American Society of Civil Engineers

Evolution of Clark’s Unit Graph Method to Spatially Distributed Runoff

by Daniel W. Kull, M.ASCE, (Hydr. Engr., U.S. Army Corps of Engrs., Hydrologic Engrg. Ctr., 609 2nd St., Davis, CA 95616) and Arlen D. Feldman, M.ASCE, (Res. Div. Chief, U.S. Army Corps of Engrs., Hydrologic Engrg. Ctr., 609 2nd St., Davis, CA)

Journal of Hydrologic Engineering, Vol. 3, No. 1, January 1998, pp. 9-19, (doi:

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Document type: Journal Paper
Discussion: by Ming-Sang Yang    (See full record)
Closure:(See full record)
Abstract: In 1945, C.O. Clark proposed a method to develop synthetic unit hydrographs for the modeling of watershed rainfall response. His technique utilizes two components: a translation hydrograph and a linear reservoir routing. Clark’s three parameters (the time of concentration T\dc, a storage attenuation coefficient R, and a time-area histogram) can be estimated for gauged basins. For ungauged basins, T\dc and R are difficult to estimate. T\dc can be approximated by analyzing physical basin characteristics whereas both T\dc and R have been successfully estimated using parameter regionalization. Technologies for observing and managing spatially distributed watershed and rainfall information are constantly evolving. The improved availability of areally oriented data brings the challenge of integration of these data into hydrologic models. The Hydrologic Engineering Center (HEC) has developed the program ModClark to take a first step in this integration. ModClark is based conceptually on Clark’s 50-year-old method and uses next generation weather radar (NEXRAD) data. The ability of Clark’s technique to accommodate the spatially distributed nature of rainfall and runoff illustrates the adaptability of Clark’s original methodology. A demonstration of this adapted methodology is provided.

ASCE Subject Headings:
Rainfall-runoff relationships
Hydrologic models
Spatial distribution
Integrated systems