Abstract

River reaches worldwide historically experience morphological regulations, as channelization, as well as flow regime alterations, which often lead to degradation of freshwater ecosystems. In last seven decades a large number of dams have been designed and built worldwide contributing to such river hydromorphological alterations. In alpine and piedmont regions river reaches often experience anthropogenic flow regime alteration due to hydropower production. The fluctuating flow regime typical of river reaches downstream hydropower plant releases (hydropeaking) is known to produce several adverse ecological effects, strongly linked to morphological characteristics of the downstream channel. Hydropeaking can also alter the thermal regime of the receiving water body (thermopeaking) if released hypolimnetic water has different temperature from surface water; also thermopeaking can have adverse consequences on river environment. In a changing world with respect to renewable energy production but also to global warming, the understanding of hydropeaking and thermopeaking ecological impacts represent a lively research challenge. The first part of the present thesis is dedicated to the characterization and quantification of hydropeaking and thermopeaking alterations. Adopting a statistical approach on an extended dataset of Alpine and Norwegian rivers, a suite of indicators have been designed and exploited to identify the degree of alteration of both hydrological and thermal regime. The study provides two screening tools that can be exploited by environmental managers in the identification of critically altered river reaches. The second part is dedicated to the development of a two-dimensional numerical shallow-water model able to simulate surface water passive tracer transport over complex morphologies, exploitable in the numerical investigation of river thermal transport dynamics. In the third part the interaction between hydropeaking waves and receiving reach morphology has been investigated via numerical modeling. The work consists on a first quantitative attempt to investigate the eco-hydraulic response of river reaches with different channel morphologies to hydropeaking waves of different intensities. Such general approach can be applied to a specific case to support the choice of the most effective river restoration strategy leading to the optimal specific eco-hydraulic conditions. Finally, the last part reports an application of the designed approaches and tools to Lundesokna River, a Norwegian river affected by hydropeaking.