Laboratory Investigation on the Evolution of a Sandy Beach Nourishment Protected by a Mixed Soft–Hard System

Abstract

A new experimental campaign on a 2D movable-bed physical model, reproducing a typical nourishment sandy beach profile, is being carried out in the wave flume of the Laboratory of Coastal Engineering at Politecnico di Bari (Bari, Italy). The main aim is to assess the short-term evolution of a sandy beach nourishment, relying on a mixed solution built on the deployment of a Beach Drainage System (BDS) and a rubble-mound detached submerged breakwater. This paper aims at illustrating the experimental findings. Tests presented herein deal with both unprotected and protected configurations, focusing on the hydrodynamic and morphodynamic processes under erosive conditions. Results show that, with respect to the unprotected conditions, BDS reduces the shoreline retreat and the beach steepen within swash and surf zone as well. Moreover, a reduction of net sediment transport rate is observed. When BDS is coupled with the submerged sill, a reversal of the prevalent direction of the net sediment transport seaward occurs offshore the sheltered region. Less considerable positive effects on shoreline retreat are induced by the submerged structure, whereas the mean beach slope remains quite stable. Secondary effects of drain on the submerged sill performance are also highlighted. BDS reduces wave-induced setup on beach, by mitigating the mean water level raising, typically experienced by such structures.

Morphodynamic Response to Low-Crested Detached Breakwaters on a Sea Breeze-Dominated Coast

“…On the other hand, the freeboard elevation changes in the geotube sections showed no correlation with high energy conditions and hence can be ascribed to external factors. (4). High spatial and temporal resolution measurements, combining DGPS and UAVs flights, were found to be important to explain far-field morphological changes.…”

“…Despite the increasing popularity of soft engineering [2,3], mixed soft-hard systems [4], and eco-engineering [5] solutions, so-called low-crested detached breakwaters (LCDBs), such as submerged rubble mounds, are popular in many locations around the world (e.g., [6]). The main parameters controlling shoreline response in the presence of LCDBs are distance offshore, length and orientation of the structure, transmission characteristics of the structure, depth at the structure, freeboard height, and wave characteristics [7,8].…”

The Effectiveness of Adaptive Beach Protection Methods under Wind Application

“…It is also eco-friendly, and there is a low probability of secondary damage occurring. Moreover, it is easier to actively respond to changes in the coastal environment with the soft-type method [12,13]. Recently, the soft-type application of nourishment has been carried out more extensively than the hard-type method has.…”

“…As can be seen from the observation data, nourishment with gravel has the effect of reducing the sediment transport [5,[16][17][18]. In the work of [13], the researchers examined topographical variation by applying a drainage system with sand nourishment and a submerged breakwater in a physical model test. Moreover, in the literature [14,19,20], sediment transport was reviewed according to variations in particle sizes when nourishment was applied.…”

“…A further goal was comparing the erosion and accretion trend between conditions with and without wind. In addition, the nourishment method based on the results of the literature [13,14,19], representing a typical soft-type method, was applied to examine appropriate measures to reduce a large degree of morphological change when it occurs on a natural coast. A submerged breakwater [13,[22][23][24][25][26], which is one among various hard-type methods, was installed, and the trend of sediment transport was compared and analyzed to verify its effectiveness.…”