Particle size characteristics of suspended sediments and subglacial hydrology of Dokriani Glacier, Garhwal Himalaya, India

Abstract

Diurnal and seasonal variations in particle size characteristics of suspended sediments of Dokriani glacier meltwater were studied during the 1994 ablation period (May-October). Diurnal suspended sediment concentration curves exhibit two prominent peaks from May to mid-August and only one peak during the rest of the ablation period. The first peak resulting from dominance of fine and medium sand contributed to the rising limb of the diurnal hydrograph, whereas the second peak was dominated by fine and medium silt which coincides with the diurnal discharge peak. The trends observed on the appearance of silts and sand particles on diurnal scales at various stages of the ablation period suggest that the subglacial drainage system comprises a diurnally-reversing hydraulic gradient between the channels and distributed system along with translatory flow through the distributed system. This study suggests that the subglacial zone is the major source of sediments in the Dokriani glacier meltwaters. However, high intensity monsoonal rainfall has contributed supraglacial sediments and resulted in bimodal distributions. Fines (clay to medium silt) are the dominant classes in the suspended sediments except during the spring event; the supraglacial sediments had coarsely skewed distributions. Caractéristiques granulométriques des matières en suspension et hydrologie du glacier Dokriani (Garhwal Himalaya, Inde)Résumé Les variations diurnes et saisonnières de la granulométrie des matières en suspension transportées par les eaux de fonte du glacier Dokriani ont été étudiées durant la période d'ablation de 1994 (mai-octobre). La courbe journalière de la concentration des matières en suspension présente deux extremums de mai à la miaoût et un seul extremum durant le reste de la période d'ablation. Le premier extremum résulte de la dominance des sables fins et moyens le long de la branche ascendante de l'hydrogramme journalier, alors que le second résulte de la présence de silts fins et moyens et coïncide avec le maximum journalier de débit. Les tendances observées concernant l'aspect des silts et des sables à l'échelle journalière pour différents moments de la période d'ablation suggèrent que le système de drainage sous-glaciaire subit tous les jours des renversements de gradient hydraulique entre ses chenaux allant de pair avec un flux d'eau transversal. Cette étude suggère que, en ce qui concerne les eaux de fonte du glacier Dokriani, le domaine sous-glaciaire est le principal fournisseur de sédiments. Les fortes intensités des pluies de mousson entraînent toutefois une contribution de sédiments du domaine supra-glaciaire et sont à l'origine de distributions bimodales. Les matières en suspension sont surtout constituées de fines (argiles à silts moyens) sauf au printemps et les sédiments supra-glaciaires sont distribués de façon très asymétrique.

Annual Sediment Transport Dynamics in the Narayani Basin, Central Nepal: Assessing the Impacts of Erosion Processes in the Annual Sediment Budget

“…This latter observation confirms that these high TOC values are not an artifact controlled by grain size but indicate significant addition of soil‐derived material to the Narayani sediment load during the premonsoon period. The smaller grain size during that time is also compatible with a soil signature (supporting information Figures S9 and S11), although we cannot rule out alternative explanations such as low discharge and turbulence limiting the coarse grain suspension and/or glacial fine‐sediment contributions (Thayyen et al, ).…”

Particle size characteristics of suspended sediment transported in meltwater from the Gangotri Glacier, central Himalaya — An indicator of subglacial sediment evacuation

“…This study has not analyzed the supraglacial sediment characteristics, but other studies carried out in the nearby region suggest that supraglacial sediment generally follows coarsely skewed patterns, whereas the sediment contribution from subglacial drainage systems usually follows symmetrical to finely skewed patterns (Thayycn et al, 1999;Owen et al, 2003). While analyzing seasonal distribution, we observed that particle sizes of the suspended sediments during peak melting seasons do show negatively skewed patterns.…”

“…The early occurrence of peak melting, when the total melt period is six months, supports the idea of reduced effectiveness of the system to produce sediment as the season progresses (Raymond et al, 1995). Localized variations in SSC with diurnal discharge could be due to translatory flow of hydraulically activated gradient within the subglacial aquifer that is controlled by the bed topography and water pressure variations in the channel (Gurnell and Fenn, 1984;Thayycn et al, 1999) and by hysteresis (Singh et al, 2005). From the point of view of particle size, low flow velocity mostly allows finer sediment to evacuate leaving behind coarser particles for the peak melt period (Fig.…”

Temporal and spatial variations in water discharge and sediment load in the Alaknanda and Bhagirathi Rivers in Himalaya, India

“…A large number of published work on the hydrological studies related to Higher and Lesser Himalayan Rivers and glaciers have focused to understand the glacial runoff characteristics, water chemistry, silicate weathering and CO 2 consumption, erosion rates, etc. (Abbas and Subramanian, 1984;Sarin and Krishnaswami, 1984;Raymo and Ruddiman, 1992;Hasnain and Chauhan, 1993;Bhatt and Saklani, 1996;Hasnain and Thayyen, 1999;Pandey et al, 1999;Thayyen et al, 1999;Jain, 2002;Hasnain, 1998, 2002;Bickle et al, 2003;Vance et al, 2003;Singh et al, 2005;Chakrapani, 2005b;Varun and Kireet, 2006 and many others). Most of these studies were based on parameters deduced from seasonal samples collected from the glaciers, and in fluvial studies considered water flow only at three locations namely, Alaknanda River at Devprayag, Bhagirathi River at Devprayag and Ganga River at Rishikesh, which were made available by Rao (1975).…”