Concept of E-flows
Figure 1: Flow regime characteristics governing the river’s ecological functioning (Bunn and Arthington, 2002)
The ecological functioning of a river is largely governed by a river’s discharge dynamics or flow regime (Bunn & Arthington, 2002; Poff et al., 2006). A flow regime can be characterized by five components: the magnitude, timing, frequency, duration and rate of change of the discharge, which all stem from climate, local geography, land-use and human interventions. These five components are important for different ecological processes (Figure 1). For example, high flood pulses shape the physical characteristics of the river and connect the main channel with its floodplains (Gran & Paola, 2001; Hupp and Osterkamp, 1996). Floods also provide migration and spawning cues for fish, while low flows can purge invasive species or concentrate prey to benefit predators (Bunn & Arthington, 2002).
The importance of the dynamics of a flow regime and its relation to ecosystem functioning led to the concept of E-Flows within water management. This concept commonly addresses the quantity, quality and timing of water and sediment flows in relation to ecological functioning of a fluvial system (Arthington et al., 2018). Frequently asked questions are how often, how long, and when a certain discharge should occur with a certain magnitude and rate of change to facilitate the right conditions for all life stages of key-species in the ecosystem. The answer might vary across the longitudinal gradient of the river due to differences in climate and topography which facilitate different types of species. Key in answering the question is knowledge on how exactly the flow regime influences a species, or group of species. Obtaining this knowledge makes EFAs time consuming and costly, as the relation between species and the flow regime vary both spatially and temporally.
An different angle on E-Flow assessments
The knowledge obtained through field campaigns on the relation between species and flow regime is invaluable: it increases understanding of the fluvial system. Yet, stakeholder involvement and discussions between stakeholders is also an important process in E-Flow assessments. Stakeholders can refine the scope of the problem, promote data disclosure and help in finding feasible management options. To guide stakeholder discussions and to obtain necessary information in an early stage, it can help to show stakeholders information on the ecological status of the considered system. This will fuel and direct the discussion and improves the EFAs when stakeholders become willing to share data and (local) knowledge. To facilitate early stakeholder engagement and provide an ecological quick scan of the system we have developed the concept of the Rapid Environmental-flow Assessment and Communication Tool (REACT).
This report continues with the description of REACT: what is its rationale, its lay-out, what data is available and suggestions for further development in Chapter 2. Chapter 3 presents a case study where the use of global data sources and tools are tested and compared to a detailed regional scale model. Chapter 4 concludes the report by reflecting on the strength and weaknesses of REACT and what recommendations are required to use it in a project setting.
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