Presentation by Rita Ley, Federal Institute of Hydrology, Germany, at the Delft3D - User Days (Day 1: Hydrology and hydrodynamics), during Delft Software Days - Edition 2018. Monday, 12 November 2018, Delft.

1. Experiences from modelling a
branched lowland river in NE Germany
with Delft3D FM Suite
Rita Ley, Markus Promny
German Federal Institute of Hydrology (BfG)

2. Structure
1. Project
2. Study area: the river Havel
3. 3 grid variations
4. Model results
5. Summary
6. Conclusion
12.11.2018 2Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

3. 1. Project
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Geesthacht
Gnevsdorf
Tangermünde
Rathenow
Berlin
© GeoBasis-DE/ BKG 2017
Untere Mittelelbe
Havelpolder
Havelstauregime

4. 1. Project: River Havel
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gauge
water
model area
pilot study area
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

5. 2. Study area: the river Havel
• 23 km river Havel:
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6. 2. Study area: the river Havel
Digital elevation model:
– land and water
– resolution: 1m
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7. 2. Study area: the river Havel
• about 23 km mainflow (navigation channel), lowland river
• impoundment, weir Brandenburg
• width (navigation channel): ≥ 75 m, river widenings
• lakes, secondary channels, trenches, navigation channel
• flow velocity: 0.1 – 0.7 m/s (flood),
• mean flow rate: 72 m³/s, pluvial regime
• very low slopes
• water surface slope: 5 – 20 cm / 20 km
• mean bed slope < 0.01%
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8. 3. grid variations
Grid generation
➢ Search for an optimal grid for this river section
Combination of curvilinear and triangular parts?
Test of 3 Grids:
A: wide curvilinear grid over all flow paths
B: small curvilinear grid restricted to the main channel
C: detailed grid with curvilinear parts for all channels
setting:
• same borders, structural lines and bed level
• similar orthogonality, smoothness and edge lengths
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9. 3. grid variations
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A: wide curvilinear grid: over all mid-water flow paths
element sizes:
• curvilinear part: from 20x20 m
• triangles: up to 400 m
grid A
channel
water area
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

10. 3. grid variations
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A: wide curvilinear grid
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

11. 3. grid variations
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B: small curvilinear grid restricted to the main channel
element sizes:
• curvilinear part: side length from 20 m
• triangles: up to 400 m
grid A
channel
water area
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

12. 3. grid variations
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B: small curvilinear grid restricted to the main channel
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

13. 3. grid variations
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Version C: detailed curvilinear grid
element sizes:
• curvilinear part: from 20 m
• triangles: up to 400 m
grid A
channel
water area
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

14. 3. grid variations
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Version C: detailed curvilinear grid
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

15. 0
20 000
40 000
60 000
80 000
100 000
120 000
140 000
160 000
180 000
200 000
< 25 25 - 50 50 - 100 100 - 200 200 - 300 > 300
Quantitygridelements
Longest element edge [m]
Cumulative Curve of edge lengths - longest element
edge
Grid A, wide curvilinear grid
3. grid variations
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Quantity and size of grid elements
< 25 m 25-50 m 50-100 m 100-200 m 200-300 m > 300 m
Longest element edge
Cumulative Curve of edge lengths - longest element edge
Grid A, wide curvilinear grid
Grid B, small curvilinear grid
Grid C, detailed curvilinear grid
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

16. 4. model results
water level,
MQ, no calibration
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A
B
C

17. 4. model results
example: secondary channels
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elevation [m]
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

18. C
4. model results
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B
A
example: secondary channels:
flow velocity at mean flow
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

19. 4. model results
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A
B
C
example: secondary channels:
water depth at mean flow
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

20. 4. model results
example: lake
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elevation [m]
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

21. B
4. model results
example: lake
flow velocity at mean flow
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C
A
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

22. 4. model results
example: lake
water depth at mean flow
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C
B
A
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

23. 4. model results
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A
broad curvilinear
B
small curvilinear
C
detailed curvilinear
Expense to
build grid:
least medium high
computing
time
[h]
DFM_OUTPUT
_FlowFM
[GB]
computing
time
[h]
DFM_OUTPUT
_FlowFM
[GB]
computing
time
[h]
DFM_OUTPUT
_FlowFM
[GB]
Testcase 1
19 days
5 2.3 1 0.95 3 1.3
Testcase 2
29 days
6.5 3.7 4.4 1.5 3.5 2.15
Testcase 3
24 days
3 1.2 1.9
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

24. 5. Summary
water level
flow velocity
computing time
size output file
expense grid building: A: least
B: medium
C: high
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similar for all grids
large differences:
Grid A: slow and largest output files
Grid B: fast and smallest output files
Grid C: between A and C
Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley

25. 6. Conclusion
Arrangement of grids
➢ less influence on model results
➢ strong influence on:
▪ computational time
▪ size of output files
▪ expense to bild grid
➢ especially for large models: Grid layout
determines the practicability of a model!
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Thank you for your attention
Dr. Rita Ley
Bundesanstalt für Gewässerkunde
Referat M2
D-56068 Koblenz
Tel +49 261 1306 5927
Mail: Ley@bafg.de