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Estimation of runoff for agricultural watershed using SCS curve number and geographic information system Land use / Land cover map The conventional land use/ land cover map of the watershed was obtained from the Soil conservation department of Damodar valley Corporation, Hazaribagh, Jharkhand State. Boundaries of different land use were digitized in ARC/INFO and the attributes were given. Five land use/ land cover were categorised in the watershed (Table. 1 and Fig 1).  Fig.1 Land use/Land cover present in the watershed Table: 1. Land use / cover classes present in the study area (Year 1993)
Soils The soil map of the watershed was traced, scanned and rectified in ERDAS IMAGINE 8.4 by using the registered topographic maps. Boundaries of different soil textures were digitized in ARC/INFO and the polygons representing various soils class were assigned and different colours for recognition (Fig. 2). hydrologic soil groups i.e. A, B, C, and D were considered for the classification of soils of the watershed. The soils of group A were of low runoff potential, high infiltration rate, the soils of group B were of moderate infiltration rate, moderately well drained to well drained. The soils of group C were of moderately fine to moderately coarse textures, moderate rate of water transmission and the soils of group D were of slow infiltration and high runoff potential.  Fig.2. Soil Map of the watershed The Curve Number Method The Curve Number method (SCS, 1972), also known as the Hydrologic Soil Cover Complex Method, is a versatile and widely used procedure for runoff estimation. In this method, runoff producing capability is expressed by a numerical value varying between 0 - 100. In the past 30 years, the SCS method has been used by a few researchers because it gives consistently usable results (Rao et. al.,1996; Sharma et al. 2001; Chandramohan and Durbude, 2001; Sharma and Kumar, 2002) for runoff estimation. The SCS method with initial abstraction consideration is given below: The curve number method assumes that 
Where, Q = Runoff depth, mm P = Rainfall, mm S = Maximum recharge capacity of watershed after 5 days rainfall antecedent Ia = 0.3 S (Initial abstraction of rainfall by soil and vegetation, mm) CN = Curve Number, CN is found out from the table. 
Where CN = weighted curve number. CNi = curve number from 1 to any no. N. Ai = area with curve number CNi A = the total area of the watershed. |