Arch Dams consist of a single curved concrete wall. They are curved in the shape of an arch, with its convexity towards the upstream side. The arch effect allows the water pressure and other forces to be transferred to the abutments. The cross-section of an arch dam is approximately triangular like a gravity dam but is comparatively thinner. Arch Dams are quite suitable for narrow, steep-sided valleys. Strong rock masses in the slopes are necessary to resist the forces transferred by the arch action.