Help yourself, the State will help you. This maxim applies to the territories of the Landes department covered by the experiment launched in 2021 by the State under the name Mirapi, an acronym for Building back better after floods. “Where the mayors wet their shirts to stimulate the support of residents, the system met the objective”specifies Etienne Capdevielle, head of the river risks department of the Adour Institution, a joint union active in the four departments of the Adour basin (Hautes-Pyrénées, Gers, Landes and Atlantic Pyrénées).
Three pilot territories
Victim of severe damage following the floods of December 2021 and January 2022, the downstream of the Adour basin, in the Landes department, joined the experiment initiated in the valleys of the Alpes-Maritimes following storm Alex . Pas-de-Calais offered a third test territory for Mirapi. Etienne Capdevielle summarizes the objective: “Among seven obligatory axes of action plans for flood prevention, the reduction of vulnerability works poorly. The Barnier fund intervenes little in this axis 5”. Result : properties rebuilt identically are exposed to the reproduction of the same damage during the next flood.
Targeted at mobilizing local stakeholders in municipalities benefiting from a natural disaster decree, the Landes Mirapi resulted in a state subsidy rate equal to 80% of the sums required for diagnostic studies and territorial coordination.. For this last position, the department covered the remaining 20%; he shared the diagnostic costs with the intercommunal authorities. But in the end, the objective of more than 50% of diagnostics, among the homes exposed, only materialized where municipal elected officials were involved in the animation.
Resist or give in
The rate of transformation into works was also established at 50%, out of 300 files. The Adour Institution classifies these operations into two types: resist or yield, in other words install defense works against the least dangerous floods, in particular cofferdams, or adapt the constructions, most often by raising equipment. The experience suffered from the lack of a clearly defined strategy upstream, depending on the degree of vulnerability.
The critical assessment also leads to questions about the scope of the experiment which includes territories covered or not by flood action and prevention plans (Papi). “When these were lacking, it was necessary to base the diagnostics on incomplete hydraulic data,” remarks Etienne Capdevielle. Another limit concerns the scope of the experiment, limited to housing, excluding public facilities and business premises.
Sustain and generalize
Rather satisfied, despite everything, with this device, the Adour Institution willingly responded to the questionnaire of the senatorial mission completed last September on “the challenge of adapting territories to floods”. Enough to bring grist to the mill of rapporteurs Jean-François Rapin and Jean-Yves Roux: the senators from Pas-de-Calais and Alpes de Haute Provence recommend “perpetuating and generalizing the “Mirapi” system, at the end of experimentation in 2026.
Demolition reconstruction: the missing lever
“The regulations adapt neither to our territory nor to our wallet.” This disillusioned reflection from an elected official from the community of communes of Terres de Chalosse (Landes) applies to the maintenance of dikes. The €10 million bill falls outside the investment capacities of the 34 municipalities and 18,000 inhabitants grouped together by the establishment, which has resolved not to classify the 16 km of dikes it inherited, and which protect four villages.
The vulnerability of several homes led the community to take expropriation and demolition measures for five of them, after delicate episodes caused by floods: a broken down motorboat, an overturned kayak… financial impasse is coupled with a lack of legal means: “No long-term land tool allows the monitoring of demolition and reconstruction operations required by this situation,” remarks Etienne Capdevielle, head of river risks at the Adour Institution. This establishment has increased alerts on this subject, aimed at parliamentarians and ministers concerned, since the entry into force of the intermunicipal competence for the management of aquatic environments and flood prevention.
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