Regressive erosion was observed on a dam owned by a private individual. The 300-m long clayey embankment structure displayed a collapse 4 m in diameter and 3 m deep at the drainage pipe location. Clayey blocks split over half the embankment width, and a permanent leak appeared. Due to the high rupture risk, capable of both destroying the lone access road serving a housing tract and washing 335 m³ of sludge from a neighbouring treatment plant into a downstream lake, the Prefecture imposed that same day, by issuance of an order, an emergency lowering of the reservoir level. An opening, 2.4 m high by 1.3 m wide at the bottom, was caused by a backhoe. The ensuing partial drainage had temporarily halted erosion.

On 7 February, the owner was formally notified to continue drainage until reaching the level of the bottom valve base plate after commissioning a technical appraisal by a certified engineer. On 10 April, the hydraulic safety body’s inspectors recorded a dam cresting level 1.38 m above that specified in the building permit and a reservoir water level remaining near 2.7 m. Inspectors recommended digging a channel downstream of the opening and draining at the dam base in order to stabilise it and facilitate monitoring.

This event exposed the lack of formalised operating instructions, and an unfamiliarity with hydraulic operations and deficient facility maintenance, as evidenced by: holes created by burrowing animals, shrubs present at the dam crest and on its sides. Erosion had progressed within a densely-rooted zone. The owner decided on his own to fell the trees rooted in the embankment. In time, such an action could jeopardise the dam once this root network has rotted.