Abstract

BHAKTA SHRESTHA, Madhusuda; KAZI TAMRAKAR, Naresh  and  MIYAZAKI, Toshitaka. MORPHOMETRY AND SEDIMENT DYNAMICS OF THE CHURIYA RIVER AREA, SIWALIK RANGE IN NEPAL. bol.geol. [online]. 2008, vol.30, n.2, pp.35-48. ISSN 0120-0283.

The Siwalik Range of Central Nepal has weakly consolidated rocks with thin soil cover. Being one of the several north-flowing subsequent tributaries, the Churiya River originated from the southern uplifted range of the Siwalik Group. Morphometry and hydraulic parameters of the Churiya River Basin (CRB) were studied to know how capable is the river for carrying its sediment out of the basin. In many cases, hypsometric integral (HI) in 1st order watershed was lower (0.33-0.57) compared to that of 2nd and 3rd order watersheds (0.45-0.54) suggesting that it had been undergoing severe erosion. The surface flow in the Churiya River appeared only during intense middle monsoon rainfall (June-August) and disappeared most of the time probably due to highly permeable riverbed. Stream powers (Ps) calculated from morphometric analyses of the drainage basin, and stream powers per unit bed area (Ω_b) computed from hydraulic data showed that 2nd order watershed in both cases were 2.5 times higher than 3rd order watershed. This suggests that stream powers of 2nd order watersheds had high potentiality of transporting sediments into 3rd order segment, where stream powers diminished due to reduction in slope, boundary shear stress, and increase of infiltration rate. Although, stream powers reduced downstream (in 3rd order segment), they were quite high enough to flush out from the basin even the largest grain size (dmax) of the riverbeds during the period of high flows. Therefore, sediment erosion should be controlled in the Churiya River Basin to reduce its impact on downstream segments and infrastructures.

Keywords : Siwalik Range; morphometry; riverbed; sediment; grain size; stream power.

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