be changed to increase
nature development and the appearance of the dike.
Methods
• Changes in dike slope � Using the effect of a gentler slope to reduce
wave run up and overtopping
• Increased overtopping � A method where the allowed flow rate of
overtopping is increased.
3.2.1 Evaluation criteria
The materials and methods will be evaluated using the same criteria. The criteria are explained here.
Nature development � This criteria tells something about the contribution to nature
development.
Safety � This criteria tells something about the contribution to safety.
Recreation � This criteria tells something about the effect on
recreation.
Needed surface Natura 2000 � This material tells something about amount of Natura 2000
area needed.
Applicability � This criteria tells something about the applicability of the
material or method in the Dollart. The aspect of the hydraulic
boundaries are important here because the hydraulic
boundaries determine the strength of the dike. For some
materials the factor climate also plays a role.
Costs � This criteria tells something about the ratio
costs/benefits of the material or method.
Origin � This criteria tells something about the origin of the material
because the origin determines transport costs and the way it
fits in the environment of Groningen.
Experience � This criteria tells something about the experience the
Netherlands has with application of the material. This is
important because there can be differences between
theoretical and practical use.
Innovation � By using an innovative ecological material or dike concept,
the Dollart can get positive attention in the Netherlands and
the world.
Climate (Ex) Change – Eco-engineering in the Dollart
41
3.3 Eco materials
3.3.1 Pile bundles
Figure 21: pile bundles
The use of wooden piles to stop or decrease waves is used for a long time. To stop waves wooden
piles are not very effective. The piles have to be placed closely next to each other in order to stop
waves effectively or the wave energy slips between them, but the piles are a good option if the wave
height has to be reduced. If a wave hits the pile, part of the energy from the wave is lost which
results in a lower wave.
The ministry of Transport, Public works and Water management (Rijkswaterstaat) is conducting a
research on the effect of bundles of piles on the protection of the coast and are investigating if they
have a positive effect on ecology. The piles they are testing are made out of wood and concrete of
which the surface is treated to increase adhesion by algal. The piles are wrapped in thick rope to give
algal an even better chance of settling on the pile bundles. The algal species are a good breeding
ground for certain worms, lobsters and shrimps.
Another advantage of the pile bundles is that the area in which they are placed silts up. Sediment
deposits between the bundles and provides the new habitat with food and increases the water
quality. The research takes place in the Nieuwe Waterweg in Rotterdam. The salinity of that water
fluctuates a lot which creates a difficult habitat for flora and fauna. The research has to conclude if
the bundles of piles have a positive effect on ecosystems and make it more easy for flora and fauna
to settle in those environments. In the Dollart, the piles have to be very high to have a positive effect
on wave height.
Evaluation Pile bundles
Nature development � Bundles of piles can be a way to develop natural values if
they are placed in the water in front of the marshes.
Safety � Because the difference between high tide and low tide is
extremely high in the Dollart, the piles have to be very high to
make a contribution to coastal safety (3 to 4 meters above
the normal water level).
Climate (Ex) Change – Eco-engineering in the Dollart
42
Recreation � The use of pile bundles won’t have a significant effect on
recreation, because the ecosystem that would be created by
using the piles would be situated far from the embankment.
Needed surface Natura 2000 � The needed Natura 2000 area is large because the bundle of
piles will have to be placed in the Wadden Sea.
Innovation � Pile bundles are an innovative solution, but not very
attractive for tourists because of pollution of the horizon.
Experience � Bundles of piles have been used before, but not with the
needed height in the Dollart.
Origin � Bundles of piles can be made from hardwood or concrete,
both not especially originating from the Dollard Area. If
materials from the Dollart area are used to make the piles,
the design period of the piles will decrease.
Costs/benefits � The costs of pile bundles are low.
Applicability � Bundles of piles have no effect on coastal safety and
recreation. Besides that they will cause horizon pollution and
will need a lot of Natura 2000 area. Bundles of piles aren’t
suited for application in the Dollart area because the costs
outweigh the benefits.
3.3.2 Eco Xbloc’s
Figure 22: Eco Xbloc's
Xbloc’s are a variant on the normal Xbloc’s and form a single layer of armor which can be used for
the protection of piers, seawalls and other coastal object against wave attacks. Eco Xbloc’s are quit
new however they already proved their use. Because of the special design they have a very high
stability coefficient and use less concrete compared to other armor layers (cubes, tetrapods, etc.).
From the ecological aspect Eco Xbloc’s are interesting. The rough concrete surface provides a very
good habitat for flora and fauna. The armor layer has a lot of space where water can be retained.
Climate (Ex) Change – Eco-engineering in the Dollart
43
Tests were performed in Ijmuiden using these bloc’s and after three years the Eco Xbloc’s were
totally overgrown by flora.
Besides the function as revetment, the Eco Xbloc’s can be used as artificial reefs as well. These reefs
can be made in front of the coast where they will reduce wave heights. A reef stimulates nature
development in two ways:
• The Artificial reef made from Eco Xbloc’s will create a habitat for fish and plants. This is
caused by the space between the bloc’s and the high porosity of the Eco Xbloc’s. The reef
environment offers protection and shelter and a place that will be silted up and provide food.
• Because the wave height is reduced, a sheltered area between the reef and the coast is
created which is good for nature development.
Evaluation Eco Xbloc’s
Nature development � Eco Xbloc’s can contribute to nature development with their
rough surface or by using them to build artificial reefs.
Safety � Eco Xbloc’s are build to withstand high wave heights of 3,5 m
or more. They are used in extreme conditions. When they are
used to build artificial reefs they will also help breaking waves
and reducing wave attacks.
Recreation � The effect of Eco Xbloc’s on recreation will be negative
because they are very big and make the sea side of the dike
inaccessible for tourists.
Needed surface Natura 2000 � There is no loss of Natura 2000 area when Eco Xbloc’s are
used.
Innovation � The use of Eco Xbloc’s is not innovative. They are being used
for years.
Experience � There is little experience of using Eco Xbloc’s in the
Netherlands, but the normal Xbloc’s, without the rough
surface, are used around the world.
Origin � Eco Xbloc’s are made from concrete, the origin is not specific
from the Dollart region.
Costs/benefits � The costs of Eco Xbloc’s are very high. It costs a lot of work to
install them in a correct way.
Applicability � The Eco Xbloc’s are meant for heavy wave attacks. In the
Dollart those high waves won’t occur. A lot of value of the
Eco Xbloc’s is in safety, so in order to make application of
them feasible, there have to be heavy wave attacks. When
they are used for building artificial reefs, the visual of the
Dollart will decrease.
Climate (Ex) Change – Eco-engineering in the Dollart
44
3.3.3 Armorflex
Figure 23: Revetment of Armorflex
Armorflex blocks are developed in the United states by the company Armortec. The bloc’s are
specially designed to protect all kind of structures against flowing water and wave attacks. Armorflex
armor layer are suitable to protect:
• Ditches
• Channels
• Dikes
• Estuaries
• Breakwaters
• Piers
• Groins
To avoid the sight of grey concrete, the bloc’s have an open texture and are shaped conically at one
side. The opening on the inside and the special shape gives vegetation enough space to grow
between the bloc’s. Another advantage of the special shape is that the can follow settlement
contours and that the bloc’s have a high water permeability. All this without losing hydraulic stability,
also caused by the special shape of the bloc’s. The bloc’s are made from concrete, which has a rough
surface and is a good living habitat for algal. The armorflex bloc’s are already used in the Netherlands
on several places under which the Ijsselmeer. They can withstand high wave heights.
Evaluation of Armorflex
Nature development � Armorflex can contribute to nature development with its
rough surface when the sea reaches the it. In the Dollart this
is not always the case.
Safety � Armorflex are designed to withstand heavy wave attacks and
is used on several dikes in the Netherlands along the
Ijsselmeer coast.
Recreation � The effect of Armorflex on recreation will be small because
the sight of them is not very special.
Climate (Ex) Change – Eco-engineering in the Dollart
45
Needed surface Natura 2000 � There is no loss of Natura 2000 area when Eco Xbloc’s are
used.
Innovation � Armorflex is not very innovative, it is used all over the world.
Experience � There is a lot of experience with Armorflex.
Origin � Armorflex bloc’s are made from concrete, the origin is not
specific from the Dollart region.
Costs/benefits � The costs of using Armorflex are normal, but the benefits that
can be achieved when the dike is situated directly to the
water won’t be achieved when marshes are present.
Applicability � The applicability of Armorflex depends on the presence of
marshes. When marshes are present, the use of armorflex is
not recommended.
3.3.4 C-star® coastal elements
Figure 24: A revetment of C-star elements
C-star elements are elements made from C-fix. C-fix is a material made from sand, fillers, aggregates
and are bound together with a visco-elastic binder. C-fix has some advantages in comparison with
the standard building materials like concrete:
• 100% recyclable
• Impermeable to liquids
• Resistant to chemicals, salt and acids
• Strong, hard , high tensile stresses possible
• Resistant to dynamic loads, no brittle behavior, no breaking of units.
• A significant reduction of CO2
emissions in comparison with use of concrete.
C-start elements have sort of triangular shape of which the edges are rounded. Furthermore the top
of the C-star elements can be provided with various ecological top layers to stimulate the flora and
fauna in the flood zone. The C-stars can be used to protect all kind of structures like:
Climate (Ex) Change – Eco-engineering in the Dollart
46
• Dikes (sea and river)
• Groins
• Revetments
• Embankments
• Shore protections (as an alternative to Standard rock and concrete breakwater armor units)
C-stars are a good option for protection of coastal structures because of the high hydraulic stability.
Economical the C-stars can also be very attractive. A relatively thin layer is necessary to protect a
coastal structure. Other materials need a thicker layer to protect the coastal structure, like rock or
concrete armor.
Evaluation C-star elements
Nature development � C-star elements can contribute to nature development with
its rough surface when the sea reaches the it. In the Dollart
this is not always the case. The top layer of C-stars can be
customized with different ecological materials to create more
diversity in the revetment. Besides these advantages, C-stars
are made from C-fix, which is 100% recyclable.
Safety � C-star elements are designed to withstand heavy wave
attacks and is used on several dikes in the Netherlands along
the Ijsselmeer coast.
Recreation � The effect of C-star elements x on recreation will be small
because the sight of them is not very special.
Needed surface Natura 2000 � There is no loss of Natura 2000 area when C-star elements
are used.
Innovation � C-star elements are not very innovative, they are used all
over the world.
Experience � There is a lot of experience with C-star elements.
Origin � Because the top layer of C-star elements can be customized,
materials from the Dollart region could be used. Which
materials could be used has to be investigated.
Costs/benefits � The costs of using C-stars are normal, but the benefits that
can be achieved when the dike is situated directly to the
water won’t be achieved when marshes are present.
Applicability � The applicability of C-stars depends on the presence of
marshes. When marshes are present, the use of C-stars is
not recommended.
Climate (Ex) Change
3.3.5 Vetiver
Figure 25: Vetiver used as slope protection in Vietnam
An effective and efficient way of protecting the outer slope is to apply the grass specie
combination of Vetiver and hard revetment. The grass can cover t
crown and inner slope.
Important aspects of Vetiver grass:
• The grass can grow up to 1,5meter high and the grass fast
reaching between 2 and 4meter deep in 12 months.
