Runoff from rain and snow

The basic principles of the idealized hydrologic cycle are reviewed with emphasis on storage and movement of water in the soil. A distinction is made between ground‐water runoff and overland runoff in terms of storage and lag, expressed as accumulated deviations from uniform flow over a period of several years. These functions are presented for the period 1920 through 1945 for three rivers in central Oregon: John Day, Deschutes, and Metolius, which exemplify minimum, moderate, and maximum effects, respectively, of storage and lag. The Metolius River is shown to have extremely small fluctuations in discharge from year to year, ascribed to a great portion of its flow being derived from ground‐water runoff; and its response to fluctuations in annual precipitation lags behind that of the John Day River by about five years. Specific techniques and measures for improving seasonal water supply forecasts are suggested.