Insights on the Impacts of Hydroclimatic Extremes and Anthropogenic Activities on Sediment Yield of a River Basin

Abstract

Streamflow and sediment flux variations in a mountain river basin directly affect the downstream biodiversity and ecological processes. Precipitation is expected to be one of the main drivers of these variations in the Himalayas. However, such relations have not been explored for the mountain river basin, Nepal. This paper explores the variation in streamflow and sediment flux from 2006 to 2019 in central Nepal’s Kali Gandaki River basin and correlates them to precipitation indices computed from 77 stations across the basin. Nine precipitation indices and four other ratio-based indices are used for comparison. Percentage contributions of maximum 1-day, consecutive 3-day, 5-day and 7-day precipitation to the annual precipitation provide information on the severity of precipitation extremeness. We found that maximum suspended sediment concentration had a significant positive correlation with the maximum consecutive 3-day precipitation. In contrast, average suspended sediment concentration had significant positive correlations with all ratio-based precipitation indices. The existing sediment erosion trend, driven by the amount, intensity, and frequency of extreme precipitation, demands urgency in sediment source management on the Nepal Himalaya’s mountain slopes. The increment in extreme sediment transports partially resulted from anthropogenic interventions, especially landslides triggered by poorly-constructed roads, and the changing nature of extreme precipitation driven by climate variability.

Moisture Sources and Pathways Determine Stable Isotope Signature of Himalayan Waters in Nepal

“…This catchment covers ∼8 km of relief, ranging from a minimum of ∼150 m at the southern mountain front to the high summits of Dhaulagiri and Annapurna (both >8,000 masl.). These mountains built an east‐west trending orographic barrier, while the low‐lying river valley functions as a natural south to north conduit for air masses across the mountain range (Struck et al., 2015; Talchabhadel et al., 2021; Zängl et al., 2001). North of the orographic barrier, local relief is more subdued, rising more gently to a low‐relief drainage divide with the upper Tsangpo River to the north.…”

Charting the Course to Resilience: Hydrodynamic Modeling for Socio-economic Insights for Flood Risk Management in Nepal’s Ungauged Roshi River Catchment

“…Annual monsoon floods from June to September continually afflict Nepal (Thapa et al, 2020). Climatic changes, shifts in rainfall patterns Talchabhadel et al (2018),land use alterations (Lamichhane and Shakya, 2019), and the proliferation of crusher industries and their sediment deposits exacerbate flood risks (Talchabhadel et al, 2021). Flood hazard mapping is essential for reducing community impact since flood events are uncontrollable.…”