• Good tolerance to extreme
temperature (from -15ºC to +55ºC)
• Vetiver can re-grow very quickly after being affected by frosts or salinity
• High tolerance level for soil pH, pesticides and heavy metals
• Medium growth in salty environm
• Intolerant to shading
• It’s a typical tropical grass. Best pe
• Vetiver hedges are a natural soft eco
• Application of Vetiver on the slope of a dike has
technologies
• Long-term maintenance costs are low
Evaluation Vetiver
Nature development �
Safety �
Climate (Ex) Change – Eco-engineering in the Dollart
: Vetiver used as slope protection in Vietnam
An effective and efficient way of protecting the outer slope is to apply the grass specie
and hard revetment. The grass can cover the dike surface
grass:
The grass can grow up to 1,5meter high and the grass fast-growing root system capable of
reaching between 2 and 4meter deep in 12 months.
Good tolerance to extreme climate variations. For example drought and extreme
15ºC to +55ºC)
grow very quickly after being affected by frosts or salinity
High tolerance level for soil pH, pesticides and heavy metals
um growth in salty environment
It’s a typical tropical grass. Best performance in a warm environment
hedges are a natural soft eco-engineering and a good alternative to hard structures
on the slope of a dike has lower costs compared to many other
term maintenance costs are low
� Vetiver can contribute to nature development because it
creates a new environment with vegetation which provides
shelter and food for specific plants and animals. No artificial
materials have to be used.
� Vetiver is a grass species that grows in tropical climates. It
has long roots that make the soil more adhesive and increase
stability more than the usual grass species used as
revetment. Vetiver gives the slope of dikes a high roughness
47
An effective and efficient way of protecting the outer slope is to apply the grass species Vetiver or a
he dike surfaces like the berm,
growing root system capable of
climate variations. For example drought and extreme
engineering and a good alternative to hard structures
ed to many other
Vetiver can contribute to nature development because it
creates a new environment with vegetation which provides
ific plants and animals. No artificial
Vetiver is a grass species that grows in tropical climates. It
has long roots that make the soil more adhesive and increase
ecies used as
revetment. Vetiver gives the slope of dikes a high roughness
Climate (Ex) Change – Eco-engineering in the Dollart
48
factor and decreases wave run-up and overtoppingl It can
withstand high wave attacks.
Recreation � Vetiver causes a natural look and is attractive for tourists.
Needed surface Natura 2000 � There is no loss of Natura 2000 area when Vetiver is used.
Innovation � Application of Vetiver in the Netherlands would be very
innovative. The species only grows in Asia, so it is never used
in the Netherlands before.
Experience � There is a lot of experience with Vetiver as revetment in Asia.
Studies are performed by technical Universities like Technical
University of Delft to investigate the strength of this grass15
.
The outcome was positive.
Origin � Vetiver originates from Asia, making it a foreign species and
less attractive to use in the North of the Netherlands when
the culture and historical values of the Dollart area have to
remain.
Costs/benefits � Vetiver has a low price, especially compared to hard
revetments (concrete or C-fix)
Applicability � Applicability of Vetiver in the Netherlands is not possible at
this time. It can’t resist periods of high frost. Genetically
improving the species to make it resistant to strong cold
could be an option. Another option could be to look for
similar indigenous species with similar properties.
The following result are the outcome from the test of H.J. Verhagen , D.J. Jaspers Focks, A. Algera
and M.A. Vu, performed for the Technical University of Delft.
• Vetiver grass is a suitable and innovate solution for the protection of sea dikes
• Vetiver protects earth structures more effectively
• Vetiver grass can be used at SWL as well as on the dikes were the water table can be low
• Vetiver barrier reduces 45% of the total overtopping discharge, with a grass density of 200
steams per square meter. The value is higher when grass density increases.
• The roughness coefficient of Vetiver grass varies from 0.33 to 0.41, depending on grass
density
• A Vetiver barrier is successful to reduce wave run-up. Wave run-up reduction increases up to
60% at density of 200 steams per meter.
15
H.J. Verhagen , D.J. Jaspers Focks, A. Algera and M.A. Vu,
THE USE OF VETIVERS IN COASTAL ENGINEERING, Dubai, 2008
Climate (Ex) Change – Eco-engineering in the Dollart
49
3.3.6 Elastocoast
Figure 26: Mixing ingridients, application and final result of an Elastocoast revetment
A new type of revetment is called Elastocoast. This protection system combines gravel with a 2-
component polyurethane (PU). The polyurethane glues the gravel together resulting in a stable
structure. A small amount of PU is used to keep the structure porous, which results in a reduced
wave run-up. The material consists of approximately 50% vegetable acids, i.e. renewable raw
materials. The production process is given in Appendix 2. The stones need to be clean and dry before
they can be processed. Simple measures regarding handling and logistics eliminate this obstacle.
The porous revetment offers a lot of advantages. If water runs up on the porous surface of
Elastocoast part of the hydraulic energy will be absorbed by friction in the volume of the pores. The
wave masses will be transformed into thermal energy and that will result in a lower wave run-up.
Two tests were performed and analyzed during the storm season in the Netherlands (wind speeds
above 17 m/s). The test results gave the following outcome:
• Negligible damages to the Elastocoast revetments
• Even layer with a thickness of only 10 centimeter performed as a stable construction
The high porosity has another advantage. Revetments are saturated with water when the water level
is against the dike and therefore subject to overpressure. When the height of the water drops the
overpressure can lead to destabilization. The decrease of water pressure is faster with porous
revetments. Tests show that Elastocoast is much more resistant to erosion and abrasion compared to
Open Stone Asphalt. Projects showed that Elastocoast is cost effective. The basic costs in the
realization of the coastal protection structure are transport, prices for raw material, simple
installation and the process of the materials. The high porosity and load bearing result in a thinner
layer of Elastocoast on the dike. This may rise to 50% compared to a conventional revetment.
Tests in the field and in a laboratory gave a positive outcome of the growth of biotic live. A couple of
species that found a habitat on the Elastocoast revetment can be found in Appendix 2. Elastocoast is
already in use or being tested in Canada, France, Germany, Great Britain and the Netherlands. The
best example is a reference project in Emden – Germany. Near the Ems sperwerk a 15m2 area with
Climate (Ex) Change – Eco-engineering in the Dollart
50
Elastocoast is set into place. The revetment is built on granite gravel (thickness between 30 and
60mm) and Elastocoast on gravel core with a geotextile base.
Evaluation Elastocoast
Nature development � Elastocoast forms a rough and open surface and a habitat for
specific plants. A prequisit is that the revetment is build next
to the seas and water can reach it. In the Dollart this is not
always the case.
Safety � Elastocoast forms a strong layer and can resist high wave
attacks.
Recreation � The Elastocoast revetment looks like tarmac and when the
dike is not overgrown with specific plants, the dike won’t look
very attractive.
Needed surface Natura 2000 � There is no loss of Natura 2000 area when Elastocoast is
used.
Innovation � Application of Elastocoast is an innovative solution of
creating a revetment with an open texture. The material is
not used a lot.
Experience � There is not much experience with Elastocoast revetments
but tests have proven its strength and are still conducted to
investigate the exact properties.
Origin � Elastocoast is a combination of gravel and PU and is not
specifically from the Dollart area.
Costs/benefits � Elastocoast has the advantage of an open texture where
specific plants can grow if sea water flows over the
revetment at high tide. In the Dollart this is not always the
case, so the benefits of Elastocoast can only be achieved at
places without marshes.
Applicability � Elastocoast can be applied in the Dollart but only on places
where there are no marshes present.
3.3.7 Hydrotex
Figure 27: Hydrotex Enviromat Lining (left) and Hydrotex Articulating Blocks
Climate (Ex) Change – Eco-engineering in the Dollart
51
This is a fabric formed armoring system usable on different types of water constructions. The
manufacturer has different types of products for different applications. We will describe two of the
products.
• Enviromat Lining
• Articulating blocks
Enviromat Lining
Enviromat Lining is a big mattress (woven double-layer fabric joined together by large interwoven
areas) with different compartments. These compartments will be filled with a mixture of Portland
cement, fine aggregate and water. The result is a solid structure. Approximately 20% of the total area
of the mats is opened by cutting the fabric. After the installation vegetation can be planted within
the open structures. Within a growing season a vegetated cover will normally extend over the lining.
The result is an erosion control system with the hydraulic and ecological features.
The Enviromat Lining is a new type of revetment that provides protection against periodic high flows
and is subject to heavy run-off. It is used in drainage ditches and on the upper slopes of canals,
channels, lakes, reservoirs, rivers and other water courses. So it is not really suitable as a revetment
on the dike. But this type of revetment is mentioned because the added value for natural
development is high.
Articulating Blocks
As a revetment for the dikes in the Ems Dollart region the Articulating blocks are more suitable when
the revetment is exposed to frontal attack by wave action. The Blocks differ from the Enviromats.
They are strengthened with reinforced concrete. The average thickness, mass per unit, area and
hydraulic resistance of each concrete lining withstands high wave attacks.
Evaluation Hydrotex Articulating Blocks
Nature development � Hydrotex Articulating Blocks form a very rough but hard
surface which retains water in the open surface and forms an
ideal surface for algal to grow on. This only works when
Hydrotex Articulating Blocks are applied on a dike next to the
open water.
Safety � Hydrotex Articulating Blocks can withstand high wave attacks
and are suitable for hydraulic conditions in the Dollart.
Recreation � The open texture attracts specific plants and animals which
make the outer layer of the dike attractive to the eye.
Needed surface Natura 2000 � There is no loss of Natura 2000 area when Hydrotex
Articulating Blocks are used.
Innovation � The use of Hydrotex Articulating Blocks is not very innovative.
Experience � Hydrotex Articulating Blocks have been used before with
success.
Climate (Ex) Change – Eco-engineering in the Dollart
52
Origin � The material is made from concrete and aggregates and
doesn’t originate specifically from the Dollart area.
Costs/benefits � The costs of Hydrotex Articulating Blocks are medium, and
the benefits will only be achieved when the material is used
in the presence of open water.
Applicability � Applicability of Hydrotex Articulating Blocks depends on the
presence of marshes along the coastline and the average
wave height. For trajectories of the coast without marshes it
could be a good choice for the revetment.
3.3.8 Smart grass reinforcement
Figure 28: Picture of the smart grass reinforcement
Smart Grass Reinforcement (SGR) is an idea from Royal Haskoning and Imfram. They made a
functional analysis of possible reinforcement systems. Finally, the Fortrac 3D-120 system from
Heusker was chosen as the most suitable erosion prevention system. The Fortrac 3D-120 system is a
synthetic gauze which can be used on slopes to prevent erosion. SGR was also used with the
overtopping tests and proven to be very helpful to prevent erosion when overtopping occurs. The
SGR protects the dike in three ways against erosion:
• Fotrec 3D-120 gives the grass extra holding power in the ground, because the roots and the
system weave in together
• The system gives extra protection to the underlying clay layer
• The system prevents shear of the slope because it pulled over the crest of the dike and
anchored
SGR can also be used at the seaside of the dike where it can be used for protection against erosion.
How much protection it will give is not known, but it probably gives extra protection against waves.
Tests have to point out the exact addition of SGR to the strength of a grass revetment. Installing SGR
is quite easy and large surfaces are also not a problem. The top layer is cut away and then the system
is installed. After the system is installed the grass can be put back in place. After some time the grass
stronger than before and ready to handle future storms.
Climate (Ex) Change – Eco-engineering in the Dollart
53
Evaluation SGR
Nature development � The current natural values are preserved because SGR is
applied beneath the current grass revetment.
