In surface-water hydrology, streamflow records are reduced into duration-frequency form to characterize water availability: a flow duration curve expresses discharge as a probability of being equaled or exceeded, enabling dependable-flow estimates for design. Mass-curve (Rippl) analysis accumulates flow volume over time to determine the storage capacity needed to meet a target demand, or the maximum demand satisfiable from a given storage, by comparing cumulative supply against a constant-demand line. Separately, unit hydrograph theory derives the direct runoff hydrograph from total streamflow by separating baseflow and estimating infiltration/abstraction losses (the phi-index), then uses the linearity and superposition principles of the unit hydrograph to synthesize runoff for storms of arbitrary duration via lagging, summation, and the S-curve method.
In surface-water hydrology, streamflow records are reduced into duration-frequency form to characterize water availability: a flow duration curve expresses discharge as a probability of being equaled…