Snow, Ice, and Runoff: Winter Runoff Monitoring Methods and Results From the University of Wisconsin-Platteville Pioneer Farm.

Winter runoff has been monitored since 2002 by researchers at Pioneer Farm, a 174-hectare (430-acre) mixed-livestock farm associated with the University of Wisconsin-Platteville. The headwaters of the Fever (Galena) River flow through the center of the farm. More than 90% of the watershed is in row crop agriculture and during snowmelt and winter rains, the watershed is conspicuously dissected by intermittent streams that clearly convey water from fields to the Fever River. Instrumentation at the edges of fields was installed to measure runoff flow rates and sample water quality to estimate pollutant export.

Monitoring edge-of-field runoff in a northern climate with below-freezing temperatures presents a number of unique challenges. Ice formation and snow obstruction during runoff events can introduce major errors in discharge estimations and sample collection unless appropriate methods are used. Methods developed from our experience in preventing and compensating for frost heave, ice dams, flume submergence, frozen sample lines, and electronic malfunctions will be discussed.

Results from edge-of-field runoff monitoring indicate an average of 30 mm/year (1.2 inches/year) of winter runoff on these fields. Winter runoff commonly accounts for greater than 50% of the annual runoff. During these events, the mean annual phosphorus loss was 1.7 kg ha^-1 with more than 85% of the phosphorus in the dissolved reactive form.  The maximum phosphorus yield was 7.8 kg ha^-1. The median suspended sediment concentration is less than 50 mg/l. Although significant winter phosphorus losses were measured over the study period, mean losses over time were well under the 6.7 kg ha^-1 benchmark in the Wisconsin Phosphorus Index.