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The representation of the wave overtopping is of unquestionable relevance for the assessment of the coastal and harbor safety and for the design of coastal defenses. The direct measurement of the wave overtopping volumes and discharges is a common practice in the laboratories, but it requires the installation of specific devices and instrumentation and may cause disturbance to the experiments. This contribution presents a procedure based on the image clustering to estimate the individual and the total overtopping volumes at coastal structures, while capturing the time-spatial evolution of the overtopping flow and avoiding any disturbance to the process itself. The procedure is validated against laboratory tests of focused waves on a sloping dike with a gentle and shallow foreshore and provided accurate and reliable estimations of the wave overtopping. The procedure automatically detects the individual overtopping volumes and its adaptability to different test conditions and structural configurations is proved. Requiring essentially a video camera to film the wave overtopping, the image clustering procedure can be applied also to prototype and field experiments, where the measurement of the wave overtopping may result complicated or unaffordable. [ABSTRACT FROM AUTHOR]

This contribution builds on an existing methodology of image clustering analysis, conceived for modelling the wave overtopping at dikes from video records of laboratory experiments. It presents new procedures and algorithms developed to extend this methodology to the representation of the wave runup at crown walls on top of smooth berms. The upgraded methodology overcomes the perspective distortion of the native images and deals with the unsteady, turbulent and bi-phase flow dynamics characterizing the wave impacts at the walls. It accurately reconstructs the free surface along the whole structure profile and allows for a statistical analysis of the wave runup in the time and spatial domain. The effects of different structural configurations are investigated to provide key information for the design of coastal defences. In particular, the effects of increased sea levels in climate change scenarios are analysed. Innovative results, such as profiling of the envelopes of the runup along the wall cross and front sections, and the evidencing of 3D effects on the runup are presented. The extreme runup is estimated for the definition of the design conditions, while the envelopes of the average and minimum runup heights are calculated to assess the normal exercise conditions of existing structures. [ABSTRACT FROM AUTHOR]

The paper investigates the influence of the resistance coefficient variability onto the spatial development of roll-waves. Two models, based on time-asymptotic solutions of the linearized St. Venant equations, subject to either impulsive or oscillating perturbation, have been modified by including the dependence of the resistance coefficient on flow conditions, wall roughness, and fluid viscosity. Independently of the perturbation type, it has been shown that the hypothesis of constant resistance coefficient leads to underestimate the disturbance spatial growth. Theoretical predictions are finally compared with results of a fully nonlinear model and with literature experimental data for several combinations of Froude and Reynolds numbers and relative roughness values. The representation of variability of the resistance coefficient fundamentally improves the performance of minimum channel length criteria, whereas its neglect may lead to noncautious channel design. DOI: 10.1061/(ASCE)HY.1943-7900.0000139 CE Database subject headings: Bed roughness: Friction: Open channel flow; Stability; Water waves; Reynolds number; Flow resistance. Author keywords: Bed roughness: Friction; Open channel flow; Stability; Water waves.

The objective of this paper is to analyze flow patterns and velocity fields around rubble-mound low-crested structures based on wave basin experiments and 2DH numerical simulations. Experiments were performed in the 12.5 x 9.7 [m.sup.2] wave basin at Aalborg University, Denmark, within the framework of the EU-funded project DELOS. Two different layouts were designed: two detached breakwaters with a gap in between and an oblique breakwater forming a rip channel with the basin side wall. Both cases of narrow and wide berm were tested under two- and three-dimensional regular and irregular wave attacks. Fluxes around and through the structures are examined by means of image analysis and measurements of free surface elevation and velocity at fixed locations. An original scheme for evaluating the overtopping discharge through a wave-by-wave analysis of wave gauge records over the barrier is described. Overtopping discharges are reconstructed and related to existing wave run-up models for emerged and zero-freeboard structures. Since no measurement was performed in the rubble mound, a 'scale' model to estimate filtration flux based on other available datasets containing filtration velocity and set-up is proposed and verified. The analysis of the datasets serves to discuss different filtration mechanisms depending on structure submergence. The approach for separately evaluating the different flux terms is then globally checked for zero freeboard and emerged structures through experimental mass balance. For deeply submerged structures, for which this approach fails, numerical simulations are carried out and the accuracy of the commercial 2DH model MIKE 21 is tested in predicting parameters relevant to the design process as set-up, overtopping and returning flows. Simulations are also presented for a sample emerged case in order to show how some limitations in the tool can be surpassed to allow general applications. The numerical model furthermore invites a description of the physical processes over the whole area of interest, where extensive measurements cannot be performed due to the test imperfect repeatability in presence of irregular waves and thus the impossibility of moving the limited number of available instruments. DOI: 10.1061/(ASCE)0733-950X(2006)132:1(10) CE Database subject headings: Experimentation; Simulation; Rubble-mound breakwaters; Wave overtopping; Currents; Filtration.

The objective of this contribution is to analyze the formation of debris waves in natural channels. Numerical simulations are carried out with a 1D code, based on shallow-water equations and on the weighted averaged flux method. The numerical code represents the incised channel geometry with a power-law relation between local width and flow depth and accounts for all source terms in the momentum equation. The debris mixture is treated as a homogeneous fluid over a fixed bottom, whose rheological behavior alternatively follows Herschel-Bulkley, Bingham, or generalized viscoplastic models. The code is first validated by applying it to dam-break tests on mudflows down a laboratory chute and verifying its efficiency in the simulation of rapid transients. Then, following the analytical method developed by Trowbridge, the stability of a uniform flow for a generalized viscoplastic fluid is examined, showing that debris flows become unstable for Froude numbers well below 1. Applications of the code to real debris flow events in the Cortina d'Ampezzo area (Dolomites) are presented and compared with available measured hydrographs. A statistical analysis of debris waves shows that a good representation of wave statistics can be obtained with a proper calibration of rheological parameters. Finally, it is shown that a minimum duration of debris event and channel length are required for waves showing up, and an explanation, confirmed both by field data and numerical simulations, is provided. CE Database subject headings: Debris; Solids flow; Shallow water; Wave equation; Stability.