A decade later: the establishment, channel evolution, and stability of innovative two-stage agricultural ditches in the midwest region of the united states

Much of the landscape in the Midwest region of the United States has been converted to agricultural use and with this conversion has come greatly altered hydrologic functioning. The elimination of wetland storage and installation of subsurface drainage systems and agricultural ditches has caused water to drain from agricultural watersheds at greatly accelerated rates. In some cases, these hydrologic alterations have led to severe water quality problems, including stream bank erosion, sedimentation, and inadequate processing of nutrients, each of which pose dire consequences for aquatic biota. Research by the authors has led to the modification of some trapezoidal agricultural ditches to two-stage geometries that are sized based on geomorphic concepts. A procedure for sizing these systems has been developed by the authors. Most of these innovative systems are located in Indiana, Michigan and Ohio. The main objective of the paper is to present details on how these systems have evolved since construction. The paper addresses issues that require further consideration. Channel evolution, determined by the assessment and analysis of physical condition, includes tracking changes in form by repeated surveys of channel dimension, pattern and profile. Pre-construction and post-construction properties are compared. Channel dimensions are also compared to regional curves. Analysis will include computing the hydrology and hydraulics for the range of recurrence intervals using the computer simulation models HEC-HMS, HEC GeoHMS, and HEC-RAS. All systems that have been studied have been stable, exhibited small adjustments on the constructed floodplains (benches), and have required little or no maintenance.