A flow and temperature model for the Vermillion River, Part I: Model development and baseflow conditions

Stream temperature and stream flow are important physical parameters for aquatic habitat preservation in river and stream systems. Water temperature is particularly important for coldwater stream systems that support trout. Summer base flow conditions with low flows and high water temperatures can be critical for maintaining trout habitat. Surface runoff from rainfall events can lead to increases in stream temperature, particularly in developed watersheds. To better understand the interactions between stream temperature, land use, and climate, an unsteady stream flow and temperature model has been developed for the Vermillion River. The model includes the main stem from Dodd Avenue to Goodwin Avenue and a number of tributaries, including South Branch, South Creek, North Creek, and Middle Creek. The EPDriv1 package was used to simulate stream flow, including distributed groundwater inputs. Simplified stream channel geometry was required to obtain converged flow solutions for unsteady low flows. A stream temperature model has been assembled based on previous work at SAFL. The stream temperature model uses flow and flow area from the flow solver, along with observed climate data to calculate surface heat transfer. Groundwater inflows are an important component of both the flow and temperature model. For the Vermillion River, groundwater inflow rates were estimated from flow gaging sites, while groundwater temperatures were estimated by calibrating the stream temperature model. The calibrated combination of groundwater flow and temperature results in a good match of simulated and observed stream temperature, with RMSEs in the range of 0.75 to 2 ºC. The assembled flow and temperature model for the Vermillion River has been calibrated for baseflow conditions, and provides a starting point for future analysis of surface runoff inputs during rainfall events.