Predicting the Summer Temperature of Small Streams in Southwestern Wisconsin1

One of the biggest challenges in managing cold water streams in the Midwest is understanding how stream temperature is controlled by the complex interactions among meteorologic processes, channel geometry, and ground water inflow. Inflow of cold ground water, shade provided by riparian vegetation, and channel width are the most important factors controlling summer stream temperatures. A simple screening model was used to quantitatively evaluate the importance of these factors and guide management decisions. The model uses an analytical solution to the heat transport equation to predict steady-state temperature throughout a stream reach. The model matches field data from four streams in southwestern Wisconsin quite well (typically within 1 ̊C) and helps explain the observed warming and cooling trends along each stream reach. The distribution of ground water inflow throughout a stream reach has an important influence on stream temperature, and springs are especially effective at providing thermal refuge for fish. Although simple, this model provides insight into the importance of ground water and the impact different management strategies, such as planting trees to increase shade, may have on summer stream temperature. (KEY TERMS: stream temperature; modeling; watershed management; ground water hydrology; meteorology/climatology; surface water hydrology.) Gaffield, Stephen J., Kenneth W. Potter, and Lizhu Wang, 2005. Predicting the Summer Temperature of Small Streams in Southwestern Wisconsin. Journal of the American Water Resources Association (JAWRA) 41(1):25-36.