Permeable rock dams: Long low but broad rock dams across valleys slow and spread floodwater as well as heal gullies. They are suitable for situations where gently sloping valleys are becoming incised. thus water is drained and lost from the land surrounding the gullies. Each dam is usually between 50 and 300 m in length. The dam wall is usually over 1 m in height within a gully, and between 80 and 150 cm in height elsewhere. The dam wall is also flatter on the downslope side (2:1, 3:1) than on the upslope side (1:1, 1:2), to give better stability to the structure when it is full. A shallow trench for the foundation improves stability and reduces the risk of undermining. Large stones are used on the outer wall and smaller stones internally. The main limitation of permeable rock dams is that they are particularly site-specific, and require considerable quantities of loose stone as well as the provision of transport. (Mekdaschi & Liniger 2013)