FLOOD DISCHARGE AND SEDIMENT TRANSPORT IN THE MENOMINEE RIVER IN JO DAVIESS COUNTY, ILLINOIS

This study investigates the variable discharge, sediment transport, and magnitude of flood events in the Menominee River in northwestern Illinois. The Menominee River flows from the north in Grant County, Wisconsin to the south through Jo Daviess County, Illinois. Much of the watershed area is agricultural, however areas have undergone developmental and land-use changes recently that may affect the flood flashiness of the river. Concerns related to increased flood flashiness of the Menominee River include more frequent flooding events, undercutting of riverbanks, and increased sediment transport from tributaries like this river into the Mississippi River. Increases in impermeable surfaces leads to greater amounts of runoff during precipitation events, which in turn causes flooding and increased sediment washed into the river. Flood events pose risks to cropland and subdivisions that reside near the Menominee River, which are subject to property or crop damage. This study focused on three goals. The first was to determine what sediment sizes the river is capable of moving downstream during events with increased of stream discharge and use the sediments moved as a method to estimate flood discharge in an ungauged river. The second goal was to evaluate the accuracy of these discharge calculations, by comparing discharges to a comparable river that is monitored with a gauging station. The final goal of the project was to address how varying weather patterns affect the discharge of the Menominee River and can increase the flashiness, resulting in clast movement. During the study period, the Menominee River flooded during two major rain events which transported the largest sediments observed in the riverbed. Estimates of discharges based on the D95 sized sediments resulted in discharges similar to the comparison river system. However, estimates of discharge using Manning’s equation were substantially lower. Additionally, in our study of discharge from upstream to downstream, we observed that during baseflow and highwater events, this river was losing discharge due to underlying karst bedrock features. Future work could include analyses of land cover data and precipitation models to constrain the impacts of land use and climate change on the flood events along this river.