A smoothed composite of the recessions of several observed hydrographs, drawn to represent the characteristic time graph of decreasing total runoff for a drainage area after passage of a peak flow. Curves of this type, designed to characterize the nature of a drainage area, may be constructed as a plot of flow (stage of discharge) versus time, or as a plot of flow versus flow at some fixed later interval; also, separate recession curves may be derived for surface runoff, groundwater runoff, and even for interflow.