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Coastal geomorphology and extreme water levels
COADAPT Project
Aart Kroon, Jørn Bjarke Torp Pedersen
26 October 2010
Department of Geography & Geology
Contents
Introduction
Coastal erosion and flooding
Extreme water levels
Approach
Team at DGG-UC
Department of Geography & Geology
Introduction
Coastal environments in Denmark
large spatial variability
Geomorphologic map(GEUS, 2009)
Department of Geography & Geology
Introduction
Two major impacts:
1. coastal erosion might be intensified;
2. coastal flooding might occur more frequent.
Department of Geography & Geology
Danish Coastal Authority, 2008
Coastal erosion along the West coast of Jutland
well monitoredwell known‘under control’
Department of Geography & Geology
Coastal erosion along the inner coastlines
less monitoredless well known
First indication by aerial photographs and satellite imagery
On its way!
Department of Geography & Geology
Westh, 2009
Department of Geography & Geology
Coastal flooding along the coastlines
A) potential flooding areas based ondigital terrain models (contour maps of the height)
- example: ‘Klimatilpasningportal’, DCA
B) inundation areas and inundation times based ondynamic models (process-based)
- example: DHI
Department of Geography & Geology
Coastal flooding: spatial patterns
KMS, 2010
Department of Geography & Geology
Example DTM: Glænø, Southern Sjælland
Department of Geography & Geology
Also activities
Example: Havvand på land (seawater at land)Cost-benefit analysis in GIS on DTM
Department of Geography & Geology
Also activities
Example: Kystplanlæggeren (coastal planner)
Department of Geography & Geology
Coastal flooding
DTM
+ easy to get an indication along all shores+ easy to track potential risk areas
-- no dynamics, no inundation times -- no distance from breaches included
Process model
+ precise idea of inundation process + precise information about inundation pathways
-- relatively time consuming computations-- relatively small spatial coverage
Department of Geography & Geology
Coastal flooding
Both approaches need to be fed by extreme water level distributions
DTM
* as exceedence curves of water levels, giving an idea of return periods
Process model
* as time-series,giving an idea of the intensity and duration of the event
Department of Geography & Geology
Summary
Why do we @ DGG need information about extreme water levels?
a) To understand erosion and accretion patterns along the shores
b) To understand the risk of flooding in coastal areas
c) To parameterize extreme events
* spatial patterns around Denmark* relative importance compared to waves, tides, …
(on its way: AKK)
d) To better understand active beach ridge systems
Department of Geography & Geology
Extreme water levels and beach ridge systems
• Detailed observations of the height of the present day active beach ridge
• Coupling of these heights among local water level characteristics:
- High-tide level
- Extreme water level with a return period of … (SL1/100x)
Beach ridge Glænø
Department of Geography & Geology
Extreme water levels and beach ridge systems
KMS, 2010
’Littorinahavets tid’ ca. 5-2.000 BC’Littorinahavets tid’ ca. 5-2.000 BC
’Littorinahavets tid’ ca. 5-2.000 BC’Littorinahavets tid’ ca. 5-2.000 BC
Beach ridge locations
Department of Geography & Geology
Description of extreme water levels
Common practice (DCA)
• Long data series (years) with frequent observations (every 10 min)
• Observed distributions of water heights with special interest in the upper tail
• Statistic description of the upper tail with- Truncated Weibull distribution;- Truncated log-normal distribution.
Department of Geography & Geology
Description of extreme water levels
Common practice (DCA)
• Exceedence curves of water levels at different locations
DCA, 2007: Extreme sea level statistics for Denmark
Esbjerg
Department of Geography & Geology
Use of extreme water level descriptions
Two questions arise:
A) Can we use existing exceedance curves and return periods to predict flooding events under a rising sea level scenario?
B) Is the existing analysis method reliable, robust and does it describe the most important features of water levels related to flooding?
