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The working features of innovative coastal defense structures that can dissipate the energy of incoming waves by the action of large-scale bottom unevennesses (rigid blades covering the lower half of the water depth) were investigated by means of a laboratory experimental campaign. The goal of the study was to characterize the ability of the structures to efficiently reduce the wave height with a minimal change in the mean water superelevations. Similar wave height reductions were achieved for both vertical and inclined blades; their efficiency was slightly superior to that of traditional submerged rubble-mound breakwaters of the same cross-shore extension. For the incident waves examined, very low mean water elevations were observed inshore of the structures, with the inclined blades producing the smallest values. These results suggest that the structures analyzed here could represent an alternative to submerged rubble-mound breakwaters from a hydrodynamic point of view to protect coastlines prone to erosion with minimal risk of dangerous rip currents. DOI: 10.1061/(ASCE)WW.1943-5460.0000028 CE Database subject headings: Coastal structures; Dissipating submerged structures. Author keywords: Coastal structures; Submerging; Hydraulic roughness; Wave forces.

A comparative assessment of available formulae for the water setup inshore of submerged breakwaters is made on the basis of a wide and varied dataset derived from basin and flume laboratory experiments. Formulae derived from a simplified view which does not account for the horizontal flow circulation provide a large overestimate (up to one order of magnitude) of the smaller setup values. A much better overall approximation of the measured data is obtained through formulae that consider the setup as part of a complete flow description, be it partially or fully accounting for the horizontal flow motion. DOI: 10.1061/(ASCE)0733-950X(2009)135:2(38) CE Database subject headings: Breakwaters; Wave measurement; Beach erosion; Submerging.

Laboratory experiments were performed in the wave flume of the Laboratorio di Idraulica e Costruzioni Marittime of the Università Politecnica delle Marche (Ancona, Italy) to study the hydrodynamic performance of coastal protection structures made of a new type of geotextile sand containers (GSCs). Such structures are used as softer and flexible alternatives to traditional hard coastal defenses made of concrete or rubble mound material. The GSC structures can also be used as temporary coastal protections during the winter period. The physical model reproduced two main configurations: in the former one, the GSCs were used as coastal revetments with three different slopes. In the latter one, the GSCs were applied to make detached submerged breakwaters with different submergences and berm widths. The geometric scale of the models was 1:10, and the weight of each GSC in the prototype was 5 t. The geotextile material of the containers and the wave characteristics were reproduced by using the Reynolds and the Froude similarity criteria, respectively. Reflection coefficients and hydraulic stability behaviors for the revetments, as well as transmission coefficients and piling-up amount for breakwaters, were obtained. [ABSTRACT FROM AUTHOR]

We investigate, within the framework of the nonlinear shallow water equations (NSWE), the generation and evolution of large-scale eddies with vertical axis (macrovortices hereinafter) which are responsible for much of the horizontal mixing occurring at the boundaries between the main channel and the flood planes of a compound channel. We show that the mechanism of generation of vorticity is essentially inviscid and is analogous to that occurring at a curved shock. Numerical experiments performed by means of a recently developed shock-capturing model for the solution of the NSWE, and described in Brocchini et al. (2001), clarify some features of macrovortices generation and allow us to quantify the momentum transfer across the channel. [ABSTRACT FROM AUTHOR]