Impacts of Farakka barrage on hydrological flow of Ganges river and environment in Bangladesh

The Ganges river is the major source of water for dry season irrigation, navigation, fisheries and reducing salinity intrusion as well as maintaining ecosystem of south-western region in Bangladesh including Sundarbans, the largest mangrove forest in the world. Farakka barrage was constructed on the main stem of Ganges river by India at 18 km upstream of India–Bangladesh border. The barrage was commissioned in 1975 to divert water for improving navigability of Kolkata port and providing saline-free water for Kolkata city. Hydrological analyses have been carried out on historical discharges and water levels data (1935–2015) at Hardinge Bridge station in Bangladesh to find out whether significant changes have occurred in the hydrological flow of Ganges river during pre-Farakka (1935–1975) and post-Farakka (1976–2015) periods. The impacts of Farakka barrage on discharges and water levels have been triggered an abrupt change in Bangladesh since 1975. During post-Farakka period, monthly maximum, average and minimum discharges have been reduced significantly in February–May, December–May and February–April, respectively. Ganges water sharing treaty has been signed between Bangladesh and India in 1996. In comparison with pre-Farakka period (1935–1975), it has been observed that during post-Ganges water sharing treaty period (1997–2015), the maximum, average and minimum discharges have remain reduced around 23, 43 and 65%, respectively, in dry season (January–May). Due to long-term significant reduction of the Ganges flow at Farakka for about 40 years, south-western region of Bangladesh has been suffering from environmental degradation.