Changes

These The sides of the check dam must be higher than the centre so that water is always directed over the centre of the dam (this avoids the dam being outflanked by the flow). The dams can be made of temporary or permanent materials in natural gullies in the land surface. Materials used are concrete, earth, vegetation, stone and brushwood. Where earth is used, erosion or destruction of the structure needs to be avoided – to do this, a concrete spillway is often constructed. As they use the existing drainage system, no design of trench is needed (as with contour trenches). Do not construct check dams in watercourses or permanently flowing streams without specific design (because of possible restrictions to fish passage). ==Maintenance==Check dams should be inspected regularly for sediment accumulation after each significant rainfall. Sediment should be removed when it reaches one-half of the original height or before. Check to ensure that the flow is over the centre of the dam and not either under or around the dam. Check that there is no erosion at the outfall.