Perforated risers are a type of alternative tile intake that increases sediment trapping efficiency through increased settling time and/or filtering. They can also reduce the velocity of flow into the tile inlet. Isolated surface depressions in agricultural fields are commonly drained with subsurface tile having surface intakes. Open intakes that are flush with the surface of the ground can provide a direct conduit for sediment and nutrients to enter the tile system, which lead to ditches, streams, and rivers.
