Watershed Model Evaluation of Agricultural Ditch Drainage Control Structures for Improved Water Quality

Abstract: Open ditch drainage water management (also referred to as controlled drainage) is an old management strategy in agriculture, but recently has gained widespread use because of its potential impacts on nitrate reduction through enhanced denitrification. This is particularly a useful management strategy for the Chesapeake Bay region in Maryland, where nitrogen loads from agriculture has been cited as major components of overall nitrate loads into the Bay. Excess nutrients (especially N & P) entering surface water have shown to increase algal production, causing eutrophication of coastal water ecosystems. Controlled drainage restricts outflow during periods of the year when equipment operations are not required in the field (i.e. winter and midsummer) and to allow natural drainage to occur during the rest of the year, maintaining the water table below the crop root zone. This practice not only restricts the water flows into the Bay, but also allows more denitrification to occur, reducing the level of nitrogen in the ultimate flowing waters into the Bay. A study is undertaken on the Choptank watershed in the Eastern Shore region of Maryland to assess the quantitative role of these control structures in reducing nitrogen loads into surface waters and their overall impact on watershed water quality.