The dam was based on sedimented shale and has an internal impervious core of organic clays (grass sods). During renovation work about 70 cm of the surface layer on the old downstream face was removed and replaced by layers of shale material. That was covered with a 10 cm thick layer of topsoil sown with grass seed. On the upstream side, 60 cm was removed and on a 30 cm thick layer of stone chippings a similarly thick protective layer of ballast. The dam was also raised in height by about 1 metre. After removing 90 cm of the old dam crest, a metre-wide toe wall was integrated from the subgrade (Planum). This extends as far as the cohesive earth material of the old dam core.
