The IUH of General Hydrologic System Model

by Ven Te Chow, (F.ASCE), Prof. of Civ. Hydrosystems Engrg.; Univ. of Illinois, Urbana-Champaign, Urbana, Ill.,
V. C. Kulandaiswamy, UNESCO Adviser and expert in Civ. Engrg. (Hydrology and Water Resources); UNDP and UNESCO Mission, Colombo, Sri Lanka,

Serial Information: Journal of the Hydraulics Division, 1982, Vol. 108, Issue 7, Pg. 830-844

Document Type: Journal Paper


This paper describes two simple and practical forms of the general hydrologic system (GHS) model, including a 5-parameter model and a 3-parameter model, and derives and compares their instantaneous unit hydrographs (IUH) which are useful to hydrologic analysis and design. It is shown that the 3-parameter model can be derived from the 5-parameter model by modifying the assumption on the boundary conditions in solving the differential equation that represents the model. It is found that the 5-parameter model is more realistic to represent the real-world system and fit the hydrologic data consistently better than the 3-parameter model. On the other hand, the 3-parameter model is slightly simpler in form and produces IUHs always of positive ordinates.

Subject Headings: Hydrologic models | Parameters (statistics) | Hydrologic data | Hydrographs | Boundary conditions

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