ISSN: 2454-1907 International Journal of Engineering Technologies and Management Research November 2020, Vol 7(11), 50 – 68 DOI: https://doi.org/10.29121/ijetmr.v7.i11.2020.815 © 2020 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 50 SEDIMENT DYNAMICS AND STABILITY STATUS OF THE KARRA KHOLA, HETAUDA DUN VALLEY, CENTRAL NEPAL SUB-HIMALAYA Naresh Kazi Tamrakar 1 , Suman Maharjan *1 *1 Central Department of Geology, Tribhuvan University, Kirtipur, Kathmandu, Nepal DOI: https://doi.org/10.29121/ijetmr.v7.i11.2020.815 Article Citation: Naresh Kazi Tamrakar, and Suman Maharjan. (2020). SEDIMENT DYNAMICS AND STABILITY STATUS OF THE KARRA KHOLA, HETAUDA DUN VALLEY, CENTRAL NEPAL SUB-HIMALAYA. International Journal of Engineering Technologies and Management Research, 7(11), 50-68. https://doi.org/10.29121/ijetmr.v7 .i11.2020.815 Published Date: 30 November 2020 Keywords: Fluvial Sediment Sediment Transport Specific Stream Power Flow Competency Stability ABSTRACT The Karra Khola in Hetauda, Siwalik region, originates within the Dun Valley, and contributes the Rapati Nadi in Hetauda Metropolitan city. The stability status of the river is of main concern because of rapid growing of the river corridor and peripheral land areas into suburban city. The river was surveyed for hydraulic parameters, sediment characteristics, and sediment loads. Rate of sediment transport and sediment yields were computed, and competency of the river was evaluated using Shield’s parameters and Reynolds numbers. The results show that the river sediments are sandy gravel to gravelly sands, and are moderately to very poorly sorted. The total sediment yield of the whole basin near the outlet is around 2% of the maximum total sediment yield. The specific stream power (SSP) ranges from 20.98 to 2866.34 Wm -2 . The dimensionless boundary shear stress to dimensionless critical shear stress ratio exceeds unity, revealing that the river is competent enough to transport its bed material loads, except in downstream stretch before the river confluences with the Rapati Nadi. The Karra Khola clearly exhibits status of degradation in the upstream stretch, high rates of transportation due to lateral erosion in the midstream stretch, and aggradation in the downstream stretch. 1. INTRODUCTION The Siwalik Group is comprised of Late Miocene to Early Pleistocene sedimentary sequence deposited in the foreland basin of the uplifting Himalaya (Tokuoka et al. 1986, Kizaki 1994, Critelli and Ingersoll 1994, DeCelles et al. 1998, Gautam and Rosler 1999). Galay (1987) explained that the steep slopes of the Siwalik Hills and weakly consolidated rocks with thin soil cover generally tends to promote severe surface erosion in spite of the thick vegetation. Likewise, Shrestha et al. (2005) also suggested that the apparent reason for the huge sedimentation within the Siwalik basins could be because of fluvial characteristics. Tamrakar and Karki (2019) concluded that there were variation in specific sediment yields and sediment delivery ratio among the sub-basins of the Karra Khola, and reported that specific sediment yields were lower in most of the southern sub-basins compared to the northern sub- basins of the Karra Khola, due to topography and streambed characteristics. Erosion, transportation and deposition of sediments depend upon hydraulic action, which is again governed by topography and climate (Grantham and Velbel 1988), tectonics and weathering (Johnson 1990), composition of source area (Dickinson et al. 1983, Dickinson et al. 1986) and riverbed materials (Cavazza et al. 1993, Cox and Lowe 1995). Deposition occurs when the critical shear stress required to entrain particles of a specific size exceeds