Vol. 7, Issue 12, Part D (2021)

Abstract
Gradient of a river is developed by a continuous process of degradation and aggradation through dynamic action of discharge over a landmass in fluvial dominant areas. Initially when a landmass emerges due to internal forces or on the landmass already existing in areas when there is rainfall, fluvial processes are operational. The earth surface is sculptured by external process found in the area. Finally, it is the product of the balance between internal and external forces operating. In this study, fluvial process is referred with respect to the changing gradient of the Kosi River and its bed profile. The characteristics of precipitation over an area determine discharge of a river. Discharge is also impacted by several factors like slope, structure and composition of rocks, vegetative cove, porosity and permeability of the soils, available human footprints, land use and land cove change caused by human beings etc. All of them are affecting discharge and sediment yield, which ultimately makes changes over an area through which it is running. The chosen area is the Kosi River in the plain and it is characterized by enormous discharge due to torrential rainfall in association with snowmelt during summer days. It is one of the largest tributaries of the Ganga River system. It is notorious for bringing flood frequently in its plain and termed as “Sorrow of Bihar”. Due to huge sedimentation from its foothills, the plain is said to be an “Inland Delta” and also called as “Kosi Megafan”. The changing gradient and bed profile is an important topic of geomorphological enquiry. Therefore, an attempt has been made in this paper to (i) study the changes in gradient of the Kosi River, (ii) investigate the changing bed level, particularly, after construction of embankment in 1958, and (iii) find long term solution of channel stability and flood management.