Flow readings from river gages are influenced by upstream diversions, impoundments, and other manmade alterations. The natural runoff at a gage is reconstructed by removing the effects of these "impairments." This calculation is done on a monthly basis for all major rivers in the state, and on a daily basis for a subset.
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.
Unimpaired runoff is computed on a monthly basis at 36 locations around the state.
Daily unimpaired runoff is computed for several major gages. These values are much less accurate because not all data is available on a daily basis. The corresponding monthly values will be different.
California Cooperative Snow Surveys