The Development, Function and Benefits of Fluvial Benches in Agricultural Drainage Ditches in Ohio

Rural watersheds in the Midwest Region of the United States are dominated by agricultural land uses that often incorporate subsurface drainage improvements. Subsurface drainage systems discharge into headwater channels that have been deepened and straightened to facilitate the flow of water from drainage outlets and to lessen flooding of agricultural fields. Natural adjustments, within these large modified or constructed ditch, often establish fluvial channels, henceforth called inset channels. These inset channels have small stable floodplains, called benches, that form by vertical accretions of deposited sediment that then vegetate with grasses (Figure 1). However, rarely do these systems exhibit out of bank flows onto a broad floodplain and, in many cases, when stable benches form they are periodically removed by human maintenance activities. Channel maintenance is performed to remove woody vegetation and deposited sediment, stabilize bank slopes, and to address toe scour problems. These routine maintenance activities are costly, disrupt the existing ecology, and sometimes adversely impact water quality. This manuscript provides a summary of two recently completed doctoral studies and several manuscripts based on these studies. The goals in reporting this information are to inform the reader on: (1) the factors that influence the establishment of inset channels and benches in agricultural ditches; (2) a method for modifying an agricultural ditch to a two stage geometry as an alternative to conventional drainage; and (3) research that is being conducted to evaluate the water quality and ecological benefits of ditches with an inset channel and benches.