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Abstract
Geographic Information Systems (GIS) has emerged as a significant support tool for managing and analysing water resources using digital elevation models (DEMs) of land surface terrain. GIS is now accepted as a useful tool for assembling water resources information. Water management agencies are building GIS data sets to support their operations. In the present work, GIS provides a consistent method for watershed delineation for the proposed and existing irrigation schemes for some districts of the state of Jharkhand, India. The types of schemes are Checkdams, Ahar, Ponds etc. Around 2500 irrigation Schemes are marked on or near the drainage network of the study area as point feature classes, which are stored in the geodatabase (GDB) format of ArcGIS.

A Digital Elevation data set has been created for the area to get basic elevation data of the area for use in watershed analysis. A Digital Elevation Model (DEM) is a grid or raster of square cells whose cell value is the land surface elevation in the centre of cell. As digital elevation data sets for land surface terrain become more refined, their cell size decreases and the number of cells increases to the point where studying a large region, like a district, with a single DEM data set is cumbersome and impractical. This is the reason why the 4 meter DEMs were created block wise, after dividing the districts in various blocks. With 4 m cell size, the information from the DEMs for watershed analysis becomes more precise and reliable. Furthermore, 1 m contours are interpolated from the DEMs using ArcGIS. The NRSA Satellite Image of the area of concern was acquired and processed for land use classification in five broad categories namely Agriculture, Forest, Waterbody/Wetland, Settlement, Wasteland (Wasteland with scrub, Wasteland without scrub and sand).

In order to carry out watershed analysis of various irrigation schemes, ArcHydro tools were used. ArcHydro is a geo spatial and temporal data model for water resources that operates within ArcGIS. ArcHydro has an associated set of tools that populate the attributes of the features in the data framework, interconnect features in different data layers, and support watershed analysis. Watershed areas of all the irrigation schemes were calculated and saved as polygon feature classes using ArcHydro tools.