Drainage channels are traditionally designed using a trapezoidal cross-section to serve as an outlet for subsurface tiles draining adjacent lands and to move that water downstream efficiently. Trapezoidal drainage channels lack floodplains and can experience bank erosion and excessive buildup of sediments as the channel attempts to regain a balance between sediment transport and supply (Figure 1). Two-stage channels are designed take advantage of the benefits of active floodplains. At the first stage, a small channel allows for enough velocity to minimize sediment deposition during normal or lower flows. The second stage provides bank stability, an outlet for subsurface drains, and capacity to drain the flow from larger storm events (Figure 2). This approach can be considered one type of in-stream best management practice and, if properly designed, should require little or no maintenance.
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University of Wisconsin Extension (Madison, Wisconsin)
University of Wisconsin Extension