Thermal pollution by surface runoff from urban areas can contribute to the degradation of
coldwater ecosystems. The hydrothermal characteristics of surface runoff from rainfall are
therefore of interest. Three hydrothermal parameters of surface runoff have been studied: runoff
temperature (oC), heat flux (W/m2) and total heat export (J/m2). Heat fluxes were defined above a
reference temperature of 20oC. The results can be used to identify storm events that have the
potential for the largest heat export from a watershed and consequently the strongest thermal
pollution of a receiving coldwater stream.
In this study, records of rainfall events and weather data are used to estimate the three
hydrothermal parameters by model simulation. The model for predicting rainfall runoff
temperatures and rates from an impervious surface (parking lot) has been described in Project
Report No. 484 from the St. Anthony Falls Laboratory, University of Minnesota (Herb et al
2006). The weather data came from the MnROAD test site in Albertville, MN, and from the
SAMSON data set. Runoff temperatures and heat export were calculated for a 100x100m paved
surface using 6 years of 15 minute weather data or 30 years of 1-hour weather data. The 6-year
data set contained 280 rainfall events from April through October.
The 280 values of the three hydrothermal parameters were related to basic rainfall event
parameters such as total rainfall, duration, and rainfall temperature (dew point). Average runoff
temperature was found to be well correlated to dew point temperature during the storm, and air
temperature and solar radiation prior to the storm. 20 extreme values of the hydrothermal
parameters were ranked and also related to basic rainfall parameters. Partial duration series of
hydrothermal parameters were analyzed separately for frequency of occurrence (return periods).
Herb, William; Mohseni, Omid; Stefan, Heinz.
Heat Export and Runoff Temperature Analysis for Rainfall Event Selection.
St. Anthony Falls Laboratory.
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