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The Sustainability and Nitrate Nitrogen Reduction Potential of Two-Stage Agricultural Ditches

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2011 Louisville, Kentucky, August 7-10, 2011  1111833.(doi:10.13031/2013.38178)
Authors:   Jonathan D Witter, Andy D Ward, Jessica L D’Ambrosio, Jennifer L Tank, Sarah Roley, Sara Kallio, Rebecca Kallio
Keywords:   agricultural ditches, benches, flood frequency, annual exceedances, nitrate removal

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. Elimination of wetland storage and installation of subsurface drainage systems and agricultural ditches has caused water to drain from agricultural watersheds at accelerated rates. Agricultural fields, subsurface drainage, and a network of modified headwater systems now dominate the landscape in the Midwest region of the United States. These systems are often the main conduits that export sediment and nutrients downstream, but very little is known about how they function. 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. Most of these innovative systems are located in Indiana, Michigan and Ohio. A procedure for sizing these systems has been developed by the authors. 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. All systems that have been studied have been stable, exhibited small adjustments on the constructed floodplains (benches), and have required little or no maintenance. Also presented is a tool for evaluating the nitrate-nitrogen reduction potential of modifying channels to two-stage geometries that provide connection to floodplains and more bank storage. Preliminary results indicate that benches (small floodplains) should be located at elevations associated with about 25-35% of the 2-year discharge, and nitrate-nitrogen removal in systems with flooded width ratios of 4 to 5 times the bankfull width might be 5-20% of exports from fields if the treatment area (surface of the benches and inset channel) is 1%-2% of the watershed area.

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