The University of Minnesota St. Anthony Falls Lab has been funded by the Minnesota Pollution Control Agency to study the physical processes by which land development impacts stream temperature (thermal pollution), and develop computer modeling tools to enable prediction of these changes. The results of this study are given in a series of project reports and peer-reviewed technical papers, listed in the publications page. A software package to simulate surface runoff and surface runoff temperatures (MINUHET) was developed in this project. Information on this software package is given in the MINUHET page.
Trout streams are particularly susceptible to thermal pollution, because they maintain cold temperatures year round. Trout streams are either well shaded or receive cold groundwater inputs, so that even in mid-summer, water temperatures can be in the range of 15 - 20 degrees Celsius (60 - 68 Fahrenheit). Trout are adapted to these cooler temperatures, and will stop reproducing or die if stream temperatures are too high.
Most of the trout streams in Minnesota are in the southeast region of the state and along the North Shore of Lake Superior. However, many trout streams exist in other part of the state, such as Vermillion River in the Minneapolis/St. Paul metro area and Brown's Creek in the Stillwater area. The Duluth area has numerous trout streams, including Miller Creek, which runs from Duluth International Airport to St. Louis Bay in Lake Superior. The Vermillion River and Miller Creek are the two trout streams that we focused on in our temperature impact study.
Impacts of Land Development on Stream Temperature
Land development dramatically alters the way rainfall travels from areas of land to lakes and streams. Rainfall on undeveloped land typically infiltrates into the ground and recharges the groundwater system. Rainfall on developed land tends to produce surface runoff that may increase the temperature of nearby coldwater streams and degrade trout habitat. A surface runoff increases, infiltration and recharge of groundwater aquifers may be reduced, and paved areas may increase the temperature of shallow groundwater that feeds trout streams.
Hydro-thermal Computer Models
To help understand the roles of stormwater discharges, groundwater inputs, and atmospheric heating on stream temperature for different flow conditions, we have created deterministic computer models for these processes. These models have included:
- surface runoff and surface runoff temperature for both impervious and pervious land
- routing of water and heat through natural and man-made drainage networks
- discharge rate and temperature for stormwater mitigation practices such as detention ponds
- stream flow and temperature models
- infiltration, recharge, and stream baseflow for changing land use
- effects of land use on shallow groundwater temperature
The MINUHET tool combines the models for surface runoff, routing, and mitigation practices with a graphical user interface. The application of these models to Minnesota trout streams are described in the Case studies page. Reports and peer-reviewed papers describing these models are listed in the Publications page.
For more information, contact:
William Herb, Ph.D.
St. Anthony Falls Laboratory
University of Minnesota
2 Third Ave. SE
Minneapolis, MN 55414