1. Introduction

River sedimentation is one of the major water related problem in the world and also in India. Most of the rivers in India are facing the problems of rapid sedimentation and associated socio-environmental hazards. In southern part of West Bengal a large number of rivers like, Damodar, Rupnarayan, Kangsabati and Haldi are being sedimented rapidly and facing the problems of drainage congestion and drainage decay, deterioration of navigability, unavailability of water resources, water storage and resultant flood, river bank erosion, loss of settlements and properties and social dislocation. These problems of sedimentation are more serious and alarming in Rupnarayan River, mainly at the lower reach, from Kolaghat to Geonkhali. During the last 26 years, the area has experienced 28.71 million m³ shoaling causing the deterioration and incapacitation of the river. The total shoaled up area has increased from 15.41 km² to 57.35 km² between the years 1973 and 2016. Causes, mechanisms and extent of sedimentation in the lower reach are explained and understood with the detailed study of channel forms and patterns, stream hydraulics, tidal character, sediment load, sediment grain size and related critical and available shear stress and identification of the environment of sediment deposition.