Establishing environmental flows for intermittent tropical rivers: Why hydrological methods are not adequate?

摘要

Effective river restoration and management programs require an understanding of the river's variable flow regimes as well as the physical and ecological perspective of the catchments. Several hydrological methods have been applied in different basins of the world to provide simple and conservative estimates of environmental flows (e-flows) based upon long-term discharge data. The climatic, geological, and hydrological variability, as well as habitat diversity, decides the suitability and application of these methods. In this study, five hydrological methods have been used to estimate e-flows for a plain-fed tropical river (Gomti River, a tributary of the Ganges, India). Long-term flow data were collected from the Central Water Commission, India, from 1978 to 2015. The comparison of e-flows estimates derived from hydrological methods with long-term hydrographs and two environmental categories, namely habitat health classes and environmental management classes, highlights the shortcomings of the hydrological methods in justifying the variable flow requirements of a tropical river. These methods have limitations of integrating diverse aquatic ecosystems, riparian vegetation, fluvial geomorphology, and groundwater contribution in overall flow allocation. This study concludes that for a robust and holistic assessment of e-flows, there is a need for refinement of existing methods. The future studies on e-flows estimation should incorporate: (i) multiple needs of aquatic-riparian habitat during high-flow floods and low-flow droughts, (ii) surface-groundwater interactions to account for baseflows in maintaining lean flows, and (iii) water quality to check the effect of pollution loading and water abstraction on the riverine ecosystems.