Streamflow Modeling of Miller Creek, Duluth, Minnesota

A Storm Water Management Model (SWMM) was constructed to model flow in the Miller Creek watershed using readily available data. Miller Creek is an urban trout stream flowing through Duluth/Hermantown, Minnesota. Miller Creek starts near the Duluth Airport, flows south through Duluth and discharges into the St. Louis River estuary of Lake Superior. In 2008 and near its mouth, Miller Creek had a mean annual flow of 9.1 cfs, a recorded peak flow of 291 cfs, and base flow of less than 0.1 cfs. Despite extensive commercial and some residential development in the Miller Creek watershed over the past 30 years, Miller Creek has still a naturally reproducing Brook Trout fishery. The urban development included the filling of wetlands to create parking lots, the removal of riparian tree cover, and the introduction of storm water runoff from impervious surfaces (SSWCD, 2001). These changes have lead to elevated stream temperatures, and consequently Miller Creek was put on the list of impaired waters by the Minnesota Pollution Control Agency (MPCA) in 2007. The Minnesota Pollution Control Agency (MPCA) has mandated a temperature Total Maximum Daily Load (TMDL) study. This report summarizes the development of a Storm Water Management Model (SWMM) for Miller Creek in support of the TMDL study. The model simulates continuous time series of stream flow at 15-minute time intervals in Miller Creek using observed precipitation, stream bathymetry, watershed hydrogeology, and tributary and storm sewer characteristics as input. The model was calibrated and validated against flow data from 2008, and is able predict mean flows, peak flows, base flows, and storm runoff volumes. The SWMM was also used to simulate the effect of a a few stream alteration scenarios on the streamflows in Miller Creek/