Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Civil Engineering (Environmental Engineering)
Chris R Rehmann
In the U.S. Midwest, agricultural subsurface drainage, or tile, is commonly used to improve crop production; however, because nitrate is easily leached, tile drainage typically has high nitrate loads. Nitrate exported via tile drainage impairs water quality and can be reduced by implementing conservation practices, such as saturated riparian buffers (SRBs). SRBs function by redistributing the nitrate-rich tile drainage through the soil of a vegetated buffer zone via a perforated distribution pipe, facilitating denitrification and plant uptake. Because this practice is relatively new, there has been limited research into how SRBs function and how to effectively design them. In the first study, an equation for the optimal SRB width was derived by applying a mass balance to maximize the nitrate removal effectiveness. The optimal width is smaller than the current width at each of the six study sites, and two sites have optimal widths that are smaller than the minimum width specified in the current NRCS design standards. In the second study, a three-dimensional, finite-difference groundwater flow model was developed to better understand how groundwater flows in SRBs. Because flow is one-dimensional in most of the SRB, assuming one-dimensional groundwater flow in an SRB is reasonable. The median error associated with computing the travel time using a one-dimensional approximation is 11.6%. The flow path of the tile drainage toward the stream depends on where it exits the distribution pipe; the flow that exits through the top perforations at the end of the distribution pipe has the greatest potential for nitrate removal. Better understanding how groundwater flows in an SRB is an important step toward improving design to more effectively improve water quality.
Andrea Rae McEachran
McEachran, Andrea Rae, "Improving the design of saturated riparian buffers for removing nitrate from subsurface drainage" (2020). Graduate Theses and Dissertations. 18185.