Natassja Sook, “Heavy Rain Events Drive Sediment Pollution Loads in the Milwaukee River”
Mentors: Val Klump & Jessie Grow, Freshwater Sciences
Like many other urban watersheds, the Milwaukee River watershed is impaired and one of the main concerns is the delivery of high quantities of suspended sediment in the river and ultimately into the harbor and the lake. Sources include agricultural runoff, urban stormwater, and combined sewer overflows which result in degraded water quality, bacterial contamination, sediments in-filling the harbor, an unattractive, murky appearance, and river plumes. This project’s goal is to determine the timing and source of the sediments transported in this system. More specifically, my study focuses on understanding what fraction of the total suspended solids (TSS) load in the Milwaukee River occurs during large precipitation “events.” The MMSD Cherry Street turbidity data was used as well as the USGS flow data to look at the combination of discharge and precipitation to get a better understanding of the timing of these sediment additions into the river and their flux downstream. Through this study we found that the majority of TSS in the Milwaukee River occur during wet weather “events.” This means that to limit sediment levels, water quality managers should focus on controlling peak concentrations during wet weather. In addition to flow and TSS load data, sediment samples were collected along the Milwaukee River watershed and throughout the main stem of the river. In the future, we will continue to characterize these samples, using elemental, isotopic, and radioisotopic tracers to determine the age and source of these inputs. Overall this project helps us to determine how to reduce the sediment runoff entering the Milwaukee River, and identify actions needed for improving and maintaining the health of the Milwaukee River watershed.