Wallingford
THE EFFECTIVENESS OF GROYNE SYSTEMSPhysical Model Study of Groynes ona Beach
Report No EX 1351October 1986
Registered Office: Hydraulics Research Umited.Wallingford. Oxfordshire OXI0 8BA.Telephone: 0491 35381. Telex: 848552
SUMMARY
This report covers a programme of physical model tests carried out as part
of Phase 11 of a research project investigating the effectiveness of groyne
systems in modifying the beach environment.
The physical modelling was assisted by two field surveys undertaken in
November 1983 and October 1984 at Sea Palling in Norfolk. The aim of the
programme was to calibrate the physical model using the prototype field data
and then study the effectiveness of the Sea Palling groyne system.
Following this, various other groyne layouts would be tested and their
effectiveness checked by varying groyne parameters and flow and wave
conditions and identifying their effects.
In the event full validation was not possible and so a series of comparative
tests were carried out using a fixed bed model of the beach at Sea Palling
and modelling, with one exception, vertical impermeable groynes.
Experiments were undertaken initially on a series of hypothetical groyne
layouts up to and including a field of seven groynes. In the second series,
comparative tests on a three-groyne system of similar configuration in plan
to that at Sea Palling, was carried out.
This final report in the series covers the work carried out between May 1982
and June 1985. Other volumes, maintained as a project record by CIRIA and
HRL, cover respectively the Summary Report (Volume 1), records of existing
groynes (Volume 2) and field data collection (Volume 3 Part 1).
The physical model study was part of a collaborative project co-ordinated by
CIRIA with additional funding under MAFF Commission B - Marine Flood
Protection, by the Ministry of Agriculture, Fisheries and Food (MAFF).
For any further information on this study, contact either Dr A H Brampton or
Mr J Welsby of the Coastal Processes Section, Maritime Engineering
Department of Hydraulics Research.
CONTENTS
Page
1
2
3
4
5
6
7
INTRODUCTION
MODEL DESIGN
EXPERIMENTAL TECHNIQUES
3.1 Instrumentation
VALIDATION AGAINST PROTOTYPE MEASUREMENTS
4.1 Initial validation attempt
4.2 Final validation attempt
TEST PROGRAMME
5.1 Hypothetical groyne systems (first test series)
5.2 Hypothetical groyne systems (second test series)
SUMMARY OF RESULTS AND CONCLUSIONS
REFERENCES
TABLES
FIGURES
PLATES
APPENDIX: A - Terms of Reference
1
4
9
13
15
15
18
22
22
30
38
50
TABLES
1. Initial alongshore current flows from mathematical model
2. Initial model proving parameters
3. Test parameters - hypothetical groyne systems (first test series)
4. Test parameters - hypothetical groyne systems (second test series)
FIGURES
Experimental techniques
1 Location plan
1-1 Plan layout of stage 1 - experimental techniques
1-2 Section through uniformly sloping model beach
1-3 Velocity profiles at mid position - experimental techniques
1-4 Theoretical alongshore current profile (Longuet-Higgins 1970)
Hypothetical groyne systems (first test series)
2-1 Plan of wave basin - for tests 1 to 10 (with Sea Palling groyne system)
2-2 Velocity profile - uniform sloping beach
2-3 Testing sequence - hypothetical groyne systems (first test series)
2-4 1-groyne system, flow pattern Test 1
2-5 3-groyne system, flow pattern Test 2
2-6 4-groyne system, flow pattern Tests 3, 4 and 5
2-7 Plan and section of Sea Palling site (October 1983)
2-8 Section through 'Winter Beach Profile' (used for tests 6 to 25)
2-9 Velocity profile on beach altered to suit Sea Palling beach contours
(see Fig 2-8)
2-10 Groyne elevation relative to beach and tidal levels (used in Tests 6 to
25)
2-11 Sea Palling groyne system, Tests 6 and 7
2-12 Sea Palling groyne system, Test 8
2-13 Sea Palling groyne system, Test 10
2-14 Plan of wave basin - paddle angled at 26 deg, Sea Palling 'winter
profile' for tests 11 to 25
2-15 Sea Palling groyne system, Test 11
2-16 Sea Palling groyne system, Test 12
2-17 Sea Palling groyne system, Test 15
2-18 Sea Palling groyne system, Test 14
2-19 7-groyne field, Test 18 (1:1 spacing)
2-20 7-groyne field, Test 17 (1: 1 spacing)
2-21 7-groyne field, Test 19 (1:1 spacing)
2-22 7-groyne field, Test 20 (1:2 spacing)
2-23 7-groyne field, Test 21 (1:L5 spacing)
2-24 7-groyne field, Test 22 (1:L5 spacing)
2-25 7-groyne field, Test 23 (1:1 spacing angled updrift)
2-26 7-groyne field, Test 24 (1: 1 spacing angled updrift)
2-27 7-groyne field, random waves, Test 25 (1:1 spacing angled updrift)
Hypothetical groyne systems (second test series)
3-1 Plan of wave basin - wave generator at 15 degrees, for tests 31 to 43
3-2 Run-up gauge positions and beach profile
3-3 Model beach plan (as moulded) showing mirrored profiles
3-4 Model/prototype currents showing differences
3-5 Velocity profile - final validation attempt
3-6 Schematic plan view of groyne field
3-7 Test 31 - at mean high water, neaps
3-8 Test 32 - at mean tide level
3-9 Test 33 - groynes raised 0.5m
3-10 Test 34 - groynes raised 0.5m - beach roughened
3-11 Test 35 - groynes raised LOm - beach roughened
3-12 Test 36- groynes raised Lam
3-13 Test 37 - raised groynes plus vertical sea wall
3-14 Velocity profiles - Tests 35 and 36
3-15 Test 38 - raised groynes - stone clad
3-16 Test 39 - raised groynes - with added T-pieces, stone clad
3-17 Test 40 - raised groynes - with fishtails added, stone clad
3-18 Test
3-19 Test
3-20 Test
41 - raised groynes - with updrift groyne damage
42 - raised groynes - permeable
43 - raised groynes - alongshore current overpumped
PLATES
Experimental techniques
1-1 General view of model basin
1-2 Distribution system for alongshore currents
first test series
2~3 General view of model basin - wave generator at 10 degrees
2-4 General view of model basin - wave generator at 26 degrees
Hypothetical groyne systems (second test series)
3-5 View of model beach showing roughening strips (Test 34)
3-6 Stone clad groynes (Test 38)
3-7 Stone clad T-shaped groynes (Test 39)
3-8 Stone clad fishtailed groynes (Test 40)
3-9 Permeable groynes (Test 42)
1 INTRODUCTION
Groynes have been used as a means of coastal
protection for many years but as yet there have been
no clear guidelines laid down for their installation
and there is a distinct lack of definite design
methods.
Although there is a good understanding of the inshore
marine climate and the ability, using mathematical
models to predict the effect of shoreline structures
on the beach shape, it seems that it is not common
practice to make full use of these techniques.
This current research project was promoted by the
Construction Industry Research and Information
Association (CIRIA) and follows an earlier literature
review, conducted by Hydraulics Research Ltd (HRL).
This review was extended in the first phase of the
CIRIA research project to consider the particular
problem being faced around the coastline of the United
Kingdom and a set of recommendations and conclusions
then drawn up (Ref 1).
One of these recommendations was that physical model
studies should be undertaken to investigate such
variables as groyne geometry, beach head structures
(ie sea walls), beach profile and groyne type in a·
controlled environment. An initial series of tests
were proposed to look at and resolve any problems with
measurement techniques and with the provision of
boundary conditions associated with the generation of
alongshore currents. Other tests would concentrate on
investigating waves, currents and their inteactions
with different groyne systems. It was recommended
that these studies should be carried out using a fixed
bed model and validated using prototype measurements.
Therefore in May 1982, HRL were commissioned by CIRIA
to carry out these studies in a large wave basin.
1
The objective of the physical model experiments was to
study the effects of different groyne systems (in
terms of groyne geometry and structure and beach
head), under different wave conditions (ie height,
period and direction), on the currents that those
waves create. It was intended that the physical model
should be validated and calibrated using data obtained
from specific prototype measurements. The decision
was also made, for this phase of the project, to carry
out the model tests using a fixed (concrete) bed.
Although this precludes direct assessment of sediment
motion, it does facilitate measurement of both the
waves and the currents they create.
It was anticipated that this would lead to a clearer
understanding of the hydrodynamic processes operating
in and around a groyne system, from which deductions
could be made on their effectiveness in controlling
the movement of beach material.
In particular, attention was focussed on the likely
performance of groyne systems on sandy coasts, ie
beaches of shallow slope. (Generally, less difficulty
has been found in designing groynes for shingle
beaches.) On sandy beaches groyne performance can be
extremely variable from site to site, and their
effectiveness in promoting healthy upper beach levels
is often doubtful.
In order to validate the model, prototype measurements
were required. Insufficient funding was available to
CIRIA to commission this work directly, but the
Imperial College of Science and Technology (ICST)
obtained grant aid from the Science and Engineering
Research Council (SERC) for a research project which
included carrying out field data collection along the
lines suggested in phase one of the CIRIA report.
Results from the work carried out by lCST and their
sub-contractor (Ceemaid Ltd) were made available to
2
the CIRIA and an at t was made to use this
data to validate the physical model,
This report describes tests carried out in the
physical model at Wallingford during the period from
May 1983 to June 1985, These tests were split into
three parts, namely,
1, Establishing experimental techniques and
procedures
2. Attempting to validate the model against
prototype conditions with the aid of field data,
and
3. Investigating the effect of a number of
hypothetical groyne layouts of different heights,
lengths and spacings on flow conditions in and
around the groyne systems,
The philosophy of the model design and details of its
construction are given in Chapter 2. The first set of
tests, to establish modelling techniques is described
in Chapter 3. Chapter 4 describes the work carried
out to validate the physical model against prototype
measurements and Chapter 5 describes the tests carried
out on a variety of hypothetical groyne layouts to
study the effects of changing groyne geometry.
Finally, Chapter 6 summarises the main findings and
conclusions of the project.
All the figures in this report are prefixed with
either 1, 2 or 3. This was done to differentiate
between stages of the modelling programme. Figures
prefixed 1, are connected with the experimental stage
when techniques and procedures were established.
Prefix 2 relates to the first series of tests (see
Chapter 5, section 5.1) and the figures prefixed 3 are
relevant to the second and last series of groyne
experiments (Chapter 5, section 5.2).
3
2 MODEL DESIGN
It is clear that the use of a physical model to assess
the effectiveness of a groyne system has many
advantages over say, direct field measurement of
groyne behaviour. The investigator can for example,
specify precisely the incident wave conditions, the
water level and the geometry of the groyne system used
in any test. In addition he can rapidly alter the
groyne layout and then repeat experiments under
similar hydrodynamic conditions.
On the other hand, the use of a scale model has
limitations, some obvious and others more subtle. It
is physically impossible simply to scale down reality
and as a consequence no model can correctly represent
or reproduce all the characteristics found in a
prototype situation. Inevitably some phenomena will
be imperfectly reproduced and it is therefore
necessary to identify those which are considered to be
most important and design the model to reproduce those
correctly.
The first decision made in the choice of parameters
was the model scale. It was clearly necessary to study
a reasonable length of coast to ensure that a
sufficient number of groyne bays could be reproduced
in the model while also allowing adequate space at
either end of the beach to dissipate any model "end
effects". This scaled reduction of the prototype must
be of sufficient size to ensure that wave heights and
periods were large enough to avoid distortion by
surface tension and capillary effects but small enough
to allow the model to be built, equipped and operated
at reasonable cost.
In view of the foregoing, a scale of 1:36 was chosen
(in both the vertical and horizontal planes) and an
existing wave basin at Wallingford extended to 36.5m
by 25.0m to accommodate the model. This enabled
approximately one kilometre of beach to be represented
4
in the model, with incident waves of up to 83mm (3
metres prototype) in height. The maximum water depth
was 300mm (10.8m prototype). Wave periods of between
0.5 and 1.33 seconds (3 and 8 seconds prototype) could
be generated, and this covered the range expected to
be encountered during the field study. The dimensions
of the wave basin allowed waves to be generated from
an angle normal to the beach to about 25 degrees away
from it. This range of angles covered the expected
wave crest approach angle during the ICST/Ceemaid
field measurements, and indeed on many coasts of the
UK.
In the prototype situation, waves usually have a
considerable spread of energy over both direction and
period. Although it is possible to build a model wave
generator to reproduce such a multi-directional
complex sea state, it would have been impractical for
the present study, both in terms of collecting
calibration data and in trying to set appropriate
boundary conditions for a rapidly changing sea state.
Apart from the delay and considerable extra expense
involved in obtaining the necessary equipment, there
would also have been the need for extremely
sophisticated field wave recording and analysis
equipment to provide suitable input data.
It was therefore decided to use two ISm long,
hydraulically operated paddles working in tandem,
which produced long-crested waves from a single
direction. These wave generators are capable of
producing waves of random height and of specified
frequency spectrum, but were used in the main to
generate wave trains of uniform height and single
period. This method of producing waves is clearly a
great simplification of what occurs in nature and the
question of whether a groyne system will behave
"typically" under the action of long crested
uni-directional waves cannot be resolved from the
present model tests. Comparison between runs with
5
uniform and random wave however did not
suggest that this simplification would be too
misleading; the main difference was that the steady
current patterns were more difficult to observe in the
latter case due to the higher rate of dispersion in
the random waves. It is also argued that (a) both
types of wave train showed a similar flow pattern (a
view shared by committee members) and (b) this
similarity results from the large inertia of the wave
induced flows around the groyne field which is not
affected to any great extent by variations from wave
to wave.
The majority of groynes to be found around our shores
are built on beaches composed of sand and shingle.
The problems associated with scaling the properties of
such materials are considerable and it is extremely
difficult to find a model beach material which will
accurately reproduce the movement of sand on a
prototype beach. It is also very difficult to measure
waves and currents especially in a mobile bed model in
shallow water and so a positive recommendation had
been made in a previous study (Ref 1) to use a fixed
(concrete) bed model. There was thus no need to
consider model sediment as a parameter.
It was realised that the model would require
calibration against observation on a prototype beach.
This is a requirement for any type of scale model. A
likely consequence of representing a sandy beach by
using a fixed concrete bed in a model is that the bed
roughness is unlikely to be correct. It is therefore
normal to change (usually to increase) the roughness
of the model surface to ensure that prototype
velocities are correctly scaled. This strategy was
foreseen as likely for the groynes model.
A further limitation with a fixed bed model was that
although it was possible to model a particular initial
beach topography. as measured in the field study. it
6
was not possible for the waves to realign the beach
during a particular test. This precluded direct
determination of the efficiency of a particular groyne
system in either retaining beach material or
increasing the beach width,
On the other hand this would not be guaranteed using a
mobile bed. where the problem of scaling the bed
material are formidable as mentioned above, The
advantage of a fixed bed model is that it enables the
measurement of current velocities even in very shallow
water. from which at least a qualitative assessment of
sediment movement and groyne performance can be made.
In most prototype situations it is the interaction of
groynes and the wave induced alongshore currents that
is most important, Of course all groyne systems
around the UK coast are influenced to some degree by
tidal effects. However this was not thought to be
particularly important at the beginning of the study
especially as the more important parameters were to be
measured landward of the breaker line where tidal
effects are negligible. Therefore a positive decision
was made to exclude tidal effects from the modelling
process. As will be seen later (Section 4,2). this
led to some difficulty in calibrating the model, This
decision was not taken because it was intrinsically
impossible to include tides and their effects; indeed
tidal modelling is routinely carried out in
laboratories all over the world. However it
would have added considerably both to the expense and
to the number of parameters to be tested within the
relatively short timespan envisaged for the study.
