Document Type : Research Paper

Authors

• Fatemeh Tarkarani ¹
• Hosein Asakareh ²

¹ Master of Geography, University of Isfahan

² Ph.D. Student of Natural Geography, University of Isfahan

Abstract

Application of the “CN” curve is in calculation of the detention coefficient’s value. This index is necessary for estimation of the delay and concentration times of the basin as well as the height of runoff by the SCS method. Since common and traditional methods of preliminary studies are time-consuming and costly, the best methods recommended in this regard are reasoning-based methods.
One of such methods for calculation of the detention coefficient and number of curve is utilization of basin’s runoff coefficient. This method was used in the Nojian basin, one of the head-branches of the Dez River in southeast of Khorramabad, Lorestan. The runoff coefficient in this basin was calculated to be 0.59, the detention coefficient 0.41 and the average CN about 19.61.
Lack of direct relationship between the basin’s monthly precipitation and runoff makes exploitation of the index mentioned above for short periods impossible. Therefore, this index can be calculated monthly only in basins where precipitation is mostly liquid and also monthly precipitation justifies runoff of the same month.