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AVSWAT- a Spatial Decision Support System for Land and water management and its application for watershed management in Bankura district of West Bengal
The Model Soil and Water Assessment Tool (SWAT) SWAT is a river basin or watershed scale model developed by the USDA Agricultural Research Service (ARS). SWAT was developed to predict the impact of land management practices on water, sediment and agricultural chemical yields in large complex watersheds with varying soils, land use and management conditions over long periods of time. SWAT is a continuous time model operating on daily time step. The command structure of SWAT is presented in Fig.2. Model Components The sub-basin components of SWAT can be placed into eight major divisions--hydrology, weather, sedimentation, soil temperature, crop growth, nutrients, pesticides, and agricultural management.
Use of a basin scale model like SWAT needs great amount of time, expertise and cost for acquiring input data, running the model and analyzing the results. Due to the intrinsic spatial-temporal variability of watersheds, GIS technology is an essential and efficient method of collecting, storing and retrieving input data required for simulation models. GIS can elucidate landscape characteristics (e.g. topography, soil, climate, land cover and management) and effects of agricultural activities overlaying intrinsic hydrological attributes. Considering the above, a user- friendly, PC based tool, AVSWAT has been developed at the Blackland Research Center integrating SWAT and ArcView GIS version 3.0a software along with Spatial Analyst version 1.1 extension. The SWAT-ArcView interface is a tight coupling between a model and GIS (Burrough, 1995). The export of data from GIS to the SWAT model and the return of results for display are accomplished by Avenue routines that are addressed directly by the interactive tools of GIS (e.g. setting up parameter values via customized menus) and the exchange of data is fully automatic. Figure 3 shows the overview of the tight coupling between SWAT and ArcView GIS. The SWAT ArcView system consists of 3 key components: (1) preprocessor generating subbasin topographic parameters and model input parameters; (2) editing input data set and execute simulation; (3) postprocessor viewing graphical and tabular results.  System/Software Requirements
In the present study, the Chhatna block of Bankura (Fig. 4) has been selected for detailed study. Chhatna lies between 23 Degrees 11 Minutes and 23 degrees 30 Minutes north latitude, and between 86 Degrees 48 Minutes and 87 Degrees 2 Minutes east longitude. Total geographical area of the block is 448.1 sq km. There are total 288 mouzas in the block. There are five main drainages or streams within the the block, from north to south they are Gandheswari, Darakeshwar, Kansachara, Arkasa and Chagalkuta. The district though having an average rainfall of 1300 mm are considered as drought- prone , because of poor water management. 
Information Need Assessment for Watershed Management In order to develop such a SDSS for watershed management , initially a workshop was organized with the official ls of the district line departments involved in watershed management activities . The objectives of such interaction were to assess the information need of the user departments in this sector and sensitise them about such tools. Apart from this, all the schemes pertinent to watershed management were also scurtinised to assess the information need for them. On such exercise, it emanated that for district-level watershed programmes basic information products expected out of such tools are:
Running SWAT through the Arcview- SWAT interface (AVSWAT) using Chhatna data. Using the input maps and data files as discussed in Fig.3 for the study area AVSWAT was run through the interface. Watreshed delineation was started by using the Digital Elevation Model (DEM) grid and then removing any depression.. Then drainage network was delineated with a threshold value of 100 as it was found to be optimum for defining minimum numbers of cells to start delineating a stream. After the drainage network was delineated , the Chhatna boundary theme was added to the view and overlaid on the drainage network (Fig. 5).  The outlet point for delineating each watershed was selected by adding or deleting point(s) on the main stream intersecting the block boundary. Then, sub-basins and watersheds were delineated (Fig. 6) to generate watershed map for the Chhatna block . The numbers of watersheds delineated for different sub-basins are as follows: Darakeshwar - 15 Kansachara - 9 Arkasa - 3 Chhagalkuta - 3  |