For example tests may equally well have been carried
out with the same groyne geometry and wave conditions
but at various states of the tide. However. it was
decided to concentrate on the effects of the groyne
systems. both on the waves and the currents that those
waves created rather than on the effects of say tidal
7
currents and water levels. On a similar basis
it was also decided to exclude wind effects,
As with all scale models, while some physical
processes will be well scaled. eg the propagation of
waves, it is necessary to check that the model does
not give unrealistic results for other phenomena. In
particular because water viscosity is unaltered while
other parameters are scaled down, it was always
considered likely that there would be some difficulty
in matching model velocities against those recorded in
the prototype. This is a standard problem which
occurs frequently in tidal models and is overcome by
artificially roughening the bed surface to obtain
correctly scaled current velocities.
It was also necessary. as discussed in the next
chapter, to provide an external flow circulating
system to overcome the fact that the model had finite
boundaries whereas in nature the beach would be much
longer and there would be a natural input and outflow
of currents at either end of the stretch of beach
being modelled.
During the first phase of this research project, a
large number of references describing laboratory tests
on groynes were reviewed (Ref 2), The vast majority
of these tests however, were carried out using a bed
of granular material and the effects of the groynes
assessed by the response of the mobile bed. Although
this is a most direct method of carrying out such an
assessment, it has serious flaws as mentioned above.
In March 1983, before design and construction of the
model had begun, a visit was made to Delft University
in the Netherlands to talk to Dr P J Visser who had
been recently involved in investigating alongshore
current flows in a wave basin (Ref 3). His valuable
advice was of great help in setting up the circulatory
system. A Dutch report entitled "Influence of groynes
8
3 EXPERIMENTAL
TECHNIQUES
on the form of the coastline" 4 was also
translated although this only proved to demonstrate
the difficulties of physical modelling, the value of
accurate moulding and the need for an external
recirculation system mentioned already.
As will be seen in the following chapter, the results
from these previous studies proved to be very useful
in establishing experimental procedures for this
study.
The first stage after construction of the physical
model was to establish suitable operating techniques
and most importantly to assess the best methods of
measuring the speed and direction of the currents.
It was necessary in the first instance to devise a
method in which alongshore currents, generated by
obliquely breaking waves, were allowed to flow
naturally without causing unacceptable circulation
within the wave basin. This was done by installing an
external pipe system which allowed the alongshore flow
of water to be extracted at the downdrift end of the
beach by means of an axial flow pump and re-introduced
at the updrift end. This arrangement is shown in
Figure 1-1 and Plate 1-2. Flow measurement was made
by means of an ultra-sonic f10~rneter situated in a
straight length of the (external) pipe and linked to
an electronic flow recorder.
The distribution at the updrift end of the model beach
was effected by a series of channels, 12 in all,
installed parallel to the beach in the updrift wave
guide wall. Each channel was equipped with its own
gate which could be operated independently. Variation
of the current flow pattern was achieved by placing
baffles in the individual distribution channels and
adjusting them until the required velocity profile was
9
obtained@ The to and extract the
correct flow at either end of the model beach whilst
allowing the currents to be driven by the obliquely
incident waves within the working area. The effect of
this was to minimise disturbance at either end of the
beach, and to avoid as far as possible unwelcome flow
circulation within the model basin.
As well as the external flow system, a series of
pressure tappings were inserted in the model beach,
with pipes from these pressure holes leading to a
batch of stilling wells enabling wave set up to be
monitored if required.
Initially a 15 metre long (540 metres prototype)
stretch of beach was modelled without groynes, with a
uniform slope of 1:29 based on the mean profile of a
sand beach surveyed at Chapel St Leonard on the East
coast. One 15 metre long wave generator was installed
in the model and placed at a 10 degree angle to the
beach. Wave guide walls placed at each end and
perpendicular to the paddle, extending right up to the
beach to constrain the waves on to the slope but
leaving an opening at the top of the beach for the
alongshore flows to pass unhindered. This set up is
shown in both plan and section in Figures 1-1 and
1-2.
At this early stage with no proving data available, it
was decided to run the wave generators using regular
waves with a period of 1.167 seconds (7 seconds
prototype) and a height of approximately 0.083m (3
metres prototype). This was for two reasons;
firstly, this tied in with the experimental work done
by Visser (Ref 3) on a similar slope and ensured that
appreciable alongshore currents were produced, and
secondly it was what was thought to be a reasonable
estimate of the conditions to be found on the east
coast. Visser's experimental velocity profiles for a
particular uniform sloping beach were converted to
10
suit the 1 29 slope of the physical model
a mathematical model.
means of
Two different types of instrumentation to measure the
alongshore currents (ie ultra-sonic and
electra-magnetic miniature current meters) were
tested. Although both types worked reasonably well in
deeper water, problems were encountered in the highly
turbulent surf zone where the presence of entrained
air bubbles made the ultra-sonic meter unreliable.
The electro-magnetic meter functioned well except near
the bed of the model where the water, forcing its way
between the bed and the disc shaped sensor head of the
meter, tended to give inaccurate results.
The electro-magnetic current meter was used in all but
the shallowest areas of the basin and mean velocities
calculated using the following equations:
1. In the constant depth part of the basin
V = 0.2S(V surface + 2V middepth + V bed)
2. On the sloping beach
V = O.S(V surface + V bed)
the 'bed' velocities being measured just above the
floor of the model (10-1Smm) while the 'surface'
velocities were taken with the head of the instrument
just below the trough of the waves.
In the shallow water zone at the top of the beach,
various techniques were used including float tracking.
It was found after considerable experimentation that
the most favourable way to measure shallow water flows
was by injecting dye and following its movement by
means of a video camera suspended directly above the
injection point. This had the advantage of measuring
the speed (a digital clock is superimposed on the
video screen) and also the direction of the currents
within the groyne field. It was found that by
following the head of the central spine of the main
11
dye streak it was possible to measure the trace, in
most cases for at least one It was also
possible, in the deeper water, to check the velocity
of the dye with the electro~magnetic current meter.
Later it was found that the most convenient way to
observe current flows near the bed was to mix the dye
with a solution of sucrose which made it just heavy
enough to remain in the lower strata.
Wave heights and periods were measured in the model
using standard RRL twin wire wave probes.
Finally, in order to obtain a first estimate of the
likely current along the model beach, created by the
obliquely breaking waves, a mathematical model was
developed at RRL using the theory given by
Longuet-Riggins (Ref 5, 6). Ris approach was to
calculate the momentum of the incoming waves and hence
the lateral thrust they exert in the surf zone. Then,
by taking into account frictional effects, it was
possible to derive a simple expression for the total
alongshore current, using the direction and height of
the waves just outside the breaker zone. That same
momentum causes an increase in the mean water level
within the surf zone called 'set up' which can also be
calculated theoretically. In the context of modelling
the set up is important from the point of view of
altering the across-shore distribution of the littoral
currents. For example a large set up will increase
inshore water depth and hence the discharge on the
upper part of the beach.
It is not appropriate here to reproduce the
formulation of the theory, but simply to quote the
equation of greatest importance, namely:
Q! 5/2
Kg Rb sin 2 ~
12
3.1 Instrumentation
where:
Q is the total alongshore discharge
Rb
is the height of the waves as they just start to
break
a is the angle between the beach contours and the
wave crests at the point of breaking,
g is the acceleration due to gravity, and
K is a non-dimensional coefficient which depends on
the frictional characteristics of the beach, the
intensity of horizontal mixing and the ratio of
local depth to breaker height.
Although more recent work has been carried out into
modelling the processes which affect the coefficient
K, the methods and numerical values proposed by
Longuet-Riggins proved to be quite accurate enough for
the initial design of the experiments. By later
comparison of the model results and the above formula,
it was possible to make a more satisfactory evaluation
of K and anticipate the discharge required for
different model situations (see Figure 1-3 for
comparison of mathematical model and physical
results).
To obtain the direction and magnitude of the
alongshore currents, circulatory flows within the
model basin and wave heights and periods, various
instruments were employed. These instruments,
mentioned briefly above, were:
Electro-magnetic current meter
This meter has a discus shaped sensor head 35mm in
diameter with four electrodes situated in two
diametrically opposed pairs. A magnetic field is set
up in the water by means of a coil in the sensor head
carrying an electric current. Water flowing through
this field produces a potential difference which is
13
detected the two of electrodes. This
potential difference is calibrated in known flows
giving a measurement in two planes.
Ultra-sonic current meter
This acoustic device comprises a sensor with four
diametrically opposed vertical prongs which measure
the travel time of sound pulses between each pair of
prongs in two horizontal directions. providing an
output which is a direct measurement of the flow in
both directions. The signals from both channels are
used to compute the resultant speed and direction of
flow.
The resolution of both current meters is of the order
of 4mm per second which compares favourably with the
standard miniature propeller current meter (20mm per
second). Both the above current meters. however. were
relatively new and untried and prone to teething
problems.
Twin-wire wave probes
Waves in the model were measured by standard HRL wave
probes spaced across the width of the wave generator
and shoreward of it. They consist of two parallel
1.5mm diameter wires set vertically 12.5mm apart and
energised with a high frequency alternating voltage.
The conductance between the wires is proportional to
the depth of immersion (and the conductivity of the
water) and the probe can resolve water level changes
of O.lmm.
Ultra-sonic flow meter
This is an obstructionless flow meter set into the
pipe system to determine the amount of alongshore
current recirculation. It is attached to a converter
which measures the time differential created by liquid
14
flowing through the sensor tube. This measurement is
converted to a voltage which is displayed by a digital
output,
Axial flow pump
Used to pump the flows from the downstream end of the
model back to the upstream end via the pipe system.
It is controlled by a rheostat which can vary the flow
from 0 to about 90 litres per second.
4 VALIDATION AGAINST
PROTOTYPE
MEASUREMENT
4.1 Initial validation
(prior and
following the
October 1983 field
survey)
FolloWing the initial testing described in the
previous chapter, the next task was to extend the
model beach by a further 16 metres in the alongshore
direction, This gave a total prototype length of over
one kilometre as shown in Figure 2-1. This was
sufficient to examine beach conditions without serious
end effects within the modelled area. The second wave
generator was installed to run in parallel with the
generator already in position, and the initial
experimental tests re-run to confirm their
repeatability on the extended beach. The wave guide
wall openings together with the velocity profile of
the alongshore currents were adjusted and calibrated
against previous experiments (see Ref 3).
Attention was then focussed on calibrating the
physical model against prototype data, The site
chosen, Sea Palling in Norfolk, was a good one, having
three groynes set on an almost straight and
predominantly sandy beach, with a considerable stretch
15
of open coast on either side, This arrangement
therefore allowed measurements to be made. not only
within a groyne system unaffected by neighbouring
coastal works. but also on the open beach on either
side. In addition, it was reasonably easy to model
this situation in the wave basin because of the
simplicity of the conditions at each end of the
beach.
In October 1983, before the first field survey. a
series of preliminary physical model tests were
undertaken on a groyne field built on a uniform
sloping beach. Three groynes were set at the top of
the beach with lengths and spacing similar to those
estimated at the site chosen for the prototype
experiments. Members of the Steering Group and the
survey contractor (Ceemaid Ltd) were then invited to
Wallingford to view the model and the flow patterns
generated around the groynes. This also allowed the
survey contractor to get a general feel for the
current flows and to help him decide where to place
his survey instruments.
The field data collection took place during October
and November 1983, but was severely hampered by storms
which destroyed much of the equipment deployed and
eventually forced the survey team to abandon the
programme. As a consequence, only a small amount of
data on waves, currents or beach topography was
obtained. However, there was sufficient information
to re-mould the physical model to represent a typical
winter profile and the wave generators were moved to
the more oblique angle of 26 degrees to the shoreline.
This approach angle was suggested by the field
experiments. With no valid proving data at this
stage, it was decided to continue running the model
with the wave height and period used in the setting up
procedure described in Chapter 3 (see Figure 2-14 for
the plan layout).
16
Recirculation within the basin was measured at
sections L and M and also section F in the
constant depth area seaward of the beach (Figure 2-2).
Spot checks were carried out at points throughout the
basin and wave set up was monitored during each test.
With the wave height and period judged to be
comparable with the anticipated conditions at Sea
Palling, the alongshore currents were adjusted to the
required profile, thus obtaining a minimal
recirculatory movement within the basin. Optimisation
of the alongshore flows was important, If currents
were either too fast or too slow they caused unwelcome
recirculation within the basin and non uniformity of
both the incident waves and the flow along the beach.
Just enough flow needed to be pumped through the
system to ensure that the input velocities were
similar to those created by the obliquely approaching
waves. These recirculatory flows are shown in Figure
2-2 together with the flows at sections L and M within
the basin.
Following these adjustments, the survey contractor
expressed the opinion that the model was exhibiting
the same general behaviour that was observed during
the field experiments at Sea Palling.
After these preliminary tests, whilst awaiting further
data from the field experiments, a series of tests
were carried out (in December and January) on 1, 3 and
4 groyne systems (Tests 1 to 5), using wave and
current data obtained in previous research on
alongshore currents (Ref 3). Later the beach was
re-profiled to a more realistic shape using an
approximate beach profile from Sea Palling. However,
it was soon apparent that little was to be gained from
the very limited data available and this attempt at
validation was brought to a close. Attention was then
turned to testing hypothetical groyne systems (Tests 6
to 25) and these are described in Chapter 5.1.
17
After these test when radar photographs taken during
the Sea became available in March
1984. it was seen that the offshore wave approach
angle was much more oblique than those earlier assumed
(up to 45 degrees relative to the shoreline).
At this late stage the model was not altered because,
(a) It was not possible to reproduce the external
flow rate anticipated and it would be difficult
to obtain the correct wave angle in the basin.
(b) This obliqueness was considered to be
unrepresentative of the bulk of conditions under
which systems would operate, and
(c) There was no current data on which to calibrate.
4.2 Final validation
attempt (following
the October 1984
field survey)
Following the failure to obtain validation data in
1983, a second field survey attempt was made in
October 1984 with a completely re-designed instrument
system.
The intention, for this final stage in the physical
model programme, was to simulate the Sea Palling
groyne field and calibrate the model from the October
1984 field survey data. Following this it was intended
to study the effects of changing various parameters
of hypothetical groyne systems under a variety of wave
conditions and tidal levels.
As the field survey data started to become available
from the October 1984 experiments, the top of the
model beach area was re-moulded. These upper beach
contours stretching to about 1750mm (63m prototype)
seaward of the baseline, were obtained from beach
levels measured along the prototype run-up gauges
placed on the upper beach and shown in plan in Figure
18
3~2. Run-up gauge 1 provided the contours north and
updrift of groyne A. (the updrift groyne) while run~up
gauges 2, 3 and 4 supplied the beach profiles between
groynes A and B. Further levels were obtained from
beach dips taken at either side of the groyne king
piles.
With no beach levels available south ie downdrift of
groyne B, (middle groyne) profiles to the north of
this groyne were 'mirror imaged' as shown in figure
3-3, to provide the beach contours to a point some
4000mm (145m prototype) south of groyne C (the
downdrift groyne). From this point the contours were
flared out to blend with the existing slope at the
downdrift extremity of the beach. The lower beach
area had to be estimated, there being very little
field data available at this time. The typical winter
beach profile given in the 1983 field survey (and
shown in figure 2-7) was used. These lower beach
contours were blended into the original uniformly
sloping beach at approximately 5100mm (184m prototype)
seaward of the model baseline at the top of the beach
(Figure 2-8).
The model beach was again constructed as a 'fixed' bed
tapering down to the floor of the basin some 9700mm
(35Om prototype) seaward of the top of the beach.
Water depth in the offshore (floor of the basin) area,
remained, except where stated, at 300mm (lO.8m
prototype depth corresponding to -9.4m aDN at the bed)
to simulate the depth at mean high water of spring
tides.
