Two-stage channel systems: Part 1, a practical approach for sizing agricultural ditches

Abstract:

Outlined is a practical approach to size and modify agricultural drainage channels to two-stage geometry to maintain drainage function and capacity while increasing channel stability. Two-stage channel systems consist of an inset channel and small floodplain (benches) within the ditch confines. The two-stage channel sizing procedure includes nine steps: (1) project identification; (2) data collection; (3) data analysis; (4) hydrologic evaluation; (5) conceptual channel system sizing; (6) project assessment; (7) design and/or final sizing; (8) construction; and (9) monitoring and assessment of performance. Channel width and depth dimensions are determined based on a weight-of-evidence approach that considers geomorphology measurements at the project site and throughout the watershed. The authors have developed spreadsheet tools to aid in evaluating the geomorphology of one and two-stage channels. Constructing a two-stage channel requires more excavation than traditional ditch maintenance, but benefits include improved conveyance capacity, a channel geometry that will be more self-sustaining, and improvement to in-stream habitat.