The unit hydrograph is a catchment-specific transfer function describing the direct-runoff hydrograph produced by one unit depth of effective rainfall distributed uniformly over a basin during a specified duration, derived empirically by isolating direct runoff (via base-flow separation) from observed storm hydrographs, normalizing to unit rainfall depth, and averaging across multiple observed storms of that duration. Under the assumptions of time invariance and linearity, the unit hydrograph can be transformed via superposition and scaling to predict the direct-runoff hydrograph for any rainfall of the same duration but different intensity, for rainfall of a different (multiple) duration by superposition of shifted unit hydrographs, or for any other duration via the S-curve (the runoff hydrograph resulting from continuous rainfall of infinite duration) obtained by summing infinitely superposed unit hydrographs; this belongs to hydrology, specifically the rainfall-runoff modeling used to predict flood discharge for structure design.
The unit hydrograph is a catchment-specific transfer function describing the direct-runoff hydrograph produced by one unit depth of effective rainfall distributed uniformly over a basin during a spec…