Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation...
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Transcript of Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation...
![Page 1: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/1.jpg)
Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent
J.S. Wong1, J. Freer1, P.D. Bates1, & D.A. Sear2
1University of Bristol; 2University of Southampton
Do channel changes affect flood extent?
![Page 2: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/2.jpg)
Background and Motivation
• Flood inundation• focus on simulation of inundation areas and flow
depths• influences of river geometry are neglected
• Morphological change• increasing recognition of geomorphological impacts
on flooding• vital but still uncertain
• How do bed elevation changes influence flood extent during an extreme flood event?
![Page 3: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/3.jpg)
Study Site - Cockermouth
• Background• North West Cumbria, UK• one major river (River Derwent) and two tributaries
(Rivers Cocker & Marron) – combined catchment area of 1235km2
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Study Site - Cockermouth
• Why Cockermouth?• extreme flood event in November 2009• significant course change • deposition of debris on the floodplain
![Page 5: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/5.jpg)
Data availability
• 3 datasets of observed flood extent• Wrack marks• 0.15m Aerial photography• 1m TERRASAR-X imagery
• presence of pre-and post-event morphological surveyed data
Number of cross-sections
234
Total length (m) 28567.04Mean Maximum Minimum
Width (m) 34.97 195.83 18.51Bed Elevation (m) 36.93 67.44 4.20
![Page 6: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/6.jpg)
Model Setup
• 1D-2D LISFLOOD-FP• inertial formulation of shallow water equations [Bates
et al., 2010]• 20m resolution DEM extracted from LiDAR• gauged data as upstream boundary conditions• free downstream boundary condition• run for 167.75hrs, from 12:00 on 17th Dec to 23:45 on
20th Dec, 2009, across domain size of 100km2
• Monte Carlo simulations
![Page 7: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/7.jpg)
Model PerformanceChannel Friction Floodplain Friction RMSE (m)
Wrack marks 0.0220 – 0.0420 0.0440 0.2751
Aerial photography 0.0380 - 0.1350 0.0290 0.4187
TERRASAR-X imagery 0.0470 0.0200 0.6303
Parameter Minimum MaximumManning’s n (channel)
0.02 0.14
Manning’s n (floodplain)
0.02 0.14
![Page 8: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/8.jpg)
Probability Flood Map
![Page 9: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/9.jpg)
Generation of Bed Elevation Scenarios
• A simplified approach• initiation motion of grains at the bed, where shear
stress exceeds critical shear stress• maximum erosion depth is defined as
• focus on scouring effect, no deposition and lateral erosion
Parameter Minimum MaximumCritical shear stress τcr 0.047 0.083
Grain size characteristic D50
0.042 0.082
![Page 10: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/10.jpg)
Bed Elevation Change Scenario (95% Quantile)
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Reevaluation of Model PerformanceChannel Friction Floodplain Friction RMSE (m)
Wrack marks 0.0660 (0.0220 – 0.0420)
0.0490 (0.0440)
0.3147 (0.2751)
Aerial photography 0.1240(0.0380 - 0.1350)
0.0340 (0.0290)
0.4179 (0.4187)
TERRASAR-X imagery 0.0470(0.0470)
0.0200(0.0200)
0.6065 (0.6303)
Parameter Minimum MaximumManning’s n (channel)
0.02 0.14
Manning’s n (floodplain)
0.02 0.14
![Page 12: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/12.jpg)
Differences in Flood Extent Probability
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Conclusions
• The channel friction is insensitive on the amount of water that flows out of bank
• The entire valley floor is acting as a single channel unit in conveying the large flows
• No significant changes in flood extent before and after the bed elevation changes, possibly due to constraints of valley wall• Further investigation on water depth
• Potential flood extent differences in response to morphological changes when given smaller flood event
• Potential errors in the specification of upstream gauged data
![Page 14: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/14.jpg)
Future Work
• A 2D morphological model (CAESAR-LISFLOOD) will be set up to fully account for the morphological changes to flood extent and water depth
• Parameter space exploration of CAESAR-LISFLOOD to build up a modelling framework for identifying realistic morphological changes
• Application of modelling framework using Cockermouth as test site for future climate scanerios
![Page 15: Sensitivity analysis of hydraulic model to morphological changes and changes in flood inundation extent J.S. Wong 1, J. Freer 1, P.D. Bates 1, & D.A. Sear.](https://reader035.fdocuments.us/reader035/viewer/2022070402/56649f255503460f94c3c6d6/html5/thumbnails/15.jpg)
The EndQuestions and comments are welcome!