Anthropogenic river barriers modify flow, degrade river habitat and disrupt the movement of fish and other aquatic animals. Several global river barrier databases (e.g. Global Dam Watch) have been developed as tools for basin management but their completeness has not been validated, especially in developing countries. We tested the adequacy of these in Bangladesh by carrying out walkover surveys of 469 km river length in the Ganges and Brahmaputra basins. We identified 218 anthropogenic barriers across six anabranches. The overall barrier density (mean ± SD) was 0.47 ± 0.22 km −1 . Complete river channel blockage occurred in 28% of cases. Barrier types recorded comprised sluices, culverts, earth banks and bamboo fences, the latter being the most frequent (78.4 ± 10.4% of barriers) and used for fishing. Almost all barriers (92.7%) were seasonally temporary and had their greatest migration-obstructing impact during the decreasing limb of the hydrograph. Across the study reaches, none of the existing global-scale databases recorded a single barrier, whereas across the whole of Bangladesh, they recorded seven barrier locations. Therefore, this study demonstrates the need for field-based surveys to generate valid barrier databases for the Brahmaputra and Ganges, that can be used for informed river management and conservation.
Kashmi et al. (Tue,) studied this question.