Monthly, Seasonal and Annual Variations of Curve Number and Runoff in BarAriyeh Nishabour

Estimating runoff from atmospheric precipitation and its quantitative understanding of various production processes is considered as one of the important issues in hydrology knowledge. Since runoff in the watershed, due to several factors influencing it, is a complex issue, therefore, it is estimated that many researches, studies and various plans for development, use of water resources and hydrostructure. According to the above mentioned it was used, rain and discharge daily data of the Bar-Ariyeh area of Razavi Korasan province were used to estimate runoff from the extracted number curve method from the Natural Soil Conservation Service (SCS-CN). For this purpose, rainfall and discharge data of Bar and Ariyeh stations during the period of 56 years and in the daily scale, the value of the curve number in the three conditions of previous moisture in low, medium and high antecedent moisture conditions of soil was evaluated. The results showed that the maximum, minimum and average values of the curve number in summer and autumn were 93, 91, 92 and 85, 81, 83 percent, and in the spring and summer were 81, 79, 80 and 78, 76 and 77 percent in The domain was studied. The highest and lowest monthly average number of curve number for April and January were 93 and 76 respectively. In addition, the maximum and minimum amount of runoff was calculated for April and September with a numerical value of 12.45 and 1.29 mm in the statistical period.