Detailed Numerical Modeling of Flood Flow in Floodplains with Complex Geometry

P Valenta,J Valentová

doi:10.14311/438

Abstract

Numerical modeling of flood flow and the evaluation of flood hazards can be based on various numerical models and modeling techniques. One-dimensional (1D), quasi two-dimensional (1,5 D), two-dimensional (2D) or three-dimensional (3D) variants of numerical models can be used. While 3D models are too demanding to be used for flood flow modeling on personal computers, quasi-2D and 2D models can be more widely used to solve even larger practical problems nowadays. Detailed two-dimensional numerical modeling of flood flow in flooded urbanized areas with complex geometry using the 2D depth averaged model is presented in this paper. The governing equations of the model are expressed with a set of depth averaged Reynolds equations consisting of the continuity equation and two momentum equations for the horizontal velocity components. The eddy viscosity, which influences the horizontal turbulent momentum exchange processes, is modeled with the aid of a depth average version of the two-equation k-e turbulence model. The partial differential equations are solved numerically with a control volume method using fine non-orthogonal curvilinear grids and a non-staggered variable arrangement. The applicability and advantages of this modeling approach for simulating the flood flow in floodplains with complex geometry, and in urban areas, are illustrated by the results of a pilot study in Choceň and Ústí nad Orlicí, towns which were severely affected during the 1997 and 1998 floods in the Czech Republic.

Highlights

Experience resulting from the extreme flood events in theCzech Republic in recent years have stressed the necessity of further development and practical evaluation of suitable methodologies enabling more detailed investigation of flood flow characteristics in domains with very complex geometry and in urbanised areas
These models enable the longitudinal water elevation distribution to be estimated along the river axis for the flood peak discharge, or analyses to be made of flood wave propagation
The system, called PREFAST [3], is oriented towards the use of personal computers, and was programmed as an application based on the ADS (AutoCAD development system) for AutoCAD graphical software

Summary

Introduction

Czech Republic in recent years have stressed the necessity of further development and practical evaluation of suitable methodologies enabling more detailed investigation of flood flow characteristics in domains with very complex geometry and in urbanised areas. The classical approach to the numerical modeling of flood events is based on the application ofvarious types of lD models These models enable the longitudinal water elevation distribution to be estimated along the river axis for the flood peak discharge (steady case calculation), or analyses to be made of flood wave propagation (unsteady simulation). While 3D models are still too demanding to be used for flood flow modeling, quasi-2D and 2D models can nowadays be more widely used to solve larger practical problems, even on personal computers These complex models can provide results of substantially higher quality than those of lD modeling tools. Togetherwith the water elevation distribution, 2D models provide a lot of other detailed information not available in the classical lD numerical model output (flow pattern evaluation, distribution of velocity magnitudes and directions (velocity fields), streamlines, etc.), which is extremely important information for hydraulic and other follow-up (flood risk, flood damage) analyses of flood events. The modeling results for Chocei from this study are used as examples in this paper

Numerical model

Application to case study

Evaluation and utilization of results