Safety � The resistance against overtopping increases by applying
SGR. The current standard of 1 l/m/s can be raised up to 50
l/m/s. Also the resistance against wave attacks increases.
Recreation � The revetment of grass with SGR doesn’t change the
appearance of the dike. This material won’t have an effect on
recreation.
Needed surface Natura 2000 � There is no loss of Natura 2000 area when SGR is used.
Innovation � The increased overtopping is innovative. This can be achieved
with SGR without changing the appearance of the dike. The
standards of allowed flow rate of overtopping are not
changed yet. If this happens it could mean that the crest
height won’t have to be raised.
Experience � There is not much experience with the use of SGR. Research
is still performed to determine the exact properties of this
material.
Origin � The material does not origin from the Dollart area, but the
grass revetment like it exists now will remain, and will give
the dike an authentic look.
Costs/benefits � The costs of SGR are low, but it has to be applied under the
current grass revetment. The current revetment has to be
removed and replaced. This can’t be done in the storm
season. The benefits of SGR are that the appearance doesn’t
change but strength increases.
Applicability � SGR can be applied in the Dollart region. It can guarantee
safety and the costs are low.
3.3.9 Road surfacing materials
The maintenance road at the landside are now made from tarmac which doesn’t give the dikes a
naturally appearance. The road’s primary goal is to give access to the embankment for water boards
when maintenance or inspections have to be done. A secondary function of the road is the access for
tourists who visit the area. There are a lot of cyclist and walkers who use the dike to enjoy the sight
of the landscape and sea. This paragraph treats materials that could be used to replace the existing
road, with the primary reason to make the dike more attractive for tourists.
Climate (Ex) Change – Eco-engineering in the Dollart
54
Grass concrete block’s
Figure 29: Drawing of grass concrete blocks
Grass concrete block’s can be an alternative for tarmac on the dikes in the Ems-Dollart region. It’s a
concrete surfacing that allows grass to grow between the block’s and in that way a natural look is
created. There are different types of grass concrete block’s manufactured by different manufactures.
The most Grass concrete blocks are suitable for cars to drive. However not all block’s are suitable for
bicycle’s and sheep. Not suitable blocks are to open or too rough too use for a bicycle road. The block
shown in Figure 29 is a type of block that can be used to construct a green road on the dike.
Baked clinkers
Figure 30: Baked clinkers made from clay
Clinkers baked from clay are used since the Middle Ages and still very popular in gardens and
driveways. The use of baked clinkers in road construction has decreased. An interesting feature for
the roads on the dike is the fact grass can grow between the stones because they all slightly differ in
shape and size. That makes a road of baked clinkers an element surfacing with a lot of space for grass
and weeds to grow, resulting in a very green appearance. The clinkers aren’t very suitable for roads
with heavy traffic loads, but for the dikes in the Dollart they would be very suitable. A disadvantage
could be the price of this element surfacing.
Climate (Ex) Change – Eco-engineering in the Dollart
55
Plastic grass stones
Figure 31: Plastic grass stones, type slimblock
Plastic grass stones are made parking spaces and roads which have to fit in the surroundings. Plastic
grass stones are suitable for roads and places with a low traffic density. The stones are strong enough
for cars and heavy trucks to drive over. The fact the plastic grass stones are open for 86% gives grass
the opportunity to grow between the stones. There are all kind of plastic grass stones but the type
seen in Figure 31 is manufactured by Three Ground Solutions. The plastic stones are made from
recycled plastic and available in green or black. All the stones are mounted together to get a strong
and even surface. Plastic grass stones can be suitable for the maintenance roads with a very light
traffic density. A disadvantage could be the fact that the plastic grass stones probably aren’t
comfortable for cyclist. Besides that it could be difficult to see the road on a dike that is totally
covered with grass.
Evaluation road surfacing materials
Nature development � The contribution to nature development by using a nature
friendly road surfacing material can be neglected.
Safety � n/a
Recreation � The use of nature friendly road surfacing materials can
contribute to recreation because it makes the dike more
attractive.
Needed surface Natura 2000 � n/a
Innovation � n/a
Experience � There is a lot of experience with these road surfacing
materials
Origin � Materials originating from the Dollart area can be used for
road surfacing.
Costs/benefits � the costs of replacing the surface road aren’t high when its
combined with the replacement of the revetment. The
benefits can be an attractive appearance of the dike.
Climate (Ex) Change – Eco-engineering in the Dollart
56
Applicability � Nature friendly road surfacing materials can be applied in the
Dollart region.
3.4 Eco methods
3.4.1 Increased overtopping
Because of the rising sea level a lot dikes in the Netherland need to be raised according to the
current guidelines. This means a lot of money has to be spent on the coastal defenses. Rough
estimates say no less than 2000 billion Euro’s are needed to bring the dikes to the desired height.
That money has to be spent in the next century. To bring back the high costs for dike raising, tests are
being conducted that investigate an increase in permissible overtopping. The current standards only
allow an overtopping flow rate of 0.1 l/m/s. Dike administrators are very cautious with overtopping
because the effects of it on the revetment on the land side are not very clear. The guidelines are not
based on scientific evidence but on personal feelings. Nobody exactly knew what would happen if
large amounts of water washed over the crest and the land side of the dike.
In 2007 the ministry of transport, public works and water management started researching what
would happen when larger amounts of water overtopped the crest. The focus was to investigate
what would happen with the inside slope and the toe of the dike. Different tests were conducted on
different locations.
Figure 32: Schematic overview of the wave overtopping simulator
The most of the tested dikes have the same properties as the dikes in the Dollart. The outer layer of
the dike is made from clay and covered with grass. This means that the landside of the dike has no
armor layer which protects the dike against water. Besides testing the actual existing dikes
“reinforced” grass and clay without grass was also tested. In total there were 3 tests.
The overtopping simulator has the capacity to simulate overtopping up to 50 l/s/m over a width of 4
meter. Every test series last for six hours in which a “storm” becomes more and more intense. Every
two hours all damages, speed of the waves and the wave height were being determined. The first
test was the dike with grass. These tests were carried out very smoothly and there was no real
damage on the dike, even with a flow rate of 50 l/s/m. The fact that the tests were more successful
than expected the engineers decided to create some damage to the dike and look what would
happen.
The second test was the dike with the “reinforced” grass. Just like the normal dike no damage
occurred when the storm of 6 hours was imitated. When artificial damage to the dike was made, and
water came over the dike no damage occurred.
Climate (Ex) Change – Eco-engineering in the Dollart
57
Figure 33: Test results from simulator test; left picture is the dike without reinforced grass and the right with
reinforcement
The third and last test investigated the strength of a dike without any revetment. The strength of the
clay layer determined the strength of the dike. It turned out that a dike without a revetment like
grass can survive a storm with an overtopping flow rate of 10 l/m/s, but little damage will occur in
that case. The test pointed out that a grass revetment makes a dike many times stronger.
Usability in the Dollart
The overtopping tests had a very positive outcome and better than the most experts expected. At
this moment the tests are being reviewed and is it expected that new regulations for overtopping are
ready in 2011. This means that from 2011 there probably will be an increase in the allowed
overtopping flow rate. The sea level rise makes an increased crest height necessary, but with an
increase in overtopping flow rates, the amount with which the current dikes have to be raised could
be less than expected.
Evaluation of increased overtopping
Nature development � The method of increased overtopping doesn’t directly
influence nature development.
Safety � This method doesn’t increase safety but redefines it, making
it possible that the current dike height is safe enough for sea
level rise in the future.
Recreation � n/a
Needed surface Natura 2000 � n/a
Innovation � The increased overtopping method is very innovative. First it
was believed that water flowing over a dike was dangerous.
Climate (Ex) Change – Eco-engineering in the Dollart
58
At this time experiments are conducted to determine the
amount of overtopping can be allowed, resulting in
overtopping flow rates of up to 50l/m/s. This means that the
definition of safety is redefined with this method.
Experience � The only experience with this method is derived from
experiments.
Origin � n/a
Costs/benefits � The benefits of this method is that the crest height doesn’t
need to be raised when the sea level rises. This means this
method reduces the costs of coastal safety.
Applicability � Because the Dollart isn’t densely populated and there is
enough space behind the dike, this method is applicable in
the Dollart.
3.4.2 Adjustments of dike slope
The slope of the dike determines the amount of wave run up and overtopping. A gentle slope causes
earlier breaking of waves and therefore reduces wave run up and overtopping. In the Dollart, where
the waves aren’t higher than 1,25 m, the dikes can be kept lower if the slope is made gentler. Figure
34 shows the influence of the slope and the overtopping flow rate on the crest height.
Figure 34: Influence of a gentle slope on the crest height
Evaluation of adjusting the dike slope
Nature development � When the dike slopes are made gentler, the sharp line
between the embankment and the marshes or the sea
becomes broader. The result could be an increase in specific
animals and plants on the sea side of the dike. But on the
other hand, the sharp line still exists on the crest, whith the
land side of the dike being as steep as before. The exact
influence from this method on nature development has to be
investigated further.
Safety � As can be seen in Figure 34 a gentler slope has a positive
effect on the needed crest height. The contribution to safety
depends on the reduction of steepness.
Climate (Ex) Change – Eco-engineering in the Dollart
59
Recreation � A gentle slope can have a positive effect on recreation when
the slope is made accessible for visitors.
Needed surface Natura 2000 � The amount of Natura 2000 area needed for this method is
high. This means that a lot of nature values are lost and have
to be retrieved elsewhere. In the Dollart area this can’t be
done.
Innovation � A gentle slope is not innovative. Germany already has a more
gentle slope of 1:6 instead of 1:4 in the Netherlands.
Experience � There is a lot of experience with gentle slopes of
embankments, but not in a nature reserve like the Wadden
Sea. The effects on nature development have to be
investigated further.
Origin � n/a
Costs/benefits � The costs of making a slope more gentle is very high. There is
a lot of material needed to stretch the dike core and also the
needed revetment materials which are the most expensive,
increase. Besides that the lost nature value of the Natura
2000 area have to be regained, with the corresponding costs.
The benefits are uncertain, besides the fact that the crest
height doesn’t have to be raised.
Applicability � Because the Dollart is a Natura 2000 area, this method will
cause a loss of nature value. Besides this the costs of applying
this method are very high because of the needed material.
These reasons make applicability of this method difficult in
the Dollart.
3.5 Multi-criteria analysis
To determine the best suitable material and method per section, 4 multi criteria analysis are made,
one for each section.The Dollart dikes aren’t the same along the coast, so the coast has to be divided
in different sections. The trajectories are based on the presence of marshes, the crest height, and the
dike slope, because that are the main characteristics of the embankment. The different sections can
be found in Figure 35.
Red section 1 (2500 m) � No salt marsh in front of the dike, the influence of
wave (representative for profile 4) wave attack is almost negligible and the crest height
is the lowest. The water stands against the toe of the
dike.
Green section 2 (8000 m) � Salt marsh in front of the dike, an average influence
of (representative for profile 10) wave attack and an average crest height compared to
the other sections. Under normal weather conditions,
the water doesn’t reach the dike.
Climate (Ex) Change – Eco-engineering in the Dollart
60
Bleu section 3 (4250 m) � Salt marsh in front of the dike, an average influence
of (representative for profile 14) wave attack and an high crest height compared to
the other sections. Under normal weather conditions,
the water doesn’t reach the dike.
Yellow section 4 (11000 m) � Salt marsh in front of the dike, assumed that the
influence of wave attack is the highest, because the
fetch is the longest (The value of the significant wave
height is unknown). Assumed that the water doesn’t
reach the dike under normal weather conditions.
