Hydrological alteration due to constant minimum flow release

Notwithstanding the emerging trends in the evaluations of environmental flow requirements for rivers, the assumption of a constant value of the so called minimum instream flow is commonly referred to in Italy. The theoretical basis of this assumption lies in the prevalence of simplification instances among water resources managers, together with the persistence of the ecological niche concept among scientists. Recently, increasing attention has been given to the importance of temporal environmental variability and disturbances that drive ecosystems away from a static or near-equilibrium condition. This statement has lead to the “natural flow paradigm”, that postulate a strict relationship between environmental variation and natural variations in flow. The IHA method has been formulated on the basis of this paradigm and has been widely applied and tested. This paper is aimed to highlight some limitations of the constant environmental flow release through an application of the IHA method to the Crati River (Italy), whose results have been compared to two typical constant minimum flow assumptions. Three different kinds of alteration have been identified, indicating a significant impact on the five critical components of flow that influence the ecological processes in river ecosystems.