ENVIRONMENTAL GEOCHEMISTRY OF NARMADA RIVER BASIN

Abstract

The Narmada river in India is a medium size river, which flows into the Arabian Sea and drains mostly over the volcanic rocks named as the 'Deccan Traps'. Masstransport and their important characteristics in the Narmada river have been studied by collection of various environmental samples such as, river water, groundwater, rain and spring water. All major dissolved chemical parameters, nutrients and strontium isotopic analysis were carried out to obtain information encrypted in the samples. Temporal and spatial variations in water flow and sediment loads in the Narmada river are inferred based on analysis of more than twenty years of data at various locations along the river and its tributaries. The monsoon rains control water flow in the river to a large extent, however groundwater discharge and dams/reservoirs also regulate waterflow. A number of important factors and their influence on water and sediment transport variability have been identified, which include rainfall, relief, catchment area, basin geology, soil characteristics and presence of reservoirs/dams. Major ion chemistry of the river water covering the Narmada river and its tributaries were carried out from samples collected during 2003-04, during different time periods, to understand seasonal variability. Daily, seasonal, annual and decadal variations have also been interpreted. Acomparative description of water chemistry ofNarmada river with other rivers in the world, flowing over basaltic terrains have been presented. Physical and chemical weathering rates in the basin show excellent correlation, indicating their complement nature. Sediment flux by the Narmada river have been estimated based on long term data. The concentrations of dissolved inorganic nitrate, phosphate and silica and their loads at different locations on Narmada river and its tributaries have been studied, temporal and spatial variability observed and flux rate calculated. The influence of the presence of dams on the retention of sediment load, chemical load, nutrient load and flux have been established. The thesis is structured and presented as follows: Chapter 1 deals with an overall introduction of physical and chemical weathering processes, their regulating factors and the role of weathering processes in the global environment. Some recent and previous works on rivers flowing over volcanic provinces have been described. The importance of studying Narmada river is identified and objectives for the present work have been delineated. The introductory chapter is covered with 2 figures and 1 table. Chapter 2 deals with the details of study area "The Narmada River Basin". Various features of the study area, including information on the drainage net work, prevailing climatic conditions, geology, soils, vegetation and land use have been described in detail and illustrated with 15 figures and 6 tables. Chapter 3 deals with the information on time of collection of samples, hydrological parameters of sampling locations and methodology adopted for analytical details and described with 1 figure and 4 tables. Chapter 4 presents the results with discussion. The chapter mainly concerns with (i) water and sediment characteristics, (ii) dissolved chemical compositions and (iii) nutrient flow patterns. The presented data are discussed with various interpretations. It focuses on major ion chemistry of the Narmada mainstream and major tributaries, by using water samples collected during the present work and the multi-annual data, from compositions of rain, spring water and ground water. Chemical and sediment flux are presented and their controlling factors established. Specific flux of strontium and nutrients have also been estimated. The methodology adopted for calculation of weathering rates and the coupling between various weathering parameters are discussed. The role of natural and anthropogenic processes involved in regulation of water and sediment flow are discussed and illustrated with 51 figures and 25 tables. In addition, abstract, conclusion and references cited in the text are included in the thesis.