 A repair was made by welding oil drums together to form a circular tube, and then grouting the gap around the outside of the tube with concrete, to form a circular concrete pipe.As the steel drums corroded away, it became clear that not all the voids had been filled, and further grouting was carried out in 1977.In the 120 years since its construction, the clay core had consolidated, lowering its top to a point where water could soak through the fill above it, which might cause slippage of the downstream face of the dam.