IMPACT PROJECT Flood Propagation Progress Review

1. IMPACT PROJECTFlood PropagationProgress Review 2nd Impact Workshop Mo i Rana, Norway September 12-13, 2002 Francisco Alcrudo University of Zaragoza WP3 Theme Leader

2. Flood Propagation Theme Area Overview • Objectives • Assess the accuracy of flood propagation models • Gain insight into flow conditions in urban flooding escenarios • Adapt and develop techniques better suited for urban flood modelling • Improve flexibility and accuracy of flood wave propagation models in real topographies • Perform case studies on real scenarios and provide measures of uncertainty

3. Flood Propagation Overview • Methodology • Review modelling techniques • Develop specific strategies well suited to severe flooding (especially for urban scenarios) • Perform physical model experiments on: • local flood effects • global flooding conditions • Mathematical model benchmarking & improvement • Case studies: Model testing against real flood events

4. Methodology Minimise uncertainties Model development Experiments & Real Data Model improvement Benchmarking Assessment

5. Flood Propagation Overview • Work Plan • Urban flooding • Test modelling techniques for urban flood propagation • Coarse 2-D models, topography or friction based • 1-D network models • Detailed 2-D modelling • Model experiments on local effects • The Isolated building testcase • Flow patterns around single buildings, wave arrival, propagation and scattering

6. Flood Propagation Overview • Work Plan • Urban flooding (2) • Model experiments on building groupings • The Model city flooding experiment • Flow patterns in a simple model of a city/village • Case study • Model validation against actual city flooding data • To be determined

7. Flood Propagation Overview • Present status • Mathematical models for city fllooding being developed and tested based on: • Representation of bed topography incorporating building elevation • Detailed 2-D modelisation of urban geometry i.e. Meshing of city area taking buildings into account. • Decreased conveyance in urban areas through increased friction levels (to be developed) • 1-D modelisation of the city as a channel network (in development)

8. Flood Propagation Overview • Present status • The isolated building testcase • Data acquisition almost complete (vector field data pending) • Preliminary math model runs accomplished • Benchmarking process ready to be launched Details to be presented in a following presentation

9. Flood Propagation Overview • Present status • The model city flooding experiment • Data acquisition completed and closed • Data selection and sorting almost complete • Preliminary math model runs accomplished • Benchmarking process close to be launched • Case study • To be selected

11. The Model City Flooding Experiment ENEL – CRIS (Milano, Italy) 2nd Impact Workshop Mo i Rana, Norway September 12-13, 2002 F. Alcrudo, University of Zaragoza, WP3 Theme Leader

12. The Model City Flooding Experiment • Performed by ENEL at CRIS facilities in Milano • Test rig comprises a model city area in a larger physical model of a valley (1:100 scale) • Experiments on a simple model city/village heavy flooding scenario without building overtopping • Data produced comprise water levels versus time at 10 different probe locations

18. Only a small portion of the physical model is used • Almost flat bottom

20. Summary of experimental test program(in red chosen for modelling tests) • Bathymetry • Original valley (?) • Simplified (vertical side walls + flattened bed) • Building arrangement • Aligned • Staggered • Flood intensity (peak discharge) • 60 l/s (closer to real flooding conditions ?) • 80 l/s • 100 l/s

21. Bathymetry Original valley  Simplified (vertical side walls) Flat bed Constant slope Interpolated original bed onto test area + Modellers options: Mesh, algorithm ... Inlet boundary conditions Imposed discharge S1 probe reading imposed as total head upsteam Building representation Increased friction level Bed modification Detailed 2-D meshing around buildings 1-D channel flow Summary of Modelling options

22. Input and output data will be distributed/collected via the project Web site Open to all groups/institutions willing to participate Experimental data available from scratch Modellers free to choose testcases to run with several cases common to all (compulsory) Benchmarking program features (preliminary)

23. Preliminary modelling results • Several runs were performed with three different modelling options on the simplified valley with aligned building lay out and 100 l/s peak discharge: • Buildings as a bottom elevation, uniform mean slope, 2884 Unstructured cells, Mannings n=0.0162 • Buildings represented as surrounded by solid walls, uniform mean slope, 2884 Unstructured cells, Mannings n=0.0162 • Buildings as a bottom elevation, 9000 Structured cells, Mannings n=0.015 • No slope (i.e. Flat bed) • Slope interpolated from original bed data

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34. Summary • The City flooding experiment aims at giving insight into the flow behavior in a city like environment under heavy flooding conditions • It offers a broad basis for model benchmarking that must be deliberately limited • Preliminary runs indicate that this type of scenario can be succesfully modelled mathematically with room for accuracy improvement and understanding of flow effects • Final benchmark configuration will be announced in the following weeks