River hydraulics and hydraulic risk management

Research focus

The Peer review has evaluated this group as Average

River hydraulics and sediment mechanics are naturally related to the concept of hydraulic risk and its management. They involve concepts leading to optimization of land protection approaches and technologies. Main axes of the research include river hydraulics and scour processes, analysis of hyper-concentrated flow, modeling of flooding processes and hydraulic risk assessment and management. Failure of river bridges has economic, social and strategic fallouts. Local scour is one of the major causes of this problem. The traditional approach to the study of local erosion has been the physical modeling, with the measurement of the temporal development of the scour depth used for the calibration of predictive equations to be applied in engineering practice; more recently, attention has been paid to the phenomenology of the process at a more detailed scale. A novel experimental technique was set up by the research group, where concentration and velocity of the moving particles are measured within the scour hole, and thus allowing for detailed spatial and temporal analysis of the sediment kinematics. Such data are complementary to literature experimental and numerical characterizations of the flow field, since they directly identify the effects of the flow structures on the boundaries in terms of sediment motion; particular attention is devoted to the role of the average and impulsive components of the flow field in determining the grains movement; with regard to the impulsive components, the study is aimed to the identification of the coherent structures which are mainly responsible for the fluid-sediment interaction. Emphasis has been devoted to understanding and modeling the dynamics of hyper-concentrated flows and their influence on hydraulic risk assessment and development of risk-reduction strategies. Firstly, a single-phase mathematical model has been developed, describing one-dimensional flow in the presence of different models of flow resistance factors. A fully two-phase model has then been developed. The models have been applied to simulate the propagation of a hyper-concentrated wave originated by a dam-break process and results have been compared against laboratory tests performed in the G. Fantoli Laboratory. Recently, attention has been devoted to more fundamental aspects of the dynamics of hyperconcentrated flows, and particularly to the development of constitutive models for the stress tensor of the solid component. In this view we have focused on the dynamics of dry granular flows, from a theoretical, a numerical and an experimental point of view. Recent extensions of kinetic theories and numerical simulations of the simple shear flows of frictional spheres have furnished some hints about the possibility of using simple constitutive models for dense flows of dry grains. In some cases, such simple models permit analytical solutions to be obtained for both the velocity and the solid volume fraction profile. Consequently, they can be useful in view of engineering applications. The numerical and analytical velocity and solid volume fraction profiles have been compared with experimental results obtained through image analysis technique in a device (rotating drum) localized in the G. Fantoli Laboratory. The generalization of this approach to the case of steady granular flows characterized by the presence of water is currently work in progress. Flood processes have been mainly analyzed in the view of risk assessment. We systematically considered methodological aspects related to the quantification of the risk components, with particular focus to vulnerability; the latter is a key point of intersection between hydraulic and territorial planning competences if flood risk analysis, and has required a multi-disciplinary approach in cooperation with colleagues from different department of the university. The studied methodologies were applied to real cases, both for rural areas and city districts; in both cases we focused on the definition of guidelines to be used by local officer and professional technicians. The hazard analysis has been also performed to evaluate risk scenarios for urban infrastructures, which generates special modeling difficulties from the side of both hazard and vulnerability analysis, due to their intrinsic systemic complexity. Several hydraulic risk analysis of complex territorial systems have been performed for different public administrations; the studies have been focused on either risk assessment or management. A collaborative research action with the Italian Railway Company (Ferrovie dello Stato) has been active since 1997 with special emphasis on the concept of vulnerability of bridges and continuous and efficient monitoring strategies.

Dipartimento di afferenza

Dipartimento di Ingegneria Idraulica, Ambientale, Infrastrutture Viarie, Rilevamento (DIIAR)

Docenti afferenti

Full Professors
Francesco Ballio
Silvio Franzetti
Enrico Larcan
Associate Professors
Stefano Mambretti
Stefano Malavasi
Assistant Professors
Diego Berzi
Alessio Radice