Abstract
This paper presents a hydraulic and morphological analysis of the Lower Jamuna in Bangladesh with a focus on two key bifurcations that are important for stabilization of the Lower Jamuna reach. We used ground measurements, historical data, multispectral satellite images from various sources as well as numerical models. We carried out hydraulic analyses of the changes and their peculiarities, such as flow distributions at the bifurcation and hysteresis of the stage–discharge relationships. We supplemented our analysis by using numerical models to simulate discharge distribution at the bifurcations under various flow and riverbed conditions. We developed an advanced and automated satellite image processing application for the Lower Jamuna, referred to as Morphology Monitor (MoMo), using the Google Earth Engine. MoMo was found to be an effective tool for a rapid assessment and analysis of the changes in deep-channel and sandbar areas. It is also useful for monitoring and assessing riverbank and char erosion and accretion, which is important not only for morphological but also ecological impact assessment. The application can be adapted as an operational tool as well. Furthermore, we assessed the evolution of deep channels at the bifurcations based on regularly and extensively measured bathymetry data. The analysis was carried out in complement with morphological modeling, particularly for short-term prediction. In this paper we present the major findings of the analysis and discuss their implications for adaptive river management.
Highlights
Instability of the upstream channel due to the channel dynamics and bank or char erosion may eventually lead to the instability of the bifurcation and downstream branches
The interaction between the Ganges (Padma) and the Lower Jamuna at Aricha shows that the Ganges flow is affected by the Lower Jamuna during lower flows of the rising stage
The effect of the Ganges flow at Aricha was only evident when the Ganges discharge was higher than the Lower Jamuna discharge, when the water level at the Hardinge Bridge was higher than at Sirajganj
Summary
The Brahmaputra River flows from the Himalayas through China, India and Bangladesh, before eventually debouching into the Bay of Bengal (Figure 1). The last 250 km of the reach in Bangladesh are referred to as the Jamuna. The banks of the Jamuna River are primarily composed of erodible loose, unconsolidated sandy soil, which, combined with the region’s powerful monsoon floods, causes large-scale devastation in this country with a population density of over 1200 people per square kilometer. It is estimated that erosion has displaced around 2.2 million people along the Jamuna and Padma rivers since the 1970s [1]. Unstable riverbanks can erode embankments, causing breaches and severe flooding
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