Spatially distributed flood forecasting in flash flood prone areas: Application to road network supervision in Southern France

Abstract

Accurate flood forecasts are critical to an efficient flood event management strategy. Until now, hydro-meteorological forecasts have mainly been used to establish early-warnings in France (meteorological and flood vigilance maps) or over the world (flash-flood guidances). These forecasts are typically limited either to the main streams covered by the flood forecasting services or to specific watersheds with specific assets like check dams, which in most cases are well gauged river sections, thus leaving aside large parts of the territory. This paper presents a distributed hydro-meteorological forecasting approach, which makes use of the high spatial and temporal resolution rainfall estimates that are now available, to provide information at ungauged sites.The proposed system intended to detect road inundation risks had initially been developed and tested in areas of limited size. This paper presents the extension of such a system to an entire region (i.e. the Gard region in Southern France), including over 2,000 crossing points between rivers and roads and its validation with respect to a large data set of actual reported road * Corresponding author. i.e. pre-positioning of rescue equipment, interruption of the traffic on the exposed roads and determination of safe access or evacuation routes. Moreover, beyond the specific application to the supervision of a road network, the research undertaken herein also provides also results for the performance of hydro-meteorological forecasts on ungauged headwaters.

MobRISK: a model for assessing the exposure of road users to flash flood events

“…The "weak" s 1 , "medium" s 2 and "high" s 3 susceptibility classes have an empirical flooding return period smaller than 1 year in 20, 35 and 65 % of their points respectively. Based on road cut classification, Naulin et al (2013) developed a method to compute a probability of submersion for each road cut by combining the susceptibility classes and simulated stream discharges at the section of river responsible for the road cut. Therefore, an interval of probability of submersion is assigned to every road cut for each combination susceptibility class and return period of stream discharge.…”

“…The risk of road flooding is computed by combining susceptibility to flooding on a given road with simulated stream discharge of the corresponding river segment (Versini et al, 2010b). Naulin et al (2013) extended the road flooding forecasting tool to the entire Gard region and proposed a method for allocating probabilities of flooding to road-river intersections (called "road cuts") depending on return periods of stream discharges . Versini and Naulin's studies contribute to better forecasting the chance of road flooding, hence providing a strong base to further analyze the impact of road users' exposure.…”

The challenge of forecasting impacts of flash floods: test of a simplified hydraulic approach and validation based on insurance claim data

“…The first approaches developed, namely the flash flood guidance, were based on a preliminary analysis of rainfall volumes generating bankfull flow, for several durations and initial soil moisture conditions (Georgakakos, 2006;Norbiato et al, 2008). More recent approaches aimed to directly forecast peak discharges at ungauged locations based on highly distributed hydrological models and radar based quantitative precipitation estimates (QPEs) or nowcasts (Cole and Moore, 2009;Rozalis et al, 2010;Wang et al, 2011;Javelle et al, 2014;Gourley et al, 2014Gourley et al, , 2017Naulin et al, 2013;Versini et al, 2014). Such models provide indications of possible flood magnitudes, but are still rarely designed to directly evaluate the possible associated impacts.…”

Improvement of resilience of urban areas by integrating social perception in flash-flood risk management

“…The flow peaks are reached within a few hours, thus giving little or no advance warning to mitigate flood damage (Borga et al, 2007;Borga et al, 2008). This hydrological response leads to the occurrence of a typology of floods known as flash floods because of their rapid onset, i.e., within six hours of rainfall (Ogden et al, 2000;Delrieu et al, 2005;Marchi et al, 2010;Hapuarachchi et al, 2011;Naulin et al, 2013;Ballesteros-Canovas et al, 2015).…”