Geospatial Data Analysis for Study of Suspended Sediments in Govind Ballabh Pant Reservoir, Singrauli Coalfield, India The EM energy incident on a water body is partly absorbed, partly reflected and partly scattered. Any primary signal from the water body is due to the total reflectance and back-scattered energy caused by the impurities in the water; these signals are used for water quality analysis. Further, the penetration depth of EM energy is influenced by the mineral content and/or size of the suspended sediments (Whitelock et al, 1978). It has been demonstrated that turbid water is more reflective than clear water both in the visible and near-infrared regions of the EM spectrum (Moore, 1978). Further, the measured signal is dependent on the wavelength used, the size & shape of the particles present, and their reflectance, absorption & refraction properties. A decrease in particle size results in an increase in reflective area. Hence, reflectance of water bodies can be studied to assess the dispersal pattern of suspended sediments in it. Data Processing & Analysis Digital satellite data were processed using Geomatica digital image processing system. Data processing was carried out to correct for geometric distortions, to calibrate the data radiometrically and to eliminate noise. Data of all the four bands were initially analyzed individually to determine the efficacy of different bands in mapping of suspended sediments. It was observed that there is a positive functional relationship between the concentration of suspended sediments and the spectral signatures recorded in band-3 (0.62 to 0.69 mm, in the Red region of EM spectrum) and band-4 (0.77 to 0.89 mm, in the near-infrared region of EM spectrum). Data of band-3, however, has a distinctive edge over the other band. Based on the histogram distribution of spectral values in bands-3&4, unsupervised classification was carried out using K-means clustering (Tou & Gonzalez, 1974). Four turbidity levels of the suspended sediments were identified namely ‘high’, ‘moderate to high’, ‘low to moderate’ and ‘low’.  Figure-2: IRS-1C (B:5,4,3) data of the year 1998 showing distribution of suspended sediments in GBP reservoir. Analysis of IRS-1C data of the year 1998 indicates that the suspended sediments are mostly concentrated in the western part of the reservoir where a number of thermal power plants and open-pit coal mining projects are situated. The ash ponds of the thermal power plants are located along the west bank of the reservoir. Moreover, the vegetation cover along the west bank of the reservoir is generally thin due to industrialization. This has caused a great deal of topsoil erosion resulting in discharge of suspended sediment load into the reservoir during the monsoon period. ‘High’ suspended sediment zone is present near Renusagar, Anpara, Singrauli and Vindhyachal power plants (locally known as super thermal power stations or STPS) (Figure-2). This is primarily due to the discharge from the ash ponds located in the periphery of the reservoir. The Balia stream (nala), flowing through Jayant and Dudhichua coal mining projects, is also discharging its sediment load during the monsoon period into western part of the reservoir. In pre- & post- monsoon periods, the load carrying capacity of Balia nala is considerably reduced; silts are deposited along the streambed only. Eastern part of the reservoir is almost free from suspended sediments except near Rihand power plant, which is mostly due to ash pond. The discharge of sediment load by the stream is negligible as compared to the overflow load from the ash ponds. Analysis of IRS-1C data of the year 2001 reveals that in addition to siltation in the western part of the reservoir, the eastern fringe has also started getting silted showing moderate to high turbidity. This is because of the discharge from the ash pond of Rihand power plant. Moreover, there is progressive depletion of vegetation cover in and around the catchment area causing a great deal of topsoil erosion resulting in discharge of suspended sediment load into the reservoir. The central part of the reservoir, however, shows low turbidity (Figure-3).  Figure-3: IRS-1C (B:4,3,2) data of the year 2001 showing distribution of suspended sediments in GBP reservoir. The amount and composition of clay minerals, particularly the Kaolinite/Illite (K/I) ratio, in the suspended sediments/accumulated silt of the reservoir is an indicator of its provenance. Similarly, metal and trace element studies allow assessment of the pollution level in the reservoir. In the present study, an attempt has also been made to integrate the available analytical data of the suspended sediments/accumulated silt using MapInfo GIS; this has helped in quantitative assessment of the sediment’s provenance and status of pollution level in the reservoir. The concentration levels of Hg, Ti, V, Cr, Ni, Cu, Zn, Cd, Pb, As, Se, Sn, F, B and Al were determined for the sediment samples collected from different locations of the reservoir. Spatial distributions of concentration values (‘Al’ normalized) were mapped using GIS. |