What are these yellow “Notice of public inquiry” signs? They have recently flourished everywhere in several communes of Châtelleraudais. This is a large-scale public inquiry concerning the revision of the flood risk prevention plan (PPRI) for the Vienne valley (downstream).
Who is concerned ? Twelve municipalities in Châtelleraudais, crossed by the waters of the Vienne, are concerned by this public inquiry: Châtellerault (1), Port-de-Piles, Les Ormes, Dangé-Saint-Romain, Vaux-sur-Vienne, Ingrandes, Antran, Cenon-sur-Vienne, Availles-en-Châtellerault, Vouneuil-sur-Vienne, Bonneuil-Matours and Bellefonds.
What is the purpose of a PPRI? Its purpose is not so much to prevent flooding as to limit their material and human consequences. The PPRI is a mandatory planning document (for municipalities affected by these risks) which must be approved by the prefect before coming into force.
Why revise the PPRI? The updating of data and knowledge, the repetition of flood episodes that portend climate change. In short, a current topic. This is evidenced by the sudden floods and floods of March 31, 2024 which affected the department including Châtellerault (a peak at 5.32 m) and which highlighted the difficulty of predicting the vagaries of the Vienne.
This plan aims to reduce the territory’s vulnerability to flooding and to define construction rules based on the risk of flooding.
© (Photo NR-CP, Denys Frétier)
What should you do ? This public inquiry allows you to share your observations, questions or even concerns. To do this, you are invited, until Thursday May 30, 2024, to go to the town hall of your home (in the presence or not of the investigating commissioner) to consult the files of the new PPRI and thus give your opinions on the dedicated registers ( 2).
On March 31, 2024, the Vienne rose to 5.32 m. One meter less than the 100-year flood (reference) of March 31, 1913 (6.35 m).
© (Photo NR-CP, Denys Frétier)
What will this PPRI change for the population? Above all, it is about reducing the risks for people and property, “by determining more or less floodable areas and therefore the possibilities or not of urbanization”. In other words, reduce the territory’s vulnerability to flooding and (re)define construction rules based on risk.
what’s this regulatory zoning? There are four zones defined according to flood “hazards” ranging from “moderate” to “very strong”: red (fields of flood expansion: “Inconstructibility is the general rule”), purple (high risk of flooding: “Urban renewal is only possible”), orange (strong hazard in urban centers: “Urban renewal and new construction with reduction of vulnerability are possible”) and blue (low risk of flooding: “Development is not prohibited but regulated”).
La Vienne at 6.09 m on January 7, 1994 in the Grand-rue de Châteauneuf…
© (Photo archives NR-CP)
… and at 5.32 m in this same Grand-rue de Châteauneuf, 30 years later on March 31, 2024. We will notice in passing, the difference in stores open…
© (Photo archives NR-CP, Laurent Gaudens)
What’s new about the PPRI? The most exposed residents will have to carry out safety work within five years. It is a question of “the prescription of a diagnosis and the carrying out of the corresponding work for both homes and economic premises within a maximum period of five years following approval of the plan”.
An effective plan to tame Vienna? According to a study by the Central Reinsurance Fund (CCR) from October 2023, the PPRI (3) reduces by 40% the proportion of housing suffering damage in municipalities that have them.
(1) In 2016, Châtellerault implemented the first local flood risk management strategy (SLGRI) validated in France by prefectural decree.
(3) At the same time, a second public inquiry, this time for the development of the PPRI for the Clain downstream valley, is open from Monday April 29 to Wednesday June 5. Four municipalities concerned: Cenon-sur-Vienne, Châtellerault, Naintré and Vouneuil-sur-Vienne.
benchmarks: the top 10 floods
Here are the top 10 of the most significant flood episodes observed in Châtellerault since the 17the century (the normal dimension is 1.50 m): February 1698: 6.77 m; March 1913: 6.35 m (reference flood) (1); July 1792: 6.33 m; December 1944: 6.28 m; January 1962: 6.25 m; March 1923: 6.20 m; January 1994: 6.09 m; April 1962: 6.05 m; November 1840: 6.02 m and January 1982: 6 m.
Note that these floods linked to the overflow of the Vienne occur mainly during the spring period (between March and April) and during the winter period (between November and February).
(1) The 100-year flood has a probability of occurring one in a hundred times each year.
“Improve Vigicrues forecasts”
Two observations in particular reached the Vienne prefecture. One comes from the Vienne Nature association. Its president, Michel Levasseur points out the absence of several documents in the PPRI file posted online. It is missing, according to him, “the explanatory note of the color codes used on the maps” and “the nature of the classification, prohibited construction, house or building to be protected”. And to wonder about the new town planning rules imposed by this PPRI (annexed to the local town planning plan): “How will the residents concerned be informed of the change in the rules of construction ? »
The second letter concerns a couple from the Vienne river aged 74 and 72 who discuss the “surprise” flood of March 31: “We have lived in a flood zone since 2011 […]. Saturday the 30th, we set off on a trip, the forecasts not allowing us to expect such a climb! These exceptional floods may well no longer be so. Obviously, we need to review the procedures for preventing and treating these crises. »
The couple calls the authorities: “ This time Vigicrues’ forecasts were not good: is it possible to improve them? […] Who are at risk of having to be rehoused? Couldn’t we benefit from help (based on income) to implement suitable solutions? »
