Streamflow records can be summarized as a flow duration curve (discharge plotted against the percentage of time it is equaled or exceeded, via a plotting-position formula) or as a mass curve (cumulative flow volume versus time), both used to characterize dependable discharge and to size reservoir storage against a target demand — the required storage equals the maximum cumulative deficit between the demand line and inflow mass curve during a dry period, and conversely a given storage constrains the maximum maintainable demand to the smallest value satisfying all deficit periods. Where streamflow records are insufficient, yield can be estimated via rainfall-runoff correlation, regional empirical runoff equations, or water-budget (mass-balance) modeling, and extreme hydrologic conditions are characterized as drought (meteorological, hydrological, or agricultural, each with its own defining index) or flood (estimated via rational method, empirical area-based formulas, unit hydrograph methods, or flood frequency analysis with an associated return period and risk of exceedance). This is core subject matter in hydrology and water resources engineering, specifically streamflow characterization, reservoir yield/storage analysis, and hydrologic extremes.
Streamflow records can be summarized as a flow duration curve (discharge plotted against the percentage of time it is equaled or exceeded, via a plotting-position formula) or as a mass curve (cumulat…