American Society of Civil Engineers


Development of a Modified Rational Equation for Arid-Region Runoff Estimation


by Xixi Wang, (ASCE Member Engineer, Registered Professional Civil Engineer, Assistant Professor and Coordinator, Hydrology and Watershed Engineering/Management Program, Department of Engineering and Physics, Tarleton State University, Box T-0390, Stephenville, Texas 76402, USA; and Guest Professor, College of Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia Autonomous Region 010018, People’s Republic of China. E-mail: xxqqwang@gmail.com.), Tingxi Liu, (Professor and Dean, College of Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia Autonomous Region 010018, People’s Republic of China), Changyou Li, (Professor and University President, College of Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia Autonomous Region 010018, People’s Republic of China), Zhongyuan Zhu, (Professor, College of Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia Autonomous Region 010018, People’s Republic of China), Shengwei Zhang, (Associate Professor, College of Conservancy and Civil Engineering, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia Autonomous Region 010018, People’s Republic of China.), and Assefa M. Melesse, (Associate Professor, Department of Earth and Environment, ECS 339, Florida International University, Miami, Florida 33199, USA.)
Section: Watersheds, pp. 4702-4716, (doi:  http://dx.doi.org/10.1061/41173(414)490)

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Document type: Conference Proceeding Paper
Part of: World Environmental and Water Resources Congress 2011: Bearing Knowledge for Sustainability
Abstract: In practice, the United States (U.S.) Soil Conservation Service (SCS) curve number (CN) method is commonly used in distributed, continuous-time hydrologic models to estimate direct runoff. However, for the standard SCS-CN method, the determination of initial abstraction (Ia) as a fraction of potential maximum retention (S) after runoff starts is very subjective and thus highly debatable. The objective of this study was to develop a Modified Rational Equation (MoRE) that combines the advantages (e.g., simplicity and global acceptance) of Rational Equation and those (e.g., easy parameterization and extensive verification in U.S.) of the standard SCS-CN method as well as that can be used to more accurately predict direct runoff depth. The MoRE has two variables, rainfall intensity and relative saturation, but it does not require Ia be determined. A verification using laboratory and field data indicated that the MoRE can more accurately reproduce the observed direct runoffs than the standard SCS-CN method as well as its improved version.


ASCE Subject Headings:
Arid lands
Runoff
Hydrology