When the prototype groyne levels became available, the
model groynes were designed, built and installed into
the model's upper beach. Groyne heights at their
seaward end were estimated from photographs.
The wave generators were positioned in the constant
depth part of the basin and at an angle of 15 degrees
19
as shown in 3~1. This gave a 30m long wave
crest (1080m prototype). No radar plots were
available at this time but the breaking angle measured
in the model tied in well with the angle (10 degrees)
visually observed at the beach. Initially only
maximum and minimum wave elevations were available
from the offshore wave rider buoy» and it was also
necessary to estimate the wave period. The offshore
significant wave height was therefore calculated by
applying the Tucker-Draper (Ref 8) method of analysis
explained below.
Assuming initially an 8 second wave period (1.33
seconds model) over the 20 minute data gathering
period, gives 150 wave crossings. Using the
Tucker-Draper charts» this gives a factor f of
approximately 0.6» so the significant wave height Hs
can be estimated using H = f x H1 where H1 is thes
height of the highest wave crest added to the lowest
recorded trough obtained from the offshore buoy data.
From the initial data» H1 was given as 2.015m so
giving H = 0.6 x (2.015m) = 1.209 metres (prototype).s
To represent this using a regular wave train» this
figure was multiplied by 0.7071 to give 0.85 metres
prototype (0.024m model). This wave analysis was
later amended» when more data became available» to an
Hs of 0.87m and a 6.05 second period.
In view of the stratification of the flows noticed
(see Chapter 6)>> currents in and around the groyne
field were measured at both mid-depth and bed level.
It was however» found that the currents although
stratified» generally followed a similar pattern.
Thus the flow patterns in the relevant figures
indicate a typical velocity and direction through the
depth. There was a continual interchange between
model and survey data analysed at this time and quite
often it was the physical model that suggested
problems associated with the prototype data rather
than the other way around.
20
The model measurements were also by
introducing anthracite granules (see Section 502). in
and around the groyne bays to determine any likely
accumulation areas.
As model calibration progressed it became clear that
comparison between model and prototype, in terms of
current velocity and direction. was unsatisfactory and
despite lengthy experimentation could not be
rectified. It was found that with the wave conditions
predicted, the alongshore currents in the model were
concentrated in a narrow band within the groyne bays,
with the velocities tapering off seaward of the
breaker zone. The data from the field experiments
however, gave an increase in velocity at the pod
positions (wave and tidal measuring stations) outside
the breaker line, which was thought probably due to
tidal currents.
A meeting with the Steering Group's working party was
arranged at which it was decided that:
(a) the model's lower beach should be re-profiled to
simulate an extended profile (recently received),
of the section offshore of run-up gauge 3, and
(b) ICST would analyse fully the field survey data
and no further work would be done by HRL with the
partly analysed data.
The model's lower beach was accordingly re-moulded to
the given profile. This profile was used for the
whole of the lower beach area and blended in with the
existing profile as shown in figure 3-2.
Model results were still not compatible with the
prototype and calibration was suspended awaiting the
ICST analysis. This analysis could not resolve the
inconsistencies and at a further meeting it was
finally agreed that the currents being measured at the
site were indeed influenced to a large extent by tidal
21
currents" The i far offshore to
record the wave induced currents except for pod 5
which gave rather strange readings and was, on its
own, insufficient; in addition there was not enough
back up prototype information from visual observations
or float tracking in the surf zone. In view of all
this, together with the fact that there was
insufficient time to change to a mainly tidally
influenced model and there was not enough data within
the groyne area for calibration, it was decided to
abandon the validation exercise.
To maximise use and value from the model, an
alternative test programme was implemented and a
series of comparative tests were devised based on the
Sea Palling beach profile and these are described in
Chapter 5 below.
Much later in the research project after the model
tests were complete, further data obtained from field
experiments on the Lincolnshire coast indicated that
velocities measured in the physical model were
probably rather too high. After allowing for scaling
(by a factor of 6) it seems likely that the model
velocities were between a factor of 1.0 and 2.0 above
what would actually occur on a beach.
In view of this, it appears that further experiments
with a roughened beach would have been worthwhile,
although the limited timescale would have made this
difficult.
5 TEST PROGRAMME
5.1 Hypothetical groyne
systems (first test
series)
Clearly there is a virtually infinite variety of tests
that could be carried out on hypothetical groyne
systems and it was necessary to choose a
22
representa selec examined the
available time, Attention was focus sed on vertically
faced groynes which predominate around the coast of
the UK and a series of plan layouts were chosen to try
and identify the effects on the alongshore currents of
changing groyne orientation, elevation, length and
spacing under different wave conditions.
The overall philosophy of these tests was not to
develop an optimum system for a particular site, but
rather to investigate the effect on flow patterns of
changing one or more of the parameters. In the
sequence of tests carried out it was thus possible to
isolate parameters which were of paramount importance
(ie elevation and length) and those which had a
lesser influence on the flow fields (ie orientation
and spacing).
The experimental schedule, together with details of
the model layout, significant wave height, return
period, alongshore current flow, angle of wave
approach and the tidal state, are shown in Table 3.
These tests can conveniently be sub-divided into four
segments:
1. Tests 1 to 5
These initial tests (1 to 5), were carried out with
the original 1:29 uniformly sloping beach modelled
with the waves approaching at an angle of 10 degrees.
The groynes were spaced 2780mm (lOOm prototype) apart
in preparation for experiments anticipated at Sea
Palling.
The direction and velocity of the flows in these and
subsequent tests were measured using dye injection and
videoing the resulting traces from a camera suspended
directly above the model, supplemented in deeper water
by an electro-magnetic miniature current meter.
23
The modification of the currents and the
consequent re~arrangement of flow patterns due to
groyne layouts were studied, modelling:
(a) 1 groyne (test 1)
(b) 3 groynes (test 2) and.
(c) 4 groynes (tests 3. 4 and 5).
Test 1 was on a single groyne. 2220mm (8Orn prototype)
long with an elevation of 38mm (1.37m prototype).
This was estimated to be of a length similar to that
of the groynes at Sea Palling and fairly typical of a
'sand beach' groyne although its height above the
beach at its seaward end was somewhat higher than is
normal.
The results of this test can be seen in figure 2-4 and
show clockwise eddies, both updrift in the shelter of
the groyne and also on its downdrift side. Seaward
flowing currents were evident along the groyne's
downdrift edge. The external flow field was little
affected.
Test 2 involved three groynes. The plan layout was
estimated by the field surveyor as being similar to
the prototype dimensions of the groynes at Sea
Palling. The two outer groynes were 2220mm (80m
prototype) long with the centre groyne 420mm shorter
at 1800mm (65m prototype).
The results (Figure 2-5) show eddies in both bays.
Clockwise eddies were also evident both updrift of the
updrift groyne and downdrift of the downdrift groyne.
Velocity of the external flows remained largely
unaffected.
Test 3 comprised a field of four groynes, as test 2
above with an added fourth short, 1800mm (65m
prototype) groyne placed downdrift of the other three.
24
2-6).
the 2780mm
This four-groyne system gave similar clockwise eddies
in each bay as observed in the previous test, with
areas of slack or dead water inshore. The external
flows were again little affected.
The resulting flow patterns around these groyne fields
for the above tests are shown in figures 2-4, 2-5 and
2-6 respectively. The arrows in the figures signify
the direction of the alongshore currents with their
respective velocities shown alongside. The extent of
the wave run-up and the still water levels are shown
as dashed or dash-dot lines, As can be seen in all
three tests, there is a significant seaward running
flow along the downdrift edge of the groynes) while
groyne influence on flows is evident for at least a
groyne length either side of the systems. In the
four-groyne layout, flow in the first two compartments
was similar in pattern to those with the three-groyne
system. The direction of eddy flow will of course
depend on the incident wave angle.
Tests 4 and 5 were as test 3 with.
(a) the camera at an oblique angle to try and
encompass the whole groyne field and
(b) general video shots of the groyne field to
combine with test 3 and to show the CIRIA
Steering Committee the effectiveness of the dye
injection technique.
In January 1984, following the field survey at Sea
Palling (Oct/Nov 1983), a profile of the beach was
supplied by ICST. This is shown in Figure 2-7 and was
stated to be a 'typical' profile. It gives a cross
section of the beach down to mean low water. Beyond
this an estimated profile was given to extend the
section seaward to about 180 metres from the top of
25
the beach. To model these prototype contours, the
upper part of the hitherto uniform beach slope was
broken out and re~moulded to this cross section (shown
in Figure 2~8) along the whole beach length with the
exception of a transitional length at each end.
2. Tests 6 to 10
After the beach had been re-moulded. a 3 groyne system
was constructed with estimated elevation. groyne
lengths. spacing and orientation to simulate the
groyne field at the Sea Palling site. Groynes 1 and 3
were constructed to be 2306mm (83m prototype) long
while the central groyne was made 417mm (ISm
prototype) shorter as shown in figure 2-1. The angles
of each groyne relative to the beach were estimated
(there were no data available at this time) from the
largest Admiralty chart available and taken as O. 6
and 13 degrees respectively (running from north to
south) from a line perpendicular to the beach. Each
groyne was embedded into the winter profile so that
the seaward ends of the groynes protruded 38mm (1.37m
prototype) above the beach profile while their
landward ends had an elevation of 19mm (0.68m
prototype). These are shown in figure 2-10. and are
referred to as 'high' groynes in table 3 and the text
below. The distance between the groynes. and their
actual height relative to the beach were estimated.
Tests 6 and 7 were run to check the direction and
velocity of the alongshore currents. together with
wave conditions. The parameters for these tests
are shown in Table 3.
The flow patterns shown in figure 2-11 indicate that
the external flows are largely unaffected by the
groyne field. Within the bays however. current
velocities were slowed and eddies formed with areas of
slack water in the shallows. Backward flowing
26
currents were formed close to the water's edge
downdrift of the terminal groyne.
The next set of tests 8,9 and 10, were run with the
lower wave height of 2.8m prototype, similar to that
in tests 1 to 5. The results of tests 8 and 9 are
shown in figure 2-12. Test 10 was run with the same
wave and current conditions but with an increased
water depth of 330mm (as opposed to the normal depth
of 300mm) to simulate mean high water springs plus one
metre. The results of this test is shown in figure
2-13.
The flow patterns around the above systems were
investigated with the (offshore) wave crest angle
still at 10 degrees to the beach and again approaching
the coast from a north-northeast direction. More
definite eddy patterns formed with the higher water
level (Test 10) as more of the groyne length became
effective. These eddies tend to push the flows out of
the bays at their updrift end, forcing the external
currents offshore. Test 8 was similar to tests 6 and
7 with slow, mainly clockwise eddies within the bays
and backward flowing currents downdrift of the
terminal groyne.
3. Tests 11-16
Early in 1984, H.R.L. were given the observed offshore
wave approach angle as 26 degrees. It was just
possible in the existing wave basin to move both
paddles to this angle and keep them together as can be
seen in the plan view of the model shown in figure
2-14. The wave generators were accordingly moved to
this angle and tests 11 to 16 carried out using the
same 'Sea Palling' beach plan shape as in the previous
tests. Changes to the various parameters in this
sequence of tests are shown in Table 3.
27
Test 11 - The zero cross period was increased in
relation to the tests to 8,5 seconds and wave
heights decreased to 2.2m prototype. Flow patterns
are shown in figure 2~15. The alongshore flows
produced a weiring effect over the seaward crest of
the outer groynes. The clockwise eddies formed in the
updrift bay tended to push the flow coming over the
updrift groyne seaward. Slack water areas were noted
downdrift of each of the groynes. External flows
seemed little affected by the groyne field.
Test 12 - The wave period was changed back to 7.2
seconds as used in the previous tests while the wave
heights remained at 2.2m prototype. The results of
this test are shown in figure 2-16. Slack or slow
flowing eddy currents formed in the updrift bay while
in the downdrift bay the alongshore flows. slowed
slightly by the turbulence updrift. were pushed
seaward at the downdrift groyne. An eddy formed
downdrift of this terminal groyne encouraging seaward
flowing currents along its downdrift edge.
Test 13 - The same wave period (7.2 seconds prototype)
as the previous test with an increase in the
significant wave height to 2.8m prototype and with a
30% increase in the alongshore flows. For the next
three tests the groynes were lowered into the beach to
stand 28mm (1.0m prototype) high at their seaward end
running flush into the beach at their landward end as
shown in the example in figure 2-10.
Test 14 - In this test the wave heights were decreased
to 2.1m prototype. similar to the 'high' groyne test
12. The resultant flow patterns are shown in figure
2-18.
Test 15 - Keeping these lower wave heights. the zero
crossing period was increased to 8.5 seconds prototype
to correspond to the 'high' groyne test 11. The
results are shown in figure 2-17.
28
Test 16 ~ For the final test in this batch, wave
heights were increased to 2.8m prototype and the
alongshore flows increased by 30%. This compares with
test 13 on the higher groynes.
It was evident from the foregoing tests that groyne
elevation is a crucial factor in interrupting the
alongshore currents and the consequent flow patterns
within the groyne bays. The angled waves approaching
the beach create a split flow along each side of the
groynes. Groyne elevation influences the effects of
this split flow. Also as the water level rises, the
alongshore flows, spilling over the groyne crests
create a weir effect as mentioned above. This extra
water alters the circulation pattern in the bays.
4. Tests 17-25
This, the last programme of tests in this first
series, was carried out using a 7-groyne system and
with the angle of wave approach still at 26
degrees, the effects to the flow pattern were
investigated by altering (a) spacing, (b) alignment,
(c) elevation, and (d) groyne length.
All tests in this set were with a "high" groyne
profile (see Figure 2~10).
Test 17 - Length of each groyne and the distance
between each groyne was 1080mm (39m prototype) ie 1:1
spacing. (Fig 2-20). All the following tests (18 to
25) had a similar layout to test 17 with the
amendments shown against each test number.
Test 18 - Wave height reduced to 1.1m prototype. Rate
of pumping of the alongshore currents was also reduced
by 28% (Figure 2-19).
29
5.2 Hypothetical
groyne systems
(second test
series)
Test 19 ~ Intermediate groynes (2 4 and 6) shortened
by 25% to 8l2mm (29.25m prototype). All other
parameters remained the same. (Fig 2~2l)
Test 20 - In this test the groyne spacing was doubled
to 2l60mm (78m prototype). Groyne lengths remained
the same at 1080mm giving a 1:2 length/spacing ratio.
All other parameters as test 17 above. (Fig 2-22)
Test 21 - Groyne spacing changed to l625mm (58.5m
prototype), ie a 1:1.5 length/spacing ratio. All
other parameters as test 17 above. (Fig 2-23)
Test 22 - As the above test except that the
intermediate groyne lengths were shortened by 25% to
812mm. (Fig 2-24)
Test 23 - Groynes angled by 10 degrees facing updrift.
(Fig 2-25.) The effect of varying the length of the
groynes and altering the spacing ratio from 1:1 to
1:2, was small.
Test 24 - Groynes angled by 10 degrees facing
downdrift. (Fig 2-26)
Test 25 - As the above test but using random waves
with a significant wave height of 2.2m prototype. (Fig
2-27)
There seems little advantage gained by inclining the
groynes at 10 degrees either updrift or downdrift to
the perpendicular, despite the alongshore current in
the model being consistently in one direction.
It was decided to retain the beach contours moulded
for the comparison between the physical model and the
30
field experiments carried out at Sea Palling, for the
final series of physical model experiments, and to
vary groyne parameters, water levels and environmental
conditions as shown in Table 4. It was also found
convenient to refer still water level (SWL) in the
basin to the corresponding tidal stage at Sea Palling
(eg 300mm water depth was equivalent to luean high
water springs). In the first tests in this series,
the groyne field was similar in profile to those at
Sea Palling. In fact these hypothetical tests were
based on the Sea Palling system, although they were
not intended to be a study of that particular beach,
as the model had not been satisfactorily validated.
