Assessment of the effect of slope on runoff potential of a watershed using NRCS-CN method

Physical verification of the effect of land features and antecedent moisture on runoff curve number

“…As seen, the method underestimates large runoff events and over-estimates few small rainfall events. Similar under-estimation of runoff has also been reported by Garg et al (2013) in India, Shi et al (2009) in China, Huang et al (2006 in the Loess Plateau of China, King et al (1999) in Mississippi, andVan Mullem (1991) for rangeland and cropland in Montana and Wyoming.…”

“…The type of soil in the study area is loam (US Bureau of Soil and PRA Classification) with an average proportion of 50-55% of sand, 35-42% silt and 8-15% clay (Kumar et al, 2012). The upper hilly area of Solani watershed is mainly consisting of sandy loam whereas lower flat terrain (experimental site) is dominated by loam and loamy sand (Garg et al, 2013). The study area constitutes three major land cover classes: Forest land, bare soil and vegetated land.…”

“…A significant portion of the vegetated land is agricultural with more than 35% of the coverage area, and fallow land accounts for 17% to the total area whereas forest covers around 30% of the total area, especially in the hilly part of the basin. Sugarcane is the perennial crop in the area, whereas wheat, maize, and pulses grow as seasonal crops (Garg et al, 2013).…”

“…However, the runoff-generation is also affected by, besides others, the watershed slope (Dodds, 1997). The SCS-CN method however does not account for its effect on runoff yield (Ebrahimian et al, 2012;Garg et al, 2013;Huang et al, 2006Huang et al, , 2013Shi et al, 2009). El-Hassanin et al (1993) found that the increasing slope from 8 to 30% increased surface runoff by 160% for Burundi watersheds located in Iran.…”

“…In Pakistan, Shafiq and Ahmad (2001) used silt loam soil plots of various slopes and found that the runoff coefficient increased with slope. The incorporation of slope parameter (Garg et al, 2013) significantly improved the estimated runoff in Solani watershed in India. The use of Huang et al's (2006) equation (Ebrahimian et al, 2012) showed a positive correlation between estimated and observed runoff depths (r = 0.56, p b 0.01).…”