River dynamics and existing stability condition of the Manahara River, Kathmandu basin, Central Nepal Himalaya

Abstract

Five representative segments of the river were surveyed in detail for evaluating its dynamics and stability condition. The first (downstream) to the fifth (upstream) segments are classified as 'F4', 'C4', 'C4', 'B4' and 'B4' streams characterised by gravelly substrates. All these streams are competent enough to transport their bed material (d 90 ) as shown by the exceeding dimensionless shear stress over critical dimensionless shear stress of the river segments. The existing depth and slope of the river is far enough to carry d 90 of the substrate grain size. Stream power of segments 1 to 5 are respectively, 622.6, 79.0, 146.6, 354.6 and 15617.0 KN/s. The 'B4' streams show greater stream power, i.e., transport capacity compared to 'F4' followed by 'C4' streams. Therefore, the 'B4 streams (3rd and 4th order streams) are potential to degradation, and the 'C4' and 'F4' (both 5th order) streams are potential to aggradation depending on river morphology and dynamics. Meander geometry of the Manahara River exhibit deviation of variables (meander wavelength vs channel width, and meander belt width vs channel width) from the stability, suggesting existence of instability to some extent in the river.

Fluvial morphology and dynamics of the Godavari Khola, southeast Kathmandu, Central Nepal

“…The stability status of the Godavari Khola shows that the stream segments 1, 2, 11 and 13 lie in the degrading condition whereas the remaining nine segments lie in the aggrading condition. Because of the huge width/depth ratio in majority of the downstream channels, bank erosion is relatively prone in the downstream segments of the Godavari Khola, whereas bed incision is prone in segments 11 and 13. sedimentation exacerbate the instability of the stream channel (Shrestha and Tamrakar, 2007a;Shrestha and Tamrakar, 2007b;Maharjan and Tamrakar, 2010;Tamrakar et al, 2011;Tamrakar and Bajracharya, 2012;Tamrakar et al 2014). The present study aims to establish fluvial morphology and stability status of the Godavari Khola.…”

Dry season discharge and sediment yield of the northern tributaries of the Kathmandu Valley, Central Nepal

“…northern Kathmandu Valley are far from the equilibrium and there existed various bank erosion problems (Tamrakar, 2004a(Tamrakar, , 2004bTamrakar, 2007a, 2007b;Tamrakar et al, 2011). Guzman et al (2013) displayed the suspended sediment concentration-discharge relationships in which concentration of suspended sediment is high for low flow and sediment concentration is low for high flow.…”

Rock Mass Rating and Geological Strength Index of rock masses of Thopal-Malekhu River areas, Central Nepal Lesser Himalaya

“…Roads are often found to extend along the hill slopes of the river course, which is prone to be disturbed by landslide and river erosion. The river corridors are frequently subjected to river bank erosion, slope movements and flash flooding (Shrestha and Tamrakar, 2007a;Shrestha et al 2008;Tamrakar et al 2011). Therefore, river bank slopes are required to be characterized for their condition.…”