The Bhagirathi streams are a major source of fresh water in the form of glaciers meltwater streams and monsoonal phenomena. The watersheds of the Bhagirathi basin is trending towards water chemistry as well as changing morphological and land cover features due to the climatic and anthropogenic activity. To understand seasonal hydrochemistry and the impact of watershed morphology a total of 32 stream water samples collected during post and pre-monsoon seasons. The bicarbonate is the most dominant ion in the streams water followed by Na+, Ca+2, SO4-2, Cl-, SiO2, K+, and Mg+2. The results were found that HCO3- is in very good correlation with the base cations Ca+2, Mg+2 and Na+ in both pre and post-monsoon seasons. The higher concentration of HCO3- in Bhagirathi stream water and its positive correlation with Ca+2 and Mg+2 indicates that their main source comes from the dissolution of carbonates. Most of the hydro-chemical parameters (EC, pH) and ions (Ca+2, Mg+2, Na+, K+, HCOf-, SO4-2, Cl-, and F-) indicated a relationship with morphometric and land cover and these parameters vary with the season. It is observed that elevation, relief, basin length, area, and perimeter impact on stream water chemistry. Due to the processes of chemical weathering, mixing of the groundwater, snow/glacier meltwater, and surface water components responsible for the seasonal variation in the hydrochemistry of streams. Impact of agriculture land is more dominant than any land cover followed by barren land and glacier cover that influence the hydrochemistry of streams.
As the discharge increases and sediment supply decreases, the rivers incise forming terraces. When considered over a long period, the sediment storage in the valleys become a source for sediment supply and may contribute a significant amount of the total sediment budget. An estimate made by mapping the area of the terraces and multiplying it with their thickness suggests ~ 4800 million tonnes of sediments is trapped between Pipalkoti and Devprayag in the Alaknanda valley (Fig. 1a). These terraces continuously get eroded by various processes such as gullying, undercutting by rivers and collapsing under the influence of gravity contributing to the adjacent rivers. Therefore, apart from the rate of erosion of the bedrock, it is essential to calculate the rates of erosion of such valley fill deposits and quantify the amount of sediment supplied by them to the river systems. In this study, an attempt has been made to determine the rate of erosion by calculating the volume of sediment removed from ã 17 ka terrace located in NW Lesser Himalaya. River terraces (referred to as terraces from here onwards) form when a river becomes unstable and incises its bed (e.g. Schumm et al., 1987; Bridgland, 2000; Wegmann and Pazzaglia, 2009). Thus, terraces record the time of instability of the channel, making it an excellent geomorphic marker. Accordingly, terraces are commonly studied to identify tectonic and climatic events causing changes in the river dynamics in the geological past (e.g. Wegmann and Pazzaglia, 2009). Study area A requirement of this study was a terrace of known age with least interference from external processes such as anthropogenic activity or sediment supply on terrace surface by local stream, so that sediment volume of the terrace is only altered due to natural erosional processes. Thus, a terrace located in the Srinagar (Garhwal) region along the left bank of the Alaknanda River was chosen for the study (Figs. 1a,b) which fulfilled the above requirement. A village named Swit is located on top of the terrace under investigation, hence from here onwards this terrace is referred to as the Swit Terrace. It is located 5 km ENE from the main Srinagar city (Figs. 1a,b). The elevation of the Swit terrace is ~ 655 m asl (above sea level) and covers an area of 0.6 km 2 and the elevation of its top from the river bed is ~ 100 m. A small stream originating from the adjacent valley walls, and locally called Swit nala, flows into the Alaknanda river. The local streams are seasonal and are fed mainly by the monsoon. The study area receives an average annual rainfall between 1000 mm to 1500 mm (Sati et al., 2007) with maximum rainfall occurring between mid-June to mid-September. Method A geomorphic map of the study area prepared by previous worker Depositional river terraces in tectonically active regions are used to determine the relative roles of tectonic and climatic changes in the landscape evolution of an area. Apart from providing evidences of tectonic and climatic shifts, these terraces over a long period act as a s...
Hydrogeochemical studies were carried out to assess the quality and evolutions of the streams in the Bhagirathi basin during high and low flow of water in the given environment. The hydrochemical characteristics of the streams water indicated that silicate and mixed type of weathering dominated in the Bhagirathi watersheds. The stream's water chemistry is mostly influenced by deeper sources of water through joints and fissures in the stream watersheds. A comparison between ion concentrations in the samples suggested that few samples have high sodium and fluoride exceeding the permissible limits. Based on dissolved ions in stream water, the water quality index falls into the excellent/good category (80%), poor quality (14%) and unsuitable class (6%), respectively. Kelly and Permeability index results suggest the impact of rock type on water quality that may affect local agricultural productivity.
Glaciated sediments are a significant source to know the glacier environment processes. Glacial meltwater streams draining from the Himalayan glaciers carry with a different type of sediment sizes, because of the supraglacial, englacial, and subglacial debris, as well as formation of sediments from erosion by the movement of the ice. This study examines mineralogical and textural characteristics of sediments transported in the selected Indian Himalayan glacier meltwater streams. The results indicate that various sedimentological diversity occurring within proximity of active glaciations due to glacio-hydrological processes. Sedimentological and mineralogical characteristics suggest that sediments of the proglacial area are polygenic in nature. A comparative change in feldspar/quartz among bedrock, sand, and clay suggested that the active geochemical weathering regime at a low-temperature environment maturing the sand composition. The less clay fraction in glacier sediment indicates limited generation of clay minerals in the glacier environment. Change in clay composition from supraglacial moraine to proglacial environment indicated a chemical alteration in glaciated valley assisted by low slope glacio-fluvial environment.
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