Derivation of Base Flow Recession Curves and Parameters

The Boussinesq equation is used to show that base flow recession is an exponential decay function. For a single peaked hydrograph, the storage delay factor K b , the time for base flow to decrease by a factor of 10, is estimated. The parameter K b is adjusted by trial so that surface flow, or the observed total flow minus base flow, is also an exponential decay function after the point of inflection on the hydrograph recession. Surface flow K s is so determined. For 22 basins in Illinois, dormant season K b ranges from 15–100 days and is associated with physiography. K s varies from 1.8–6.0 days.