Figure 35: The Dollart coast divided in different sections
The materials and methods have to be classified to determine the best and the least suitable
solution. This is done by the same criteria as were used in the evaluation of the materials and
methods:
• Nature development
• Safety
• Recreation
• Needed surface Natura 2000
• Innovation
• Experience
• Origin
• Costs/benefits
• Applicability
Climate (Ex) Change
The criteria are of different importance. That is why different weighing factors are assigned to each
of them. The scores of a material per criteria are multiplied with the weighing factor and the total is
divided with the addition of the weighing factors resulting in a score per material.
The weighing factor varies from 1 to 5 where 1 equals very unimportant and 5 equals very important.
The scores of each material vary from
effect.
The header materials analyses the situation where the only change in design is the material on the
outer layer of the primary embankment.
change in design is the use of one of the two methods described in this chapter (an increase in
allowable overtopping and a more gentle slope).
The materials that can be used for road surfacing
because they don’t have a significant ef
development.
Analyzed materials
1. No different material used
2. Bundle of piles
3. Eco Xbloc’s
4. Armorflex
5. C-star elements
Analyzed methods
1. No changes
2. Increased overtopping
3. Slope changes
4. Raising the crest height
Figure 36 till Figure 39 indicate the scores of the materials and method mentioned above. The
numbers on the x-axis correspond with the numbers mentioned above for the materials and the
methods.
Figure 36: MCA for the materials and methods applied in section 1
Climate (Ex) Change – Eco-engineering in the Dollart
The criteria are of different importance. That is why different weighing factors are assigned to each
of them. The scores of a material per criteria are multiplied with the weighing factor and the total is
with the addition of the weighing factors resulting in a score per material.
The weighing factor varies from 1 to 5 where 1 equals very unimportant and 5 equals very important.
The scores of each material vary from 1 to 5 where 1 equals a negative effect and
analyses the situation where the only change in design is the material on the
outer layer of the primary embankment. The header methods analyses the situation where the only
of one of the two methods described in this chapter (an increase in
allowable overtopping and a more gentle slope).
for road surfacing are not included in the multi-criteria analysis
because they don’t have a significant effect on the most important issues: safety and nature
material used 6. Vetiver
7. Elastocoast
8. Hydrotex Articulating Blocks
9. Smart Grass Reinforcement
indicate the scores of the materials and method mentioned above. The
nd with the numbers mentioned above for the materials and the
: MCA for the materials and methods applied in section 1
61
The criteria are of different importance. That is why different weighing factors are assigned to each
of them. The scores of a material per criteria are multiplied with the weighing factor and the total is
with the addition of the weighing factors resulting in a score per material.
The weighing factor varies from 1 to 5 where 1 equals very unimportant and 5 equals very important.
t and 5 equals a positive
analyses the situation where the only change in design is the material on the
The header methods analyses the situation where the only
of one of the two methods described in this chapter (an increase in
criteria analysis
fect on the most important issues: safety and nature
Hydrotex Articulating Blocks
Smart Grass Reinforcement
indicate the scores of the materials and method mentioned above. The
nd with the numbers mentioned above for the materials and the
Climate (Ex) Change
Figure 37: MCA for the materials and methods applied in sectio
Figure 38: MCA for the materials and methods applied in section 3
Figure 39: MCA for the materials and methods applied in section 4
3.5.1 Conclusions MCA’s
• Hard revetments score high on nature developm
4. That is because section 1 is the only section without marshes in front of the coast. In
section 2, 3 and 4 the hard revetments lo
• Smart Grass Reinforcement scores
appearance of the dike, but improves strength, is easy to apply and relatively cheap.
• ‘No different material used’ scores high in every MCA and in the last three it even comes at
the second place. This is because it is the cheapest method and in MCA 2, 3 and 4 the hard
revetments lose their advantage of contributing to nature development.
Climate (Ex) Change – Eco-engineering in the Dollart
and methods applied in section 2
and methods applied in section 3
and methods applied in section 4
Hard revetments score high on nature development in section 1, but low in sections 2,3 and
4. That is because section 1 is the only section without marshes in front of the coast. In
section 2, 3 and 4 the hard revetments loose their contribution to nature development.
Smart Grass Reinforcement scores high in every section. This is because it doesn’t change the
appearance of the dike, but improves strength, is easy to apply and relatively cheap.
‘No different material used’ scores high in every MCA and in the last three it even comes at
. This is because it is the cheapest method and in MCA 2, 3 and 4 the hard
revetments lose their advantage of contributing to nature development.
62
ent in section 1, but low in sections 2,3 and
4. That is because section 1 is the only section without marshes in front of the coast. In
se their contribution to nature development.
high in every section. This is because it doesn’t change the
appearance of the dike, but improves strength, is easy to apply and relatively cheap.
‘No different material used’ scores high in every MCA and in the last three it even comes at
. This is because it is the cheapest method and in MCA 2, 3 and 4 the hard
revetments lose their advantage of contributing to nature development.
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63
• Vetiver has good results in these MCA’s, but this material is not suitable for the Dutch
climate. Vetiver is in the MCA because it would be the best nature friendly material to use.
More research has to be done to the use of Vetiver on Dutch dikes.
• The method of increased overtopping scores highest in every MCA. This is because it’s no
real method, but a change in standards. It has the advantages of a ecological method, but
not the disadvantages like application problems or costs.
• The method of raising the crest height scores highest in section 1 because the West bank of
the Dollart is subjected to higher subsidence and has a lower average crest height.
• The scores of methods are similar in every MCA. This is because the criteria with the highest
weighing factor are the same along the Dollart coast (See Appendix 7: Multi criteria analysis)
3.6 Conclusions Chapter 3 Eco engineering
Conclusion 3.1: The use of ecological materials only, doesn’t contribute to an increase of both nature
development and coastal safety
If marshes are present in front of the dikes, the problem of combining nature development with
coastal safety cannot be solved by using one specific method or material. The most of the available
materials are only applicable in situation where seawater reaches the toe of the dike continuous. In
the Dollart this is only the case in section 1.This can be seen in Figure 36. Ecological materials used as
revetment have to be covered with water at least one period a day to create more natural value. If
not, they only cause higher protection.
Conclusion 3.2: The most ecological materials focus on vegetation and animals that live in a wetland
area, not in a relatively dry environment like the Dollart dike.
Most materials are developed to be wet for a certain amount of time a day. Especially in brackish
water nature develops very well on these materials. However when the materials are being used in a
mainly dry environment almost no nature will develop.
Conclusion 3.3: Section 1 is the only trajectory where eco materials could be useful.
Section 1 is the only trajectory where water reaches the toe of the dike during high tide. In front of
the other part of the Dollart coast marshes are present, limiting the use of eco materials to their
safety function.
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64
4 Concepts
With the MCA’s from chapter3 and the trajectories that can be seen in Figure 35, concepts are made
for each section. A concept is a combination of a method, a material and a location. The location is
the considered trajectory and its most important properties are length, type of foreshore and a wet
or dry embankment. Per section the properties of the location are given as well as the best suitable
materials and methods. These are derived from the corresponding MCA’s (see paragraph 3.5).
Section 1
Location Length trajectory � 2500 m
Foreshore � No marshes, Natura 2000 area
Wet/dry embankment � Wet
Material Material 1(MCA 1) � Armorflex
Material 2 � C-star elements
Material 3 � Elastocoast
Method Method 1 � Increased overtopping
Method 2 � Slope changes
Method 3 � Raising the crest height
Concept 1.1: Elastocoast + gentle slope + Raised crest height + Increased overtopping
Motivation:
Section 1 is situated along polder Breebaart which is used as a nature reserve. The sea reaches the
dike so a hard eco material can be used as revetment. The revetment material can vary. The three
materials have almost the same score. There are two methods chosen with different scores. The
allowed overtopping can be raised because there is no agriculture on the land side of the dike. The
slopes have to be made gentler because section 1 has a low crest height. An increase of overtopping
has no negative effects on the hinterland and both methods are chosen for concept 1.1. The crest
height has to be raised because the review level will become higher in the future than the current
crest height. The loss of nature value has to be investigated further.
Climate (Ex) Change – Eco-engineering in the Dollart
65
Figure 40: Concept 1.1: A gentle slope and raised crest height in combination with a Elastocoast revetment on the berm.
Advantages
• Increasing coastal safety
• Increase in nature value on the dike
Disadvantages
• Loss of Natura 2000 area
• High costs
Section 2
Location Length trajectory � 8000 m
Foreshore � Marshes, Natura 2000 area
Wet/dry embankment � Dry
Material Material 1 � No other material
Material 2 � SGR
Method Method 1 � Increased overtopping
Method 2 � Slope changes
Concept 2.1: No other material + Slope changes + Increased overtopping
Motivation:
The embankment is dry so hard revetments aren’t useful. The area suffers from medium hydraulic
conditions because it is mostly situated in the lee. The Slopes can be made more gentle to increase
nature development on the dike and increase safety. Increased overtopping can be allowed, the
agriculture has to adapt to the increase of salinity. The costs of a higher crest height/slope changes to
minimize overtopping have to be compared with the costs for agriculture to adapt to the increased
salinity.
Climate (Ex) Change – Eco-engineering in the Dollart
66
Figure 41: Concept 2.1: No other material used, slope changes and increased overtopping
Advantages
• Increasing coastal safety
• Increase in nature value on the dike
Disadvantages
• Loss of Natura 2000 area
• High costs
• Increased salinity of agricultural hinterland
Section 3
Location Length trajectory � 3500 m
Foreshore � Marshes, Natura 2000 area
Wet/dry embankment � Dry
Material Material 1 � SGR
Method Method 1 � Increased overtopping
Concept 3.1: SGR + Increased overtopping
Motivation:
The embankment is dry under normal conditions, so hard eco-materials aren’t useful. The area
suffers from medium hydraulic conditions and the crest height of the dike is high compared to the
other sections on the Dutch side. In other words the waves in this section are only 1.25m and the
embankment is only several times a year under water. Therefore overtopping will be less compared
to section 1 and 2. SMR and increased overtopping come out as best. The fact the dike is still relative
high is a gentle slope to reduce waves and overtopping not necessary.
Climate (Ex) Change – Eco-engineering in the Dollart
67
Figure 42: Cross section of the dike, SGR is installed under the grass revetment
Advantages
• Current nature value will be maintained
• The current image of the dike is preserved
• Costs are relatively low
Disadvantages
• No increased value for nature development
• Not much practical experience
• Loads on the inner slope will be increased
Alternative: Overtopping with retention basin
Another option for this section is using a retention basin. Comcoast came up with a new design for
increasing the overtopping over the crest of the dike. In this part an alternative for the increase of
overtopping will be worked out. As mentioned before the requirements for the volume of wave
overtopping will change. More overtopping will be allowed during a storm event. The result is a
greater effect of erosion on the inner slope of the dike. But with this new concept the inner slope will
be less disturbed.
A concrete construction will be installed in the crest of the dike. This concrete construction has an U-
shaped profile and acts as a retention basin. Most of the overtopping water will be caught by the
retention basin and discharged to the inner side of the dike. So for this concept, a retention basin is
used instead of the SGR. The function of the SGR is negligible.
The crest width of the dikes in the current situation should be enlarged to fit the construction.
Further investigation is needed to determine how width the construction has to be, to catch all
Climate (Ex) Change – Eco-engineering in the Dollart
68
overtopping water.
