Integral porosity shallow water model at district scale - Case study in Nice

¹ Chair of Water Resources Management and Modeling of Hydrosystems, Technische Universität Berlin, Germany
² RIKEN Advanced Institute for Computational Science, Japan
³ University of Nice Sophia Antipolis, France
⁴ Department of Engineering, University of Cambridge, UK
⁵ Research Center for Urban Safety and Security, Kobe University, Japan

^* e-mail: ilhan.oezgen@wahyd.tu-berlin.de

Abstract

After three hours of intense rainfall, the city of Nice was flash flooded on October 3, 2015, resulting in casualties and severe damages in property. This study presents a porous shallow water-model based numerical simulation of the flash flood event in a district of Nice, and compares the results with a high-resolution conventional shallow water model. This contribution aims to discuss practical aspects of applying a porous shallow water model to a real world case. The porous shallow water model is an integral porosity-type shallow water model. It uses unstructured triangular meshes. The conventional shallow water model is a distributed memory parallelized high-performance computing code, that uses a uniform Cartesian grid. The study site is an approximately 5 km2 spanning district of the city of Nice, France. Topography information is available in a 1m resolution and in addition, the available digital elevation model includes inframetric structures such as walls and small bridges. In the presentation of the case study, challenges of the pre-processing step of the integral porosity shallow water model are addressed. Notably, a method to semi-automatically generate “good” triangular meshes using the open-source geoinformation system QGIS and the mesh generator Gmsh is presented. During the post-processing step, the results of the porous model are mapped back onto the high-resolution topography to make the results more meaningful. The agreement between the high-resolution reference solution and the porous model results are poor. A speed up of about 10 to 15 was observed for the present case.