Hydrologic alteration assessment in Mediterranean rivers: perspective from a South Italy case study

Water diversions from rivers are a main cause of ecosystem damage. The watercourses characterized by scarcity of flow and irregular flow regime, like Mediterranean rivers, are more prone to hydrologic alteration. The EU Water Framework Directive (WFD) prescribes conservation or recovery for rivers, but protection is often based on simple and empirical flow rules used to define release flow downstream of diversions. In this paper, according to the prescription of the WFD, a hydrologic alteration analysis has been conducted for the Crati River (Calabria, South Italy), which is characterized by irregular flow regime and pronounced summer droughts. The IHA-RVA method was chosen as an analysis method and four scenarios, resulting from constant and variable flow release regulation of the Calabria Basin Authority, have been examined. Different kinds of impact have been defined, namely deficit of flow, absence of flow event and excess of flow, which is specifically felt in rivers characterized by pronounced droughts. The inadequacy of a few common practices – such as increasing constant flow release or total release volume regardless of natural flow regime – is highlighted. Finally, the overall hydrologic alteration has been associated with the WFD classification of river quality, while difficulties related to the management of Mediterranean rivers are discussed.