American Society of Civil Engineers


Field Test of the Variable Source Area Interpretation of the Curve Number Rainfall-Runoff Equation


by Helen E. Dahlke, (corresponding author), (Dept. of Physical Geography and Quaternary Geology, Stockholm Univ., Svante Arrhenius väg 8, 10691 Stockholm, Sweden; Dept. of Biological and Environmental Engineering, Cornell Univ., 62 Riley-Robb Hall, Ithaca, NY 14853. E-mail: helen.dahlke@natgeo.su.se), Zachary M. Easton, (Dept. of Biological and Environmental Engineering, Cornell Univ., 62 Riley-Robb Hall, Ithaca, NY 14853; Assistant Professor, Dept. of Biological Systems Engineering, Virginia Tech, 103 Research Drive, Painter, VA 23420. E-mail: zme2@cornell.edu), M. Todd Walter, (Associate Professor, Dept. of Biological and Environmental Engineering, Cornell Univ., 222 Riley-Robb Hall, Ithaca, NY 14853. E-mail: mtw5@cornell.edu), and Tammo S. Steenhuis, (Professor, Dept. of Biological and Environmental Engineering, Cornell Univ., 206 Riley-Robb Hall, Ithaca, NY 14853. E-mail: tss1@cornell.edu)

Journal of Irrigation and Drainage Engineering, Vol. 138, No. 3, March 2012, pp. 235-244, (doi:  http://dx.doi.org/10.1061/(ASCE)IR.1943-4774.0000380)

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Document type: Journal Paper
Abstract: The Soil Conservation Service Curve Number (SCS-CN) method is a widely used empirical rainfall-runoff equation. Although the physical basis of the method has been debated, several researchers have suggested that it can be used to predict the watershed fraction that is saturated and generating runoff by saturation excess from variable source areas (VSAs). In this paper, we compare saturated runoff-contributing areas predicted with the VSA interpretation of the SCS-CN method with field-measured VSAs in a 0.5 ha hillslope in central New York State. We installed a trench below a VSA and simultaneously recorded water flux from different soil layers at the trench face and water table dynamics upslope of the trench. This setup allowed us to monitor runoff initiation and saturation-excess overland flow in response to rainfall and different water table depths in the hillslope during 16 storm events. We found that the SCS-CN method accurately predicted the observed VSA and showed best agreement if the VSA was defined as the area where the water table was within 10 cm of the soil surface. These results not only demonstrate that the VSA interpretation of the SCS-CN method accurately predicts VSA extents in small watersheds but also that the transient water table does not necessarily need to intersect the land surface to cause a storm runoff response.


ASCE Subject Headings:
Runoff
Slopes
Field tests
Rainfall

Author Keywords:
Runoff
Variable source areas
Trenched hillslope studies
Curve number