Climate change, land clearing, and artificial drainage have increased the Minnesota River Basin's (MRB) stream flows, enhancing erosion of channel banks and bluffs. Accelerated erosion has increased sediment loads and sedimentation rates downstream. High flows could be reduced through increased water storage (e.g., wetlands or detention basins), but quantifying the effectiveness of such a strategy remains a challenge. We used the Soil and Water Assessment Tool (SWAT) to simulate changes in river discharge from various water retention site (WRS) implementation scenarios in the Le Sueur watershed, a tributary basin to the MRB. We also show how high flow attenuation can address turbidity issues by quantifying the impact on near-channel sediment loading in the watershed's incised reaches. WRS placement in the watershed, hydraulic conductivity (K), and design depth were varied across 135 simulations. The dominant control on site performance is K, with greater flow reductions allowed by higher seepage rates and less frequent overflowing. Deeper design depths enhance flow reductions from sites with low K values. Differences between WRS placement scenarios are slight, suggesting that site placement is not a first-order control on overall performance in this watershed. Flow reductions exhibit power-law scaling with exceedance probability, enabling us to create generalized relationships between WRS extent and flow reductions that accurately reproduce our SWAT results and allow for more rapid evaluation of future scenarios. Overall, we show that increasing water storage within the Le Sueur watershed can be an effective management option for high flow and sediment load reduction.
Bibliographical noteFunding Information:
Funding: This research was funded by the Minnesota Department of Agriculture with support from the Clean Water Legacy Fund, two grants from the National Science Foundation (EAR-1209402 and ENG-1209445) through the Water and Sustainability and Climate Initiative, the US Department of Agriculture NRCS (69-3A75-14-269), the Minnesota Agricultural Water Resources Center, and a 319 Grant from the US Environmental Protection agency via the Minnesota Pollution Control Agency (70549).
Acknowledgments: This research was supported by the Utah Agricultural Experiment Station, Utah State University, and approved as journal paper number 9113. Guidance was also provided by Peter Wilcock and Benjamin Hobbs.
- Le Sueur
- Soil and water assessment tool