Standard Article

Unit Hydrograph Theory


  1. Vijay P. Singh

Published Online: 15 APR 2005

DOI: 10.1002/047147844X.me412

Water Encyclopedia

Water Encyclopedia

How to Cite

Singh, V. P. 2005. Unit Hydrograph Theory. Water Encyclopedia. 4:355–360.

Author Information

  1. Louisiana State University, Baton Rouge, Louisiana

Publication History

  1. Published Online: 15 APR 2005


The fundamental premise of unit hydrograph theory is that the hydrologic system is linear and time invariant. Although the assumptions implied or made in the theory are, strictly speaking, seldom true, the theory, nevertheless, does yield reasonable results in practice. The theory is applicable to a wide range of problems in hydrology and water resources.

The unit hydrograph is based on these postulates: (1) For a given drainage basin, the duration of surface runoff is constant for all uniform-intensity storms of the same duration, regardless of differences in the total volume of surface runoff. (2) For a given drainage basin, if two uniform-intensity storms of the same length produce different total volumes of surface runoff, then the rates of surface runoff at corresponding times, after the beginning of the two storms, are in the same proportion to each other as their total volumes of surface runoff. (3) The time distribution of surface runoff from a given storm period is independent of concurrent runoff from antecedent storm periods.


  • channel flow routing;
  • direct runoff hydrograph;
  • effective rainfall;
  • groundwater flow;
  • instantaneous sediment graph;
  • instantaneous unit hydrograph;
  • rainfall–runoff models;
  • unit graph;
  • unit hydrograph;
  • unit sediment graph