Developing sediment and bacteria Total Maximum Daily Loads for the Big Sioux River.

Project Details

City of Sioux Falls Public Works Department

2008 - Present

Sioux Falls, South Dakota


RESPEC developed sediment and bacteria Total Maximum Daily Loads (TMDLs) for the Big Sioux River from Dell Rapids to Brandon, South Dakota. The Big Sioux River Watershed, which is located in southeastern South Dakota, encompasses a mixture of rich agricultural land as well as the densely populated area within and surrounding the city of Sioux Falls.

The assessment was completed in three phases: planning, monitoring, and TMDL development. During the planning phase, available water quality and water quantity data as well as relevant background watershed data were compiled to gain an understanding of the impairment, the waterbodies, and the watershed characteristics.

The subsequent monitoring phase involved implementing an innovative adaptive monitoring plan that filled in historical data gaps. The final phase of the project required calibrating and validating an HSPF watershed model application by using the data gathered in the first two phases to develop the TMDL document and identify scenarios to bring the Big Sioux River into compliance with water quality standards.

After the TMDL was developed, the City of Sioux Falls contracted RESPEC to develop a watershed master plan for the Central Big Sioux River Watershed from the northern Brookings County line to Brandon. A major challenge faced by decision makers within the Central Big Sioux River Watershed has been how to select the best combination of practices to implement from the many options available that results in the most cost-effective, achievable, and practical management strategy possible.

RESPEC developed a watershed-scale, decision-support framework that is based on cost optimization to support government and local watershed planning agencies as they coordinate watershed-scale investments to achieve improvements in water quality. This decision-support framework will assist in revising the TMDL implementation plan, identifying management practices to achieve pollutant reductions under a Municipal Separate Storm Sewer System (MS4) stormwater permit, and developing a phased best management practices (BMP) installation plan that is optimized for cost and water quality effectiveness.

The final portion of the project will develop a pilot water quality trading program for the Central Big Sioux River Watershed. This collaborative effort involves multiple local, state, and federal stakeholders with a vested interest in successfully implementing the program. This watershed contains municipalities with permitted stormwater discharges surrounded by highly productive agricultural lands; therefore, municipalities have the opportunity to contribute resources to help the rural communities implement water quality BMPs, and rural communities can help the municipalities meet the water quality goals identified in their permits at a potentially reduced cost.