A comprehensive morphological and hydrological analysis of the Dharla River, northwestern Bangladesh

Abstract

 The Dharla River is one of the right bank tributaries of the Jamuna River. It is a transboundary river and flows through the countries of Bhutan, India and Bangladesh. In its upper course, the river originates in the Lower Himalaya and passes through the piedmont plain of northeastern India. The riparian area of this river is known for flash flood and recurrent bank erosion. However, study related with the Dharla River is very insignificant. In this study, different types of dataset ranging from chronological satellite image, river discharge, water level, cross-section, precipitation and Digital Elevation Model have been employed for a comprehensive understanding of the morphological and hydrological characteristics of the river so that a sustainable riparian landuse planning can be implemented. The study indicates that on a basin scale, the morphology of the Dharla River is influenced by complex interplay of relief, climate and tectonics. In Bangladesh part, the river shows two distinct types of planform, the upstream part is characterized by braided and the downstream part shows meandering planform. Satellite image indicates that the overall width of the Dharla River decreased about three times from 600 m to 200 m in the past 45 years. The river is now migrating its channel mostly in the north-eastward direction often with the rate of about 66 m/year. The confluence location of the Dharla River with the Upper Jamuna River is not stable and is influenced by the backwater effect from the Jamuna River. The backwater effect induces erosion adjacent to the confluence area. Considering the complex nature of the bank erosion a setback buffer at the most erosion prone area like in Holokhana union is recommended for the sustainable landuse management of the area.