JBA Risk Management has produced a footprint of the recent flooding in the French Riviera which benefits from the inclusion of an extra layer (a hazard index). The extra layer takes into account the velocity of the flood waters as well as their depth, allowing for better exposure assessment.
Why did we create a hazard index?
We created the hazard index to give re/insurers a better overview of their risks following or during a flood event, in this case, the flooding in the French Riviera. During surface water flood events, it is the combination of water depth and rapid water flow which causes the major threat to people and property. In order to capture this, JBA has produced a hazard index layer. During the hydraulic modelling simulation, the product of the flood water’s depth and velocity was recorded every one thousandth of a second. The hazard index relates to the highest result from this process and it is classified as low, moderate, significant and extreme.
For a full explanation of the effects associated with each hazard classification and how to calculate it, see Defra’s Flood risks to people - Phase 2: Guidance Document, FD2321_3437_TRP.
The French Riviera event
Extremely heavy rainfall between 2 and 4 October 2015 caused extensive flooding in certain parts of the French Rivera. Rainfall between 1900hrs and 2200hrs on 3 October amounted to 180mm in Cannes, 159mm in Mandelien-la-Napoule, and 100mm in Valbonne (near Biot). The footprint extends north along the French coast from Theoudle-sur-Mer in the south to Nice in the north. Areas particularly badly affected include the streets of Cannes, Antibes, Mandelieu-la-Napoule, Villeneuve-Loubet and Nice. The small coastal River Brague also broke its banks. The Caisse Centrale de Réassurance (CCR) has estimated the insured loss at between €500 and €650 million (CCR, 13 October 2015).
A flood event footprint for this event is now available and is designed for re/insurance companies to examine their aggregate exposure and estimate their past / present accumulation against the event.
The three outputs are the extent, depths and hazard index layers. They are all provided at 10m resolution and in GIS format as follows:
- Raster depth grid – indicating maximum flood depth during the simulation
- Raster hazard index grid – indicating the maximum combined depth and velocity of water during the simulation
- Polygon extent – indicating the maximum flood extent