For each test, current and flow patterns were measured
by dye, injected at 0.5 metre (18m prototype)
intervals, in plan, both along and down the beach.
There was a runnel just seaward of the groynes
which was left insitu and all the following tests had
their groynes terminating on that line. This is a
commonly observed feature of groyne fields on sandy
coasts and therefore felt worth retaining. Dye mixed
with sucrose was used to measure the flows near the
bed and each excursion recorded, as in the earlier
tests, via the video camera suspended directly above
the beach.
In this second and final series of tests it was found
useful to not only measure currents but also to study
the sediment transport at the sea bed with particles
of anthracite which gave an indication of how sediment
may be moved in the prototype. Scattered at strategic
points, the material was allowed to migrate in and
around the groynes showing up areas where it was
likely to accumulate. It was not, however, meant to
simulate the beach material at any specific site.
Tests carried out in this final phase are numbered 31
to 43. The gap in the test numbers, between this and
the first series, was to differentiate the 1984 series
and avoid confusion with the first series of tests
31
CUlH~~eted afte 1983 field
tests were aimed at:
These
1. examining the flow patterns around the three
groyne system at mean high water, neap tide,
2. and at mean tide level,
and to study the effects of;
3. elevating the groynes by 0.5 metres,
4. elevating the groynes to 1.0 metre above normal,
5. roughening the top of the beach,
6. cladding the groynes with stone,
7. using stone clad T-shaped groynes,
8. using stone clad fish-tailed groynes,
9. placing a vertical sea wall along the top of the
beach, and
10. cutting slots in groyne A to simulate damage.
The relevant parameters for the following tests (31 to
43) are given in Table 4.
All these tests were run using regular waves and with
the offshore wave approach angle at 15 degrees to the
beach. Comments made after each test refer to the
groynes as A, Band C. A is the updrift groyne, B the
middle groyne and C the downdrift groyne. The
alongshore flows running from the top of the
respective figures down.
Tests 31 and 32
The first two tests (31 and 32), were carried out to
study the effects of different water levels and the
wave and current parameters remained unchanged.
Groyne heights were as at Sea Palling.
Test 31 - The water level in this test was reduced by
14mm (0.5m prototype). to simulate mean high water
neaps. Wave heights at the paddle were 24mm (0.87m
prototype) with a period of 1.01 seconds (6.05 seconds
prototype). Figure 3-7 shows the resulting flow
32
The result indicate that the t
groyne had little effect on the alongshore flows at
mid-depth. The current near the bed tended to move
inshore downdrift of the groyne. Clockwise flowing
eddies formed updrift and inshore of groynes Band C
through the depth and accumulation of the anthracite
granules was evident at these points, with slow
downdrift movement over the groynes from this
accumulation.
Test 32 - The water level in this test was reduced a
further 14mm to simulate mean tide level. Wave height
and period was as for the previous test. The results
of this test are shown in Figure 3-8.
Seaward flow was evident along both sides of the
updrift groyne through the depth, with a small
clockwise eddy inshore on the updrift side. Some
offshore material in the vicinity of the updrift
groyne (A) transported around the end of the groyne
and into the first bay. In both groyne bays clockwise
eddies formed at either side with a compensating
anticlockwise flow inshore in the centre of each bay.
This was more evident at mid-depth. Deposition of
material occurred inshore on the updrift side of
groynes Band C with a steady flow downdrift over the
groynes at their landward end. No retention noted
updrift of groyne A.
It is worth making the point here that submerged long
groynes at one tidal level will become emerged short
groynes at a lower level. It is therefore difficult
to know at what tidal level one should test or assess
a groyne system. Most of the tests carried out in
this series were with the water level simulating mean
high water springs and with the groynes elevated one
metre above the field measurements for maximum effect.
It was decided at this point to increase the wave
heights to record 1.Sm (prototype) at pod A, while the
wave period was reduced slightly to 6.0 seconds
33
(prototype). This was done to study what was deemed a
more realistic wave climate.
Tests 33 to 35
Test 33 - Groynes raised by 0.5m prototype. Results
are shown in Figure 3-9. A similar pattern to that
noted in test 31 with a more pronounced seaward flow
along the updrift sides of groynes Band C. No
retention of material updrift of groyne A, a small
accumulation inshore and updrift of groyne B with a
steady flow over the groyne at its landward end. Some
retention also inshore between groynes Band C with
again a steady downdrift feed over the landward end of
the downdrift groyne (C).
Test 34 - As the above test with the upper beach
roughened with metal strips as described below. This
configuration is shown in Plate 3-5, while the
resulting change in the flow patterns in and around
the groynes is shown in Figure 3-10. The main
difference noted was an eddy which formed inshore and
updrift of the updrift groyne (A). This was confirmed
with the anthracite granules which accumulated inshore
and updrift of the groyne. Accumulation was also
evident updrift and inshore of the two downdrift
groynes. A slight eddy formed near the seaward end of
the downdrift groyne (C) on its downdrift side.
These metal strips were 0.08m wide and 1.22m long.
Placed 0.23m apart, they covered an area from 6m (216m
prototype) updrift of the groyne field to
approximately the same distance beyond the downdrift
groyne. Running from the set-up line seaward, they
protruded approximately 5mm above the beach.
Test 35 - Groynes raised a further 0.5m to a total of
1.0m prototype above normal with the upper beach
roughened as above. The interruption to the
alongshore flow pattern is shown in Figure 3-11.
34
Little difference to t 34, with material
accumulating inshore and updrift of each groyne,
Tests 36 to 40
Test 36 - For this and all the remaining tests in this
section, the groynes were elevated as in the previous
test, 1.0m above normal. All roughening was removed
and Figure 3-12 shows the resulting flow patterns.
More turbulence evident within the groyne bays with a
generally clockwise motion along the updrift side and
inshore of the two downdrift groynes (B and C).
Anticlockwise flows formed in mid bays and along the
downdrift side of groynes A and B. Material reaching
the updrift side of groyne A was transported seaward
along the groyne and accumulations were confined to
updrift and inshore of groyne B and an area just
offshore and updrift of the downdrift groyne (C).
Figure 3-14 shows the velocity profiles at sections
updrift and downdrift of the groyne field with and
without roughening.
Test 37 - A vertical sea wall was placed parallel with
the beach in approximately 1.Om (prototype) of water
(at still water level) and 1.425m (51m prototype)
seaward of the baseline as shown in Figure 3-13. The
flow patterns in these shortened groyne bays were very
mixed and it was decided not to pursue this because of
time constraints. This type of experiment warrants a
separate study.
Test 38 - All three groynes were clad with stone
seaward of the set-up line as shown in Plate 3-6.
Figure 3-15 shows the flows in and around the groyne
fields during this test. It was noted during this
test that some stones were being washed away midway
down groyne C, mostly on the downdrift side. Clearly
they were not heavy enough and larger stones with a
35
prototype weight of 2 tonnes would have been more
appropriate,
Clockwise eddies formed inshore and updrift of groynes
Band C. and inshore and downdrift of groyne C, An
anticlockwise eddy at the seaward end and downdrift of
groyne A suggests a deposition area and is evident at
both mid-depth and near the bed.
The stones used in tests 38 to 40. were limestone
chippings typically 3S-40mm - 20-2Smm in size and
represented rocks of approximately 1 tonne weight in
the prototype.
Test 39 - As test 38 above but with stone clad
T-pieces added to the end of each groyne. These
T-pieces were placed symmetrically. perpendicular to
the groyne at the same elevation and protruded 140mm
(Srn prototype) either side as shown in Plate 3-7 and
Figure 3-16. Downdrift scour was effectively
eliminated and material tended to collect at the
seaward end of the T-pieces then transported slowly
inshore. Turbulence was noted at the seaward end of
the updrift groyne (A) with clockwise eddies along the
updrift side of groyne C and inshore on its downdrift
side.
Test 40 -Again as test 38 above but with stone clad
(Y-shaped) fishtails added to the seaward end of each
groyne. Each fishtail was 140mm (Srn prototype) long
and angled at 120 degrees from the groyne as shown in
Plate 3-8 and Figure 3-17.
A large clockwise eddy formed just seaward of the
updrift groyne (A) stretching almost to groyne B with
an anticlockwise eddy downdrift and just inshore of
the fishtail at groyne A. This situation was
reflected in the movement of near bed currents. with a
large anticlockwise eddy in the same area. Further
eddies along the updrift side of the downdrift groyne
36
(C) suggest of material in these
areas. As with the T~pieces material collected at
the Y-intersections and was transported slowly into
the groyne bays while on the downdrift sides scour is
effectively curtailed.
Tests 41 to 43
Test 41 - With all stone removed this was as test 36
but with groyne A, the updrift groyne, damaged. This
was done by cutting three 10-12mm (0.36 to 0.43m
prototype) vertical slots at discreet intervals in the
seaward half of the groyne (ie at 7, 22, and 36m
prototype from the groyne tip). Figure 3-18 shows the
resulting flows in the groyne field. No obvious large
scale changes. The eddy down drift and level with
with the seaward end of groyne A, found in the
previous test had moved inshore into the first bay,
allowing the flow to sweep round the end of the groyne
possibly inducing scour. Eddies formed along the
updrift sides of groynes Band C. All in all, little
noticeable effect probably due to the damage not being
extensive enough.
Test 42 - The original groynes were replaced in this
test, by permeable ones. As is seen in Plate 3-9,
these groynes were of PVC material, 10mm thick and .cut
to give a 50% permeability. The resulting flow
patterns are shown in Figure 3-19. A reduction in the
alongshore flows was noted with clockwise eddies
forming up drift of groynes Band C at the bed. At
mid-depth this eddy was evident only updrift of groyne
C.
Test 43 - This, the last test, was as test 36 but with
alongshore currents overpumped to give a similar
velocity at Pod A to that found in the prototype
(Figure 3-20).
37
6 SUMMARY OF
RESULTS AND
CONCLUSIONS
clockwise eddies formed t of groynes Band
C pushing flow seaward. Otherwise the flows were
little affected, the weiring over the groynes allowing
some deposition of material along the updrift face of
all three groynes. External flows were also little
affected.
Finally for all the results, shown in plan in the
relevant figures, the arrows indicate the dominant
flow patterns through the depth, while the figures
give an indication of the flow velocity. For the
above tests the figures also show the spread and
accumulation of the anthracite granules giving an
indication of where sediment build up may occur.
The flow pattern observations shown in the figures are
a mean of the 'just below the surface' and 'just above
the bed' velocities measured on the sloping beach. It
is not feasible to relate these to the actual rate of
sediment movement. This would depend, among other
things, on grain size and density of the beach
material which in turn are influenced by wave
conditions and water depth. Detailed information on
sediment motion can be found in articles such as those
by Ippen (Ref 10) and Bijker (Ref 11).
Although some stratification in flow was noted on the
upper beach and commented upon in this report, it was
not practical to describe definitively, because of the
shallowness of the water.
Before commenting on the model results, it is worth
reviewing the behaviour of a groyne system in general
terms.
The first and most direct effect of constructing a
groyne system on a beach is to alter the pattern of
38
the currents) and hence the sediments,
flowing parallel to the coast, In particular currents
along the top of the beach and within the groyne bays
will be reduced. On an open beach the current
velocity profile is similar to that shown
schematically in figure 1-4, which is based on the
work of Longuet-Higgins (Ref 5,6) It can be seen that
the maximum current lies slightly landward of the
breaker line but noticeable velocities are also
created seawards of this line.
The effects of a groyne field on such a profile is
demonstrated in figure 3-5, which shows results from
the three-groyne system studied in the physical model.
The current profile on the open beach is shown as a
dashed line and can be compared with the profile
within the groyne field shown as a solid line. It can
clearly be seen that currents have been reduced
landward of the groyne tip. However, further seawards
the currents are greater than the open beach profile
and extend farther offshore.
This increase in current strength is a common feature,
and on a sandy beach may cause a lowering of beach
levels along a line just beyond the groyne tips.
If the groynes are surface piercing and impermeable
over a large proportion of the surf zone width then
the flow patterns are particularly distinct within
each groyne bay although the velocities may be quite
small. In such a situation it is not unusual to have
flows travelling in completely opposite directions on
either side of a groyne. Clearly this phenomenon
produces strong lateral forces on a conventional
groyne and will exploit any gaps in the planking.
When the groyne crests are b~low the water surface,
then only a proportion of the alongshore current is
diverted offshore, leading to a strongly stratifiedflow within the groyne bays. A particular feature of
39
the submerged groynes was the 'wei I effect of the
alongshore flows over the groyne crests. This however
was largely restricted to the surface layers, and near
the sea bed the onshore and offshore flows still
occurred. This is important since the greatest
sediment motion occurs at this level. Clearly then
groyne elevation is an important parameter in the
effect that a groyne field has on the beach.
Turning now to specific results from the initial test
programme (Chapter 5, Section 1), tests 1 to 5 (Figs
2-4 to 2-6) investigated, with the offshore
wave approach angle at 10 degrees, the interruption to
the alongshore currents and the subsequent alteration
of the flow patterns caused by the introduction of 1,
3 and 4 groynes on the upper beach. All the tests in
this section, with one exception, were with the water
level in the model simulating mean high water springs.
The exception being test 10, where the water level was
raised by one metre prototype above mean high water
springs.
In the physical model it was found that all groyne
systems tend to split the alongshore flow into two
regimes, one the 'internal flow field' on the upper
beach and the other the 'external flow field' which
passes seaward of the groynes in the alongshore
direction. This external flow can be and generally is
to some degree, influenced by the circulatory flow
within the groyne bays.
Two important results noted in these tests were that;
(a) with vertical impermeable groynes such as those
tested, the internal flows circulating within the
bays, created rip currents which ran along the
downdrift side of each of the groynes. These flows
could be strong enough to cause erosion along the
length of the groyne and the consequent risk of
undermining. Secondly, (b) the forcing of the
alongshore flows seaward due to groyne placement,
40
created a strong current passing around the groyne
tips, and was strong enough to cause erosion gullies
and possibly undermine the groyne structure.
Tests 6 to 10 studied the effect of three groynes on a
foreshore moulded to a profile of the beach at Sea
Palling and with an offshore wave approach still at 10
degrees to the shoreline. In each of these tests
(Figs 2-11 to 2-13) the water level simulated mean
high water springs with the exception of Test 10
where the water level was increased by one metre
prototype to MHWS plus 1.0m.
One effect noticed immediately was the backward
flowing currents on the upper beach downdrift of the
terminal groyne, with a divergence of flows about one
groyne's length downdrift (Fig 2-12). With the
increase in water depth in test 10 (Fig 2-13), more
definitive eddy patterns formed within the groyne bays
as more of the groyne length became effective. The
seaward floWing rip currents were also more pronounced
forcing the external flows offshore.
For the next series of tests (11 to 16) the offshore
wave approach angle was more oblique, at 26 degrees to
the shore. This was as a result of data received from
the field survey. The same 'three groyne system' was
used and the effect of both 'high' and 'low' groynes
were studied (see Fig 2-10).
From these tests it was clear (Figs 2-15 to 2-18)that
apart from an increase in the velocity of the
alongshore flows, groyne elevation was most important,
as mentioned above. The angled waves approaching the
beach split along each side of the groynes. This
influenced the water levels within the bays creating
an imbalance and affecting the inshore circulation
pattern. Groyne elevation in turn affects this split
flow. With the lower groynes (tests 14 to 16) the
alongshore flows also spilled over the crests creating
41
a 'weiring' effect and imposing a shearing force in
the surface layers of the water. These stratified
flows within the bays are extremely complex. The
higher groynes were more effective in slowing down the
alongshore internal flows but in showing a vertical
face to the incoming angled waves created a
circulatory flow within the bays and set up seaward
flowing currents along the downdrift side of the outer
groynes.
