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

摘要

The aspect of capturing temporal details by a space born platform (Satellite) is helpful inrnmonitoring of environmental aspects for any hydropower projects especially its catchment, pre &rnpost-project land use status, etc. with appropriate ground truthing. The use of satellite remoternsensing coupled with GIS has been realized as an effective tool for formulation as well asrntemporal monitoring of Catchment Area Treatment (CAT) plan. A multi-spectral satellite remoternsensing data with its synoptic and multi-temporal capability provides spatial information onrnforest cover, geology, hydrogeology, soils and landuse pattern to effectively characterize andrnmonitor catchment properties.rnRangit Hydroelectric Project (60 MW), constructed and owned by National HydroelectricrnPower Corporation Ltd. (NHPC), was completed in December 1999 and started commercialrngeneration since February 2000. The Catchment area of this project consists of 26 subwatershedsrn(SWS) covering an area of 979.02 sq km. Out of these, six sub-watersheds havernbeen considered for treatment under CAT works based on priority categorization as per All IndiarnSoil and Landuse Survey (AISLUS) methodology. Subsequently, land falling under 'very high' &rn'high' severe erosion intensity under these SWS were considered for treatment throughrnbiological measures viz., afforestation, horticultural plantations, agroforestry, silvi-pastoralrndevelopment, bamboo plantation, avenue plantation etc. and engineering measures viz., checkrndams, catch water drain, trenches etc. The Catchment area treatment work was taken up inrnphased manner (year wise) starting from 1995-96 and completed in 2002-03. To assess the prernproject scenario the November 1994 satellite data of IRS-1B LISS-II was used and further CATrnstatus was evaluated by using IRS 1D LISS-III Imagery of December 2002 and IRS P6 LISS-IIIrnImagery for December 2006.rnThe present paper, a case study, portrays application of Remote Sensing & GISrntechniques to evaluate the effectiveness of CAT Plan implemented in the free drainingrncatchment of Project. A comparative analysis in effectiveness of CAT works has been done.rnThe result shows that there is an increase of 8892 ha of overall forest cover in the area i.e. fromrn41378 ha to 50270 ha between November 1994 to December 2006, respectively. A decrease inrnthe area under soil erosion category of 'very severe' has been recorded. A larger area whichrnwere under agriculture practices during 1994 are now converted into Open forest and,rnsimultaneously, a declining trend in earlier Dense forests have been observed due to cuttingrndown by the local residents, as the area is prone to shifting cultivation. The present study showsrnthe effectiveness of CAT plan execution, as the study area shows gradual improvement andrnstability in the terrain in respect of Landuse changes and soil erosion after implementation ofrnCAT plan.