Estimating ground-water recharge from stream hydrographs

It is possible to separate graphically the base flow on stream hydrographs by plotting the logarithm of the discharge against time. Total potential ground-water discharge (Qtp) at the beginning of any given base-flow recession is where K1 = ground-water discharge at the beginning of the base-flow recession (t0), in acre feet per day; K2 = time increment corresponding to one log cycle change in Q, in days. The difference between the actual amount of ground-water discharge at the end of the baseflow recession and the total potential ground-water discharge at the beginning of the same recession is called ‘remaining potential ground-water discharge.’ The difference between the total potential ground-water discharge at the beginning of any given base-flow recession and the remaining potential ground-water discharge at the end of the preceding base-flow recession is a measure of ground-water recharge. The method is illustrated by the computation of the groundwater balance of the Calgary area (Alberta, Canada).