The next series of tests (Figs 2-19 to 2-27) were
undertaken on a field of seven groynes, perpendicular
to the beach and investigations included both changing
the intermediate groyne lengths and their spacing.
There is no doubt that the effect of longer groynes on
flow was greater as they interrupted more of the
alongshore current. In contrast, the effect of
changing the groyne spacing along the beach was much
smaller within the limits tested and there seemed
little advantage in a length/spacing ratio of 1:1
compared with say 1:2 on the basis of the beach
modelled. There also appears little advantage in
changing groyne orientation to 10 degrees either side
of the perpendicular to the shoreline as far as
current generation is concerned, despite having the
alongshore current always in the same direction. This
however may not be true with a tidal flow situation.
Groyne spacing for a small angle of approach is
perhaps not critical. However, for varying and large
angles of wave incidence the spacing must become more
important.
The second and last series of tests (Chapter 5,
Section 2) were conducted on a three groyne system
similar in plan to that at Sea Palling. With the
exception of the first two tests below, the water
level in the model, simulating mean high water
42
springs, remained the same for all tests. In addition
to the dye/camera measurement of flow, a granular
material was scattered on the bed of the model and
allowed to migrate in and around the groyne field to
give an indication of how and where mobile material
would tend to accumulate. In the first two tests (31
and 32) the effect of different water levels,
simulating mean high water neaps and mean tide level
were studied.
The tests (Figs 3-7 and 3-8) showed very different
results. The lower water level producing the most
disturbance within the groyne field. The granular
material in this test, at mean tide level, flowed
along the groyne tips with little entering the groyne
bays. In contrast, at mean high water neaps, material
was pushed landward into the bays.
All the following tests were made with the water level
simulating mean high water springs.
Raising the groynes had a similar effect (tests 33 and
36, Figs 3-9 and 3-12) to that of lowering the water
levels above.
Tests studying the effect of roughening the upper
beach (34 and 35, Figs 3-10 and 3-11), showed that the
alongshore currents were slowed sufficiently to
promote a build up of material inshore and updrift of
the first, updrift groyne. Flows around the groyne
tips forced the external flows offshore, while
material accumulated inshore and updrift of the two
downdrift groynes.
The higher groynes (test 35) contained the flows more
effectively, forming eddies within the bays.
A vertical seawall was placed in the model parallel
with the shoreline, within the effective groyne field,
43
and standing in one metre of water (test 37. Fig
3-13).
The effect of this wall and the subsequent wave
reflections caused much agitation of the water within
the bays, with little eddy formation and high
dispersion. The groynes, shortened because of the
wall, were largely ineffective.
An alternative groyne design was incorporated in this
next test set, retaining the original groynes but
cladding their sides with rubble. In the first of
these tests (Test 38,Fig 3-15) all three groynes were
clad on both sides with rubble from the set-up line
seaward.
No dramatic change in flow formation was observed.
For the next test (Test 39. Fig 3-16) rubble clad
T-pieces were added to the seaward end of each of the
three groynes.
The addition of the T-pieces resulted in a dramatic
reduction in flows adjacent to the groyne stems,
although there were still strong currents at the
updrift tip of the first (updrift) groyne which could
cause problems. This however could indic~te one way
of avoiding scour along the groyne length and thus
reduce maintenance.
An essentially similar situation was evident in the
next test (Test 40, Figure 3-17) when the T-pieces
were replaced by rubble clad fishtails. Material also
accumulated within the Y-shaped intersection at the
groyne tips and transported slowly into the bays.
Tests conducted with the updrift groyne damaged (Test
41, Fig 3- 18) produced no large scale changes to that
of test 36. the undamaged state. This was possibly
because the damage was too localised.
44
In the next test (Test 42, Fig 3~19). the impermeable
groynes were replaced with permeable ones. The
permeable groyne system tested was one with a 50%
voids ratio. With this system many of the potential
problems associated with surface piercing groynes were
greatly reduced, and the alongshore current magnitude
was diminished due to turbulence at each groyne. This
type of groyne would be worth further investigation
although the associated disturbance around each
individual post could cause localised erosion.
The final test (Test 43, Fig 3-20) was carried out on
the vertical impermeable groynes with the alongshore
currents overpumped to give a similar velocity to that
found at Pod A (Figure 3-4) in the field experiments
at Sea Palling. Large eddies formed within the groyne
bays with the alongshore flows 'weiring' over the
groyne crests. Otherwise internal flows seemed little
affected although the external flows showed an
expected increase in velocity and were pushed seaward
by the rip currents running along the downdrift side
of the groynes.
The main conclusions from these tests can be
summarised as follows;
(i) Groynes that project above still water level
create relatively weak circulatory flows in the
intermediate bays, at the expense of diverting
a proportion of the alongshore currents
seawards past their tips. Currents in such
groyne bays often have a reverse flow near the
water line and seaward flowing rip currents on
the downdrift side of a groyne.
(ii) The longer such groynes are, the greater their
effect, but their length should be less than
the width of zone in which alongshore currents
occur naturally. If groynes are too long then
45
there is a risk of losing sand from the beach
system.
(iii) Groynes with crests below the water surface
lead to strongly stratified flow in the groyne
bays, and divert less of the alongshore drift
offshore. Although there will be less scour at
the end of such groynes, or along their
downdrift face. their effectiveness in
retaining or attracting beach material is less
but how much so is not easy to determine.
(iv) Varying the groyne length/spacing ratio between
1:1 and 1:2 on the model beach seemed to have a
rather small effect on current circulation
patterns and was of little advantage in terms
of current generation. This however was based
on a limited incident wave angle and does not
imply that length/spacing ratio is unimportant
in groyne design.
(v) There seemed to be no advantage in inclining
groynes at 10 degrees. either updrift or
downdrift. to the perpendicular; despite the
alongshore currents in the model being
consistently in one direction.
(vi) A groyne consisting of a row of vertical
individual piles (eg Plate 3-9) reduced flow
close to the shore without creating substantial
increases elsewhere. Such a groyne type merits
further investigation although turbulence in
the area of the individual piles may cause
localised beach scour. Any research in this
context would. however. need to be either
"on-site" or use a much larger model scale to
obtain the correct turbulence and permeability
factors.
46
(vii) Rubble mound groynes seemed not to create any
substantial improvement in flow patterns until
they are extended to have a broad seaward end
(eg Plates 3 -7 and 3-8) ie a T-head or a
Y-head. The addition of such 'heads' did
improve the flow pattern and also merits
further investigation.
(viii) Although using random waves in some experiments
led to a much higher dispersion and turbulence,
they did not seem to produce any major change
in the pattern of steady currents.
(ix) Tidal currents although important do not appear
to have much effect on the travel of beach
material which is predominantly wind and wave
induced (Ref 9) landward of the breaker zone.
It has been pointed out in the foregoing chapters that
full validation of the physical model against field
data was not possible and that the Steering Group
advocated the testing of hypothetical groyne systems.
The following observations, repeated in the summary
report (Vol 1, Phase 11) of March 1986, identifies the
outcome of the amended physical model studies.
The initial tests in the model and later improvements
introduced into the programme, have led to the
development in the techniques for carrying out scale
model tests of groyne systems.
The tests carried out to study the effects of
particular layouts have given a valuable insight into
the basic hydrodynamics of groynes. In particular the
tendency for a strong seaward flowing current to occur
close to the downdrift face of a straight, vertical
sided impermeable groyne has been identified, and
methods to counteract this unwelcome characteristic
have been tested. It has also been possible to
identify the more important parameters governing the
47
of a groyne sys sand beach (eg
height and length), in contrast to less important ones
(eg groyne orientation, spacing and wave direction).
However, the latter are more important when
considering shingle beaches.
Although the model studies have been carried out with
a fixed bed, thus preventing direct evaluation of the
effect of groynes on sediment movement, the ability to
both measure and observe the current patterns created
has been a major advantage. The introduction of a
sediment 'tracer' in the later stages of the project
also enabled areas of likely erosion and deposition to
be predicted.
The physical model was not fully validated against
prototype measurements, but a number of meaningful
comparisons can be made. A review of the results from
the physical model tests shows that at model scale the
wave induced currents were similar in magnitude to
those inferred from data measured at Anderby Creek and
Sandilands on the Lincolnshire coast. The standard
scaling factor from model to prototype using Froude
scaling would be 6.0 corresponding to the model linear
scale of 1:36. However, the differences in wave
height and possible differences in wave direction at
the breaker line need to be considered.
Wave heights used in the physical model were two to
three times greater than the equivalent prototype
values. Further, the results from the physical model
showed a reasonably linear relationship between peak
current velocity and incident wave height. The
possible differences in wave direction at the breaker
line cannot be accurately evaluated, but theory
dictates that current velocities should be practically
linearly dependent on the breaker line angle for small
angles of incidence.
48
Consideration of the above leads to the conclusion
that in the absence of additional roughening of the
physical model bed, the velocities in the physical
model were approximately twice to three times the
equivalent prototype values. Tests with an
artificially roughened model bed reduced the
velocities to 50% which is consistent with similar
experiments carried out elsewhere (Ref 3). In this
case the model current velocities would have been one
to one and a half times the equivalent prototype
values demonstrating the original supposition that
artificial roughening of the physical model would be
appropriate. It is also demonstrated that there was
some overlap between the physical model and field
studies results. In addition the wave heights used in
the physical model (approx 1.Om Hs at prototype) were
not large in relation to the size of storm waves that
could feasibly occur on the East Coast. It might thus
be deduced that the physical model results without bed
roughening may be related to rather higher wave
heights which are well within the range of typical
storm events.
49
7 REFERENCES
1. CIRIA Note Ill. Groynes in coastal engineering:
A review by L Summers and C A Fleming, 1983.
2. Hydraulics Research Limited. Groynes in coastal
engineering: A literature survey and summary of
recommended practice. Report No IT 199 by J H
Tomlinson, March 1980.
3. P J Visser. The proper longshore current in a
wave basin. Report No 82-1 Pept of Civil
Engineering, Delft University of Technology.
4. Dutch report. Influence of groynes on the form
of the coastline. TOW Report on Model
Experiments M918 Part V, April 1979. Translated
by C van Beesten, April 1983.
5. M S Longuet-Higgins. Longshore currents
generated by obliquely incident waves, 1.
Journal of Geophysical Research, Vol 75, No 33,
November 20, 1983.
6. M S Longuet-Higgins. Longshore currents
generated by obliquely incident waves, 2.
Journal of Geophysical Research, Vol 75, No 33,
November 20, 1983.
7. Hydraulics Research Limited. The effectiveness
of groyne systems: Physical model tests Phase
11. Report No EX 1221. June 1984.
8. Tucker M J and Draper L. Simple measurement of
wave records. Proc Conf of Wave Recording for
Civil Engineers, 1961.
9. Steers J A. The coastline of England and Wales.
Publ by the Cambridge University Press,
Cambridge, 1946.
50
10. Ippen AT). Estuary and coastline
hydrodynamics. Publ by McGraw~Hill, New York,
1966.
11. Bijker E W. Littoral drift as a function of
waves and currents. Proc 11th Conf on Coastal
Engineering, London, 1968.
51
Tables
Table 1: Initial Flows MaitbE~matl~::a! Model
MODEL PROTOTYPE
Depth Angle at Wave Wave A1ongshore Wave Wave
offshore paddle height period discharge height period
(metres) (deg) (metres) (secs) (litres/sec) (metres) (secs)
0.30 10 0.078 1.167 73.27 2.808 7.002
0.30 26 0.061 1.167 95.14 2.196 7.002
0.30 26 0.061 1.417 88.85 2.196 8.502
0.30 26 0.078 1.417 174.19 2.808 8.502
0.30 26 0.078 1.167 187.42 2.808 7.002
0.30 38 0.028 1.417 16.05 1.008 8.502
0.30 38 0.042 1.417 36.95 1.512 8.502
0.30 38 0.056 1.417 97.38 2.061 8.502
0.30 38 0.069 1.417 159.38 2.484 8.502
Beach slope 1:29
Table 2: Initial Model
A Model
1
Proto
36
Waves (regular):
* Period
* Mean height
Still water depth
* Adjusted angle of incidence
ie paddle angle relative to the beach
Measured angle of incidence
ie at the breaker line
Mean width of surf zone to wave run-up
line
A.B
A.B
A.B
A.B
A.B
Sz
1.20 sec
0.06 sec
0.30m
10 deg
8.3 deg
3.95m
7.20 sec
2.16 sec
10.80m
Alongshore current opening (updrift)
ie 12 channels. each 0.4m open
Alongshore current opening
(downdrift) ie to wave run-up line
Wave run-up line (from model origin)
* External current recirculation
1.6 x Sz 4.8m
1. 2 x Sz 3.66m
1.70m
50 lis
* Beach slope (uniform) A 1: 29
A parameters unchanged throughout model proving tests
B - in constant depth part of basin
* - final model parameters shown in Tables 3 and 4
Table 3: Test Parameters - (First Test Series)
Date Test Groyne arrangemant Hp Tz Wave Tidal Q
No m s Angle State l/s
Preliminary tests carried out in November/December 1984.
23.1.84 1 Single groyne 2.8 7.2 10 MHWS 45
24.1.84 2 3 No. perp groynes 2.8 7.2 10 MHWS 45
25.1.84 3 4 No. perp groynes 2.8 7.2 10 MHWS 45
26.1.84 4 4 No. perp groynes 2.8 7.2 10 MHWS 45
27.1.84 5 4 No. perp groynes 2.8 7.2 10 MHWS 45
For the above tests the groynes were laid on the top of the uniformly (1:29)
sloping beach and were 1.37m prototype high.
Model broken out and replaced by the 'typical winter profile' of the Sea
Palling beach (Figure 2-7)
22.2.84 6 3 No. Sea Palling 3.3 7.2 10 MHWS 45
'high' groynes
23.2.84 7 3 No. Sea Palling 3.3 7.2 10 MHWS 45
'high' groynes
27.2.84 Alignment of alongshore current altered.
1. 3.84 8 3 No. Sea Palling 2.8 7.2 10 MHWS 45
'high' groynes
2.3.84 9 3 No. Sea Palling 2.8 7.2 10 MHWS 45
'high' groynes
5.3.84 10 3 No. Sea Palling 2.8 7.2 10 MHWS 45
'high' groynes +lm
Table 3: Continued
Wave generator angle changed to 26 degrees normal to the beach
22.3.84 11 3 No. Sea Palling 2.2 8.5 26 MHWS 70
'high' groynes
23.3.84 12 3 No. Sea Palling 2.2 7.2 26 MHWS 70
'high' groynes
27.3.84 13 3 No. Sea Palling 2.8 7.2 26 MHWS 90
'high' groynes
28.3.84 14 3 No. Sea Palling 2.1 7.2 26 MHWS 70
'low' groynes
29.3.84 15 3 No. Sea Palling 2.1 8.5 26 MHWS 70
'low' groynes
30.3.84 16 3 No. Sea Palling 2.8 7.2 26 MHWS 90
'low' groynes
9.4.84 17 7 No. perp groynes 2.2 7.2 26 MHWS 70
1:1 spacing
10.4.84 18 7 No. perp groynes 1.1 7.2 26 MHWS 50
1:1 spacing
12.4.84 19 7 No. perp groynes 2.2 7.2 26 MHWS 70
1:1 spacing. inter
groynes 25% short
13.4.84 20 7 No. perp groynes 2.2 7.2 26 MHWS 70
1:2 spacing
17.4.84 21 7 No. perp groynes 2.2 7.2 26 MHWS 70
1: 1.5 spacing
Table 3: Continued
18.4.84 22 7 No. perp groynes 2.2 7.2 26 MHWS 70
1:1.5 spacing, inter
groynes 25% short
25.4.84 23 7 No. perp groynes 2.2 7.2 26 MHWS 70
1:1 spacing, angled
10 degrees updrift
26.4.84 24 7 No. perp groynes 2.2 7.2 26 MHWS 70
1:1 spacing,angled
10 degrees downdrift
27.4.84 25 7 No. perp groynes Hs 2.2 7.3 26 MHWS 70
run using random
waves
NOTES
1. For tests 6 to 13 and 17 to 25, all groynes were set in to the beach and
were 1.37m (prototype) high at the seaward end and 0.7m (prototype) above
the top of the beach profile at the landward end (see Figure 2-10).
