Abstract:

The aim of this study is to apply a state-of-the-art methodology for the estimation of environmental flows by predicting how different in-stream flows affect fish microhabitats. A habitat modelling approach was adopted to simulate and assess the ecological effects of physical aquatic habitat changes in Greek upland rivers downstream of water abstraction schemes (dams, river diversions, etc), since there is an intense debate about the construction of small hydroelectric plants in montane rivers. Two sites on the Acheloos river were chosen as study areas (Tripotamo and Mesochora upstream of the Mesochora dam), because they are located in relatively undisturbed conditions. Standard hydraulic simulation and aquatic habitat modelling was based on data surveyed along cross-sectional transects in a representative river reach. After field data collection a hydraulic model (HEC- RAS) was applied for different flows. The representative reach comprised of the habitat types and approximated proportions detected in a previous exploratory charting of hydromorphological units over a longer piece of river. Thus, a river segment for hydraulic modelling was identified in each of the study sites (segments with relatively homogeneous conditions in terms of hydrology, geomorphology, and habitats). The basic scheme of the physical habitat simulation was applied, based on a 1-dimentional hydraulic modelling, habitat evaluation with Habitat Suitability Curves (hereafter HSC) and generation of Weighted Usable Curves in function of river flow. This way, the habitat changes can be estimated for various stream flow conditions based on an indicator of habitat quantity and quality. Generic habitat suitability curves are used from Brown Trout, a relative of the native Balkan Brook Trout inhabiting local streams. In a later stage, several river flows will be integrated in the model calibration, in order to reduce the uncertainty of the model and simulate the habitat changes in terms of habitat time series within an ample range of river flows. The habitat evaluation was based on HSC; such curves are ecological models in a simple univariate format, indicating the habitat suitability of certain hydraulic conditions for a given fish species and life stage. The HSC are frequently defined by scientific studies, for the variables depth, mean velocity, substrate and cover (obtained by field observation using visual assessments by snorkelling). The habitat modelling in representative reaches enables an ecological assessment and the proposal of environmental flow regimes in the segments affected by a given water abstraction scheme. Finally, this preliminary application promotes the need for further science-based eco-hydrological approaches that are relevant to both biological quality elements and current EU policy.