Why does a constant-angle arch dam work well in a V-shaped valley?

A constant-angle arch dam is highly effective in a V-shaped valley because its design optimizes the transfer of water pressure to the surrounding rock. By curving upstream, the dam acts as a horizontal arch that directs the thrust of the water directly into the valley sides or through concrete abutments.12

The efficiency of this design is rooted in the geometry of the valley. Theoretically, the ideal constant-angle arch—also known as a variable-radius arch dam—utilizes a central angle of 133° of curvature to best distribute these forces. Because the dam's structural integrity depends entirely on the support provided by the abutments, this design is specifically suited for narrow gorges where sound rock is available to withstand the pressure. This curved profile not only provides immense strength but also helps keep the joints in the masonry closed under the weight of the water.12