Abstract
This study presents the results of sediment transport measurement in the Koshi River with a comparison between historic and recent measurement techniques. Based on the historic sediment measurement data for the period 1948-1981, the yearly sediment load at Barakhshetra varied between 49 and 283 million m<sup>3</sup>, with an average of 95 million m<sup>3</sup>. The coarse, medium and fine fraction contribute by respectively 19, 25 and 56% to the total sediment load of the Koshi River. The average total yearly sediment load at Chatra was estimated as 130 million m<sup>3</sup>, of which about 60 million m<sup>3</sup> is bed material load which contributes to the aggradation on the alluvial fan. This historic data relate to measurements with depth-averaged sampler form cableways. Recent practices collect surface sediment samples from the riverbank to estimate the sediment transport in the river, which include the JPO-SKSKI and DHM sediment samples. The average yearly sediment load at Chatara on the basis JPO-SKSKI and DHM measurement correspond to 44.5 million m<sup>3</sup> and 57 million m<sup>3</sup> respectively. Moreover, a comparison between the percentages coarse, medium and fine sediment for the historical measurements (EDI method) and JPO-SKSKI and DHM measurements (surface sampling near the bank) concluded that sampling from the bank results in a serious underestimation of the contribution of the coarse sediment to the total sediment load of the river.
Highlights
The total sediment load at Chatara is estimated with three corrections
As can be concluded from this table sampling from the bank results in a serious underestimation of the contribution of the coarse sediment to the total sediment load of the river
The average yearly sediment load determined by Department of Hydrology and Meteorology (DHM) was about 57 million m3
Summary
Laboratory analysis using flume under steady uniform flow with 0.5 mm sand showed that the COV for sand concentration data was 62 per Mukesh Raj Kafle: Sediment Transport Measurement in the Koshi River: Comparison Between. The Koshi River, located on one of the most active alluvial fans in the world, poses major challenges in flood management and in coping with the excessive quantities of sediment entering the alluvial plain. In this context, estimation of yearly sediment load in the Koshi River is the prevailing issue for policy makers and planners
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