Frozen precipitation has important implications for water quality and soil biology. Nutrients in landspread animal manure are transported to surface waters by snowmelt, and winter survival of forages often depends on snow cover. Further development of mechanistic snow behavior models would be assisted by improved measurements of the disappearance of water from snowpacks. We developed a system to measure the equivalent water equivalent (SWE) of a snow cover based on attenuation of gamma rays. A Eu-152 source (about 70 MBq) was pushed through raceways which were placed on the soil surface prior to snowfall. Attenuation of the emitted radiation by solid and liquid water in snow was measured with a GeLi detector held above the snow and a multichannel analyzer. Use of four energy peaks and solution of the six resulting equations reduced dependence of the measurement on source-detector geometry. In laboratory tests, a fixed water depth was constant to =B11.5 mm following displacement of the detector by 50 mm laterally and 100 mm vertically, a much larger repositioning error than occurs in the field. Field tests showed that the system detected melting conditions with greater sensitivity than was attained with collecting of snow cores. Errors in estimated SWE due to repositioning of the detector was about =B1 3 mm. Estimated energy balance terms were in reasonable agreement with observed melting during a field experiment. The new device will allow nondestructive SWE measurements to assess the influences of a number of agricultural management practices on winter hydrology.

Bill Bland
Assistant Professor
Dept. Soil Science
Agricultural Climatology Extension Specialist
University of Wisconsin-Madison
1525 Observatory Dr.
Madison, WI   53706-1255
608/262-0221 (Voice)
608/265-2595 (Fax)
E-mail: wlbland@facstaff.wisc.edu