Water Storage in the Minnesota River Basin River Flow Reduction Modeling and Recommendations for Goal-Setting: Report 3A/3B

The Minnesota River Basin Sediment Reduction Strategy has established a goal to reduce sediment in the Minnesota River by 50 percent by 2030. The strategy also suggested flow reduction targets of 25% (reduce peak flow by 25% and duration of peak flow by 25%). Conservation practices that mitigate sediment erosion, such as reduced tillage and cover crops, support progress towards the sediment reduction target. However, recent studies have shown that a larger source of sediment loading is a result of erosion of near-channel sources during high-flow periods. Water storage practices can further enhance progress towards Sediment Reduction Strategy goals by detaining or retaining water during critical flows to reduce sediment scouring and transport. Water storage can also be beneficial for reducing nutrient loss to waters, reducing floods, meeting local water management goals, and more. The broader objective of this project seeks to identify and evaluate the benefits of potential water storage opportunities in the Minnesota River Basin (MRB). The goals of this phase of the MRB water storage project were to (1) modify the Hydrologic Simulation in FORTRAN (HSPF) models for the Cottonwood, Le Sueur, and Watonwan subbasins to represent the impacts of six water storage practices, (2) estimate the typical runoff amounts that can be stored by the six practices in the three subbasins and the river flow reductions that result from such storage, (3) develop recommendations and considerations for water resources managers for setting realistic water storage goals and river flow reduction goals at the subbasin-scale and the MRB-scale, (4) provide examples of water storage amounts and river reductions that are achievable in each subbasin in the MRB, and (5) recommend how river flow reduction and water storage goals can be improved with additional HSPF modeling.