Assessing the impact of large barrages on habitat of the Ganga River dolphin

Abstract

AbstractRiverine habitats are degrading at an alarming rate due to anthropogenic interventions. Construction of large dams and barrages on the Ganga River has severely fragmented the riverine habitat of dolphins. This study examines the impact of structural barriers on the habitat of the Ganga River dolphin (Platanista gangetica) in a reach between Bijnor and Narora barrage in the middle Ganga and at the Farakka barrage in the lower Ganga Plain. We use time‐series remote sensing images and flow discharge data to assess the morphological and ecological impact in the proximity of these barrages. Our result suggests that after the construction of Bijnor barrage in 1985, the total bar area of the Ganga River has reduced from 150 to 45 km2, but the channel width has remained unchanged during the period between 1980 and 2010. A time‐series analysis of the discharge shows a slightly declining trend after the year 1982. However, this observed trend is not adequate to explain the habitat degradation of the Ganga River dolphins. Further width of the Ganga River in the downstream of the Farakka barrage has reduced from 4 to 1 km, and the total bar area has increased from about 5 to 35 km2 during the period between 1965 and 1980. Also during this period, the pre‐monsoon discharge of the Ganga River has reduced by one‐third in the downstream of Farakka barrage. This study concludes that the loss of dolphins in the downstream reaches of the Farakka barrage could be associated with the change in hydraulic geometry, flow characteristics, and loss of longitudinal and lateral connectivity. Conversely, the impoundments of water upstream of the Narora barrage have maintained the suitable habitat conditions for the dolphins to thrive. This has resulted in a reported growth in the dolphin population during the years 1993–2010.