Accuracy Assessment of Unit Hydrographs: Point versus Spatially Integrated Rainfall Input
Publication: Journal of Hydrologic Engineering
Volume 17, Issue 1
Abstract
A unit hydrograph (UH) reflects the hydrologic response of watershed processes to a rainfall event. Most UH analyses use measured rainfall from a single rain gauge even though rainfall from a single gauge may not adequately reflect either the spatial or temporal variation during a storm event. The intent of this study was to better understand factors that influence UH accuracy, especially the spatial characteristics of rainfall. Analyses were made by using runoff and rainfall data, including radar rainfall measurements, from the densely monitored Walnut Gulch watershed, Arizona. Transmission loss (TL), as a physical process, is shown to be an important factor that influences UH shape. Multiple-storm, multiple rain gauge analyses show that rainfall from a single gauge is unlikely to yield a UH that reflects the watershed response. A comparison of UHs spatially averaged by using the temporal Thiessen method agree with UHs developed by using radar rainfall measurements. Intra-watershed analyses indicate that spatial variation of the physical processes, including channel processes that control transmission losses, can greatly influence the shape of a UH, thus suggesting that watershed subdivision is appropriate for analysis and design on even moderately-sized watersheds.
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Acknowledgments
The authors would like to thank the researchers at the University of Iowa and their partners at Princeton University, the National Climatic Data Center, and the Unidata Program Center, for their work in developing the Hydro-NEXRAD system for obtaining radar data. We also would like to specifically thank the researchers at the University of Iowa for all of the time that they gave explaining how to use the program. We also would like to thank the staff at the USDA’s Southwest Watershed Research Center for making rain gauge and flow gauge data from Walnut Gulch Experimental Watershed available.
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Published In
Journal of Hydrologic Engineering
Volume 17 • Issue 1 • January 2012
Pages: 23 - 31
Copyright
© 2012 American Society of Civil Engineers.
History
Received: Sep 23, 2009
Accepted: Mar 18, 2011
Published online: Dec 15, 2011
Published in print: Jan 1, 2012
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