Figure 43: Cross section of the dike with retention basin installed in the crest
Less amount of water will run over the inner slope, because the retention basin will catch a large
amount of overtopping water. The result is a reduction of the loads on the inner slope. In extreme
conditions it is possible that the retention basin is not able to discharge all the water, so water will
run over the inner slope. But the energy of the water is decreased by the retention basin compared
to the smooth crest right now. The construction and the drainage pipes must be placed in clay to
prevent instability.
Discharge
The allowable amount of wave overtopping depends on the capacity of the retention basin with the
discharge pipes. Comcoast calculated with a wave overtopping of 15 l/s/m during their investigation
to apply a retention basin.
In Table 9an overview is given of the possible combinations of pipe diameters and their capacities.
The results from the table are determined by the Darcy-Weisbach formula, see Appendix 3:
Calculation of the overtopping capacity of the retention basin. With the current height of the dikes
the discharge capacity of the dikes is approximately 250l/s for a pipe diameter of 250mm. A pipe
needs to be installed every 17m to discharge all the water from a wave overtopping of 15l/s/m. The
result is not very satisfying. The cost will be too high for the installation and purchase of the pipes.
But for the calculation, the worst scenario is taken into account. If the height of the dike is enlarged
and the distance from the trench to the crest is shortened, the discharge capacity increases
significantly. In this section of the Dollart the dikes are relatively high compared to the other location.
This would be the best location if you want to use a retention basin.
The fact that the pipe will never be totally filled with water is neglected in the calculation. Based on
this calculation can be concluded that the use of a retention basin with discharge pipes will be a bad
solution for the Dollart dikes. The possibility of using an open drain instead of a discharge pipe looks
as a good alternative. This is not investigated. Further study is needed for the overtopping and
discharge of water at the crest.
Climate (Ex) Change – Eco-engineering in the Dollart
69
Pipe
diameter
[mm]
Pipe capacity
[m3/s]
Pipe
frequency
Catch-off
capacity crest
[l/s/m]
200 0,14 Every 100m 1
200 0,14 Every 50m 3
200 0,14 Every 25m 6
250 0,25 Every 100m 2,5
250 0,25 Every 50m 5
250 0,25 Every 25m 10
300 0,40 Every 100m 4
300 0,40 Every 50m 8
300 0,40 Every 25m 16
Table 9: Overview with possible combinations for the discharge pipes.
Durability
The durability of the construction should not be considered as a problem. The working live of this
construction is around 80 years. The working live of the retention basin on the dike is expected to be
less, 50 years.
Environment
The concept is mentioned because it minimizes the environmental effects. At the crest of the dike
the construction doesn’t allow nature development but because of the construction the grass
revetment can be preserved at the inner slope of the dike. Nature development can be maintained at
the inner slope of the dike and there is no negative influence on the landscape values within the dike
area.
Maintenance road
The retention basin can also be used as a maintenance road beside its function as drain. In the
current situation the maintenance roads are located at the bank of the dike. It is a good option to
investigate:
• If the landside road of the dike can be placed on top of the dike. This increases the landscape
value.
• If the seaside road can be removed. That would be helpful for the concept of changing the
slopes of the dikes at the seaside. See concept changing the slopes. The problem could be
the accessibility to the salt marshes.
Climate (Ex) Change – Eco-engineering in the Dollart
70
Section 4
Location Length trajectory � 11000 m
Foreshore � Marshes
Wet/dry embankment � Dry
Material Material 1 � SGR
Method Method 1 � Increased overtopping
Concept 4.1: SGR + Increased overtopping
Motivation:
Section 4 is the dike trajectory in Germany from which not much information is available yet. During
our research was it difficult to get contact with the different German authorities, which have the
dikes in management. There was also no information about the hydraulic conditions of the German
dikes. However looking to the Dutch hydraulic conditions it looks plausible that the waves and the
review level will increase at the German dike when going more to the north. This is because the dike
there is more in line of sight with the Ems, were waves from the North Sea are. The German dike has
already a gentle slope compared to the Dutch dike. Therefore the method of changing the slope is
not chosen here. Based on this motivation concept 4.1 is chosen.
It can be said that the development of the concepts for dike trajectory 4 is based on assumptions.
Advantage:
• Current nature value will be maintained
• The current image of the dike is preserved
• Costs are relatively low
Disadvantages
• No increased value for nature development
• Not much practical experience
• Loads on the inner slope will be increased
Climate (Ex) Change – Eco-engineering in the Dollart
71
5 Conclusions
The main goal of this research is trying to find out if application of ecological dike concepts in the
Dollart can contribute to a combination of coastal safety and nature development. An ecological dike
concept is defined in this research as a location, a revetment material and a change in the shape of
the dike (method). The use of no material is also defined as a material and for method the same
applies. This can be seen as the situation with no changes at all.
The Dollart region is an estuary with specific properties. During this research it became clear that
during a storm the water level can increase dramatically. Were the normal high tide is 1.5 m +NAP
do the hydraulic conditions say that a water level can as be high as 6.8 meter + NAP at Nieuwe
statenzijl. This extreme high water level is caused by the fact that storm surges occur in the Dollart.
The fact that the Dollart is a bay also contribute to the extreme high water, water is enclosed and the
only way is up. Waves in the Dollart a relative low when compared to the Dutch and German coast.
The waves are according the hydraulic condition on the Dutch Dollart coast 0.9 meter at Punt van
Reide and up to 1.25 meter at Nieuwe Statenzijl. The wave height at the German dikes is unknown
but is to be expected be higher than 1.25 meter.
The philosophy behind this research goal is that the dike and the sea are in contact with each other.
When hard revetments are used or special techniques like water retaining structures on the outer
slope, a habitat is created for specific plants and animals. This is a form of eco engineering and
contributes to nature development and coastal safety. These two features make eco materials very
useful in some places.
The use of ecological materials only, doesn’t contribute to an increase of both nature development
and coastal safety. The most ecological materials focus on vegetation and animals that live in a
wetland area, not in a relatively dry environment like the Dollart dike. The Dollart coast can be
considered dry except the trajectory along polder Breebaart. The marshes in front of the dike hinder
the water of reaching the dike. At high tide there is still a couple of hundreds of meters between the
water and the dike. The average high water is 1,50 m +NAP and the height of the marshes deviates
between 1,50 m +NAP and 2,00 m +NAP. Section 1 is the only trajectory where eco materials could
be useful.
The west side of the Dollart along polder Breebaart is probably subjected to higher subsidence. The
reason for this can be the gas extraction and local soil properties. However it is clear that the dike
along the Breebaart the lowest in the Dollart and not high enough is. The settlement in that side is
not investigated but the expected review level will be higher than the current crest height. This
means the West side of the Dollard has to be raised to withstand the expected sea level rise. By using
methods like overtopping, gentle slope and materials SGR can the heightening of the dike be reduced
to a minimum.
The dikes at the south of the Dollart have salt marshes in front of them and the length of these salt
marshes vary from 500 to 100 meter. The crest height at the south side of the Dollart varies from 8
meters in the West and up to 9 meters on the East side. With methods like increased overtopping
and SGR and creating gentle slopes it is possible to increase the safety.
The dikes on the East side in Germany, have a gentle slope of 1:6. This means they suffer from less
wave run-up and overtopping. The German trajectory suffers from the highest wave attacks and
water boost due to the Ems sperwerk. The average crest height is 8 m +NAP. Possibly the crest height
has to be raised, but this depends on the German hydraulic boundaries. Also here, methods and
materials like overtopping and SGR could help to keep the increase of the crest height to a minimum.
Climate (Ex) Change – Eco-engineering in the Dollart
72
In this research it becomes clear that there are no easy ecological solutions for the dike. With the
materials and methods that are available today it is not possible to find a solution to increase safety
and increase nature development together. When nature development must be created in the
Dollart region it is recommended to find solutions in front of the dike or behind it.
Climate (Ex) Change – Eco-engineering in the Dollart
73
6 Recommendations
• Research has to be done on different ways to increase nature development besides using
ecological materials as revetment. This research shows that the possibilities to create nature
development on the Dollart dikes is marginal. The Natura 2000 area in front of the coast
makes nature development on the sea side difficult, but the chances of nature development
are highest on the marshes on the border of water and land. The hinterland could be used
like the way polder Breebaart is developed. This will result in high costs and resistance of
local inhabitants. Further research has to be done to investigate the possibilities.
• The use of ecological materials is not directly useful but the chances of those materials with
regard to safety are interesting. The dikes might have to be reinforced with future hydraulic
conditions and although nature development is not directly increased by using ecological
materials, the use of them should be investigated further for section 1.
• The Dollart is divided in four sections based on hydraulic conditions, crest height and the
presence of marshes. The recommended concepts that could be worked out further:
Section 1: Elastocoast + gentle slope + Raised crest height + Increased overtopping
Section 2: No other material + Slope changes + Increased overtopping
Section 3: SGR + Increased overtopping
Section 4: SGR + Increased overtopping
• The soil structure has to be investigated further by comparing CPT’s taken from the Westside
and from the Southside. This to determine the cause of settlements and subsidence. This
could affect the needed crest height.
• The hydraulic boundaries in front of the German coast have to be investigated further. This
will lead to more insight in adaption of the German dikes to sea level rises
• The eco system in the Dollart determines which ecological materials are most suitable. A
research on the eco systems has to be done to get a better fine tuning between the existing
nature and the dike design.
• Investigation should be done on nature development with materials for a dry environment.
This research focuses on dike revetments but other materials have to be investigated and
their applicability on the Dollart dikes.
• Research has to be done on dikes with incorporated marshes and the conflicts that would
have with regulations in the Dollart
Climate (Ex) Change – Eco-engineering in the Dollart
74
7 Definitions
Eco-engineering: The design, construction, operation and management (that is,
engineering) of landscape/aquatic structures and associated plant
and animal communities (that is, ecosystems) to benefit humanity
and, often, nature.
Ecological dike concept: A conceptual design of the considered cross section of the dike. The
considered area includes the foreshore or marshes, the dike body
and the seepage zone, which is assumed to run to the seepage ditch
on the land side.
Eco- materials: Materials used in eco engineering that serve human and natural
development purposes.
Fetch: The unobstructed area wind can blow over water to create waves
Negative storm surge: Exceptionally low tides caused by wind blowing offshore and high
atmospheric pressure
Natura 2000 Area: Nature reserve area where the European nature laws are in order.
NAP: NAP stands for “Normaal Amsterdam Peil”, the reference height used
in the Netherlands.
NN: NN stand for “Normal null”, The reference height used in Germany,
the same height as NAP
Positive storm surge: Exceptionally high tides caused by wind blowing ashore and low
atmospheric pressure
Revetment: Sloping structures placed on banks in such a way as to absorb to
energy of incoming water
Sea level rise: An increase in sea level with approximately 120 centimeters in the
next 100 years excluding a decreasing ground level.
The Dollart: The pelvis found in the South of the Ems Dollart estuary.
The Ems Dollart estuary: The estuary that includes the Dutch and German Wadden Sea and
the salt marshes.
Climate (Ex) Change – Eco-engineering in the Dollart
75
Figure 44: Top view of the Ems Dollart estuary, red line indicates the estuary
The Ems Dollart region: The region that includes the Ems Dollart estuary, the coastal
defenses and the hinterland.
