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Unimpaired Runoff Calculations
"Unimpaired Runoff" or "Full Natural Flow" represents the natural water production of a river basin, unaltered by upstream diversions, storage, or by export or import of water to or from other watersheds. Gauged flows at the given measurement points are increased or decreased to account for these upstream operations.
The result is the "full natural flow," expressed as a rate (in Cubic Feet Per Second [CFS]), or as a volume over a fixed time interval, Acre-Feet (AF). Generally, "thousands of Acre-Feet" (TAF) is used. Our convention is to use "TAF" rather than "KAF," which would designate kilo-acre-feet.
The flows reported here are based on calculations done by project operators on the respective rivers, the US Army Corps of Engineers, and/or Snow Surveys. These calculations are done on a monthly basis for all major rivers in the state, and on a daily basis for several major gauges.
Daily Full Natural Flow (FNF) calculations are less accurate because they are based on less data than is available at the completion of each month. The sum of daily FNF reported here will not exactly match the calculated monthly FNF reported on the seasonal and water year reports. Due to the lag between the effect of upstream operations and downstream flow measurements, calculated daily FNF will fluctuate from day to day.
California Cooperative Snow Surveys