MINERAL LOAD AND TRANSPORT IN UPPER GANGA BASIN

Abstract

In recent years studies on the effect of geochemistry on the environmental health has become an interesting area for technologists. Any rational study on a riverine system cannot be full fledged without a fairly adequate knowledge of its mineral quality. Mineral quality, commonly known as salinity, is a basin wide problem of a river and critically important to the users of lower reaches. The in-depth study of mineral occurrence, behavior and transport is an extremely important aspect in river pollution studies because minerals are the first to enter the water-body in its virgin state and exist within it till the river joins the ocean. River alimentation and flow regimes play an important role in the occurrence and transport of minerals in a riverine system. In general, the geology, weathering and erosion of rocks play a key role in the mineral transport in the areas where the human activities are minimum, but in the lower stretches of the river, human activities also contribute alongwith the abovesaid natural processes. Sometimes, the mineral concentrations in a riverine system are helpful in identifying the mineral sources in geochemical prospecting practices. (ii) The riverine system under the present investigations is Ganga river, the mighty and holy river of India, originating from the snow clad peaks of Himalayas. Ganga river travels approximately 2525 km in its long journey passing through U.P., Bihar and West Bengal. In addition to the traditional religious bearings, the waters are being used for irrigation, domestic and industrial purposes. The present investigation involved an in-depth study of occurrence and transport of minerals in the unexplored and zero pollution region of Ganga river, comprising of 510 km stretch from Badrinath to Rajghat Narora, 'The Upper Ganga Reach'. The investigations included the visualisation of the variation in other physico chemical parameters to identify the mineralized zones, the influence of important tributaries, identification of human activities and their impact on mineral transport and to develop a suitable mineral index which reflects the mineral transport. The physico chemical parameters, which influence the occurrence and transport of minerals like pH, ORP, conductivity and total dissolved solids alongwith the important cationic and anionic mineral constituents were chosen for the study. To identify the zones of importance extensive surveys were

conducted from Dec. 1984 to May 1985 at the primary network sampling stations. The stations were fixed on the basis of reconnaissance surveys. The data collected has been analysed and the spatial variations explored. The observations between Rishikesh and Haridwar revealed the importance of the stretch with respect to mineral loading of Ganga river. In this 22.2 km stretch the withdrawal of Ganga water into a canal at Chi 11a head works leaves very little water to flow downstream and the Song river, which carries a lot of mineral matter joins Ganga at this point. In this stretch the recharge of ground water during lean flow season was also found to be significant. Song river drains Doon Valley in its course, which is known for its richness in limestone and phosphorite mineral reserves. To assess the impact of Song river on Ganga river, the stretch of Song river was also chosen and the secondary network sampling stations were fixed. The data of extensive sampling on Ganga and Song rivers was exposed to checks for its accuracy of the analysis. To represent the chemical composition of river systems Hill-Piper Trilinear diagram was plotted which revealed that the composition of Ganga river is dominated by alkaline earths and weak acids throughout the stretch, except at Satyanarayana. At Satyanarayana, the waters showed a mixed type of quality, which is due to the (iv) confluence of Song. Same effect was also observed in the spatial trends of other parameters. Besides the general profiles of physico chemical parameters, Principal Component Analysis was resorted to classify the Ganga river into mineralized and non-mineralized zones, to find out dominating parameters at different locations, and to evaluate the validity of the sampling network and frequency. The results obtained from PCA are in concordance with the observations. The flow of Song river is chiefly derived by the effluent ground water springs. The four major tributaries Baldi, Bandal, Tawa and Bangla Rao, are the major sources to add more mineral content to the river. The chemical composition of Song river and its tributaries showed distinct spatial variations. The composition of Song water in the initial stages is constituted by alkaline earths and weak acids. After the confluence of Bandal river the composition of waters change and is governed by the presence of alkaline earths with strong acids. Later the waters exhibit a mixed type of chemical composition in which no single cation or anion pair exceeds 50 percent of the total ions. The temporal variation in mineral parameters clearly indicated the base flow and run-off conditions of the river, whereas, the spatial variations reflect the gradient of mineral

deposits in Song river stretch as it passes towards Ganga river through Doon Valley. To represent the mineral transport and the impact of various tributaries on the mineral profile of Ganga an attempt was also made to calculate mineral indices by using physico chemical parameters. The proposed indices were aimed to provide tangible information about the mineral quality of Ganga river by avoiding huge amounts of data. The formulations of the reported general WQI and statistical approaches were considered. Out of the reported indices the formulations of Horton's and Mc Duffie's RPI were considered because of the parameter flexibility. Among the statistical approaches, Harkins index was selected. To minimise the subjectivity in the proposed index, opinion poll was conducted for the selection of parameters, rating scale and weightages for the selected parameters. On the basis of responses received, the following parameters pH , total dissolved solids, bicarbonates, carbonates, chlorides, sulfates, calcium, magnesium, sodium, cadmium, nickel, manganese, total anions and total cations were included in the calculation. To assess the contribution of heavy metals in the mineral index values, indices were calculated separately by including and excluding the heavy metals. (vi) The trends of all the three indices were observed to be similar, but the extent of increase or decrease was different, because of difference in the formulations. In the trends of mineral indices in Ganga river the impact of Song was clearly visible and is supported by the trends of mineral parameters. From the mineral index profiles of Song river, the impacts of Baldi and Bangla Rao were distinct. Comparison of index values in Ganga and Song rivers, with and without heavy metals, clearly indicated the significance of heavy metal contribution in both the rivers.