Interpreting a Century's Sediment in Redwood Lake

The Redwood River watershed is formed in the glacial sediment of the Des Moines lobe, the parent material for much of the agricultural area of the state. This is also the region that contributes anomalously high concentrations of suspended sediment to Lake Pepin. The sediment is typically 60% or more fine sediment (clay and silt). Although it is usually very tightly packed and cohesive, if it is broken up by surface activities, it is easily removed by water and wind because the particles are so small. Part of the Redwood River occupies the broad, sandy valley of a former glacial stream that was hugging the former ice front. The gradient of the river is unusually low for this reason and did not quickly drain the nearby upland fields, approximately half of which were originally poorly drained. The gradient has been steepened by ditching shorter channels that lead more directly to the Minnesota River, which did not exist when the Redwood was formed. The overall goal of this project was to enable RCRCA staff to effectively manage the current resources of Redwood Lake and Redwood River by: 1) collecting a comprehensive sediment core; 2) extracting the sedimentation history of Redwood Lake using several methods; 3) communicating these results to RCRCA staff and other interested local units of government. Lastly, the immediate goal of making a more informed water management decision regarding the proposed dredging and future Total Maximum Daily Load (TMDL) efforts will be facilitated as part of the study.