Flood Maps and Bank Shifting of Dharla River in Bangladesh

Abstract

Bangladesh is prone to severe flooding as being located at the confluence of three mighty rivers named the Ganges, Brahmaputra, and Meghna. As a consequence, river flooding and erosion are common natural disasters that severely affect the landscape, lives and economy of the country. Dharla River, one of the trans-boundary rivers originated in the Himalayas, along with Brahmaputra River has a great influence on the recurring floods and erosion in north-western Bangladesh. Almost in every year, excessive erosion and embankment damages caused by Dharla render a thousand of people homeless with massive loss of crops and poultries. As per the environmentalists, this is a matter of huge concern as development of accurate flood maps and erosion prediction for Dharla River has been very challenging. In this study, the flood map and Dharla River bank shifting study have been developed by using HEC-RAS 4.1.0 hydrodynamic model and Landsat satellite images. In addition, the HEC-GeoRAS was used to establish the river reach for HEC-RAS. The calibration and validation have been performed using the observed and simulated water levels for the years of 2013 and 2014 respectively. The HEC-RAS flood water level output was used in HEC-GeoRAS for raster interpolation followed by overlain onto the land surface elevation of the study area. Then, the difference between water level interpolation and land elevation surfaces has been considered as a depth of inundation which is performed in Arc-Map 10.2. Flood maps have been generated for the years 2010, 2013, and 2014 for highest water level of each year. The erosion prone areas have been indicated by analyzing bank shifting of Dharla River for the years 1987, 1997, 2007, and 2017 by digitizing the satellite images in Arc-GIS 10.2. From the observation it has been found that the course of the Dharla River has been shifted vastly since 1987 to 2017 due to erosion.

Strengthening institutional capacity for disaster management and risk reduction through climate-resilient agriculture

“…Bangladesh is primarily an agrarian country, with long coastlines, making it one of the most susceptible countries to climate change. In Bangladesh, Chapai Nawabgonj in the north-west is a drought-prone area (Ramamasy and Baas, 2007), Bagerhat in the south-west is a saline-prone coastal area (Miah et al, 2011) and Kurigram is flood-prone (Bose and Navera, 2017). Soil salinization in river water and soil in south-west Bangladesh has increased over time and is aggravated by the increase in sea level caused by climate change (Dasgupta, 2017).…”

Assessing the bridge construction effect on river shifting characteristics through geo-spatial lens: A case study on Dharla River, Bangladesh

“…A flowing river is always dynamic and therefore anti-erosion measure can never be stable for a long time ( Mitra, 2015 ). The change of the flow of the river as well as the change of the river bank mostly has drastic effects on the people of the riverside ( Bose and Navera, 2017 ). The river channel migration through time and space is very important considering many river management problems ( Pal et al., 2017 ).…”

“…Bangladesh is a riverine country and vulnerable to affect with acute inundating as it is located at the confluence of three mighty rivers called the Ganges, Brahmaputra, and Meghna. As a result, river inundating due to flood and bank shifting by erosion are common natural disasters that rigorously affect the land, lives and economy of the country ( Hossain et al., 2020 ; Bose and Navera, 2017 ; Best et al., 2007 ). But recently, in Bangladesh Bridge construction has a great effect on the dynamics of morphological characteristics of River as an on river bed and width changes, bank shifting, and land use change etc.…”

“…), much more study is necessary to see its effect analyzing by satellite imagery, experimentally, simulating, and also field measurement ( Biswas, 2010 ; Madej et al., 1994 ). If we cannot manage bridge construction effect on the river the flow path of the river will be shifted prominently and the river channel will eat into the surrounding flood plain by losing huge amount of civilized and cultivated land ( Bose and Navera, 2017 ). Therefore, the assessing of the pre- and post-bridge construction effect on river shifting characteristics is very important to visualize the actual fact in Bangladesh.…”

“…River is subjected to erosion and deposition, shifting along the reaches ( Wang, 1984 ; Thoms, 2017 ). The Landsat satellite images study revealed that the higher flood occurs in the downstream and serious erosion take place in Dharla River ( Bose and Navera, 2017 ) and the Dharla River has been shifted vastly. In their study they did not consider the channel central line (i.e.…”