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 Miscellaneous

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

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

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

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

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

State of the Art 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 City Flooding

State of the Art 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 Flood propagation

City Flooding WP3_WP.xls 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

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.

Flood Propagation WP3_WP.xls 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

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)

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

MISCELLANEOUS ISSUES Infiltration (cities / valleys) 1D/2D coupling Implicit / explicit Internal BC: Weirs, culverts Wetting - drying Source terms Diffusion / Turbulence Boundary conditions Mass conservation Grid convergence / independence Resolution (10  10 3 )

A simple idea to treat departures from SWE assumptions Step transitions Zhou et al Vertical movement effects Local loss Function of h 1 /  z or h 2 /  z and scaled with kinetic energy

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