Resolution matters: An evaluation of EFlows assessment methods used for hydropower in developing countries

Sustainable development of river infrastructure requires the use of contemporary Environmental Flows (EFlows) assessment methods that are based on an understanding of river functioning, and which provide information useful for designing potential mitigations and evaluating trade-offs between socio-ecological impacts and economic benefits. Through a systematic search and review, EFlows assessments of 42 hydropower projects in developing countries in Africa and Asia were analysed to understand the factors that explained the resolution of the methods used and whether the resolution used was suitable for the context in which it was applied. In general, reaches downstream of the tailrace were deemed more sensitive to hydropower development than dewatered sections, and in greater need for higher resolution EFlows studies. Despite this, most assessments focused only on the dewatered reaches. Low-resolution hydrological ratio methods were commonly used and did not match the resolution recommended by international good practice, although this is improving with time. Assessment date and the designation of Critical Habitat (a habitat classification based on the threatened status of species in the IUCN Red List) were the only significant drivers of increased resolution of EFlows assessments. However, despite most projects being in the IUCN habitat range of at least one Endangered freshwater species, the environmental studies of only five classified the aquatic area as Critical Habitat. This calls into question the dependence on Critical Habitat as the driving factor in the selection of suitable methods. Moreover, many hydropower specific EFlows assessments were redundant since, on average, 20 additional hydropower projects were planned in the same basin as each of the projects reviewed. In these cases, basin-scale EFlows assessments are needed to provide the requisite knowledge to mitigate impacts. The disconnect between EFlows theory and practice is a cause of concern for the sustainable development and use of river ecosystems.