Estimate and zoning of runoff due 24-hour rainfall with use SCS-CN model (case study: dam catchment Yamchi, Ardabil, Iran)

One of the most common methods for estimating direct runoff from 24 rainfalls is The Soil Conservation Service of America methods (SCS) that is known number of curves (CN). This method estimated quantity of runoff obtained from precipitation in different parts of the basin with considering the soil characteristics, hydrological status of land and land use. In this paper quantity of runoff was calculated for 24-hour rainfall dam catchment Yamchi (Ardabil) with using this method and the effective factors has been studied in runoff production in different parts of the basin. In this study is using 24-hour rainfall with return periods of 5, 25, 50 and 100 years. Also, using the combination of hydrologic soil groups, land use and hydrological conditions, the curve number (CN) was obtained which with Using existing relationships in the model was calculated keeping quantity of soil surface and penetration for catchment basin and finally quantity of runoff produce. The results of study indicate that the greatest potential to produce runoff is in the northern and western parts of the basin that is marked with arid and low permeability. Also estimate the volume of rainfall becomes runoff for several period indicate which with increasing return period a greater percentage of rainfall becomes runoff. For example, the quantity of runoff produced by precipitation of 5 years, from 39 percent to 55 percent in the period is 100 years old.