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Initial Abstraction and Curve Numbers in a Semiarid Watershed in Southeastern Arizona
Citation:
YUAN, Y., W. Nie, AND S. C. MCCUTCHEON. Initial Abstraction and Curve Numbers in a Semiarid Watershed in Southeastern Arizona. Hydrological Processes. John Wiley & Sons, Ltd., Indianapolis, IN, 28(3):774-783, (2013).
Impact/Purpose:
The Soil Conservation Service (SCS, now the Natural Resources Conservation Service) curve number method is widely used to estimate direct runoff from a specific or design rainfall (SCS 1985; Hawkins et al. 2009). Reasons for the wide application of this method are (1) the computations are efficient; (2) the required soil type, land use, and management practices are readily available; and (3) satisfactory runoff estimates are feasible for many agricultural and urban watersheds (Ponce and Hawkins 1996; Yuan et al. 2001; Gassman et al. 2007; Hawkins et al. 2009; Wang et al. 2009). However, the estimated runoff is inaccurate where watershed retention is a large fraction of the rainfall, as in semiarid watersheds in southeastern Arizona (Hjelmfelt 1980).
Description:
The Soil Conservation Service curve number estimates of direct runoff from rainfall for semiarid catchments can be inaccurate. Investigation of the Walnut Gulch Experimental Watershed (Southeastern Arizona) and its 10 nested catchments determined that the inaccuracy is due to an unsuspected relationship between initial abstraction and maximum potential retention. Sensitivity analyses indicate that runoff estimation can be very sensitive to the initial abstraction ratio, especially for relatively light rainfall and for watersheds covered by deep, coarse, and porous soil, conditions that dominate many semiarid watersheds worldwide. Changing the ratio of initial abstraction to the maximum potential retention that was defined originally by the Soil Conservation Service to be 0.2, to a range of 0.01 to 0.53 for different Walnut Gulch catchments improved runoff estimates. The larger the channel area and the finer the soil, the smaller the initial abstraction ratio is. The variation of initial abstraction ratio for Walnut Gulch Experimental Watershed is due to the variation of maximum potential retention and initial abstraction, which are channel area and soil dependent parameters. The larger the channel area, the higher the maximum potential retention S is and the coarser the soil, the larger the initial abstraction Iais. In addition, the effect of initial abstraction ratio on runoff estimation increases with decreasing curve number. Thus, impacts of initial abstraction ratio on runoff estimation should be considered, especially for semiarid watersheds where the curve number is usually low.
URLs/Downloads:
YUAN 11-059 FINAL JOURNAL ARTICLE..PDF (PDF, NA pp, 363 KB, about PDF)Initial Abstraction and Curve Numbers in a Semiarid Watershed in Southeastern Arizona
