Carla Faraci

Geometry, migration and evolution of small-scale bedforms generated by regular and irregular waves

Abstract Ripples generated by both regular and irregular waves have been experimentally investigated. In particular, their geometry at the equilibrium (i.e. height, length and steepness) has been analyzed and compared with semi-empirical predictive models. It has been observed that in the investigated range no distinction between ripples generated by regular or irregular waves is detectable, even though the equilibrium configuration is reached through different mechanisms. Moreover, it has been found that ripples migrate as soon as they appear and their velocity of migration qualitatively agrees with theories based on stability analyses recently proposed. Starting from results in literature, new semi-empirical formulae are provided for calculation of equilibrium characteristics of ripples.

Reflection of Sea Waves by Combined Caissons

AbstractThis paper presents the results from several experiments aimed at determining the effectiveness of combined caissons with an internal rubble mound to dissipate incident sea wave energy. Techniques for assessing the reflection coefficient from wave tank data are discussed via a comparison between the established two- and three-probe methods and a new method using four probes. It is shown that obtaining reliable results for the incident and reflected waves requires the determinant of the linear system derived from the Fourier transform to be sufficiently greater than zero. This requirement was always satisfied for the three- and four-probe methods, but it was not always satisfied for the two-probe method. The experiments showed that the calculated reflection coefficient decreased when the ratio of the water depth, D, to the wavelength, L, increased. Increasing the caisson chamber width b and the upper frontal opening h also substantially decreased the reflection coefficient. Plotting the reflection ...

Stereo vision for noninvasive dynamic measurements of the scour process around a circular cylinder in an oscillating flow

A novel three-dimensional measurement technique which uses a stereo vision approach to recover the morphological evolution of a sandy bottom around a vertical pile is presented. In particular, the bottom time evolution due to the wave action was observed from the initial flat bed condition until a stable configuration was attained. Moreover, some morphological parameters of the scour, such as the maximum scour depth, the extension of the eroded area and the position of the maximum scour toe, were measured at equilibrium condition. These quantities were estimated with an average relative accuracy of about five percent, which appears particularly appropriate if compared to the results given by traditional measurement strategies. The key parameter which controls the phenomenon is the Keulegan-Carpenter number (KC). The experimental measures of the scour depth at equilibrium stage were compared with the empirical relations proposed by Sumer et al. (1992) giving a fairly good agreement, while for other three-dimensional features, such as the eroded area, new relations with typical dimensionless parameters useful for design purposes are proposed.

Waves Plus Currents Crossing at a Right Angle: Sandpit Case

AbstractThe present paper explores the possibility of exploiting sandpits at intermediate and shallow water depths by analyzing both the hydrodynamic and the morphodynamic response in the proximity of a dredged area. More precisely, a laboratory investigation was carried out to analyze the effects of the wave-current interaction over a borrow area, particularly in terms of the morphodynamic evolution of the pit. The influence of both regular and irregular waves on the current was analyzed. It was found that the flow is significantly influenced by such interaction in the presence of the borrow area. The morphodynamic evolution of the sandpit is mainly affected by the waves, while the superimposition of a current does not introduce qualitative modifications but increases the mobilization of sediments, with repercussions on the speed of the evolution process. The results of the experimental campaign suggested that the analysis of the morphodynamic evolution can be approached at a laboratory scale. Indeed, th...

Bottom Profile Evolution of a Perched Nourished Beach

AbstractThe evolution of a toe-protected nourished beach, located at Belvedere Marittimo (Italy), was investigated by means of both a physical model and a numerical morphological approach. Several surveys, including bottom profiles, sedimentology, and wave climate, were available after the nourishment for this site. Results showed that the physical model is in a fairly good agreement with the field surveys regarding localized phenomena such as the scour around the barrier, whereas it lacks in predicting the slope of the beach profile. The results of the morphological model, carried out on the basis of the field data, well reproduce the beach slope. On the other hand, when it is applied with the same parameters of the physical model, it lacks accuracy in predicting the experimental beach profile.

Analysis of small scale bedforms with 2D and 3D image acquisition techniques

Reviews a two-dimensional measurement technique based on a structured light approach. The technique is applied to the recovery of bedform morphodynamics. Along with this technique a three-dimensional measurement strategy, which uses a stereo vision approach coupled with structured light, allowing the morphological evolution of a sandy bottom to be recovered, is presented. The bottom evolution under wave action was observed from the initial flat bed condition until a stable configuration was attained. In particular, the three-dimensional approach allows a reconstruction of the bedforms to be performed, and their irregularities, such as defects, change of wavelength, etc., to be shown.

Experimental investigation on sea ripple evolution over sloping beaches

This paper reports on a wave flume experimental campaign carried out to investigate the appearance, the growth and the migration of small scale bedforms on a sloping sandy bed due to both regular and random waves. A Vectrino Profiler along with a structured light approach were used for velocity and morphodynamic measurements at two positions, one located above the horizontal bed, and the other one above the sloping beach. The velocity was computed by phase averaging the velocity measurements. Several velocity profiles were analyzed, identifying an offshore-directed steady current that extends from few centimeters above the bottom for all the analyzed water column. Ripple geometry was measured by a structured light approach and compared with that predicted by several models to shed light on the effects induced by the sloping beach on the shape and asymmetry. Along the sloping beach, the ripples appeared strongly asymmetric with the onshore half wavelengths smaller than the offshore ones. Finally, ripple geometry and migration triggered by regular waves were compared with those generated by random waves with comparable flow orbital amplitude showing a good agreement.

Waves plus currents crossing at a right angle: near-bed velocity statistics

ABSTRACT Wave–current flow over a bottom covered with different roughness elements was analysed to provide new insights into the statistical properties of the near-bed velocity. Experimental data of three different experimental campaigns, with orthogonal waves and currents over a sandy bed, a gravel bed and a rippled bed were used. Velocity profiles were acquired by means of a micro-ADV. The paper focuses on the effects that the waves have on the statistics of the velocity in the current direction. In particular, in the case of a steady current only, the near-bed velocities closely follow a Gaussian distribution. When waves are added, the distribution becomes double-peaked. In order to get single-peaked velocity distributions the total velocity events in the current direction were split in two classes according to the sign of the wave directed velocities. The nature of the distribution functions is influenced by the mass conservation principle and, in the rippled bed case, by the vorticity dynamics.

Estimate of Storm Induced Beach Erosion Through the ETS Approach

In the present paper the risk of beach erosion is evaluated by applying the Equivalent Triangular Storm (ETS). The selected case study is ‘La Plaja’ beach located in the South of Catania, Sicily. The proposed approach has shown that when the ETS model is applied, a shoreline retreat has been found which on average overestimates the one obtained by means of actual storm data of about 35%. The model has been applied for the determination of the return period of shoreline recession due to beach erosion during extreme events in order to recover risk maps, which can provide useful information in the planning of coastal interventions. Finally the model has been applied to predict the shoreline retreat in the presence of a submerged breakwater, confirming that the introduction of such coastal protection work strongly limits the risk of coastal erosion.Copyright