Presentation by Thomas Stolp (HKV, Netherlands) at the Symposium on Emulating 2D flood modelling, during the Delft Software Days - Edition 2023 (DSD-INT 2023). Wednesday, 27 September 2023, Delft.

1. Flood hazard maps for spatial development
A pragmatic approach based
on existing LIWO scenarios
27 September 2023
Thomas Stolp

2. Flood information system
Motivation
Flood hazard maps are available in the Water and
Floods Information System (LIWO).
Up to date flood information, for all of the
Netherlands.
Consist of a set of +-3000 simulations.
2
https://basisinformatie-overstromingen.nl/
Maximum water depth in the Netherlands

3. Use of flood scenarios
Motivation
3
We use existing flood scenarios to
create water risk profiles.
All locations in the Netherlands, you
may be at risk of floods from:
Primary, regional defences or
precipitation.
Breach locations
Primary defences

4. Use of flood scenarios
Motivation
4
All locations in the Netherlands, you
may be at risk of floods, from:
Primary, regional defences or
precipitation.
Risk profile

5. Use of flood scenarios
Motivation
Risk profiles can be used to creates maps and provide information to
decisionmakers. Now, and for the future.
5

6. Changes in boundary conditions
Motivation
Different climate scenarios, effect on sea level
rise.
Boundary conditions of flood scenarios
change.
There is a need for new scenarios to assess the
year 2100 (even 2150?).
6
Discharge
Lobith
[m3/m]
Sea
level
rise
[m]
Year
Return period

7. New flood scenarios needed
Motivation
Due to climate change, we expect more
extreme conditions. Besides, big system
interventions are being considered.
The current set of flood scenarios on LIWO are
not sufficient for these existing situations and
interventions.
7
Protect, closed Protect, open
Seaward Move along

8. Create a new set of scenarios, based on existing LIWO set
Goal
Create a tool for rapid generation of flood
inundation maps with boundary conditions
defined by the user:
- Other (more extreme) hydraulic boundary
conditions
- Other spatial development
To be used for climate risk analyses and
adaptation studies.
8
To be defined
Scenario R = 4.000 years
Scenario R = 40.000 years
Scenario R = 400.000 years

9. Simplified models
Motivation
How far can we get with simplified models?
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10. Consist of two components
Methodology
1. Volume estimation
How do you estimate the volume of water that
passes through a breach for the more extreme
situations?
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2. Flood pattern
How does the flood propagate over land?

11. Linear fit of volume against inflowing volume with return periods
Concept
The method is based on a fit of the volume in the flooded area of
existing LIWO scenarios and the relation with the boundary
condition for certain return periods.
If no new situation arises in the river but only more extreme, then it
is possible to extrapolate based on the return period.
Does the hydrograph change? Then hydrographs per scenarios must
be considered and the volume under the curve must be decided to
extrapolate.
Hydrographs can be available in the original LIWO scenario. If not, it
a standard hydrograph must be derived for the location of the
breach.
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12. Multiple possibilities
1. Volume estimation
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On this location I have only
a single LIWO scenario
On this breach location I
have multiple LIWO
scenarios
New hydrograph
Climate risk
1. Estimate the volume of
maximum water depth
map and the
corresponding return
period.
2. 2. Create a linear fit
between volume and
return period.
3. 3. Extrapolate to
desired return period
It’s not possible to
extrapolate on one of these
methods.
Check if adjacent breach has
more than one scenario.
Do you have an original
hydrograph with the LIWO
scenarios?
Do you have access to a
standard hydrograph?
1. Estimate area under
original hydrograph.
2. Estimate volume
maximum water depth
LIWO scenario.
3. Estimate new
hydrograph and
estimate area under
original discharge.
4. Create a linear fit to get
a new volume.
1. Create a standard
hydrograph based on
hydrograph tools for
existing scenarios.
2. Make new
hydrographs.
3. Estimate area under the
curve for all
hydrographs.
4. Estimate volume
maximum water depth
maps.
5. Make a linear fit and
estimate the new
volume.
Create a new scenario

13. Various possibilities
1. Volumebepaling
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Volume under curve
of used hydrograph
Volume
max.
inundation
map
Normative water level
(NWL) + height factor 10
larger freq. of exceedance
NWL NWL+1D
Volume under curve
Standard hydrograph
More extreme scenarios New hydrographs
NWL+2D

14. Example
1. Volume estimation
14
TP
TP+1D
Scenario R = 4.000 years
Scenario R = 40.000 years
1. For every flood simulations in the LIWO set, we can
get a volume of the resulting inundation map.
2. This volume can be coupled to the 2D-volume
corresponding to the used hydrograph.
3. We plot these points and make a linear fit.

15. Example
1. Volume estimation
4. A new hydrograph gives a new volume
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Time of breach
V_in
New volume, from
hydrograph
TP
TP+1D

16. Example
1. Volume estimation
5. Next, we can estimate a new volume of the maximum
water depth map corresponding to our linear model.
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Time of breach
V_in
TP
TP+1D
Volume of
inundation map

17. Steps
Flood pattern
1. Increase water depth in already flooded
cells.
2. Find additional flooded areas.
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18. Steps
Flood pattern
1. Increase water depth in already flooded
cells.
2. Find additional flooded areas.
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→ Per pixel, estimate max water depth increase

19. Steps
Flood pattern
1. Increase water depth in already flooded
cells.
2. Find additional flooded areas.
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Iterative process:
I. Locate surrounding dry cells
II. Interpolate with nearest pixel value of
water height
III. Check larger than or smaller than DEM
IV. Assign water depth if > DEM

20. Estimate additional flooded area – iterative process
Method
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Retrieve boundary of wet cells Assign nearest water height value
Check DEM
Als h hoger dan maaiveld:
d = h - maaiveld
Anders:
d =0
Assign waterdepth

21. Operations on images
Method
Morphological operations, set of
techniques that use shapes and
structure in images for adjustments
(based on binary).
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• Dilation
• Erosion
• Closing
• Opening
• Hit-or-miss
Operators
Example: simple dilation

22. IJsselmonde dike ring 17
Example
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Maximum water depth NWL+2D
Water depth of iteration 1

23. IJsselmonde dike ring 17
Example
23
Maximum water depth NWL+2D
Water depth of iteration 7

24. IJsselmonde dike ring 17
Example
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Maximum water depth NWL+2D
Water depth of iteration 14

25. IJsselmonde dike ring 17
Example
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LIWO scenario NWL+2D
Approximation NWL+2D Absolute difference

26. IJsselmonde dike ring 17
Example
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LIWO scenario NWL+2D
Approximation NWL+2D
Add filter based on the distance to breach location.

27. IJsselmonde dike ring 17
Example
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LIWO scenario TP+2D
Approximation TP+2D Absolute difference

28. To refine our method
Research questions
What are ways to improve this method? Use
of AI?
Can we reconstruct the simulations in current
LIWO set, to validate this method?
How can we incorporate more domain
knowledge?
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29. Thomas Stolp
stolp@hkv.nl
Thanks for listening