Figure 45: Top view, red line indicates The Ems Dollart region
The Tide Rise and fall of the water in the sea caused by moon and sun
and other influences
Wave overtopping: The flow of water over a dam or embankment
Wave run-up: The ultimate height reached by waves after running up to a
coastal barrier, f.e. a dike
Climate (Ex) Change – Eco-engineering in the Dollart
76
8 Bibliography (TAW), T. A. (2002). Technical report wave run-up and wave overtopping on dikes. Retrieved from
www.helpdeskwater.nl.
Anh, V. M. (n.d.). Wave overtopping reduction through Vetiver grass. Retrieved from www.tudelft.nl.
B.V., V. d. (n.d.). Information wave overtopping simulator. Retrieved from
www.vandemeerconsulting.nl.
BASF, T. c. (n.d.). Information revetment type Elastocoast. Retrieved from www.elastocoast.com.
C-fix. (n.d.). Information revetment type C-star. Retrieved from www.c-fix-coastalelements.com.
Comcoast. (n.d.). Technical solutions for wave overtopping resistant dike. Retrieved from
www.comcoast.org.
Deichacht, R. (n.d.). Information German dikes. Retrieved from www.rheider-deichacht.de.
Deltacommissie. (2008). Deltaplan: Samen werken met water. Retrieved from
www.deltacommssie.com.
Ecomare. (n.d.). Information about the vegetation and animals in the Wadden Sea. Retrieved from
www.ecomare.nl.
Fabriform. (n.d.). Information revetment type Enviromat. Retrieved from www.fabriform1.com and
www.greenbanks.nl.
Huesker. (n.d.). Smart grass reinforcement products. Retrieved from www.huesker.com.
International, T. V. (n.d.). Information Vetiver grass. Retrieved from www.vetiver.org.
Rijkswaterstaat. (n.d.). Report Eco-engineering "Harde werken met zachte trekken". Retrieved from
www.rijkswaterstaat.nl.
Secretariat, C. W. (n.d.). Information about ecosystems in the Wadden Sea. Retrieved from
www.waddensea-secretariat.org.
Van de Maarel, i. A. (2009). Climate (Ex)Change, Klimaatbewuste verdediging en natuurontwikkeling.
Vekeer&Waterstaat, M. v. (n.d.). Instruction manual for safety requirement 2006. Retrieved from
www.helpdeskwater.nl.
Verkeer&Waterstaat, M. v. (2006). Hydraulic Boundaries 2006. Retrieved from
www.verkeerenwaterstaat.nl.
Verkeer&Waterstaat, M. v. (n.d.). Pictures from the Dutch coastline. Retrieved from www.kustfoto.nl.
Waterkeringen, T. A. (1999). Leidraad Zee-en Meerdijken. Retrieved from www.enwinfo.nl.
Xbloc's. (n.d.). Information about Xbloc's. Retrieved from www.xbloc.com.
Climate (Ex) Change – Eco-engineering in the Dollart
77
Climate (Ex) Change – Eco-engineering in the Dollart
78
Appendix 1: Hydraulic conditions Ems-Dollart region
Climate (Ex) Change – Eco-engineering in the Dollart
79
Appendix 2: Tide table Nieuwe Statenzijl
Climate (Ex) Change – Eco-engineering in the Dollart
80
Appendix 3: Calculation of the overtopping capacity of the
retention basin
In this annex a calculation is performed for the discharge capacity of the PP pipes for the retention
basin. In this simple equation is assumed that the quantity of wave overtopping depends on the
capacity of the discharge from the crest.
A pipe of 200mm and the average height of the dikes is used in the next calculation.
Flow velocity in the pipe
The negative flow is negligiblev 4.6
m
s:=
1
λ L⋅ D+( )2
1
2⋅ λ L⋅ D+( ) dH⋅ D⋅ g⋅
1
2⋅
1−
λ L⋅ D+( )2
1
2⋅ λ L⋅ D+( ) dH⋅ D⋅ g⋅
1
2⋅
4.6
4.6−
m
s=
dH λL
D⋅
v2
2 g⋅⋅
v2
2g+
Gravitational acceleration g 9.807m
s2
=
Length of the pipe
Longest distance from the crest to the trench, landside of the dike. L 81m:=
Natural drop pipe line
Average height of the dikes at the Dutch side of the Dollart regiondH 8.3m:=
Determine the flow velocity in the pipe under normal drop
λ 0.017=
Friction factor
Depends on the wall roughnessλ
0.25
log 3.7D
k⋅
2:=
k 0.1 103−
⋅ m:=Factor for the wall roughness
Discharge pipes will be made from synthetic Poly Propyleen pipes
Diameter of the pipeD 0.2m:=
Determine the friction factor
Model for determining the discharge capacity of the pipes.Representative for the
discharge of the water in the retention basin
Darcy - We isbach e quation
Climate (Ex) Change – Eco-engineering in the Dollart
81
Freqpipe2 101
m=Freqpipe1 29
1
m=
Freqpipe2Q
Requirement2:=Freqpipe1
Q
Requirement1:=
Requirement2 15 103−
⋅m
3
s
m
⋅:=Requirement1 5 103−
⋅m
3
s
m
:=
Determine the frequency of the pipe for a wave overtopping of 5 and 15 l/s/m
Q100m 1.4liter
s=Q100m
Q
100:=
Q50m 2.9liter
s=Q50m
Q
50:=
Q25m 5.8liter
s=Q25m
Q
25:=
Discharged water through PP pipe when the pipes will be installed every 25,50 and
100m
Q 0.145m
3
s=
Flow capacity of the PP pipeQ v A⋅:=
Discharged water through PP pipe per meter of the dike
A 0.031m2
=Surface of the pipe
A1
4πD
2⋅:=
Determine the capacity of the pipe
Climate (Ex) Change – Eco-engineering in the Dollart
82
Appendix 4: overtopping calculations with CRESS
Calculation dike profile 4 current hydraulic conditions
Input data
g : 9.81 m/s2
wave height : 0.9 m
Peak period : 3.087 sec
Wave direction : 0o
Horizontal water level : 6.5 m
X-position toe :0 m
Y-position toe : 2.254 m
Accuracy : 1%
Storm duration : 21600 sec
Average wave period : 3 sec
admissible over topping : 0.005 m3/m/s
Percentage volume : 5%
Aantal dijkprofielen : 4
X-co-ordinaat : 1.399
Y-co-ordinaat : 2.59
Roughness factor : 1
X-co-ordinaat : 4.42
Y-co-ordinaat : 2.85
Roughness factor : 1
X-co-ordinaat : 16.071
Y-co-ordinaat : 7.011
Roughness factor : 1
X-co-ordinaat : 22.01
Y-co-ordinaat : 7.509
Roughness factor : 1
Output data
Needed crest height 5.0 l/s/m : 0.756 m
Needed crest height 0.1 l/s/m : 1.461 m
Needed crest height 1.0 l/s/m : 1.046m
Needed crest height 10 l/s/m : 0.632 m
Needed crest height 100 l/s/m : 0.217 m
Volume overtopping wave exceed in x : 0.117 m3/m
Volume overtopping wave exceed 1% : 0.208 m3/m
Volume overtopping wave exceed 10% : 0.082 m3/m
Volume overtopping wave exceed 50% : 0.016 m3/m
Volume of highest overtopping wave : 0.344 m3/m
2%-wave run-up height : 1.35 m
Remark: The 2%-wave run-up is higher than the dike.
Climate (Ex) Change – Eco-engineering in the Dollart
83
Calculation dike profile 10 current hydraulic conditions
Input data
g : 9.81 m/s2
wave height : 1.0 m
Peak period : 3.254 sec
Wave direction : 0o
Horizontal water level : 7.8 m
X-position toe :0 m
Y-position toe : 2.034 m
Accuracy : 1%
Storm duration : 21600 sec
Average wave period : 3 sec
admissible over topping : 0.005 m3/m/s
Percentage volume : 5%
Aantal dijkprofielen ` : 3
X-co-ordinaat : 3.226 m
Y-co-ordinaat : 2.988 m
Roughness factor : 1 m
X-co-ordinaat : 6.042 m
Y-co-ordinaat : 3.38 m
Roughness factor : 1 m
X-co-ordinaat : 26.985 m
Y-co-ordinaat : 8.351 m
Roughness factor : 1 m
entage volume : 5%
Output data
Needed crest height 5.0 l/s/m : 0.991 m
Needed crest height 0.1 l/s/m : 1.869 m
Needed crest height 1.0 l/s/m : 1.353 m
Needed crest height 10 l/s/m : 0.836 m
Needed crest height 100 l/s/m : 0.319 m
Volume overtopping wave exceed in x : 0.588 m3/m
Volume overtopping wave exceed 1% : 1.044 m3/m
Volume overtopping wave exceed 10% : 0.414 m3/m
Volume overtopping wave exceed 50% : 0.017 m3/m
Volume of highest overtopping wave : 2.351 m3/m
2%-wave run-up height : 1.688 m
Remark:
Climate (Ex) Change – Eco-engineering in the Dollart
84
Calculation dike profile 10 future hydraulic conditions
Input data
g : 9.81 m/s2
wave height : 1.0 m
Peak period : 3.254 sec
Wave direction : 0o
Horizontal water level : 6.6 m
X-position toe :0 m
Y-position toe : 2.034 m
Accuracy : 1%
Storm duration : 21600 sec
Average wave period : 3 sec
admissible over topping : 0.005 m3/m/s
Percentage volume : 5%
Aantal dijkprofielen : 3
X-co-ordinaat : 3.226 m
Y-co-ordinaat : 2.988 m
Roughness factor : 1 m
X-co-ordinaat : 6.042 m
Y-co-ordinaat : 3.38 m
Roughness factor : 1 m
X-co-ordinaat : 26.985 m
Y-co-ordinaat : 8.351 m
Roughness factor : 1 m
Output data
Needed crest height 5.0 l/s/m : 0.991 m
Needed crest height 0.1 l/s/m : 1.869 m
Needed crest height 1.0 l/s/m : 1.353 m
Needed crest height 10 l/s/m : 0.836 m
Needed crest height 100 l/s/m : 0.319 m
Volume overtopping wave exceed in x : 0.123 m3/m
Volume overtopping wave exceed 1% : 0.219 m3/m
Volume overtopping wave exceed 10% : 0.087 m3/m
Volume overtopping wave exceed 50% : 0.017 m3/m
Volume of highest overtopping wave : 0.224 m3/m
2%-wave run-up height : 1.688 m
Remark: The 2%-wave run-up is higher than the dike.
