Testing and applying baseflow approaches to environmental flow needs

Abstract

Environmental flow need (EFN) is defined as the quantity, quality, and timing of flow that are required to maintain the health of riverine ecosystems and human and societal sustainable development. Numerous research frameworks have been developed and used with a range of sophistication, data requirements, and management strategies. Recently, 90% of the monthly baseflow derived from groundwater has been proposed as the presumptive standard for the groundwater contribution of EFN. However, this proposed groundwater presumptive standard has not been compared to the field-based EFN, which limited its practical application in water management. Therefore, we ask whether baseflow can be used as an index of EFN, and if so, is 90% of monthly baseflow robust for aquatic ecosystems? We selected nine watersheds in the Okanagan Basin (Canada) with well-established EFN based on extensive fieldwork and local experts' knowledge to address this research question. Four baseflow separation methods were adopted to derive the long-term monthly baseflow. We then compared the baseflow against field-based EFN and found that different ranges of baseflow can represent field-based EFN. Specifically, 86%-159%, 93%-151%, and 128%-139% of monthly baseflow can be used as EFN standards for snow-melting, summer, and fall-winter, respectively. Further, we found that 102%-150% of the monthly baseflow should be maintained, implying that the presumptive standard underestimated EFN in our study region. Finally, we recommended that baseflow can be an effective index for EFN; however, watershed management should recognize local aquatic conditions in applying the baseflow EFN index for conjunctive watershed management.