While periodic visual inspections were being conducted on 24 June, the operators found a deficiency along the upstream face of a dam at the junction between two strips of bituminous concrete. This face is not protected with rockfill because the dam’s height opposite the profile in question is no more than 4 m.

Highly localised break-up of the drainage material was found under the porous bituminous face. The dam’s structural strength is not compromised, but exposure of the dam’s body (clay backfill) for too long could ultimately lead to gradual scouring.

These deficiencies cause the filter material located under the bituminous concrete to contract. They are caused by splashing (at a height of 30–40 cm recently) opposite the area made vulnerable (the opening of the joint between the bituminous concrete slabs). This area is not protected with rockfill and is usually not loaded by water because the deficiencies are located between a height of 139.30 mNGF and 140 mNGF.

The reservoir has remained above a height of 139.62 mNGF since 5 May, i.e. one month and a half. Lastly, the strong winds in recent days have affected the structure.

Similar deficiencies have been reported in the past and were caused by weakening of the bituminous joints connecting the slabs of porous bituminous concrete. These joints are periodically patched. Ultimately, it would be wise to protect the areas of the face below 4 m with rockfill.

Each day, the operator has the structure monitored to ensure that the deficiencies do not change substantially. The main reservoir is gradually lowered to reduce the splash-induced loading of the damaged areas of the face.

The repairs planned by operator consist in removing the broken-up bituminous concrete, pouring filter material in the cavity, laying a protective geotextile membrane on the surface, and then laying one or two Reno mattresses (3 × 2 m each) along the current face.

Another similar deficiency was reported on 21 June 2013 at nearby dam (see ARIA 44079).