Stream Temperature Modeling of Miller Creek, Duluth, Minnesota

This report summarizes a modeling study of heat loading and stream temperature in Miller Creek in support of the MPCA Miler Creek temperature TMDL. The MINUHET surface runoff modeling tool was used to characterize runoff temperatures for typical residential and commercial watersheds for the continuous period June 15 to September 15, 2008. These results were then generalized to the entire Miller Creek watershed using runoff volumes from a SWMM model developed at SAFL. These simulated runoff temperatures and volumes were then used to estimate point source heat loadings to Miller Creek for the same time period. Separate models for wet detention ponds, infiltration basins, and underground stormwater vaults were used to estimate possible reductions in heat loading from surface runoff. Standard wet ponds were found to increase overall heat inputs, but reduce peak heat loading rates and maximum stream temperature increases due to stormwater. The use of wet ponds with bottom outlet structures and underground vaults gave some reductions in effluent temperature for smaller rainfall events (< 1 cm), but were of little benefit for larger events. Infiltration practices give the greatest benefit in reducing temperature impacts of runoff, by direct reduction in runoff volume, however, widespread implementation of infiltration practices in the Miller Creek watershed may be difficult.Minnesota Pollution Control Agenc