Evaluating the Impact of an Upstream Reservoir on Surma-Kushiyara River Flow Using a Hydrologic Model in SWAT

The Meghna River basin is poised to face climate change-induced challenges, including increased flood risk, unpredictable rainfall patterns, and rising surface temperatures, posing a threat to the northeastern haor region of Bangladesh. Moreover, any human-made structures (such as dams or barrages) on the upstream side of the basin will impact the rivers downstream. The Surma-Kushiyara River, the central part of this basin system, is anticipated to experience the most severe consequences due to the aforementioned factors. The goal of the present study is to assess the effects that an upstream reservoir/dam (placed downstream of the Barak and Tuivai River confluence in India) will have on the Surma-Kushiyara River flow at Amalshid (where the Barak River bifurcates and enters Bangladesh as the Surma and Kushiyara rivers). A calibrated and validated hydrological model of the Meghna River basin using the Soil & Water Assessment Tool (SWAT) is used to simulate pre-dam and post-dam flow under the recent meteorological condition (1998-2018) and RCP (Representative Concentration Pathways) scenarios (4.5 and 8.5) defined by IPCC. Results reveal that post-dam flow may decrease by more than 60% in the monsoon and post-monsoon and increase by more than 200% during the dry season if the current weather condition prevails. Similar trends can be observed in the 2050s due to a wet-warm climate scenario under RCP 4.5 and 8.5. These findings will assist researchers and stakeholders in comprehending how these changes will affect the basin's hydrology and the area's wetland ecosystem.