Modified hydrologic regime of upper Ganga basin induced by natural and anthropogenic stressors

Abstract

Climate change and anthropogenic activities pose serious threats to river basin hydrology worldwide. The Ganga basin is home to around half a billion people and has been significantly impacted by hydrological alterations in the last few decades. The increasing high-intensity rainfall events often create flash flooding events. Such events are frequently reported in mountainous and alluvial plains of the Ganga basin, putting the entire basin under severe flood risk. Further, increasing human interventions through hydraulic structures in the upstream reaches significantly alter the flows during the pre-and post-monsoon periods. Here, we explore the hydrological implications of increasing reservoir-induced and climate-related stressors in the Upper Ganga Basin (UGB), India. Flow/sediment duration curves and flood frequency analysis have been used to assess pre-and post-1995 hydrological behaviour. Our results indicate that low and moderate flows have been significantly altered, and the flood peaks have been attenuated by the operation of hydraulic structures in the Bhagirathi (western subbasin). The Alaknanda (eastern subbasin) has experienced an increase in extreme rainfall and flows post-1995. The downstream reaches experience reservoir-induced moderate flow alterations during pre-and post-monsoon and increasing extreme flood magnitudes during monsoon. Furthermore, substantial siltation upstream of the reservoirs has disrupted the upstream–downstream geomorphologic linkages.

Channel morphodynamics and sediment budget of the Lower Ganga River using a hydrogeomorphological approach

“…A global survey of 145 large rivers suggests that 50% of these rivers show a declining trend in sediment load (Walling & Fang, 2003), and several of these—such as the Mississippi, Red, Hanjiang, and Ganga—have been impacted by anthropogenic interventions (Blum & Roberts, 2009; Hu, 2019; Milliman & Syvitski, 1992). A recent study in the upper Ganga basin suggests that apart from natural forcing (rainfall), the dams and barrages (including channel modifications because of siltation behind them) have contributed significantly to the increase in frequency of extreme events in this region (Swarnkar, Mujumdar, & Sinha, 2021).…”

Increasing Flood Frequencies Under Warming in the West‐Central Himalayas

“…The Bhagirathi River originates from the Gangotri glacier (30.92°N, 79.08°E) at about 4,023 m. The Alaknanda originates from the Satopanth glacier (30.79°N, 79.37°E) at about 4,600 m. Both the tributaries join at Devprayag to form the River Ganga downstream. Four dams are present in the Bhagirathi basin (Swarnkar et al., 2021). Most of them became operational before 2010.…”

“…Most of them became operational before 2010. Only two dams in the Alaknanda basin are present (Swarnkar et al., 2021), which became operational after 2015 (Figure 1a). This study selects four Central Water Commission (CWC) gauge stations: Tehri (in the Bhagirathi basin), Alaknanda basin outlet, Devprayag, and Rishikesh (Figure 1a).…”

More than one landslide per road kilometer – surveying and modelling mass movements along the Rishikesh-Joshimath (NH-7) highway, Uttarakhand, India

“…The NH-7 ascends from 400 m at Rishikesh to approximately 2000 m at Joshimath, crossing steep terrain with soil mantled slopes that range in inclination from 20° to 40°. Mean annual rainfall varies from 1500-2000 mm around Rishikesh to 1000-1200 in Joshimath with 80-86 % and 60-70 % delivered by the Indian summer monsoon (June to September), respectively (Pai et al, 2014;Swarnkar et al, 2021). Air temperature in Rishikesh is always above freezing and ranges between 4 and 40 °C, whereas the temperature in Joshimath varies between -10 and 20 °C.…”