Withens Clough reservoir is an impounding reservoir in the Pennines. Typical of dams built in the second half of the 19th Century it has a clay core and its upstream face was protected by hand-placed stone pitching. Over the years fines had been washed away from behind the pitching leaving voids.
The solution was to fill the voids with Lean Sand Asphalt (LSA) and overlay the pitching with Open Stone Asphalt (OSA). The water from the moors is quite acidic in the upper catchment resevoirs so the OSA was made with a non-limestone aggregate which still had good adhesion to bitumen.
Dam length 250m, max. slope length 12m
Lean Sand Asphalt placed to fill voids between stone pitching
Withens175mm Open Stone Asphalt placed over upstream face.