Abstract
Extensive research of the variability of flows under the impact of climate change has been conducted for the Upper Indus Basin (UIB). However, limited literature is available on the spatial distribution and trends of suspended sediment concentrations (SSC) in the sub-basins of UIB. This study covers the comparative assessment of flows and SSC trends measured at 13 stations in the UIB along with the variability of precipitation and temperatures possibly due to climate change for the past three decades. In the course of this period, the country’s largest reservoir, Tarbela, on the Indus River was depleted rapidly due to heavy sediment influx from the UIB. Sediment management of existing storage and future planned hydraulic structures (to tap 30,000 MW in the region) depends on the correct assessment of SSC, their variation patterns, and trends. In this study, the SSC trends are determined along with trends of discharges, precipitation, and temperatures using the non-parametric Mann–Kendall test and Sen’s slope estimator. The results reveal that the annual flows and SSC are in a balanced state for the Indus River at Besham Qila, whereas the SSC are significantly reduced ranging from 18.56%–28.20% per decade in the rivers of Gilgit at Alam Bridge, Indus at Kachura, and Brandu at Daggar. The SSC significantly increase ranging from 20.08%–40.72% per decade in the winter together with a significant increase of average air temperature. During summers, the SSC are decreased significantly ranging from 18.63%–27.79% per decade along with flows in the Hindukush and Western–Karakorum regions, which is partly due to the Karakorum climate anomaly, and in rainfall-dominated basins due to rainfall reduction. In Himalayan regions, the SSC are generally increased slightly during summers. These findings will be helpful for understanding the sediment trends associated with flow, precipitation, and temperature variations, and may be used for the operational management of current reservoirs and the design of several hydroelectric power plants that are planned for construction in the UIB.
Highlights
Erosion from the relatively younger mountain ranges of the Hindukush, Karakorum, and Himalaya yield a huge amount of sediment that enters the Upper Indus Basin (UIB) and its storage reservoirs, such as the Tarbela reservoir
The results reveal that the annual flows and suspended sediment concentrations (SSC) are in a balanced state for the Indus River at Besham Qila, whereas the SSC are significantly reduced ranging from 18.56%–28.20% per decade in the rivers of Gilgit at Alam Bridge, Indus at Kachura, and Brandu at Daggar
This study focuses on the Upper Indus Basin (UIB) upstream of the Tarbela dam with a total catchment area of 172,000 km2 and a length of 1125 km [18,28]
Summary
Erosion from the relatively younger mountain ranges of the Hindukush, Karakorum, and Himalaya yield a huge amount of sediment that enters the Upper Indus Basin (UIB) and its storage reservoirs, such as the Tarbela reservoir. The assessment and quantification of variations of fluvial sediment fluxes and their spatiotemporal patterns are important for a better understanding of river geomorphology as well as the planning, design, and operation of hydraulic structures on the river. The variation of sediment fluxes affects the depletion of reservoirs, channel erosion and deposition, abrasion of hydropower turbines, pollution of river ecosystems, and the operation and management of hydropower as well as storage reservoirs. Assessment of spatio-temporal variation of suspended sediment concentrations (SSC) or yields due to precipitation, temperature, and flow process variations are vital to adapt watershed management practices and to better understand the landslide activities in the basin
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