Estimating the runoff coefficient by combining Arc CN-Runoff, SCS-CN and ICAR empirical relationship (Case study: Selseleh Study area - Lorestan province)

Document Type : Original Article


1 PhD in Watershed Science and Engineering, Kashan University, Kashan, Iran

2 Associate Professor, Department of Water Engineering, University of Lorestan, Khorramabad, Iran

3 PhD student Water structures, University of Lorestan, Khorramabad, Iran

4 PhD in Water structures, Lorestan Regional Water Joint Stock Company


Determining the value of the runoff coefficient is one of the biggest problems and the main source of uncertainty in many water resources projects. The aim of the current research is to estimate the runoff coefficient by combining Arc CN-Runoff, SCS-CN and ICAR experimental relationship in the Selseleh watershed. Selseleh Study area is located in the north of Lorestan province and is one of the sub-watersheds of Kashkan. In order to carry out this research, data including digital elevation model information, land use classes, soil texture and meteorological and hydrological statistics (rainfall and runoff) related to the research area were used. The map of the land use layer and soil hydrological groups was entered into the Arc CN-Runoff tool environment, and Intersect was applied on two layers the Land soil layer was prepared, and the runoff coefficient map was prepared based on this layer. Finally, the runoff coefficient was estimated in three conditions dry, medium and wet moisture conditions and a comparison was made. The results of the research showed that the runoff coefficient (CR) in the Selseleh Study area is 0.26, 0.53, and 0.77, respectively, in dry, medium, and wet conditions. Therefore, the dry humid state has decreased by 68% compared to the average, and the more humid state has increased by 37% compared to the average. Investigating the correlation between the runoff coefficient and watershed characteristics showed that the runoff coefficient is influenced by the six physiographic features of the Study area: area, slope, length of the waterway and Gravelius coefficient, the maximum height and density of the waterway, which has a significant effect on the value of the runoff coefficient in this Study area. The value of the runoff coefficient in the ICAR method for the entire Study area was 0.48. In the Selseleh Study area, the runoff coefficient has a decreasing trend from April to September. The type of land and soil use in the basin under study is one of the influential factors that affect the runoff coefficient and, consequently, the peak discharge of the Study area. Also, in early spring, the flood potential is high in the said Study area. Among the measures to increase water infiltration are the establishment of a rainwater collection system and the operation of the Farrow meter along with the increase of plant cover with seeding and planting and intercropping of pasture plants.