REMOTE SENSING AND GIS IN LANDUSE MODELLING OF DWARKESHWAR WATERSHED, WEST BENGAL

Abstract

Land is a non-renewable resource and hence assessment of landuse change in a temporal sequence is essential for planning and development of land and water resources. Integrated remote sensing and GIS technique provides excellent information, understanding of the relationships between different influencing variables and spatial distribution and change of landuse in a cost-effective manner. In the present study, an integrated remote sensing and GIS based methodology have been developed and successfully demonstrated to analyze landuse-groundwater relationship in the Dwarkeshwar watershed, West Bengal, India. There are four components of this study; (a) to evaluate the nature of changes in the selected landuse categories, (b) to identify the factors influencing this change, (c) their role in controlling the groundwater scenario of the study area and (d) to suggest remedial, measures to improve the groundwater regime of the area through delineation of the groundwater potential zones and suitable artificial recharge sites. The Dwarkeshwar Watershed with a semi-elliptical shape (86°37'E- 87°28'E and 23o00'N-23o32' N) occupies the north central part of the Purulia district but the major part of it is situated in Bankura district of West Bengal state, India. The total area of the watershed is 2270 sq.kms. The major river draining the entire watershed is the Dwarkeshwar river, which is the tributary of Damodar river. The Dwarkeshwar river originates from the eastern highlands of Purulia district flows through Bankura district from NW to SE. After leaving Bankura district it confluences with river Silai (or Silabati), and thereafter it falls into river Bhagirathi as river Rupnarayan, just before Bay of Bengal. Physiographically the whole of the watershed forms an intermediate tract between Chotanagpur plateau in the west and the alluvial plains in the east, presenting a variety of landforms varying between the dissected plateau in the west and the undulating alluvial plains in the east. The study area consists of pink granite and granite gneiss of the Pre-Cambrian Shield of India with a thick mantle of laterite and older alluvium lying over it. Towards the eastern part of the area, newer alluviums of recent time basically sand, silt, and clay. I The present study is aimed to achieve the following objectives: (i) to develop an integrated remote sensing and GIS technique to establish and evaluate the relationship between landuse and groundwater hydrology, (ii) to identify factors influencing this relationship and their role in controlling the groundwater scenario of the study area, (iii) to evaluate the nature of changes in selected landuse categories, (iv) to have a quantitative assessment of groundwater recharge, (v) to delineate the groundwater potential zones in the area, (vi) to suggest suitable sites for artificial recharge to augment groundwater in the study area, and (vii) To develop a software in the form of an extension to the Arc View 3.x GIS package for immediate extraction of groundwater related properties of an area. Three types of data have been used for the present study, namely remote sensing data, e.g. IRS-1B-LISS-II and IRS-1C-LISS-III data, field data, e.g. depth of water level, rainfall data, etc. and the existing maps, e.g., topographic, geological, geomorphological and soil maps, etc. In order to bring these into a single spatial georeferencing scheme, all the data have been registered to the base map, prepared from the Survey of India topographic maps. Remote Sensing data (IRS LISS - II and LISS - III) have been enhanced to extract pertinent information using suitable image processing techniques. Classified landuse maps have been generated for both the years 1988 and 1996 from the satellite data and landuse change has been determined with area statistics by subtracting the two images. Thematic information layers on geology, geomorphology, lineaments, soil and landuse have been prepared from remote sensing images supported by ancillary data. Digital Elevation Model has been generated from elevation contour from topographic maps through interpolation. Automatic extraction of drainage network has been performed and analysed with other datasets in GIS. Depth of water level data have been analysed to study in the long-term behaviour of the water level in the area. Groundwater recharge has been calculated by Thomthwaite and Mather Model of water balance and specific yield and water level fluctuation method in GIS environment. Rainfall data have been analysed and used to estimate runoff depth and peak discharge for the prioritisation of the watershed using SCS curve number method. This is used to prioritise the watershed on the basis of runoff generated due to existing landuse condition and soil type. Potential soil loss due to erosion for the watershed has been calculated using USLE (Universal Soil Loss Equation) Model. Moreover, Normalized Difference Vegetative Index (NDVI) has been calculated from the classified landuse images for both the years 1988 and 1996 and the NDVI difference image is generated to identify the change in vegetation cover. All the information layers have been integrated through GIS analysis and the criteria for groundwater prospective zones mapping and artificial recharge site selection have been defined. Each parameter and also each class of the parameters have been assigned appropriate weights on the basis of their relative contribution towards the output. Finally, the changes in groundwater resources are correlated with the landuse changes. Programs are developed in ArcView Avenue programming language to create an extension for ArcView 3.1 and 3.2 for immediate extraction of groundwater potential zones and artificial recharge sites. In this study, an integrated remote sensing and GIS technique has been developed for evaluation of landuse groundwater relationship and has been successfully tested for the Dwarkeshwar Watershed, West Bengal, India. This study has illustrated that integrated remote sensing and GIS approach is an appropriate tool for convergent analysis multidisciplinary data sets required for landuse groundwater relationship studies.