2. For tests 14 to 16 inclusive, the groynes were 1.0m (prototype) high at
the seaward end and flush with the beach at the landward end (see Figure
2-10).
Q Total recirculatory flow
(l/s model)
Hp Wave height of regular waves
(prototype)
Tz Wave period Wave angle The angle at which the
wave generators were
positioned relative to the
beach.
Hs The significant wave height (i.e. average height of the one-third
highest waves).
Table 4: Test Paralmeitelcl!'i Test Series)
Date Test Groyne arrangement Hp Tz Wave Tidal
No m secs angle state
20.3.85 31 water level -0.5m 0.87 6.05 15 MHWN
25.3.85 32 water level -1.5m 0.87 6.05 15 MTL
Change wave height to record 1.5m at position A (see Figure 3-4), reduce
wave period to 6.0secs and retain water level at +1.4rn ODN(MHWS). Regular
waves.
1. 4.85 33 groynes raised 0.5rn 1.50 6.00 15 MHWS
4.4.85 34 groynes raised 0.5rn 1.50 6.00 15 MHWS
upper beach roughened
12.4.85 35 groynes raised loOm 1.50 6.00 15 MHWS
upper beach roughened
16.4.85 36 groynes raised 1.Om 1.50 6.00 15 MHWS
26.4.85 37 groynes raised loOm 1.50 6.00 15 MHWS
vertical sea wall
1. 5.85 38 groynes raised loOm 1.50 6.00 15 MHWS
and clad with stones
3.5.85 39 groynes raised loOm 1.50 6.00 15 MHWS
stone clad T-pieces
added
9.5.85 40 groynes raised loOm 1.50 6.00 15 MHWS
stone clad fishtails
added
15.5.85 41 groynes raised loOm 1.50 6.00 15 MHWS
groyne A damaged
Table 4: Continued
28.5.85 42 groynes raised 1.Om L50 6.00 15 MHWS
permeable groynes
21.5.85 43 groynes raised 1.Om 1.50 6.00 15 MHWS
alongshore current
overpumped
Wave parameters are in prototype units
Figures
Fig 1
Norfolk
Location plan
English Channel
East Caister
~Great~Yarmouth
ST
ILLl
NG
BA
SIN
J J.J
--OR
IGIN
++ +++
++ + + + +++
DIS
TR
IBU
TIO
NS
YS
TEM
--
+FO
RLO
NG
SH
OR
EC
UR
RE
NT
S
+ + + + + + + + +T + + t + +
FLO
WM
ETE
R
SC
AL
E
o1
23
45
m!
!!
:1
!I
l>
++
FLU
SH
MO
UN
TED~
TA
PP
ING
SFO
R+
+M
EA
SU
RIN
GW
AV
ES
ET
++
UP
(ST
AG
E11
)
++
++
++
++
++
++
~II
\S
HIN
GLE
SP
EN
DIN
GB
EA
CH
CIR
CU
LATO
RY
FLO
W/P
UM
P
25·1
4m
3 I'D :J ..... o......
...... ..... I'D () :::r
:J ..Q C I'D Vi
-0 ....- o :J rn x ""0 ([) -,o - ......
o '< o c ..... Vi ..... o 1.0 I'D." lB'
~II...
35
·6rr
rJ
I
:!J lO .......
N U> (I)
() .....
. o· ::J
SLO
PE
1:2
9S
CA
LE1:
36N
AT
UR
AL
0·3
00 1
ST
ILL
WA
TER
LE
VE
L
OR
IGIN
I~-~
S-::
::::'"
:::1..
0·04
3
~050
I:9
23
_II
T9·
50ill
"
\~10
·97
JD
IME
NS
ION
SIN
ME
TR
ES
T0·
361
3 o Q.
(I) 0
(I) o () ::J......
::J ...., o C lO ::J
C ::J o ...., 3 - '< U1 o U ::J lO
Typ
ica
lp
rofi
leo
fa
san
db
ea
chon
the
Ea
stA
ng
lian
coa
st
l
SURF ZONE MEAN WAVE SET UP LINE MEAN BREAKER LINE
o<Xl
-.:r
1
A
+
L
B
++ ++ -<I + Q
+ +T---+-
+ ++ ++ +
C
+D
+
+
E
+--- -----"f:7--
+ + ~;+ + .'/ +If
+ + ~ +~--------- \;~----+ + \. -j-
'1\
+ + 'W-+ + t
+ ~~
11lO MwM
1
O·5m/sI I
VELOCITY SCALE
1 metreI I
MODEL SCALE
VELOCITY PROFILES FROM VISSER'SMODEL MODIFIED VIA MATHEMATICALMODEL
MODEL PROFILE AT C. L and M
Q = 501/5
Figl'3 Velocity profiles at mid position - experimental techniques
oN
Q)
0...Q1Il
.J::UoQ)
CD
Q)C
~-----------------~
oQ)I-
CD
0..::JI
C::JI-
Q)
>o:s:
Q)UC0--1Il
""d
l-Q)~
0Q)I-
e:'CD
"~
Q)UC0--1Il
""d
Q)I-
0.J::1Il--0
LO
0
__...:L- -..::!j 0
uoQ)
>
Fia 1·4 Theoretical alonqshore current profile (Longuet - Higgins 1970)
-:L 0·5
0
9·27
2·00 t 3·00 10
'27~.
0:g3
T-\
BOTT
OM
OF
1:29
SLO
PEIF
CO
NTI
NU
ED
10M
OD
EL
FLO
OR
0·30
DIM
EN
SIO
NS
INM
ETR
ES
WA
VE
GU
IDE
CO
NC
RE
TEB
LOC
KS
(WIT
HA
SIN
GLE
SH
EE
TO
FP
OLY
THE
NE
WR
AP
PE
DR
OU
ND
BLO
CK
S)
OR
IGIN
H
Jl"'"
---B
A0·
19J
II
0.25
C+
++
I+
+tr2j~'
+-.
++
2·30
LI
++
_+
T~
1·00
13'
I+
-L+
++
+-+
+I-
---3
·oo--
----G>
jI
+-+-
++
I+
++
++
...-
...'H
--.J
++-
++
I+
++
++
I+
++
+-+
+I
++
+--
:\r-
i.-l
++-
++
I+
++
++
++
++
I+
++
++
I
12·1
4
+\
.\..
\'.\
==
-~
31·6
6L-
-~\
+ + + + + + +..- -:::
r(f
lI'D o -0 o..... o ~-.. o .,
I25
.14
~ ~~ ::J la~ la N ..- o.......... .- I'D Ul .- Ul
~~
110
......<
1)I'D
3 ~o- o Ul
::J
D-0
a0-
<::J
::l 1)0 -.
.
W-.J
«uV1
w l-.J
~rE >-
<!+ -+- +e-
t + + + + + If) -. u
o 0-.JW>
-I
"'"CO+ +, t -r + + -I- +,EIf)
ut t t T t + + + +
0+ + + + + + + + + 0
\,,,,u
W+ + +~ + + + + + +C::::J0<1> If)El.... 01
::::J C..c If).-If)l/l 0.::::J <1> 0.~l....dIJ... 0. .....
IJ...+ ,+ \I + + + + + + + + + + + +,,,
<D+ + + + +~
+ + + + "'0CCl
.....J.,:r:
:r:-I- + + +- + + + + iIJ..., 6, rn'\,
\ l/lC0
iJ<1>
-+ + + + + + + + + III
dl/l<1>
'<-0"-
CL
.,+ + + + + + + + +\\\\,,
::s::+ +- +
Fig 2·2 Velocity profile - uniform sloping beach
JAN
UA
RY
FE
BM
AR
CH
AP
RIL
GR
OY
NE
AR
RA
NG
EM
EN
T1
23
45
67
89
1011
1213
1415
1617
1819
2021
2223
242
5
UN
IFO
RM
1:29
SLO
PIN
GB
EA
CH
AN
GLE
OF
WA
VE
AP
PR
OA
CH
10
·G
RO
YN
ES
LAID
ON
TOP
OF
BE
AC
HS
ing
leg
royn
ela
idp
erp
en
dic
ula
rto
be
ach
W3
No
gro
yne
sla
idp
erp
en
dic
ula
rto
be
ach
~4
No
gro
yne
sla
idp
erp
en
dic
ula
rto
be
ach
~~~
BE
AC
HB
RO
KE
NO
UT
AN
DR
EP
LA
CE
DB
YW
INT
ER
PR
OF
ILE
OF
BE
AC
HAT
SE
AP
ALL
ING
3N
og
royn
es
asa
tS
eaP
allin
g'h
igh
'(se
efi
g2-
10)
~A
LIG
NM
EN
TO
FLI
TT
OR
AL
CU
RR
EN
TA
LTE
RE
D
3N
og
royn
es
asa
tS
eaP
all
ing
'hig
h'
(se
efi
g2-
10)
~~
AN
GLE
OF
WA
VE
AP
PR
OA
CH
CH
AN
GE
DTO
26
·N
OR
MA
LTO
BE
AC
H
3N
og
royn
es
asa
tS
eaP
alli
ng
'hig
h'
(se
efi
g2·
10)
~~~
3N
og
royn
es
asa
tS
ea
Pa
llin
g'lo
w'
(se
efi
g2·
10)
~~~
MO
DE
LT
ES
TS
ON
AF
IELD
OF
SE
VE
NG
RO
YN
ES
Gro
ynes
pe
rpe
nd
icu
lar
tobe
ach
1:1sp
aci
ng
Hp
:2·2
m~
Gro
yne
sp
erp
en
dic
ula
rto
beac
h1:1
spa
cin
gH
p:1
'1m
~A
sa
bo
ve.
inte
rme
dia
tegr
oyne
ssh
ort
en
ed
by2
5%
~G
royn
esp
erp
en
dic
ula
rto
beac
h,1:
2sp
aci
ng
f%G
royn
esp
erp
en
dic
ula
rto
beac
h,1=
1.5
spa
cin
g~
As
ab
ove
.in
term
ed
iate
groy
nes
sho
rte
ne
dby
25
%~
Gro
ynes
an
gle
d10
"u
pd
rift
1:1
spa
cin
g~
Gro
ynes
an
gle
d10
"d
ow
nd
rift
1=1
sp
acin
g~
As
ab
ove
.ra
nd
om
wa
vep
att
ern
~
11
lD N W
Jl~
'l) ,U
l15'~
Jl::J
..;o
lD Ul
('I)
..0 C C'I) ::J () C'I) I I '< U 0 .......
-:::T
C'I) ....... o' 0 lD .., 0 '< ::J C'
I) Ul
'< Ul
.......
C'I) 3 Ul ........ -... .., Vl ..... ..... ('I)
Ul
.......
FOR
MO
DE
LP
AR
AM
ET
ER
SS
EE
TA
BLE
3H
p=
PR
OT
OT
YP
EW
AV
EH
EIG
HT
+ +
+ +
Q)0..>.
:§e0..
.8
+
+
+
+
.....Q)
>couo
Q) -
01 ~-c Q)
o-g..c Euo Vl0--
+ ..... E
~.~Q) iG> .o~
~.9o Q)
$2>
+
+
+
+
+++
... Q)
~ :=: Q)o 0 .....Q) L.. 0... o..c
en o..Vl
Z<..90::
\
Fig 2· 4 1.... Groyne sysfem flow patt ern (test 1)
"to N U1
/OR
IGIN
Bre
ake
rlin
ep
ara
llel
toth
esh
ore
E +
Off
sho
rew
ave
cre
st
+10
°
F I++t
+lm
+~
+I..
3m
~I
++
--
+ ++
+
++
++
++
++
++
++
10°
wa
vea
pp
roa
cha
ng
leV
elo
citi
es
inm
/sm
od
el,
toco
nve
rtto
pro
toty
pe
mu
ltip
lyb
y6
IH
G
++
++
+W
AVE
RU
NU
PS
LA
CK
WA
TE
RS
LA
CK
WA
TE
RS
LA
CK
WA
TE
RS
LA
CK
ED
DY
SL
AC
KA
RE
A
/°
fE
DD
Y\\
tD/~
-',-
"...
--:
\3~
0_
Cl'
\---
:=.-
/\\
----
-
+~~O.~i~_)'
~(t6~~K\~
U\
\/?10_)~~
f7i~:~~00'17_+
00
..'-
/0
·\4
I"
)~
DV
0.\
"~:g
'-/--
./~
I1
,./
__
0·2
0-
__0·
20--
-.t
0·\8
0.10
-1S
.---
---
...\
\,$
0.
02
5-
r..
,y-
.-
_0
,...
0.7.
.1....
..0',
,/""
O.\
u...J
-----..
---
/....
....0
·25
+-
_°.2
5-_
°.3
3-1
"__
0.2
5-
.......0
.25
-+..
...-
----
..,.
.-0
.7.0
---0
.2°-1
----
.......--
---
W I G> ., o '< ::J C'I)
IJ)
'< IJ)
.-0
-C'
I) 3 ,.-.
.. ..... (1)
IJ) .....-. o ~ N --"'"
0 o ..... ..... Cb ., :J
r-!!A
_V_E
_RU
N_U
_P_
_D_
EA_D
~WAT
ERD~EADWAT
_ER
S_LA_C~K
WA
TER
.n--
D_E_
ADW
A_TE
_R_S;:~)IAT_ER
_
S.W
.L.
~0
'01
f\g
~0.
02-,
,;-°
06_.
1_1-·_·-=o;.O.'2-o.g11~0"3·Q
0°0
2--'
-·o
os-
'\..
>_
6'1
7_
"",\~I
"rC
f'iT
·---
;:'·
-=';
'O·,
S':
y"
/'~~~-,d-~q
/)~&'l'-'-'-'-
/-
0"~
7 0"
~O"Q
'(
/0·1
7.....
"'"~
1<~
0~
\2
__
-0'7
6~
,(t::~O
°10
(j(
0.1
1---_~
c::;
C)~0
·06
~005
B'
<')
\i'
'('1
00.
07
/0
0'14
"-O.~
a,\
SI'
(jG
;I'\
/....
-0,
.\
N.
\/---,
,~.0 1'7
Q'-t/)~~o
\1.
--...
..~
I'\'\
r:::,'\
~(S
LO
W-0
-13 "
',,
<?.....O
o.>
'SL
AC
K'~,~
f--'
,t6
be)"
-...._
/t
/0
-0
7.;
"",'
0'
~r::
:,./
-.-
0.0
8--\
ED
DY
+)
If,
)\\EDD~I
$;?
o\E
DD
Ylj/'
"(/
.......
,~
~.P
I<6
(\/
\ry"
-.l-
'"""
"'--
-~,\
")0
,2,
//'J
'..../:j;
/cr
\L.
il)
\E
DD
Y'
~'':;:
'C)
~r:::
,'\°
/1\0
:<,
~0'2
./
y-'-
--./
~O
~/
",0
r:::,\ry
/"'"
i,,~
)\.\S
//
~(J'
\~B
rea
ker
line
__
-0'2~~,/
0·7..1~
).']
