Author(s): Jagat K. Bhusal
Linked Author(s):
Keywords: River discharge; Sediment; Deposition; Lothar river; Sediments matting
Abstract: The prediction of sediment yield from Nepalese watershed is a difficult task. The river flows are laden with high concentration of sediment during rainy period. Surface erosion is highly pronounced with high intensity pre-monsoon rain. Sediment transport in streams during pre-monsoon period is higher than in post monsoon period. Streams that are draining the lands with degraded soil on sloping surface are transporting high amount of sediments annually. Soil erosion, sediment transportation, and deposition process vary with topographical zone and show an increasing trend in the Siwaliks region of Nepal. In extreme events, the riverbed temporarily rises and falls. As long as tributary streams flood with slurry and debris torrents the main channel bed swing up and up and extend along some hundred meters of the reach. Floods and surges form layer to layer of bed load matting. When flow velocity suddenly reduces then temporary matting of transporting sediments settle down and form bed materials. This paper illustrates an example of depositional activities of Lothar river in Nepal This river is a non-snow fed river and swells with monsoon rain. Erosion and sediment transport activities are accelerated during monsoon season (June to September). The riverbed aggradations and scouring was found to be within one-meter depth from 1992to 2001 where as deposition increased to 5.5 m by 2003 events.
Year: 2004