A public meeting was held in the village on Wednesday on the risks of flooding from the Verdus. Exchanges between residents and Gemapi were nourished.
Gemapi (Management of aquatic environments and flood prevention) organized a meeting last Wednesday on two aspects: communicating the results of the hydraulic study of the Verdus, and sharing concrete proposals to limit damage in the event of flooding.
A small refreshing stream in summer, the Verdus can turn into a devastating torrent in the event of torrential rain. In the village, the hundred-year flood of 1907 is still present in everyone’s minds. But the overflows of this tributary of the Hérault have been known for more than 700 years. Texts relate a flood as early as 1310. Since then, there have been recorded in 1628, 1723, 1725, 1817 and more recently, in 1976 and 1997. If the last two are not significant, some have been dramatic, causing major damage and victims.
Limit the risk of ice jams
The particularity of Verdus is that it has two sources. One is a karst resurgence at the end of the Infernet cirque, which supplies the town with water. The second is on the front plateau of the Seranne massif, which appears when it rains. Another aspect is that it disappears underground, in tunnels built under the houses. The water flow of the reference flood of 1907 was estimated at 80 m3/s. However, the hydraulic capacities of urban vaults are between 7 and 13 m3/s. We understand in this case that the water can only overflow. Still according to estimates, the next flood could reach between 96.2m3/s on unsaturated land, and 233.3 m3/s on saturated land.
For Gemapi, ice jams constitute a major problem. This accumulation of dead wood blocks waterways. In 1907, stories indicate the formation of jams made up of wood, but especially agricultural and wine-growing equipment, which blocked the underground works, effectively leading to the flooding of the village. To remedy this, two solutions are put forward. Plant hedges of trees and shrubs of suitable species before and after the stadium, to slow down the water and retain floating wood, i.e. “doing with nature”. And install metal stakes approximately 2 meters high and 30 cm in diameter across the minor bed of the Verdus, to filter the floating wood.
Much-discussed proposals
The proposals did not really appeal to those present. Most note that it is necessary to intervene well upstream of the village, by regularly clearing dead trees from the national forest. Some question the relevance of the plantations: “there is a lot of silt and sand, it risks being washed away before it is well rooted.” Hubert asks about the piles, and wonders if the use of concrete to hold them in place will be approved by the authorities. Parking lots are also a black spot, since they are in a flood zone. In addition to preventive measures to evacuate vehicles, stakes would also be installed so that they are not washed away by water.
For residents, consideration must be global. Located in the hollow of the valley, the village is exposed to risks. In 1907, the church, flooded, formed “a sort of sucker” before the water poured violently into the Val de Gellone path. These discussions with residents should have extensions with the various actors responsible for this issue.
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