Comments about selected recession parameters

Recession analysis can be used for qualitative comparisons between basins and for quantitative analysis involving the slope and the shape of the recession curve. The groundwater-level recession hydrograph can be used to derive an estimate of the hydraulic diffusivity of a surficial aquifer. The recession index can be obtained from streamflow data and from a formulation that includes aquifer properties. The analysis of the method reveals nonlinear recession which can result from the down-valley flow component, a dual-aquifer effect, and leakage to or from the aquifer. Important concepts include the dominant recession index and secondary recession characteristics which can affect low flow. Under conditions of down-valley flow, the cross-valley flow component tends to be important for determining recession characteristics, including hydraulic diffusivity and the recession index. These findings are relevant to another recession parameter a which is the distance from the stream to the hydrologic divide and results are supported by test simulations of a technique for estimating recharge.