Climate (Ex) Change – Eco-engineering in the Dollart
85
Calculation dike profile 14 current hydraulic conditions
Input data
g : 9.81 m/s2
wave height : 1.1 m
Peak period : 3.413 sec
Wave direction : 0o
Horizontal water level : 6.7 m
X-position toe :0 m
Y-position toe : 2.454 m
Accuracy : 1%
Storm duration : 21600 sec
Average wave period : 3 sec
admissible over topping : 0.005 m3/m/s
Percentage volume : 5%
Aantal dijkprofielen : 3
X-co-ordinaat : 1.896 m
Y-co-ordinaat : 2.973 m
Roughness factor : 1 m
X-co-ordinaat : 5.074 m
Y-co-ordinaat : 3.435 m
Roughness factor : 1 m
X-co-ordinaat : 33.402 m
Y-co-ordinaat : 9.372 m
Roughness factor : 1 m
Output data
Needed crest height 5.0 l/s/m : 0.981 m
Needed crest height 0.1 l/s/m : 1.834 m
Needed crest height 1.0 l/s/m : 1.332 m
Needed crest height 10 l/s/m : 0.830 m
Needed crest height 100 l/s/m : 0.328 m
Volume overtopping wave exceed in x : 0.000 m3/m
Volume overtopping wave exceed 1% : 0.000 m3/m
Volume overtopping wave exceed 10% : 0.000 m3/m
Volume overtopping wave exceed 50% : 0.000 m3/m
Volume of highest overtopping wave : 0.000 m3/m
2%-wave run-up height : 1.64 m
Remark:
Climate (Ex) Change – Eco-engineering in the Dollart
86
Calculation dike profile 14 future hydraulic conditions
Input data
g : 9.81 m/s2
wave height : 1.1 m
Peak period : 3.413 sec
Wave direction : 0o
Horizontal water level : 6.7 m
X-position toe :0 m
Y-position toe : 2.454 m
Accuracy : 1%
Storm duration : 21600 sec
Average wave period : 3 sec
admissible over topping : 0.005 m3/m/s
Percentage volume : 5%
Aantal dijkprofielen : 3
X-co-ordinaat : 1.896 m
Y-co-ordinaat : 2.973 m
Roughness factor : 1 m
X-co-ordinaat : 5.074 m
Y-co-ordinaat : 3.435 m
Roughness factor : 1 m
X-co-ordinaat : 33.402 m
Y-co-ordinaat : 9.372 m
Roughness factor : 1 m
Output data
Needed crest height 5.0 l/s/m : 0.981 m
Needed crest height 0.1 l/s/m : 1.834 m
Needed crest height 1.0 l/s/m : 1.332 m
Needed crest height 10 l/s/m : 0.830 m
Needed crest height 100 l/s/m : 0.328 m
Volume overtopping wave exceed in x : 0.133 m3/m
Volume overtopping wave exceed 1% : 0.237 m3/m
Volume overtopping wave exceed 10% : 0.094 m3/m
Volume overtopping wave exceed 50% : 0.019 m3/m
Volume of highest overtopping wave : 0.317 m3/m
2%-wave run-up height : 1.64 m
Remark: The 2%-wave run-up is higher than the dike.
Climate (Ex) Change – Eco-engineering in the Dollart
87
Calculation dike profile 14 future hydraulic conditions with slope 1:6
Input data
g : 9.81 m/s2
wave height : 1.1 m
Peak period : 3.413 sec
Wave direction : 0o
Horizontal water level : 6.7 m
X-position toe :0 m
Y-position toe : 2.454 m
Accuracy : 1%
Storm duration : 21600 sec
Average wave period : 3 sec
admissible over topping : 0.005 m3/m/s
Percentage volume : 5%
Aantal dijkprofielen : 3
X-co-ordinaat : 1.896 m
Y-co-ordinaat : 2.973 m
Roughness factor : 1 m
X-co-ordinaat : 5.074 m
Y-co-ordinaat : 3.435 m
Roughness factor : 1 m
X-co-ordinaat : 40.732 m
Y-co-ordinaat : 9.372 m
Roughness factor : 1 m
Output data
Needed crest height 5.0 l/s/m : 0.759 m
Needed crest height 0.1 l/s/m : 1.437 m
Needed crest height 1.0 l/s/m : 1.038 m
Needed crest height 10 l/s/m : 0.639 m
Needed crest height 100 l/s/m : 0.241 m
Volume overtopping wave exceed in x : 0 m3/m
Volume overtopping wave exceed 1% : 0 m3/m
Volume overtopping wave exceed 10% : 0 m3/m
Volume overtopping wave exceed 50% : 0 m3/m
Volume of highest overtopping wave : 0 m3/m
2%-wave run-up height : 1.30 m
Remark: The 2%-wave run-up is higher than the dike
Climate (Ex) Change – Eco-engineering in the Dollart
88
Calculation dike profile 14 future hydraulic conditions with slope 1:8
Input data
g : 9.81 m/s2
wave height : 1.1 m
Peak period : 3.413 sec
Wave direction : 0o
Horizontal water level : 6.7 m
X-position toe :0 m
Y-position toe : 2.454 m
Accuracy : 1%
Storm duration : 21600 sec
Average wave period : 3 sec
admissible over topping : 0.005 m3/m/s
Percentage volume : 5%
Aantal dijkprofielen : 3 m
X-co-ordinaat : 1.896 m
Y-co-ordinaat : 2.973 m
Roughness factor : 1 m
X-co-ordinaat : 5.074 m
Y-co-ordinaat : 3.435 m
Roughness factor : 1 m
X-co-ordinaat : 52.186 m
Y-co-ordinaat : 9.372 m
Roughness factor : 1 m
Output data
Needed crest height 5.0 l/s/m : 0.557 m
Needed crest height 0.1 l/s/m : 1.069 m
Needed crest height 1.0 l/s/m : 0.767 m
Needed crest height 10 l/s/m : 0.466 m
Needed crest height 100 l/s/m : 0.164 m
Volume overtopping wave exceed in x : 0 m3/m
Volume overtopping wave exceed 1% : 0 m3/m
Volume overtopping wave exceed 10% : 0 m3/m
Volume overtopping wave exceed 50% : 0 m3/m
Volume of highest overtopping wave : 0 m3/m
2%-wave run-up height : 0.99 m
Remark: The 2%-wave run-up is higher than the dike
Climate (Ex) Change – Eco-engineering in the Dollart
89
Appendix 5: Calculation wave periods
Wave period 0.9 m
Wave period 1.0 m
Calculation peak period
Hi 0.9m:=
Tp
2 π⋅ Hi⋅( )0.05g⋅
:=
Tp 3.396s=
Calculation spectral wav e period
Tm_1.0
Tp
1.1:=
Tm_1.0 3.087s=
Calculation peak period
Hi 1.0m:=
Tp
2 π⋅ Hi⋅( )0.05g⋅
:=
Tp 3.58s=
Calculation spectral wav e period
Tm_1.0
Tp
1.1:=
Tm_1.0 3.254s=
Climate (Ex) Change – Eco-engineering in the Dollart
90
Wave period 1.1
Calculation Piek period
Hi 1.1m:=
Tp
2 π⋅ Hi⋅( )0.05g⋅
:=
Tp 3.754s=
Calculation spectral wave period
Tm_1.0
Tp
1.1:=
Tm_1.0 3.413s=
Climate (Ex) Change – Eco-engineering in the Dollart
91
Appendix 6: Manual calculation wave overtopping
Figure 46: Picture were the freeboard is indicated (free crest height for wave overtopping)
Solve wave overtopping at the Dollart dikes
(Technisch rapport golfoploop en golfoverslag bij dijken)
Determine the freeboard at the crest•
SWL 6.6m:= Average sea water level
Hprofile4 7.51m:=Crest height of the Dutch profiles used for the comparison
Hprofile10 8.35m:=
Hprofile14 9.37m:=
Hcrest 8.3m:= Average height of the crest, of all 19 Dutch profiles
Rc Hcrest SWL−:=
Rc 1.7m= Freeboard at the crest, with respect to the Sea water level (SWL)
Hm0 1.25m:= Significant wave height at the toe of the dike
Influence factor for the roughness of the top layers of the dike revetment during wave •overtopping [-]
γf.grass 1:= For grass revetments, the grass has no influence on the roughness
γf.armorflex 0.9:= For Armorflex
γf.elastocoast 0.7:= Lowest roughness factor for elastocoast products
Influence factor for the angle of wave attack, the wave impact •will be less when the waves strike the dike under an angle
β 0:= Angel of wave attack (degrees)
γβ 1 0.0022β⋅−:=
γβ 1= Influence factor for the angle of wave attack
Climate (Ex) Change – Eco-engineering in the Dollart
92
Figure 47: Definition angle of wave attack, red line indicated the angle of attack
g 9.81m
s2
= Gravitation
Note:
The crest height is too low based on the current overtopping discharge requirement
because qgrass > qcurrent.
But this conclusion is too quick because not all waves go actually over the top of the crest
Possible requirement for wave overtopping dischargeqnew.maybe 5.0 103−
⋅m
2
s:=
New requirement for wave overtopping dischargeqnew 1.0 103−
⋅m
2
s:=
Current requirements for wave overtopping dischargeqcurrent 1 104−
⋅m
2
s:=
This average wave overtopping discharge is above the current requirements for wave
overtopping.Research is ongoing to get a better view on the relationship between wave
overtopping and the capacity of the inner slope. The requirements for wave overtopping
change, because of the already performed research
The average overtopping discharge, m3 / m per secondqgrass 0.04m
2
s=
qgrass .20 exp 2.3−Rc
Hm0 γf.grass γβ⋅⋅⋅
⋅ g Hm03
⋅
1
2
⋅:=
For grass
Solve the wave overtopping
q
g Hm03
⋅
0.2 e
2.3−Rc
Hm0
⋅1
γ f.gras γβ⋅⋅
⋅
With the maximum:
Emperical formula TAW formula for wave overtopping at dikes
Calculate the wave overtopping
Climate (Ex) Change – Eco-engineering in the Dollart
93
For Armorflex
qarmorflex .2 exp 2.3−Rc
Hm0 γf.armorflexγβ⋅⋅⋅
⋅ g Hm03
⋅
1
2
⋅:=
qarmorflex 0.027m
2
s= The average overtopping discharge, m3 / m per second
For Elastocoast
qelastocoast .2 exp 2.3−Rc
Hm0 γf.elastocoast γβ⋅⋅⋅
⋅ g Hm03
⋅
1
2
⋅:=
qelastocoast 0.01m
2
s= The average overtopping discharge, m3 / m per second
Determine overtopping volumes per wave
The calculation is only the made for the grass revetment because it is the top layer of the
current dikes in the Dollart region
Tm 1s:= Average wave period
qgrass 0.038m
2
s= The average overtopping discharge, m3 / m per second
hk Rc:=freeboard, crest height with respect to the SWL
hk 1.7m=
Climate (Ex) Change – Eco-engineering in the Dollart
94
s0 0.08=
Wave steepness [no dimension]
s0
2 π⋅ Hm0⋅
g Tm_1.02
⋅
:=
Calculation of the wave steepness•
Tm_1.0 3.25s=
Spectral wave periodTm_1.0
Tp
1.1:=
Calculation spectral period•
Peak periodTp 3.58s=
Tp
2 π⋅ Hi⋅( )0.05g⋅
:=Formula to calculate the wave piek period
Hi 1.0m:=
Calculation piek period•
Influence factor for the berm of the dike. In this calculation is
assumed that the influence of the berm is negligible. Normally this
needs to be taken into account.
The width of the berm and the position of the berm in respect to the
waterline influence is important
γb 1:=
Influence factor for grass revetmentsγf.grass 1=
Influence factor for the angle of wave attackγβ 1=
Determine the wav e run-up
Climate (Ex) Change – Eco-engineering in the Dollart
95
Figure 48: Left picture; determination of the characteristic slope for a cross section, right picture; The situation for the
manual calculation of the Dollart dikes
The tan(α) is the average angle in the zone between the sea water level minus 1,5Hm0 and the wave
run-up. The berm should not be taken into account. So the representative berm is depending on the
water level.
Determine the representative angle of the upper slope of the •dike at the seaside
Hm0 1.25m= Significant wave height at the toe of the dike
Horizontal length between two points 1,5xHm0 above and
under the review level on a slope of 1:3Lslope 11.3m:=
B 0m:= Width of the crest
There is a berm on the dike, but the berm is lower then the
review level. Therefore it is not taken into account, so zero.
The width of the lower berm seaside is 3meters
Normally the wave run-up needs to be taken into
account. Only the wave run-up is not yet determined.