./,
__..
...-
0·2
7_
'_/~1>
'~
/~
I-
019~/./
-:,r
:::,/0
·1?v
"...0
·17--
()1'
pi
.....a
a:]
.S/.
'].1
/a·1
'J..
...-
0·7.
.3~
.....O
ff.:
:::-
-'...()'l
(Ja1
-"O·\~/
.1']
./p
ara
lle
lto
the
__
---+
/.;;
>()
.t'
..;0.
--".
../a
.,tY
-"""
'0'2
8...
...a·
3 .;_
_.p
"#
.;~
~jJ
sho
re...
0'2
5-
,0
-0.
18.--
;:"02
0-0
25
-0
·5_
.P'
03
3-
L..
-0·3
2-
__
00·
33...
..0·
30
·3-
02
-0
·7..5
--
.....0
·7..
......
_.
--
0. 2':>-
-I'
....
....
....
..I
.---
++
++
+t 1m
++
++
t+
I~3m
>1
++
++
++
++
++
++
++
+10
°w
ave
ap
pro
ach
an
gle
Vel
ociti
esin
m/s
mo
de
l,to
con
vert
top
roto
typ
em
ult
iply
by
6
"TI
1O N 0'>
.t-- n G) ., o '< :J CD III
'< III ..... (1) 3 - 5" ~ "U o ..... ..... (1) ., :J ....
......
......
(1)
III ..... III
W .t'- o :J Q.
(J1
........
I +H +
G +F +
E +
~ORIGIN
10<1
~100m-
..10
II-!!
-lO
Om
~I..
150m
...1
"1.0 N -....,J
TA
KE
NF
RO
MA
CO
PY
OF
I.C
.S.T
.
AW
AD
AN
GE
RLE
VE
L3
00
mH
W
DA
TE
D28
-10-
83W
ITH
MIN
OR
AD
DIT
ION
SW
ALL
27m
PO
SIT
ION
OF
RA
DA
RH
UT
IA
CC
ES
S
PR
OP
OS
ED
INS
TR
UM
EN
TP
OS
ITIO
N
Q9E
MS
EM
IZJQ
VM
SE
M
TT
ELE
ME
TR
Y
EM
ELE
CT
RO
MA
GN
ET
ICC
UR
RE
NT
ME
TE
R.S
EM
SU
RF
AC
EE
LEV
ATI
ON
MO
NIT
OR
QV
MP
AR
TIC
LEV
ELO
CIT
YM
ET
ER
RU
G
---------------l
....
...
(NO
V.)S
EC
TIO
N1b
----------
T1
,--
----
'.....
.-..,,-
--.....
...""
......_-
-_...
2m
MA
X.
EX
PE
CT
ED
TID
E(N
OV
.)
40
m 1
44
mW
OO
DE
NS
EC
TIO
NG
RO
YN
ES
39m
ST
EE
LG
RO
YN
ES
11m
MLW
L--
T3
MA
XH
W(N
OV
.)
f---
-50
m1>0
1
MIN
HW
(NO
V.)
-S
EC
TIO
N3
-I
-I ~ o
4
_1
·4m
MH
WS
·_O
·Bm
MH
WN
--------
0t-
O'l
mM
TL
--0
'6m
MLW
N-1
--1
·2m
MLW
S
-21
lil151~
15:>:1
~~'!t
I~
I-----
l'-"~I
~~~:O_
~~':".
"~~oo
::.:::
0::
w>
->
z0:
:u
wW
W0
ow
<.9«
CDCD
I-
0::
ZCD
~<.9
:322
m57
m67
72
CH
AR
TD
AT
UM
-1·8
2mA
TW
INT
ER
TO
NN
ES
S(
RE
L.TO
OD
N)
TID
AL
RA
NG
ES
FR
OM
AD
MIR
ALT
YT
IDE
TA
BLE
S
5·6 5
z 01
o--
-" ~ woI
3()
~
o~2
CT
11) ...,l.J}
11) o d'-0 - o ::J o ::J Q.
IJl
11)
() .....
.O
·::J o --- .....
.... ........
::J 1.0 IJl
;:;.:
11)
O~5 T
WA
TER
LEV
EL
ATM
.HW
S.
OR
IGIN
AL
MO
DE
LB
EA
CH
PR
OFI
LE
Mo
de
lb
ase
line
0.04
3
T
I--0·
08--l0
8..
/f-
----
1·36
~2·
11...
12·
81-=-~
-.J1
--:-----=
--3
·3
1-I
I3·
94...
4·2
8...
1
..3
.6m
O.D
.N.
4'4
8....
1
(pro
to)~
5·10
~I~!
0.0
.S
WL
0'2
61
m0
'30
0m
..1
·4m
O.D
.N.
T(p
ro
tO)
oII
O.D
.N.
0-36
1m
C IJl
Cl) 0.
...-
Cl)~ :J ..... (()
"""'l .........
(fl
Cl)
() ..... 0- :J"T1
LO N 00 ..... =r o c LO =r eT C
l) o () ::J"
"U a - -o """'l
DIM
EN
SIO
NS
INM
ETR
ES
(MO
DE
l)E
XC
EP
TW
HE
RE
STAT
ED
............... Cl) Vl ..... IJl
(J) 0"
-.L
I-9
-4m
O.D
.N.
.,
,,
67
IN
(pro
to)
12
3m
etr
es
(mo
de
l)fr
o4 mo
rig
in5
----
.J(J
1
2"!
1.0 N --"~
/OR
IGIN
0'--
:-.•
01
4-4'
t'~'-::~
~i<:K~
";0m)~
.--"
17~=~
--
AR
EA
.....0
.\3
-
0·2
5-
--0
·2
5--0
20
-0
·2
8-
....
.-..
..._
0·2
0--
---
E
--Il
-
~0_33--0-50-----
---0
.2
5-_
O.1.S
/
+++.~
_o
·33
--0
·3
4-
_0
-3
3-
_0·2~i-------
_0
·38_
_
+F -tt- +t
+1m
+t
+10{
3m
)01
++
+
_0
'33
-+
-
__
__
0-3
3-
--0
-2
5-
---0
'50
+
_0
·50
_
_0
-3
3-
~0-33-
++-+
--0
-2
5-
++G + +
H +
---0
·3
1-
++
--0
-4
2-
__
_0
-4
4-
++
__
0-4
4-
Bre
ake
ra
ng
le16
-5..
....
-0·2
5-
++
++
++
++
++
--"
(J1~ VI
r+(fJ ~
I
"1Jf
+§:
WAV
ER
UNU~
-=-~~
~.S
.Wi:
.:--T
,---
----
-+-....
.0-\3-
/
1.0 ., o '< ::J I'D VI
'< VI
r+ I'D 3
MH
WS
26°
wa
vea
pp
roa
cha
ng
le
Vel
ociti
esin
m/s
mod
el,
toco
nver
tpr
otot
ype
mul
tiply
by6
-n lO N...
.----O
RIG
IN
_0
·2
5---
__
_0
·3
5-
E--
-#--
-
fF --+
G + ....
..-0
.33
----
0·3
3-_
_0
·33
-0.
33--
-°.15
-0
·3S
----
-h
-o
-3
3-
0.3
0~32-t0'33----°
31
-'-
d-0
32
-t-
++
t+
lm
++
i+
I"3
m~I
++
++
++
++
+
H +I +
--"
00
(fl C'D o ~
WA
VE
RU
N~-------_-SLACK_~-_-_~----f-
_=
:if
i['L
AR
EA
.._
_.
..
.__
.__
:::J.~-.-._=f-----.------=r=----0'17-~
.~
DIS
PE
RS
ION
0'1
5-_
0'2
5)-
__
0.13
\0
-2
2-
0.1
5-
lO-0
·19
0·1
4--
.....0
·08
-.\3
.!;::
!!:..
...-
__
0<:
i<:
ilO
-0
·2
2-
.._
__
__
_°.
10
-_
_0
.25
----0
·20
-~
/...
,-0
·2
2-
__
0·2
00.18~
o~
~+
--0
'40
+-
_0
·4
5-
-h
-0
'33
--
0'3
0_0.25~025----
01
8-
+C'D V
I.---0
'44
-_
_0
,5
0-
'< VI
+..
....
..-0
.35
+.....
.C'D
Bre
ake
ra
ng
le-0
'4
0-
316
·5·
i+
+o;i ~I
++
--"
.t'
++
++
++
MH
WS
26
·w
ove
ap
pro
ach
an
gle
Ve
loci
ties
inm
/sm
od
el,
toco
nve
rtto
pro
toty
pe
mu
ltip
lyb
y6
"1.0 N N W -...J
OR
IGIN
~O·SO-
"_
-r-----------
O·']
.k-
+~0'28_-
-
E +ED
DY
--0·25--~--.--
.3,.-...p-~.aw-
0,2
3-
~--0
·33
-
__0
·37
--
SL
AC
K
F +
--0
'25
-+
---J.-0
·26
-
G +
....,-°-
33-
H +D
ISP
ER
SIO
N
cC )~'--i~DY
__
0·3
3"'-
--
....
.-0
.33
-+
_0
,22
-
-1
--0
'33
-
I +AV
ER
UN
UP
__
._~
.W
__
"".W
;L.
-+.
--0.14
-/'\
) 0:-G) .., o '< :J /'\
)
+f
+1m
+t
+I",
3m
"'I
++
_0
·3
1--
+
0""-
~ ........
...0·"
3-
-0
-3
5--
+0.
40"'-
...
.....-
__
_0
·50
-
-...
-0·5
0-
+
--0
·5
0-
__
0.3
3--
d
I
---0
·33
-_
_0
·26
-
....
.-0
-34
-
---l
::-0
.34
-
+ ++ +
_0
·2
0-
__
0·5
0-
_0
'50
--
-0
·3
3-
+ ++
--0
'40
-+
___0
·33
-
__
_.0
·29
__
_0
.20
_+
+
~ Ul
--i-
-0
'33
-.-
+
N --"
-0
'45
-,...
...-+=
-0·2
0-
7~rangle
U1
16-5
°
~+
0 n _. :JI
+1.
0 ........
++
++
+P
erp
en
dic
ula
rto
be
ach
1:1·
5sp
aci
ng
Tz=
7se
cH
p=
2·2
mV
elo
citie
sin
m/s
mo
de
l,to
con
vert
top
roto
typ
em
ult
iply
by
6
26°
wa
vea
pp
roa
cha
ng
le
-n \0 N N .to-
---J
v--0
RIG
IN
__
_0
·3
1---
G>I
HG
FE
(3+
SLA
CK
AR
EA
S+
SLA
CK
AR
EA
S+
SLA
CK
AR
EA
-+S
LA
CK
AR
EA
+~
~A:~L.
RUNU
P)~~~-:-:=:..
.-.
E~DD
6"PE
R5'D
<!E~
~~__~
7¥~'T1-Cl~~~~·
--=t::"
'd=
I°2
4~
0,0
8-
~_.
""
.cf)~
Cl.---
0·2
1~
r00
8->-
--.::
::If
)/0.
04
I/-
0·0
9t
0.0
-';P
t~"~
CJ<D
__
0,1
2-
);;~
Jl>Cl·(jj"'-~
../.------
~/)~
A1\
~\
l-
..'-
-,;I
_0
·2
4--
.Cl1
$'---~
\'
-'Q
.0
.'2
."'-
....
,..-
0.33
......0
.3 '2.0
1-'
:>/"
"-
.....
0·25
/,.6"
Cl
_0
'20
/~
0·3~~
~025~
--+
-0
.2
7-'---
-i:
:.-0
.26
--0
'39
+.....-0
.3
3--+
++
t+
1m
++
t+
I~3
m..I
++
++
++
~ ~I
-t- 0
.5O_
--+-
0'4
4-
N N ...-.
10
=-0
.22
-+
0·2
4-
Bre
ake
ra
ng
le(J
l1
6.5
0
Vi
++
"U 0 () _. :::J
++
\0 ........
++
++
+0
.30
--
to
.1
8-
--0'3~+
---=°
.20
-=t-
__
_0
,41
-
__
_0
·22
-
+ I +-
__
__0
·31
---
__
_0·
21--
Wit
hin
term
ed
iate
gro
yn
es
25%
sh
ort
er
-p
erp
en
dic
ula
rto
be
ach
1:1·
5sp
aci
ng
Tz
=7
sec
Hp
=2.
226
0w
ave
ap
pro
ach
an
gle
Ve
loci
ties
inm
/sm
od
el,
toco
nve
rtto
pro
toty
pe
mu
ltip
ly6
"le N N U"1
.....:J
HG
F
yO
RIG
IN
;:oi
__
0,4
2-
--0
·3
3-
.---0
·3
4-
__
0,5
0-
..--0
·35
-
VI
++
__
_0
'42
-~0'44-
-0
'41
-+
1._
.._
0.4
1-_
_0.
35-
.......
_0
·3
4-
N_
0·3
9-
-0
·3
3-
__
0'4
1--
-0
·2
9-...
..-0
'25
-W
....
--0
,28
-
.......
++
_0
·2
3-
~0'25-
_0
.25
-=
\-_
__0
'2
7_
+_
0·2
0--
--"
Bre
ak
er
an
gle
..
16·5
°V
I"0
++
++
+0
tn :::J
1mIQ
++
++
t+
01-
-3m
1:::J IQ C'
i)
++
++
+0
..
C u ~I
++
++
+-.....
Gro
yn
es
an
gle
d10
°in
tocu
rren
t1:
1sp
acin
gT
z=
7sec
Hp
=2·
2mV
elo
citi
esin
m/s
mo
de
l,to
con
vert
top
roto
typ
em
ult
iply
by
6
"to N N enO
RIG
IN
.....:
I
__
0·3
3-
--0
·25
-
-0
·3
3-
____
0·17~
-0
25
-
-0
·3
3-
_0
·3
3-
E --t- +
_0
,3
3-
++t
+1m
+t
+\""
3m1>
1
++
F +
_0
·3
1--
_0
·5
0-
....
...-
0·3
3-
-0
.3
54
-_
_0
·50
-+_
__0.5
0-
-0
·2
8-
-.-
0·3
3-
_0
·2
5-
4-0
'27
+_
0·2
0-
+___0.2
5-
--+
++G + +....
.--0
·34
-
*-0'22
-
_0
·3
3-
+.____°
.43-
+
H +I +
WBL
A\CO
KTDD
V-SL
ACKis
LACK
------
SLACK
WAV
ER
UN
UP
----
----
----
---
.'
.0
':,\~
S.v
y.L.
'T-'
-'-,-'
-'-=
f~~
t-'J
A,.
LcV~A/
----0
·21
--
-:;0
::3
3
~0'25-
Ctl 0::-...
++
--0
·3
4-
~_
__
0·3
5-
Vl ......
++
_0
,4
1-
N ~ ....
.1
__
0·3
0-
+----
-+
...-0
·1
8-
Bre
ak
er
ang
le
lP+
+::J to o
I+
+::J to (j
) 0..1
++
C -0 0.. ~I
++
......
........
Q ., o '< ::J Ctl
Gro
ynes
ang
led
10°
aw
ay
fro
ma
lon
gs
ho
recu
rren
t
1:1
spac
ing
26
°wa
ve
an
gle
Tz=
7sec
Hp
=2
·2m
Vel
oci
ties
inm
/sm
od
el,
toco
nve
rtto
pro
toty
pe
mu
ltip
lyby
6
~ORIGIN
____
_0
,33
-
-0
-5
0-
.--0
-38--
---0
'33
--t-
_0
-3
5--
~0-34-
---0
-3
7_
.--0
·30
-+H
GF
E
+S
LAC
K+
++
-~-
\\RCl~~ff~7JB~\~'.r-~
,._.
_._
.-
+-_
..
n.
