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OVERVIEW ON FLOOD PROPAGATION AREA WORK

OVERVIEW ON FLOOD PROPAGATION AREA WORK. First Impact Workshop Wallingford, UK May 16-17, 2002. F. Alcrudo University of Zaragoza WP3 Coordinator. Overview. Objectives Methodology Deliverables State of the Art Work plan Urban flooding Flood propagation in natural topographies

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OVERVIEW ON FLOOD PROPAGATION AREA WORK

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  1. OVERVIEW ONFLOOD PROPAGATIONAREA WORK First Impact Workshop Wallingford, UK May 16-17, 2002 F. Alcrudo University of Zaragoza WP3 Coordinator

  2. Overview • Objectives • Methodology • Deliverables • State of the Art • Work plan • Urban flooding • Flood propagation in natural topographies • Miscellaneous

  3. Objectives • To assess the accuracy of present models of flood propagation (uncertainties) • To gain insight on flow conditions in urban flooding escenarios • 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

  4. Methodology • Review current modelling techniques • Develop specific strategies well suited to severe flooding (esp. urban flooding) & address key modelling issues • Perform physical model experiments on: • local flood effects • global flooding conditions • Mathematical model benchmarking & improvement • Case studies: Model testing against actual documented flood events

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

  6. Methodology • Experiments • Designed such as to minimise uncertainties • Simple topography • Simple boundary conditions • Roughnesses • Benchmarking • Test/study one effect per benchmark

  7. Deliverables • Guidance on phenomena likely to occur in urban areas under severe flooding • Estrategies/Techniques for best predicting flooding conditions (water levels, duration, discharges) • Model performance assesment (level of accuracy available) • Improvement of models  bringing models closer to reality

  8. State of the Art City Flooding • Modelling of extreme, catastrophic city flooding scarcely documented • Lack of specific extreme city flooding simulations & methods • Storm sewer simulations not pertinent • It is expected that flood propagation models can be applied to city flooding

  9. State of the Art Flood propagation • Models based on Shallow Water equations (for extreme flood waves – inertia dominated) • Flat pond & diffusion models when important storage effects & low flow velocities (diffusion dominated) • 1-D and 2-D models available (practical 3-D models still far ahead) • Wetting & drying, resistance, source terms, singularities, BC, still areas of active research

  10. City Flooding WP3_WP.xls • Development of specific techniques for urban flood modelling (UZ) • Coarse 2-D models, topography or friction based • 1-D network models • Detailed 2-D modelling • Model experiments on local effects (UCL) • Flow patterns in streets, crossings, squares • Wave arrival, propagation and scattering

  11. City Flooding • Experiments on a model city/village flooding (ENEL) • Set up a model city in a physical model of a valley • Timing and water levels data • Case study (All) • Identify, select and collect data from an actual city flooding event Candidates: Nîmes, Florence, Algemesí, Fréjus • Testing of mathematical models against collected data.

  12. Flood Propagation WP3_WP.xls • Revisit & address key issues relevant to flood propagation modelling (UZ, CEMA) • Discretisation of source terms: bed slope & resistence • Simulation of drying and wettting effects • Model inclusion of singularities (math. formulation, discretisation): bed discontinuities (drops, banks) hydraulic structures • Mesh convergence and indepence • Coupling of 1-D and 2-D models

  13. Flood Propagation • Model experiments on key issues of flood propagation (UCL) • Flood wave propagation over a hill model • Wetting and drying • Experiments on flood propagation over a physical model of a valley (ENEL) • Testing of mathematical models against benchmark data (UZ, UCL)

  14. Flood Propagation • Case Study selection (All) • Collection of data from an actual flood wave propagation over real terrain Norwegian experiment, Tous, Malpasset, Aznalcóllar • Model testing versus actual flooding data (All) • Assesment of model performance against data • Comparison of old/newly developed strategies

  15. Infiltration (cities / valleys) 1D/2D coupling Implicit / explicit Internal BC: Weirs, culverts Wetting - drying Source terms MISCELLANEOUS ISSUES • Diffusion / Turbulence • Boundary conditions • Mass conservation • Grid convergence / independence • Resolution (10  103 )

  16. A simple idea to treat departures from SWE assumptions • Step transitions • Zhou et al. 2001 • Vertical movement effects • Local loss • Function of h1/Dz or h2/Dz • and scaled with kinetic energy

  17. Departure from SWE assumptions • 20 different cases • Godunov-like method ? • Embed the Riemann solution + Losses • Into the numerical scheme

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