Use of base flow in forecasting runoff during the non-flood season

A study is presented of streamflow for the period July through September for the Salmon river at Whitebird, Idaho as related to 'Base Flow' on July first. 'Base Flow' is considered to be the flow of a river after the snowmelt flood has drained from the soil and ground water aquifers and the recession graph has started to flatten off. Base flow on July 1 and precipitation during the period account for 97% of the variance in runoff. It is possible to forecast the total runoff from July through September within limits of error normally acceptable in water supply forecasting by means of base flow alone. The approach to each river would, of course, be different, but the theory holds. Relationships are shown graphically with probability and frequency curves being exhibited together with tabulated data and formula development.