MAPPING WATER AND SEDIMENT RETENTION STRUCTURES IN AN AGRICULTURAL AND TOPOGRAPHICALLY VARIABLE WATERSHED IN SOUTHEASTERN MINNESOTA

Winona State University and the Minnesota Pollution Control Agency partnered to map water and sediment retention structures in the Root River Watershed (RRW), a tributary of the Mississippi River in southeastern Minnesota. This inventory study was performed to help inform water quality models and aid decision makers to focus water quality efforts within the basin. The RRW covers 4,300 km² and is dominated by cropland (48%). The landscape is primarily composed of steep bluffs and incised valleys in the central and eastern portions of the watershed and glacial till in the west. The RRW is known for its many high quality trout streams, making water quality a priority conservation concern. In this study, we used airborne lidar derivatives collected in 2008, and corresponding satellite imagery to map two main types of structures throughout the RRW: (1) water and sediment control basins (WASCOBs), and (2) sediment ponds. Both features have similar construction and are designed to limit the downslope flow of water, and trap sediment and associated nutrients in areas of high relief. Once the structures were located, a hydrologically conditioned lidar-derived digital elevation model was used to calculate the contributing area to each structure. These contributing areas are portions of the watershed considered to be treated by these structures. Overall there were more than 7,600 features identified, treating 776 km² (18%) of the RRW. Mapping these conservation practices is a necessary step in continued efforts to improve water quality in a changing climate where event-based precipitation is increasing (https://arcgis.dnr.state.mn.us/ewr/climatetrends/).