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Deliverable 6.3 DEMO Insurance Value Assessment - PART 7: FRANCE - Brague

Abstract : The Brague River basin is a 68 km² catchment located along the French Mediterranean coast between the cities of Cannes and Nice. On 3rd Oct. 2015, the basin was severely hit by an extreme flash flood (time return was over 100 years). The basin very flat lowlands experienced numerous damages and casualties related to this flooding event. The several campsites located in these areas were closed by State decision because of the flood risk but dozens of houses remain at risk. The closing of the campsite opened a window of opportunity to redefine the economic activities of the valley and the river corridor in order to improve its life, landscape and environmental quality and to decrease the flood risk. Within the NAIAD project, several teams of researchers and experts in forest and river management, natural hazards (flood, erosion, wildfire), vulnerability and damage assessment, economy and decision aid gathered to perform an in-depth study of the Brague River catchment. More precisely, we studied its peculiarities, the potential efficacy and efficiency of flood protections measures based on green or grey measures, as well as their co-benefit. NBS flood alleviation strategies studied for the Brague catchment are a combination of both retention measures by small natural retention areas in the upper catchment, along with a widening of the river corridor in the lowlands enhanced by floodplain reconnection. Floodplain works consist in several measures as bed and bridge widening, forest corridor and wetlands restoration, and large woods debris management. They are integrated in a so-called “giving-room-to-the-river” strategy. Two levels of ambition, namely high and very high, are considered as well as a more classical grey scenario based on huge retention dams. This report presents the assessment of the Basin state in term of flood risk and river quality. Total costs of the three protection strategies were evaluated. Damage related to historical events and to theoretical floods with known return period were computed in the current and projects’ situation, thus enabling to compute mean annual avoided damage. The co-benefit related to NBS strategies were also evaluated using two different methods: transfer of values based on a meta-regression-analysis of values provided in other catchments and a contingent valuation performed locally through the interview of more than 400 peoples in the basin. The cost-benefit analysis demonstrates that costs are higher than the main benefit, i.e., avoided damage, but when including co-benefit the balance may reach higher benefits than costs for NBS strategies, though not for the grey solution. It worth being stressed that several intangible criteria, e.g., the improvement of the natural status of the river, are poorly captured by the monetary methods and a complementary multicriteria decision framework was developed to handle both tangible and intangible criteria.
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https://hal.inrae.fr/hal-03027263
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Submitted on : Friday, November 27, 2020 - 9:35:23 AM
Last modification on : Wednesday, November 3, 2021 - 6:51:16 AM
Long-term archiving on: : Sunday, February 28, 2021 - 6:41:41 PM

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Amandine Gnonlonfin, Guillaume Piton, Roxane Marchal, Muhammad Badar Munir, Z.X. Wang, et al.. Deliverable 6.3 DEMO Insurance Value Assessment - PART 7: FRANCE - Brague. 2019, pp.267-428. ⟨hal-03027263⟩

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