~')~!
.~.,:.~
O~O,,_-<-{j16-~
))/
(/
;)~~
~/
}n
02
2-_
-0
·1
8...
,./~
_0
·10
<_
-,-
0-2 1...-/'--
---+
--0
·2
0-
+__
03
6_
~0-35-
..4
1-0
.25
-+---
0'3
3-
.IA\).
.......-
-
/'
\)-
0·27
____
____
_
11--
---
~O
__
__
0·3
0-
....
..-0
·29
-.-
-0
-5
0--
-0
·31
-0
·2
8-
+L
0-2
5-
_0
.2
0±
--f:
;~
016
_--0
-2
4-
__
0-2
0_
_0·
27
++
++
f lm
++
+t
+lE
3m"I
++
++
++
++
Gro
ynes
an
gle
d10
°a
wa
yfr
om
alo
ng
sh
ore
curr
ent
1:1
spac
ing
26°
wav
ean
gle
ran
do
mw
aves
Tz=
7·3
sec
H1/
3=
2·2
m
Vel
oci
ties
inm
/sm
od
el,
toco
nver
tto
pro
toty
pe
mu
ltip
lyb
y6
I~.--~-
....<lJ....<lJE~oiL
....<lJ....<lJEoco~
-0'x«
Fig 3·1 Plan of wave basin - wave generator at 15° for tests 31-43
Ori
gina
lm
od
el
slo
pe
con
tinu
ed
tob
asi
nfl
oo
r
Cl.> 011
::::l o 01 ::::l I C ::::l
er:
160
150
140
130
120
Est
ima
ted
pro
file
Oct
.19
83us
edfo
rin
itia
l/m
ou
ldin
ga
nd
rep
lace
d...
..""
!'"
Jan.
1985
'..
« Cl.> C >, o L. o
pro
file
Pro
file
use
d
N Cl.> 01 ::::l o 01
0..
::::l I C ::::l er:
M Cl.> 01
::::l o 01 0..
::::l I C ::::l er:
1 I I I I I IExt
en
de
d
I I I I I I 1
Se
aP
alli
ng
layo
ut
24
3.0
m+
-20
a·a
m+
17
3.1
m-I
"14
2·5m
..B
ase
lin
e-l
a
Ru
n-u
pg
au
ge
3p
rofi
le
-.:t
Cl.> 01 ::::l o 01 0..
::::l I C ::::l
er: Ori
gin
al
un
iform
mo
de
lsl
op
e
70ao
9010
011
0C
ha
ina
ge
fro
mb
ase
line
(m)
60Q)
(l) c >,
o l... o
5040
30
-..;; .....
...... .....
....... .....
.........
........,
......
Ext
en
de
dp
rofi
lere
ceiv
ed-----.....:.-~
Dec
.19
84o
ffsh
ore
pa
rtus
ed----~
===::
:::---..
an
db
len
de
din
toin
sho
rep
rofil
e~
20
I..In
sho
rep
rofi
le1>+
.B
lend
edle
ngth
..I..
Off
sho
rep
rofil
eI>
I..i"
Insh
ore
prof
ilere
ceiv
ed
Nov
.19
84a
nd
use
dfo
ru
pp
er
be
ach
::!11
1984
fie
ldsu
rve
y\.C
l
W N :::0 c ::J I C '"tJ
\.Cl Cl C \.Cl
(1)
'"tJ 0 Vl ..... 0 ::J Vl
Cl
::J Q.
0-
s(1
)1Cl ~I
4 3'"t
J ., 01
2~ .-
-(1
)'O
DN
0·1m
MTL
(m)
0 -1-1
2m
MLW
S
-2 -3 -410
0
,--------,-----------------------------------I
l a5no5 dn -unCj<L>.£;
<L>(/)o(I)
«
Z a5no5
I-a-0"O~(1)0(/)::J..c
u
~2;;:.0aI-l...0.<1>
~"00(1)-
"O<L>dn-unCj ~.::
I~ ~~ ~IE-a-5~n-o-5~d~n---u-n-Cj-------------------
'7 a5no5 dn-unCjCD(1)c>.o
I~=:-~~-_~~.:7 a5no5 dn unCj -
E a5no5 dn-unCj*------
*z a5no5 dn-unCj
u
,d a5no5 dn -u nCj(/)
<L>- >.aL.. <L>0. >
l-::J
"0 Vl(1)L.. :gaL..
(1)L..
:::E -* """co
0>....
Fig 3·3 Model beach plan(as moulded)showing mirrored profiles
-n lO CA
)
.t"-
3::
o 0
0)
r- - "'0 ., o .......
o .......
'< "'0 0) n C ., ., 0)
::J .......
VI
VI
:J o :E ::J lO 0- - -Cl) ., C
l) ::J n 0) VI
C'G
royn
eB
·P7
......
......
....
leS
Ta
me
nd
ed
da
ta1
6-4
-85
----
-...
.H
Rl
ori
gin
al
run
78--..
HR
lo
verp
um
pin
gte
sts
~5
OI!
:;pF
....m
i4'P
6G
royn
eA
Sa
se
-l
""""l'
"••
•P
3<l
!,...
P2
~.P
S<
lllI
<l!
l---
-:...:::
:-.;:':':
":•..._
....
....
.'It
:
"III
IIu
","P
A
1984
fie
ldsu
rve
y
o0
·'0-
20·
30-
40·
5rn
lsI
II
II
Ip
roto
." lO W U1
I
Just
do
wn
stre
am
ofg
royn
eB
of
gro
yn
efi
eld
", '.....
..........
......._-
--
S.W
.L.
(MH
WS
)
III
C Qj .::£ tl ~ m
/--
,//
--........
....;//~
,,,~
UPdr
ift
I~
~'
//'
I l
E-2
<IJI
Ve
loci
typ
rofil
e'"0 0 E
0.1
Ul - E >- ..... u 0 <IJ >
0
a.
:::l , C :::l
"- III > tl
33=
z2
0 0 <IJ >0
..... a ~-l
LG
royn
e8
< (I)~ o () < o ~ Q. o ......
:::J o-~ (I)......
'< "'0 ., o - o :::J o .....
......
.(I
) 3 "'0 .....
.
-31I
IJ
II
I!
I:=
Ii
I-:
430
4050
6070
8090
100
110
120
130
140
150
160
Me
tre
sfr
om
ba
se
lin
e(p
roto
)
1984
fie
ldsu
rve
y
- ........coo<l>E V1 V1
o 0'"0 <l> <l>
<l> .... ....([l « «
-.... co 0 c~ a; 0c .... V1o u 0.... u ...._ 0 <l>
V1..c-oc..
I\\ \I \ \ \I \ \ \I \ \\ \ \\ \ \\ I \\ \ \\ \ \\ \ \ \\ \ \
@\ \ (0
\8 '--+\ r \ \\ \ \\ VI\ \ \
@~\ ~I ~{ 9(\ I \ I\ \ \\ \ ~\ \ \\ \ \
@\~\ ~
I
\ 9 \ \\ \
\ \ \ \\\ \ \I I \I I II I I
Fig 3'6 Schematic plan view of groyne field
0-- + + + + +
Fig 3· 7 Test 31 - MHWN
o~ Lf)(IJ ~
-g (IJ
E ~c
Ul 0--E ~
. .~ ~
~ (IJ"- ........ 0·u .s:o 1Il~ ....(IJ ....
>0
o + ~ + + +
III <lJ09:! '-..... 0,- J::U III.9 '+<lJ '+->0
o~ Lfldl ~
\J dlo ~
E (JlC
III a-E <lJ>
C a.- ~
+ +
+ +
+ +w
~if~
:;)~ ~~
~ \0 ~io~0\\ ¥! If . i...,,,x~r~
G ~?~~6l.L-r-~~-L:\:j··Ilit..,; ~ It
\..)~:'I:::'::t'~;, lo' / z!:P:'::~.o ~ i··X,,;. ~
q,.~ .~,;; ~
- 'co" \;.' . Or i: 't
9~ ··.i'· ,'~\?:"~~';: /. ~Jo :)J 6
':,:
dlC
Q;III0
.D
>-dl>'-:J
CIII
02' \J.... a>
° u::
Fig 3· 8 Test 32 - MTL
O-r + + + + +
r::O'll-
Q
+
+
+ + o~ LO(J) ~
Ll (J)o ~
E 01r::
Ul Cl--E ~
.s ~
~ (J)._ I-...... 0'u ..r::o Ul~ .....(J) .....>0
Fig 3· 9 Test 33 - groynes raised O' 5m
o + ++ + +
"~ LDQJ ~
-g QJ
E 0,c
Vl 0--E QJ>
C 0- ~
~ QJ._ I-...... 0U .L:o Vl~ -QJ >0
+
+
+
+
+
+
. :;.
>.QJ>I-
::JVl
lJa:;iL
QJC
QJVlo.D
~ \.
L ~>i \jg'{;{)iii- ~ +I ++
w i\) ~ +~~ 4'.'
~.;' \ .~\~~ J ~(,';i. ~
'~... ~ '6
d"'" .·.. \l\'. ,;:~; \ ~
.~.:.S~· \ ~ ~
0\ .... Jb \6C
01...o
Fig 3'10 Test 34- groynes raised 0'5m, beach roughened
o + + + + +
cO'l
b-
o
+
+
+
+
+
+ o~ 1.0(\) ~
-g (\)E 01
cUl Cl--E ~
"~ ~
~ (\)"_ b-...... 0"u J:o Ul~ 0+-(\) 0+-
>0
Fig 3·11 Test 35 - groynes raised 1·0m, beach roughened
•,,
'\Q W
IOri
gin
N
o ++ +
.-- -----E
FG
/"
'I!:
.---
--'.
.....
)0
·14
-.,
l~\.
'-
./
--"';;Y:::·:~·:'J.·'.:~:.~~t:
'--
..,
--0;2 ~/-F
0·0
4
'-'q
-'
/~f(;-
/f4
(.
'.,.,.~;
:..:~.".
./L
,,<>
Y--'.'
"..::.--:.~.,
..:'.~
::<"
,c,.
...""
.,'
•.
r_
,\O
:-,~
~_e
O.~
'..:'.
..:,
•:.'
':""
.•;."'~O
14-.
:I~
0.\".
...
.,.
.'.
......
______y
~10
t::s'--
OlD
,/",
\OC~
'k;;
~:;~•
.it.~:
»,--+
£--~~
__
.;;)~V;;~~~07
/
o 3......
..., o Vi'
I'!)
0..~ :IFi
eld
surv
ey
0) I
\Q a '< ::J I'!)
III
++
++
++
+V
elo
citi
es
inm
Ism
od
el
Off
sh
ore
wa
ve
an
gle
15°
cO"lL-
a
+
+
+
+
Fig 3·13 Test 37 - raised groynes plus vertical seawall
"U) w
SW
.L.
(MH
WS
)
....
....
...
....
....
W"O
CC
I>.-
C-C
l>....
.cW
en
~:::l
Cl
oCI>
....
....c
CO
:::l
....
....
~W
ith
ou
tro
ug
he
nin
g(d
ow
nd
rift
).
'.
......
.~W
ith
ou
tro
ug
he
nin
g(u
pd
rift
)
··..r~
Wit
hro
ug
he
nin
g(d
ow
nd
rift
)
Wit
hro
ug
he
nin
g(u
pd
rift
)
..'
101
Ro
ug
he
ne
dI
~a
rea
Cl ::
Gro
yn
eB
rais
ed
1·0
m
Ve
loci
typ
rofi
lese
cti
on
se
ith
er
sid
eo
fg
royn
efi
eld
wit
ho
rw
ith
ou
tro
ug
he
nin
g
o -2
E-15 4
-o Q> ....z o2
o Q> >
-31
II
II
II
II
==:
II
-
3040
5060
7080
9010
011
012
013
014
015
016
0
01I
II
Vi
II
i......·_·_.~
······
·c···
·.....
.I
II
Ii_
0·3
>- 50·
1~ Q> >(j)
\J o E ~0·
2
E
--"~ < C'D - o () l'D lJl
.-+
l'D tn .-+
lJl
W Ul o :::J Q.
w en.-+
'< U ....... o -..
Me
tre
sfr
om
ba
se
lin
e(p
roto
)
C
0\
'-o
o ~ ++ t\ \
+ + +
+
+
o~ LO(l) ......
U (l)o ~
E 01C
l/l 0--E (l)>
c 0"- 3:~ (l)"- '-..... 0"u J::o l/l~ ....(l) ....
> 0
Fig 3·15 Test 38 - raised groynes, stone clad
+
+
L-
a
+
+ o~ LO<IJ .....
U <IJo ~
E enc
Ul 0--E ~
.~ ~Ul <IJ.~ L...... 0·u J::o Ul~ ....<IJ ....>0
Fig 3·16 Test 39 - raised groynes, with added T- pieces, stone clad
cCl...o
+ o~ Ln(\) ....
-g (\)E Q,
C1Il a......E ~
.s ~
la (\)._ I......... 0'u ..cE ~(\) ....>0
. Fig 3 -17 Test 40 - raised groynes with fish tails added, stonerlnrl
c:OlI-
o
0-- + + + + +
+ o~ LO(]) .---g (])E en
c:Ul 0--E (])
>c 0- 3:~ (])._ I-
~ 0U J::o Ul~ ....(]) ....>0
Fig 3'18 Test 41 - raised groynes with updrift groyne damage
+ +
+ +
+ +
+ + ~~U <lJo ~
E 01C
III 0--E ~
.S: ~
ill <lJ._ L-...... 0'u .co 11l~ .....<lJ .....>0
Fig 3-19 Test 42 - raised groynes - permeable
c.21...°
o~ lJ)(j) .--
U (j)o ~
E (Jlc
~ 0
E ~
S ~
~ (j)._ L....... 0'u ..co lJ)
~ -(j) ....
>0
Fig 3· 20 Test 43 - raised groynes - alongshore current overpumped
Plates
1-1 General view of model basin
1-2 Distribution system for a1ongshore currents
2-3 General view of model basin - wave generator at 10 degrees
2-4 General view of model basin - wave generator at 26 degrees
, ,i I III
'".... - fO'J
~
~l I IIl_tt·_
...,J'"........
. '.
-<' ,:.~. :'-.
"
3-5 View of model beach showing roughening strips (Test 34)
3-6 Stone clad groynes (Test 38)
3-7 Stone clad T-shaped groynes (Test 39)
• •
3-8 Stone clad fishtailed groynes (Test 40)
3-9 Permeable groynes (Test 42)
Appendix
APPENDIX A
CIRIA Research Project 310: Effectiveness of Groyne Systems
Phase 11
Proposal for a Physical Model Study of Groynes on a Beach
Stage 1: Establishing Experimental Methods and Preliminary Testing
Parts 1 and 2
The objectives of the Stage 1 physical model study
will be as follows:
(i) To measure the alongshore currents generated by
random waves on a straight, parrallel contoured
beach without groynes. The profile of the beach
used will be moulded to a mean profile of a
stable sand beach on the East Anglian coast •
(ii) To investigate the problems of 'end effects' on
the physical model, and to use a pump to supply
and recover a carefully regulated alongshore
flow at each end of the beach to solve the
problems.
(iii) To investigate the effect of the model surface
roughness on both the alongshore currents and
wave heights on the upper part of the beach.
This will be of great value when comparing model
and prototype beaches.
(iv) To study the effects of a single groyne on the
distribution of wave energy and the alongshore
currents. This is the easiest groyne 'system'
to study, and should give useful information on
the behaviour of the first 'updrift' groyne in a
system. It should also be a valuable situation
to compare with both prototype measurements and
mathematical models.
(v) To study the current and wave distribution for a
particular groyne system for comparison with
prototype measurements being carried out on the
East Anglian coast.
DDS 12/86
