Author(s): Philippe Gourbesville; Masoud Ghulami

Linked Author(s): Philippe Gourbesville

Keywords: Extreme floods; Deterministic modeling; Aquavar; Alex storm

Abstract: Extreme floods events have been recorded over the last five years in various regions of the world and have demonstrated the vulnerability of our modern environments regarding those specific situations. In most the cases, the extreme flood events and the associated inundations are generated by specific meteorological conditions that combine warm and wet air masses. Under the climate change conditions and the gradual increase the sea temperature especially in close seas like the Mediterranean environment, the possibility to generate conditions for the development of convective and intense events is increasing. Over the last two decade, several events have been recorded along the Mediterranean coastline: Algeria, Spain, Italy and France are some of the recurrent locations for those disasters. The recorde events have generated massive losses that frequently exceed € 1 billion for teh direct damages. This type of situation requests from the managing authorities the capacity to forecast impacts and to define mitigation plans based on the resilience approach. In fact and as demonstrated in many previous cases, most of the structural measures - embankments, dikes, diversion structures, ...- are insufficient and can not cope with the magnitude of the processes. At the same time and despite the large efforts deployed in technical developments, the field data about the flow discharges and the associated processes remain scarce and limited validity. Within this context, a reasonable approach is to develop modeling tools that can produce a meaningful and trustable estimation of the processes. The deterministic hydrological models offer this possibility and can be deployed within decision support systems that are used for flood forecasting and realtime management. In October 2020, the Alex storm has affected the Vésubie catchment in the Var catchment, close to Nice, France. During about 6 hours, a convective and stationary rainfall event has produced more than 500 mm. The massive runoff - above 80% - has generated a massive erosion within the valley and produced tremendous damages estimated to almost € 2 billions. To answer to this challenge, Nice Côte d'Azur Metropolis has decided to develop a DSS based on deterministic modeling tools that can represent the full hydrological behavior of the Var catchment (about 3000 km2) and its various tributaries. The development of the AquaVar system is based on the coupling of 3 models covering hydrology, free surface flows and underground resources. The 3 models are operated in realtime in order to produce, every hour, a forecast for the next 3 days and for all the variables of the different models. The Aquavar was used to simulate the event and the obtained hydrography have been confronted to field observations. The results are very satisfactory and accurate hydrographs can be produced all over the catchment.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221402

Year: 2022