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Title: Watershed SWAT Evaluation of Control Drainage Structure in Ditch management for Improved Water Quality

Author
item Sadeghi, Ali
item McCarty, Gregory
item MORIASI, DANIEL - USDA-ARS-GRL
item Hively, Wells - Dean

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: 2/5/2008
Publication Date: 3/29/2008
Citation: Sadeghi, A.M., McCarty, G.W., Moriasi, D., Hively, W.D. 2008. Watershed SWAT evaluation of control drainage structure in ditch management for improved water quality. In: Proceedings of the American Society of Agricultural and Biological Engineering International Conference, March 29-April 3, 2008, Concepcion, Chile. 2008 CDROM.

Interpretive Summary:

Technical Abstract: In the Eastern Shore region of Maryland, extensive land areas used for crop production require drainage systems either as tile drains or open ditches. Increased nutrient loading of the Chesapeake Bay is being partly linked to the prevalence of ditch drainage in the region. Studies have shown that annually an average of 6% of nitrogen applied to agricultural fields can be transported as nitrate in drainage water to receiving surface waters. One of the best management practices (BMPs) being used in these open ditches is the installation of a water control structures at drainage outlets. These control structures can be used to control water levels in agricultural fields to reduce water flow from the field and promote nitrate nitrogen removal processes such as denitrification. A typical management schedule is to increase water elevation at the outlet such that the water table is just below the root zone during the growing season and lower water elevation to or near the bottom of the drainage ditch (free drainage) during planting and harvesting operations. Our research site, Choptank River basin located within the Eastern Shore region, also consisted of extensive open ditches. We have instrumented four control drainage structures with V notch weirs along with a number of shallow monitoring wells both upstream and downstream of the structures. Information from this research site will be used to validate newly modified SWAT control drainage component to assess the effectiveness of this BMP for water quality evaluation at the watershed level. Preliminary findings show reduction of nitrate in drainage water from 15% to 30%. Findings from this study will provide quantitative efficiencies for both water and nitrate reductions and better management strategies for more efficient use of these control drainage BMPs.