Testing a method to classify flow regime alterations in temporary rivers. The Candelaro river case study

The evaluation of the "Hydrological Status" (HS) of a water body in a catchment is of the greatest importance in order to achieve the final objective of the European Water Framework Directive (WFD). It represents the distance of the actual hydrological regime from its natural condition and it may be responsible for the ecological status of a river. The WFD doesn't provide specific guidelines or recommendations on how the alterations should be evaluated and quantified. In this paper a new approach to evaluate the Hydrological Status of a temporary river was tested. The flow regime of a river has been classified through the analysis of two metrics: the degree and the predictability of dry flow conditions which were evaluated on monthly streamflow data. Both indeces were also used as indicators to assess the river's natural flow regime and its alterations. This method was applied to the Candelaro river basin (Puglia, Italy) where we had to face the problem of limited data availability. The SWAT model was used when streamflow data were not available, and a GIS procedure was applied to estimate potential water abstractions from the river. Four types of rivers were identified whose regimes may exert a control on the aquatic life. By using the two metrics as coordinates in a plot a graphic representation of the regime can be visualized in a point. Hydrological perturbations associated with water abstractions, point discharges and the presence of a reservoir were assessed by comparing the position of the two points representing the regime before and after the impacts. The method is intended to be used with other biological metrics in order to defining the ecological status of a stream. It is a useful tool when identifying river bodies under hydrological pressures and it can be used in planning the "measures" towards the WFD goals.