Sediment Sources, Erosion Processes, and Interactions with Climate Dynamics in the Vakhsh River Basin, Tajikistan

Abstract

The Vakhsh River is tributary to the Amu Dayra, supporting numerous hydropower facilities as well as irrigation and community water supplies. High sediment loads are major concerns for these uses, yet little is known about the spatial distribution of the dominant sediment sources or their connectivity to fluvial systems. Here, we address this gap by combining findings from a series of field expeditions, remotely sensed climate and vegetation assessments, systematic sediment sampling, hydrograph analysis, and a review of local literature. Our preliminary findings show that various mass wasting processes (e.g., landslides, debris flows, rockfall, dry ravel, bank failures) constitute the major connected sources of sediment, particularly in the mid- to downriver reaches, many of which are unaffected by land use. Surface erosion, including the large gullies in loess deposits of the lower basin, are more affected by poor agricultural practices and road runoff, and can supply large loads of fine sediment into the river. Climate trends detected through remote sensing show an increase in rainfall in the lower half of the basin from spring to early summer while solid precipitation has increased in the eastern half in March. These trends may lead to more runoff and increases in sedimentation if they continue.