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Hydrological Modelling of canal command using Remote Sensing and GIS
Pre-processing To develop a topographic map of the command, topographic data are digitized and interpolated using the topogrid interpolation technique available with GIS, Arc Info. A grid size of 200 x 200 m is used. The optical and RADARSAT, SAR data are used to develop the land use map of the study area (Fig.1). The command has six distinct land uses, namely, early paddy (10.9%), medium paddy (41.5%), late paddy (15.5%), fallow (12.5%), homestead (9.5%), and water bodies (10.1%). Paddy is the only crop in the Kharif season, which covers about 68.0% of command area. Fig. 2 shows the conventional soil distribution map of the command as obtained from NBSS, Calcutta. Four major types of soil covering the whole study area, namely, loamy sand (30.6%), sandy loam (35.3%), fine sandy loam (19.7%) and fine loamy sand (14.3%) are found. Sandy loam is the predominant soil of the command. Also, a soil distribution map is prepared using the IRS-1C LISS III data for December 1998 (Fig. 3). The percentage area coverage by different soils, loamy sand, sandy loam, fine sandy loam and fine loamy sand, are 13.1%, 29.6%, 32.7% and 24.5% respectively. Here also, the same four soils are found, however, the spatial distribution and the area coverage differs. Soil moisture retention curve was experimentally determined for each of these soils by using the pressure plate apparatus up to 15 atmospheres. The empirical van Genutchen model (Maidment, 1992) is fitted to the experimental data and the relationship is extrapolated over the required range for MIKE SHE (pF = 0 to 6, i.e., up to 1000 atmospheres). Fig. 4 shows the depth to the pyretic surface for the pre-monsoon periods of 1999. Water table depths for pre-monsoon period vary from 4 m at the upstream to 18 m at the downstream, whereas for post-monsoon period the depth varies from 4 to 16 m, with downstream end getting waterlogged. Fig. 5 shows the delineated polygons map having different total applied water depth (sum of irrigation and rainfall). This polygon map is prepared by overlaying the precipitation polygon map (three stations i.e., Burdwan, Kalna and Katwa) on the polygon map of distributary commands (13 reaches). 
Fig. 1 Land use/cover map 
Fig. 2 Soil distribution map (NBSS) 
Fig. 3 Soil variability map(Remote Sensing) 
Fig. 4 Irrigation and rainfall distribution polygon map 
Fig 5. Ground water table variation map For the year-1999 (pre monsoon) 
Fig. 6 Observed & simulated ground water table variations for the Kharif-1999 Methodology The output from Arc Info digitising program is transformed into the type 2 format (grid) files of MIKE SHE using the developed link. Number of grids in the x- and y-directions are taken as 166 and 187 respectively with the cell size of 200 m x 200 m. The time series data files of potential evaporation, precipitation plus irrigation, and vegetation parameters, such as leaf area index and root depth as a function of time, are prepared for running the simulation for Kharif season. MIKE SHE model is applied to 6 main canal system of DVC to see the feasibility of integrating RS data with DHM for the hydrological analysis of the command area. The model was calibrated for the study area during 1 May to 30th October 1999. The calibration was done by varying the saturated hydraulic conductivity, 'Ks', drainage constant and exponent 'n' in the hydraulic conductivity function and by comparing the post-monsoon observed and simulated groundwater levels at measured locations. The calibrated model was then used to simulate different scenarios. Simulation scenarios Model simulations are done with four different combinations of Remote Sensing (RS) and conventional data. The different combinations are:
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