REACT has a high level of abstraction as it focusses on producing a first approximation of E-Flows which is based on the minimal impacted situation (i.e. the climatological situation which is based on geology, topography, climate and land use – climatological run). As the climatological run is based on global data and models, the spatial resolution is low, especially when compared to holistic E-Flow approaches (e.g. Drift and ELOHA). The current state scenario should consider the effect of current human interventions like dams and water abstractions and requires input from stakeholders when this information is not publicly available.
The spatial resolution of REACT dictates also the scale of analyses. As presented by Thoms and Parsons (2002, Figure 1), E-flow studies should use the right scales of hydrology, geomorphology and ecology to bring about the desired geomorphological and ecological response. From satellite data, functional process zones (FPZs) can be discerned, which are reasonable homogeneous patches within a heterogeneous system. FPZs differ in numerous ways in bio-complexity, like their characteristic productivity, system metabolism, organic matter dynamics, nutrient spiraling, and community composition as the physical and chemical conditions between FPZs differ (Thorp et al., 2006). The zonation of a catchment or river basis in hence viewed from a biological perspective.
Figure 1: Multiscale relation between hydrology, fluvial geomorphology and ecology. Taken from Thoms and Parsons (2002).
FPZs have been tested for various river types and organism groups (Petts and Amoros, 1996) and can be deduced from spatial river characteristics, like tributary confluences, divergence and convergence areas in braided/anastomosing rivers, vegetated islands, parafluvial ponds, and various slack water areas in general (Thorp et al., 2006, Figure 4). Testing these assumptions with field work, led to a match of about 70% for riverbed sediment patterns (Collins et al., 2015). Additionally, Maasri et al., (2021) used the GIS based program RESonate (Williams et al., 2013) to delineate FPZs by extracting alley-scale hydrogeomorphic variables from existing geospatial data. However, a drawback may be that the same FPZ, like a floodplain FPZ, may differ between ecoregions, but this needs further research.
Figure 2: Schematic overview of FPZs (a) and FPZs may be present in several parts of a single tributary (b). Taken from Thorp et al. (2006).