52 - Converting Borrow Pits to Constructed Wetlands to Improve Water Quality in the Middle Missouri River Basin

The U.S. Army Corps of Engineers (USACE) and local partners build and maintain a vast network of levees on U.S. rivers, including the lower Missouri. When levees are repaired, maintained, or realigned, significant amounts of fill material are collected locally from “borrow pits”. In some cases, these borrow pits have been converted to wetlands to enhance habitat. Recently, some agricultural drainage ditches have been re-routed through these created wetlands to enhance water quality (primarily through nutrient removal) before these ditches discharge into the Missouri River. Currently, however, these wetlands are not being designed specifically for nutrient retention, and their water quality benefits have not been quantified. The goal of this research is to determine the potential water quality benefits of routing agricultural drainage through constructed wetlands in the lower Missouri River basin and help improve the design of these nature-based solutions. This research has three tasks: first, we are quantifying the potential water quality benefits of this approach using published data on nutrient removal in constructed wetlands and GIS analysis of potential wetland/drainage ditch locations in the middle Missouri. Second, we are monitoring hydrology and water quality in an existing constructed wetland receiving agricultural runoff to quantify nutrient removal. Finally, we are using the field data to calibrate a numerical model to test different design alternatives and provide recommendations for optimizing nutrient removal in these wetlands. The results of this work will help USACE prioritize locations for constructed wetlands and inform their design to enhance water quality benefits.