GIS-Based Monitoring and Evaluating Effectiveness of Execution of Catchment Area Treatment Plan of Rangit Hydroelectric Project (Sikkim), India

摘要

The aspect of capturing temporal details by a space born platform (Satellite) is helpful in monitoring of environmental aspects for any hydropower projects especially its catchment, pre & post-project land use status, etc. with appropriate ground truthing. The use of satellite remote sensing coupled with GIS has been realized as an effective tool for formulation as well as temporal monitoring of Catchment Area Treatment (CAT) plan. A multi-spectral satellite remote sensing data with its synoptic and multi-temporal capability provides spatial information on forest cover, geology, hydrogeology, soils and landuse pattern to effectively characterize and monitor catchment properties. Rangit Hydroelectric Project (60 MW), constructed and owned by National Hydroelectric Power Corporation Ltd. (NHPC), was completed in December 1999 and started commercial generation since February 2000. The Catchment area of this project consists of 26 subwatersheds (SWS) covering an area of 979.02 sq km. Out of these, six sub-watersheds have been considered for treatment under CAT works based on priority categorization as per All India Soil and Landuse Survey (AISLUS) methodology. Subsequently, land falling under 'very high' & 'high' severe erosion intensity under these SWS were considered for treatment through biological measures viz., afforestation, horticultural plantations, agroforestry, silvi-pastoral development, bamboo plantation, avenue plantation etc. and engineering measures viz., check dams, catch water drain, trenches etc. The Catchment area treatment work was taken up in phased manner (year wise) starting from 1995-96 and completed in 2002-03. To assess the pre project scenario the November 1994 satellite data of IRS-1B LISS-II was used and further CAT status was evaluated by using IRS 1D LISS-III Imagery of December 2002 and IRS P6 LISS-III Imagery for December 2006. The present paper, a case study, portrays application of Remote Sensing & GIS techniques to evaluate the effectiveness of CAT Plan implemented in the free draining catchment of Project. A comparative analysis in effectiveness of CAT works has been done. The result shows that there is an increase of 8892 ha of overall forest cover in the area i.e. from 41378 ha to 50270 ha between November 1994 to December 2006, respectively. A decrease in the area under soil erosion category of 'very severe' has been recorded. A larger area which were under agriculture practices during 1994 are now converted into Open forest and, simultaneously, a declining trend in earlier Dense forests have been observed due to cutting down by the local residents, as the area is prone to shifting cultivation. The present study shows the effectiveness of CAT plan execution, as the study area shows gradual improvement and stability in the terrain in respect of Landuse changes and soil erosion after implementation of CAT plan.