For z2%, 1,5xHm0 can be taken into account for a first
estimate.
tan α( )1.5 Hm0⋅ 1.5 Hm0⋅+( )
Lslope B−( )
α1 1.− atan 3.Hm0
1.− Lslope⋅ B+( )⋅
⋅:=
α1 0.32= Angle of the average slope
tan α1( ) 0.33=
Climate (Ex) Change – Eco-engineering in the Dollart
96
Determine the breaker parameter•
ξ0
tan α1( )s0
:=Breaker parameter
ξ0 1.21=
Determine the wave run-up•
z2% is the wave run-up height, that is exceeded by 2% of the waves
General formula for the wave run-upz2%
Hm0
1.75γb⋅ γf⋅ γβ⋅ ξ0⋅
z2%1 1.75γb⋅ γf.grass⋅ γβ⋅ ξ0⋅( ) Hm0⋅:=Wave run-up above the sea water level
z2%1 2.64m=
Second estimate: Improved approach for the average slope of the dike
Determine the representative angle of the upper slope of the •dike at the seaside
tan α( )1.5 Hm0⋅ z2%1+( )
Lslope B−( )
α2 1.− atan .503. Hm0⋅ 2. z2%1⋅+( )
1.− Lslope⋅ B+( )⋅
⋅:=
α2 0.38=
Angle of the average slopetan α2( ) 0.4=
Determine the breaker parameter•
ξ0
tan α2( )s0
:=Breaker parameter
ξ0 1.45=
Determine the wave run-up•
z2%2 1.75γb⋅ γf.grass⋅ γβ⋅ ξ0⋅( ) Hm0⋅:=Wave run-up above the sea water level
z2%2 3.178m=
Climate (Ex) Change – Eco-engineering in the Dollart
97
The wave run-up is higher than the freeboard at the crest. For this calculation this fact is neglected.
So for the further calculation the Z2%3 is used.
Determine the chance of overtopping per wave•
Rayleigh equation
Pov e
ln 0.02( )−hk
z2%3
⋅
2
−
:=
So a possibility of wave overtopping of:
Pov 0.07=
(If Pov=0,1 that means 10% of the incoming waves go over the top)
z2%3 2.517m=
Wave run-up above the sea water levelz2%3 1.75γb⋅ γf.grass⋅ γβ⋅ ξ0⋅( ) Hm0⋅:=
Determine the wave run-up•
ξ0 1.15=
Breaker parameterξ0
tan α3( )s0
:=
Determine the breaker parameter•
tan α3( ) 0.316=
Angle of the average slopeα3 0.306=
α3 1.− atan .503. Hm0⋅ 2. hk⋅+( )
1.− Lslope⋅ B+( )⋅
⋅:=
tan α( )1.5 Hm0⋅ hk+( )Lslope B−( )
Determine the representative angle of the upper slope of the •dike at the seaside
In this case the wave run-up exceeds the freeboard at the crest. Therefore 3th estimate
for the average slope and wave run-up:
For the determination of the average slope
and also the wave run-upz2%2 hk:=than z2%2 hk>So if
Because the run-up needs to be smaller than the freeboard for the determination of the
average slope
Check if the wave run-up is smaller then the freeboard from the SWL to the crest•
Climate (Ex) Change – Eco-engineering in the Dollart
98
N 5.028 103
×=
Total amount of waves that strike against the dike during a
storm period
NTimestorm
Tp
:=
Estimate of storm duration of 5hoursTimestorm 18000s:=
Tp 3.58s=
For a first estimate of the maximum volume of one wave that can be expected at a certain
moment, can be calculated with the total number of overtopping waves
V a ln 1 P−( )−( )
4
3
⋅
The formula to calculate the volume at a certain probability of exceedance
P 1 e
V
a
0.75
−
−
Weibull equation
The average wave overtopping doesn't say much about the amount of water that
instantaneous will flow over the crest of the dike at a particular overtopping wave.
With the information of the wave-overtopping the probability for wave overtopping volume
per wave is calculated.
Determine the chance that wave overtopping per wave V is greater than or same as V •
a 0.453m2
=
a 0.84Tm⋅qgrass
Pov
⋅:=
This scale factor is needed for the Weibull equation,
Determine the scale factor•
Pov
Nov
NThe possibility of wave overtopping, already determined
Nov Pov N⋅:=
Nov 358= Number of overtopping waves
So the volume of the overtopping waves will be:
Alternative formula to calculate the maximum volume. This
can be used for a first estimateV a ln Nov( )( )1.33⋅:=
V 4.77m
3
m= Volume of the overtopping waves
Climate (Ex) Change – Eco-engineering in the Dollart
99
Appendix 7: Multi criteria analysis
Multi criteria analysis section 1
Multicriteria–analysis of applicable ecological materials and methods
Features tarjectory 1: no marshes
low crest height (+/- 7 m +NAP)
slope 1:4
Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28
Score per criteria on a scale of 1 to
5
contribution
to nature
development
contribution
to coastal
safety
contribution
to recreation
needed
surface
Natura2000 innovation experience origin
costs/
benefits Applicability Overall score materials
materials
1. No different material 1 1 1 5 1 5 3 5 5 No different material 2,64
2. Bundle of piles 3 2 1 2 4 2 4 4 1 Bundle of piles 2,32
3. Eco-Xblocks 4 4 1 5 1 5 1 2 2 Eco-Xblocks® 2,86
4. Armorflex 3 4 1 5 2 3 2 4 5 Armorflex® 3,32
5. C-star coastal elements 4 2 1 5 2 4 3 4 5 C-star® coastal elements 3,29
6. Vetiver 3 3 2 5 3 4 1 4 1 Vetiver 2,68
7. Elastocoast 4 3 1 5 3 3 2 5 4 Elastocoast 3,29
8. Hydrotex Articulating Blocks 4 4 1 5 3 2 2 3 4 Hydrotex 3,29
9. Smart grass reinforcement 1 4 1 5 4 2 3 4 5 Smart grass reinforcement 3,11
Methods Overall score concepts
1 No changes 1 1 1 5 1 5 3 3 2 No changes 2,07
2 Increased overtopping 2 5 1 5 4 2 3 5 5 Increased overtopping 3,54
3 Slope changes 1 3 2 3 2 3 3 1 3 Slope changes 2,32
4. Raising dike height 1 5 1 2 1 5 3 2 3 Raising dike height 2,54
Climate (Ex) Change – Eco-engineering in the Dollart
100
Multi criteria analysis section 2
Multicriteria–analysis of applicable ecological materials and
methods
Features tarjectory 1: marshes
medium crest height (+/- 8 m +NAP)
slope 1:4
Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28
Score per criteria on a scale of 1 to 5
contribution
to nature
development
contribution
to coastal
safety
contribution
to
recreation
needed
surface
Natura2000 innovation experience origin
costs/
benefits Applicability Overall score materials
materials
1. No different material 1 1 1 5 1 5 3 5 5 No different material 2,64
2. Bundle of piles 2 2 1 2 4 2 4 4 1 Bundle of piles 2,14
3. Eco-Xblocks 1 3 2 5 1 5 1 1 1 Eco-Xblocks® 2,07
4. Armorflex 1 2 1 5 2 3 2 1 1 Armorflex® 1,82
5. C-star coastal elements 1 2 1 5 2 4 3 1 2 C-star® coastal elements 2,11
6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver 2,39
7. Elastocoast 1 2 1 5 3 3 2 1 1 Elastocoast 1,86
8. Hydrotex Articulating Blocks 1 2 1 5 3 2 2 2 1 Hydrotex 1,89
9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4
Smart grass
reinforcement 3,14
Methods Overall score concepts
1 No changes 1 1 1 5 1 5 3 3 2 No changes 2,07
2 Increased overtopping 2 5 1 5 4 2 3 5 5 Increased overtopping 3,54
3 Slope changes 1 4 2 1 3 3 3 1 3 Slope changes 2,32
4. Raising dike height 1 4 1 2 1 5 3 2 2 Raising dike height 2,21
Climate (Ex) Change – Eco-engineering in the Dollart
101
Multi criteria analyisis section 3
Multicriteria–analysis of applicable ecological materials and methods
Features tarjectory 1: marshes
high crest height (+/- 9 m
+NAP)
slope 1:4
Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28
Score per criteria on a scale of 1 to 5
contribution
to nature
development
contribution
to coastal
safety
contribution
to recreation
needed
surface
Natura2000 innovation experience origin
costs/
benefits Applicability Overall score materials
materials
1. No different material 1 1 1 5 1 5 3 5 5 No different material
2. Bundle of piles 2 2 1 2 4 2 4 4 1 Bundle of piles
3. Eco-Xblocks 1 4 2 5 1 5 1 1 1 Eco-Xblocks®
4. Armorflex 1 4 1 5 2 3 2 1 1 Armorflex®
5. C-star coastal elements 1 4 1 5 2 4 3 1 2 C-star® coastal elements
6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver
7. Elastocoast 1 4 1 5 3 3 2 1 1 Elastocoast
8. Hydrotex Articulating Blocks 1 3 1 5 3 2 2 2 1 Hydrotex
9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4 Smart grass reinforcement
Methods Overall score concepts
1 No changes 1 1 1 5 1 5 3 3 2 No changes
2 Increased overtopping 2 5 1 5 4 2 3 5 5 Increased overtopping
3 Slope changes 1 3 2 1 3 3 3 1 3 Slope changes
4. Raising dike height 1 3 1 2 1 5 3 2 2 Raising dike height
Climate (Ex) Change – Eco-engineering in the Dollart
102
Multi criteria analyse section 4
Multicriteria–analysis of applicable ecological materials and methods
Features tarjectory 1: marshes
medium crest height (+/- 8 m +NAP)
slope 1:6
Weight criteria from 1–5 5 5 4 3 1 1 3 2 4 28
Score per criteria on a scale of 1 to 5
contribution
to nature
development
contribution
to coastal
safety
contribution
to
recreation
needed
surface
Natura2000 innovation experience origin
costs/
benefits Applicability Overall score materials
materials
1. No different material 1 1 1 5 1 5 3 5 5 No different material 2,64
2. Bundle of piles 2 2 1 2 4 2 4 4 1 Bundle of piles 2,14
3. Eco-Xblocks 1 3 2 5 1 5 1 1 1 Eco-Xblocks® 2,07
4. Armorflex 1 2 1 5 2 3 2 1 1 Armorflex® 1,82
5. C-star coastal elements 1 2 1 5 2 4 3 1 2 C-star® coastal elements 2,11
6. Vetiver 2 2 3 5 3 4 1 3 1 Vetiver 2,39
7. Elastocoast 1 2 1 5 3 3 2 1 1 Elastocoast 1,86
8. Hydrotex Articulating Blocks 1 2 1 5 3 2 2 2 1 Hydrotex 1,89
9. Smart grass reinforcement 1 5 1 5 4 2 3 4 4 Smart grass reinforcement 3,14
Methods Overall score concepts
1 No changes 1 1 1 5 1 5 3 3 2 No changes 2,07
2 Increased overtopping 2 5 1 5 4 2 3 5 5 Increased overtopping 3,54
3 Slope changes 1 3 2 1 3 3 3 1 3 Slope changes 2,14
4. Raising dike height 1 4 1 2 1 5 3 2 2 Raising dike height 2,21
Climate (Ex) Change – Eco-engineering in the Dollart
103
Appendix 8: Drawings cross-section 4, 10, 14
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Climate (Ex) Change – Eco-engineering in the Dollart
105