Runoff estimation in steep slope watersheed with standard and slope-adjusted curve number methods

Abstract

The objective of this study was to evaluate the applicability of the standard and slope-adjusted NRCS-CN methods in estimating runoff depth in a steep slope watershed. The study was carried out in the Kardeh watershed, northeastern Iran. The CN method was followed to estimate runoff depth for selected storm events. The effects of slope on CN values and runoff depth were determined using a slope-adjusted CN equation. Positive correlation was found between estimated and observed runoff depths (r = 0.56, P < 0.01). About 9 and 6% of the estimated and slope-adjusted runoff values were within ±10% of the recorded values, respectively. In addition, about 43 and 37% of the estimated and slope-adjusted values differed with recorded values by more than ±50% error, respectively. While the slope-adjusted CN equation appeared to be inappropriate for runoff estimation in steep slope watershed, the standard CN method can be used with 55% accuracy in such watersheds.