Trapezoidal drains are often a source of water quality problems in headwater areas. Bank erosion can be common because the bank heights greatly exceed the bankfull depth. Even where the banks are stable, the channel is typically over-wide which promotes sediment deposition, increases temperatures, and causes turbidity during runoff events. Two-stage and multi-stage design options are effective ways to provide conveyance while improving water quality.
Although Michigan’s 1950s drain code does not address water quality issues, new drain design methods emphasize the reduced long-term maintenance costs as part of a sound engineering design. Ongoing dredging and extensive bank stabilization measures should not be necessary maintenance costs if drains are properly designed. The challenge has been to incorporate the analysis of complex channel morphology, sediment transport and hydraulics in to conventional drainage design. Michigan Sea Grant recently provided funding to develop technical guidelines to describe procedures for more sustainable drain design.