Due to a number of problems, a dam used to supply drinking water had been in repair since 2011. In order to better understand the dam/foundation contact and mechanical characteristics of this masonry dam, the reservoir was lowered and investigations were conducted between December 2012 and February 2013. They comprised 14 boreholes drilled at the base of the dam (and which penetrated 10 m into the foundations) and which were to be converted into drains to relieve excess pressure. When drilling was completed, the unexpected ingress of water was handled (see 43194) and the reservoir was refilled .

On 9 March, the operator noticed a large flow of water coming out of a drain located at the middle of the dam. On 6 March, the flow had been zero at a height of 114.46 mNGF (base of the dam at 92 mNGF). The flow rose to 136 l/h at height 123.2 (normal reservoir maintained by a weir at 123 mNGF) on 7 March and to 1875 l/h at the same height on 9 March (the day the problem was noticed). The operator lowered the level of the reservoir by opening one of the spillways by 85% and had rounds conducted once every 4 hours to monitor the decrease in the flow rate down to 115.5 mNGF.

On 14 March, video inspection of the boreholes revealed cracks on 10 drains and particularly the presence of a crack having an opening of 36 mm and a depth of 35 cm under the contact area along the axis of the drain that caused the incident. This crack was completely filled in two steps (foundation on 27 March and top portion on 2 April) using an inflatable plug and by injecting a bentonite/cement grout. Between these two steps, the operator closely monitored the piezometry and flow rate in the adjacent drains. As a precaution, the nine others were filled to just below the foundation/masonry contact to prevent the ingress of negative pressure into the body of the dam. Only four healthy drains are still used. The suspicious flow rates disappeared and the dam resumed operation at the end of the repair work.