A flash flood hazard assessment in dry valleys (northern France) by cellular automata modelling

Johnny Douvinet,Daniel Delahaye,Marco J Van De Wiel,Etienne Cossart

doi:10.1007/s11069-014-1470-3

Abstract

This paper presents an application of a cellular automaton-based runoff model (RUICELLS) to a series of small dry valleys in the Seine-Maritime department, northern France, to better assess their susceptibility to flash flood. These muddy floods shortly follow high rainfall (50–100 mm in less than 6 h) and occur in very small areas (\20 km 2). A surge generally rushes down through the main valley just a few minutes after rains have peaked. Previous events (n = 69, in the period 1983–2005) have occasionally threatened human lives and have caused significant damage to property and infrastructure. Nonetheless , given the variation among the valleys and the infrequency of events, these floods have not been numerous enough to permit a statistical analysis. Instead, we numerically simulate the possible future flash floods using RUICELLS, a cellular automaton model driven by a set of three deterministic hydrological rules. Simulations have been conducted for 148 basins, each subject to 16 different rainfall scenarios (2.368 simulations in total) to (1) estimate the peak flow discharges (Q), the specific peak flows (Q s), and the lag times (T) of the flash floods and (2) detect the critical rainfall intensities that would trigger warnings and increased vigilance. Our simulations indicate that the number of basins susceptible to flash flooding greatly increases with the higher rainfall intensity, the distribution of sensitive crops (sugar beet, corn, maize, and flax) and the basin morphology. Several small basins could also induce by convergence a bigger flood in the downstream humid valleys. The location of the highest simulated discharges is aligned with observed events, and this comparison provides an evaluation of the modelling performance and of the credibility of the results.

Highlights

Flash floods in northern France (Masson 1987; Devaud 1995; Merle et al 2001; ArnaudFassetta et al 2011) induce serious risk conditions on populated outlets, especially in the Seine-Maritime department (Delahaye et al 2001; Douvinet 2008, 2014; Douvinet et al 2013)
This paper presents an application of a cellular automaton-based run-off model (RUICELLS) to a series of small dry valleys in the Seine-Maritime department, northern France, to better assess their susceptibility to flash flood
Simulations are analyzed for three main variables that characterize basin susceptibility of flash flooding: peak flow discharge (Q), peak unit discharge (Qs), calculated by dividing Q by the basin size and lag time (T), i.e. the duration between the beginning of rainfall and the onset of peak discharge, for each of the 148 studied basins and each of the 16 rainfall intensities

Summary

Introduction

Flash floods in northern France (Masson 1987; Devaud 1995; Merle et al 2001; ArnaudFassetta et al 2011) induce serious risk conditions on populated outlets, especially in the Seine-Maritime department (Delahaye et al 2001; Douvinet 2008, 2014; Douvinet et al 2013) These hazards are generated shortly after rains ranging from 50 to 100 mm in less than 6 h and occur in small dry valleys (\20 km). The latter occur in basins with higher slope gradients, larger basin area (ranging from 50 to 300 km2) and are typically associated with higher rainfall intensities ( et al 2001; Collier and Fox 2003; Reid 2004; Barrera et al 2006; Ruin et al 2007; Ortega and Heydt 2009; Gaume et al 2009; Morin et al 2009; Marchi et al 2010)

Methods

Results

Discussion

Conclusion