Alaska Section, American Water Resources Association

Richard Kemnitz, Alaska Section AWRA Northern-Region Director

I would like to invite you to the February 2001 Brown-Bag presentation by Jerome B. Johnson, USA CRREL, US Army ERDC-Cold Regions Research and Engineering Laboratory. Please note this meeting is the second Wednesday in February. We look forward to seeing you, please feel free to bring a colleague to the meeting.

February 14, 2001
Alaska Section AWRA, Northern-Region Brown-Bag Presentation
Alaska Department of Natural Resources, Large Conference Room
Noon to 1300

"The physical causes of snow pillow measurement errors"
US Army ERDC-Cold Regions Research and Engineering Laboratory

Jerome B. Johnson
Research Geophysicist
US Army ERDC-Cold Regions Research and Engineering Laboratory
PO Box 35170
Ft. Wainwright, AK 99703-0170
ph: 907-353-5179 fax: 907-353-5142

Abstract

Fluid filled snow pillows have been used for over forty years to measure the amount of water stored as snow in the US and around the world. Snow pillow measurements of snow water equivalent (SWE) are used with energy balance models to predict water runoff to estimate flooding potential, and to manage the water resource for agriculture, fish production, hydroelectric generation and other applications. In general, the snow pillow has functioned adequately, however, long term experience with the snow pillow demonstrate that it can yield unpredictable and erroneous results that make it difficult for water resource managers and researchers determine what is occurring. Snow pillows with diameters smaller than the standard 3 to 4 m diameter may over predict SWE one year and under predict it the next. The signal record may be delayed from the actual storm precipitation and during the spring melt a sudden over prediction followed by a settling to a more accurate result may occur. The general explanation for these strange behaviors is usually given as some form of bridging of the snow over the snow pillow. The actual cause of snow pillow measurement excursions is, however, much more interesting and is due to the thermal and mechanical interaction of the snow pillow with the snow and ground. For the past three years I have been working with the Natural Resources Conservation Service to develop a replacement sensor for the snow pillow, which has required that we first learn about the physics of SWE sensor/snow interaction. In this presentation I will describe what we have learned and how it might help the water resource manager/researcher better understand the cause of snow pillow measurement anomalies.