ORIGINAL RESEARCH
Runoff Estimation in Steep Slope Watershed
with Standard and Slope-Adjusted Curve
Number Methods
Mahboubeh Ebrahimian1, Ahmad Ainuddin B. Nuruddin2, Mohd Amin B. Mohd Soom3,
Alias Mohd Sood1, Liew Ju Neng4
1Faculty of Forestry, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia
2Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia
3Faculty of Engineering, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia
4Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
2Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia
3Faculty of Engineering, Universiti Putra Malaysia, 43400, Serdang, Selangor, Malaysia
4Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
Pol. J. Environ. Stud. 2012;21(5):1191–1202
KEYWORDS
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.
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