Snow Surveys and Water Supply Forecasting

Snow Surveys

Since 1935, most of the American West has relied on the U.S. Department of Agriculture's cooperative snow survey program for predictions of meltwater runoff. This program is a Federal, State, and local partnership directed by the Natural Resources Conservation Service. Its survey activities encompass Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. Alaska and southern Canada are partners also. California has an independent program.

Snow surveys in the West date back to around 1906, when the University of Nevada's Dr. James Church laid out the first western snow course. Dr. Church also invented key sampling procedures and equipment. The next three decades saw a proliferation of snow survey activity throughout the West. In some States, independent power or irrigation companies spearheaded the surveys; in other States, universities or State engineers were in charge.

Federal leadership of snow survey activities came as a result of the unprecedented western drought of 1934. Agricultural leaders requested USDA's help in forecasting water supplies for the ensuing crop-growing season. Because many of the watersheds and streams were interstate, Federal help was needed to coordinate the surveys and to develop uniform procedures and equipment for surveying and forecasting (fig. 5).

Figure 5. The snow surveyors are well-equipped for a
full day's work.

To find out how much water will be available in summer, snow surveyors from NRCS and the other cooperating agencies collect data from some 1,600 snow courses several times each winter. They determine the depth and the water content of the snowpack and estimate the amount of runoff from the mountain watersheds.

In 1977, NRCS began developing a network of automated radio telemetry data sites for collecting snow survey data. This snowpack telemetry (SNOTEL) network provides NRCS offices with daily or more frequent information on streamflow potential. The information is especially valuable during periods of flood or drought.

The information collected by the telemetry system (see Remote surveys) and snow surveyors (see Manual surveys) is translated into water supply forecasts that NRCS State offices issue monthly from January to June in cooperation with the National Weather Service. Major sectors of the Western economy -- agriculture, industry, and recreation -- base their plans on these forecasts.