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" SNOW RUNOFF AND SNOW FORECAST by R. A. Work, Head Water Supply Forecast Section U. S. Soil Conservation Service Portland, Oregon , 10 western mou ntai n streams about th ree-quarters of the flow comes more or less directlY; from melting snow. The snow builds up in mountain areas during the winter months: starting as much as seven or eight months before it appears in the streams as runoff.: It has long been recognized that there was a relation between the winter snow pack and the subsequent spring and summer runoff. . Some 50 years ago, the late Dr, J. [ Church, of the University of Nevada, whom many of you knew personally, started to measure the winter snow pack on the water- shed of:Lake Tahoe. The purpose was to estimate the rise in the lake level during the next rU.noff season. Some of you are very familiar with the early work of this forward looking'scientist. Time here will not be taken to review his work, but he must be remem- bered as the individual who made the initial effort toward western snow surveys and water supply forecasting. It was some twenty-five years after the early work of Dr. Church that snow surveys were extended to all areas of the west including the Colorado River Basin. It took that quarter century for the pressure on the use of our western water supplies to build up. A drouth ,period during the middle thirties accentuated value of snow surveys and water supply forecasts. I n fact, a relatively few snow measurements and water supply forecasts in UtaH and the Colorado River Basin in t~at state, initiatep by the present governor, the Hon. George D. Clyde in the extensive drouth year of 1934, supplied the major ijnpetus to the west-wide snow survey network with assistance from the federal government These west-wide snow surveys were first made during the 1935-36 season through co-ordination by the United States Department of Agriculture. From 1936, snow surveys and water supply forecasts have been and remain a co- operative activity among several federal, state, and local organizations. Snow su rveys are made to provide the principal item of hydrologic data for water supply forecasts. I n addition, the snow measurements provide valuable information as a part of the hydrologic data net-' work, for development of winter sports facilities, for road and building design, for estimates of fore$t fire control facilities to be needed and other pu rposes. Their principal value, however, is for immediate use in making water supply forecasts. Water supply forecasts by themselves are somewhat academic until they are applied in water management. There is the payoff. The term, multiple-useof water, has become rather common-place. Practically every . . . " -1-