Department of Geography & Geology
Flooding events under a rising sea level scenario
DCA, 2007: Extreme sea level statistics for Denmark
Esbjerg
Department of Geography & Geology
25 cm sea-level rise:
Return period (yr) for what is now a 100 yr event
Department of Geography & Geology
Flooding events under a rising sea level scenario
This will result in higher return periods, but (!!)
A) Extreme values have another distribution than the bulk of the water levels. Previous extremes are no longer extreme values and need to be described by other functions.
B) Is it a valid assumption that a rising sea level will not lead to another character of the basin? (is the rest stationary?)
C) …
Department of Geography & Geology
Existing analysis method reliable, robust
Reliable yes,
but there is a lot of tuning:
Distribution parameters are fitted and the truncation level for the truncated distribution is fitted. Especially the latter is extremely sensible and determines the outcome!
One distribution type for all data series is preferred. Physical variable is the same and spatial comparison of outcomes is not hindered by the method.
Department of Geography & Geology
Are the most important features included?
Water level statistics is based on very detailed high-quality long-term series
Both types of flooding analysis (DTM and inundation models) will probably need other information as well:
Water levels:
intensity, duration, frequency of occurrence, sequence
(similar to erosion due to storm events or flooding due to intense rainfall events)
Department of Geography & Geology
Description of water level: peak-over-threshold / duration curve
Statistics of extreme water levels
using GEV (Generalized extreme value) distribution
creating water-level/duration frequency plots
Approach
Department of Geography & Geology
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000-5
0
5
10
15
20
25
30
35
Year
Mea
n a
nn
ual
wat
er l
evel
Esb
jerg
Hab
ou
r D
VR
90,
m
Yearly measured mean water level
10 years running average
Esbjerg 1890-2000
Department of Geography & Geology
Jan0000 Nov0136 Oct0273 Sep0410 Jul0547 Jun0684 May0821 Apr0958-400
-200
0
200
400
600
Time, 1962-2004
Wat
er le
vel a
bove
DV
R90
, cm
-400 -300 -200 -100 0 100 200 300 400 5000
1
2
3
4
5x 10
4
Water level above DVR90, cm
Hou
rs o
f oc
cura
nce
-400 -300 -200 -100 0 100 200 300 400 5000
0.2
0.4
0.6
0.8
1
Water level above DVR90, cm
Cum
. fr
eq.
Esbjerg 1962-2004
Department of Geography & Geology
Jan 1990 Jan 1991 Jan1992 Jan 1993 Jan 1994 Jan 1995-2
-1
0
1
2
3
4
5
hei
gh
t (m
)
time (year) from 1990-1994
Surge observations=37
Esbjerg 1990-1994
Peak-over-threshold detection
Department of Geography & Geology
Jan 1990 Jan 1991 Jan1992 Jan 1993 Jan 1994 Jan 1995
0.5
1
1.5
2
2.5
3
x 104
inte
rval
bet
wee
n s
urg
es (
ho
urs
)
time (year) from 1990-1994
Esbjerg 1990-1994
Sequence analysis
Department of Geography & Geology
Relation between intensity and duration
Probably not linear
Certainly not the same at all locations(shoreline with tides react different, often restrictive to the
duration of the high-water event)
Department of Geography & Geology
0 2 4 6 8 10 12 14 16 183
3.2
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
max
. su
rge
leve
l (m
)
duration of surge (hours)
Surge observations=37
Esbjerg 1990-1994
Department of Geography & Geology
Summary - work in progress
Mapping accretion-erosion based on aerial photographs
Helping with flood mapping procedures using KMS DTM
Detailed analysis of present day behavior in some specific areas (with master students)
Detailed analysis of beach ridge systems (with master student)
Parameterization of coastal processes (with AKK)
Detailed analysis of extreme value statistics coupled to water levels
Department of Geography & Geology
Since last meeting
PhDAlina Kabuth started on 15-07-2010
Parameterization of coastal processes
MSc Mette Bendixen
Beach ridges and water levels in DenmarkBertram Hacke
ICZM and Danish Municipalities
PresentationsSUSCOD in SorøGeoforum in Copenhagen