Experimental Study on the Influence of an Artificial Reef on Cross-Shore Morphodynamic Processes of a Wave-Dominated Beach

Abstract

Artificial reefs are being implemented around the world for their multi-functions including coastal protection and environmental improvement. To better understand the hydrodynamic and morphodynamic roles of an artificial reef (AR) in beach protection, a series of experiments were conducted in a 50 m-long wave flume configured with a 1:10 sloping beach and a model AR (1.8 m long × 0.3 m high) with 0.2 m submergence depth. Five regular and five irregular wave conditions were generated on two types of beach profiles (with/without model AR) to study the cross-shore hydrodynamic and morphological evolution process. The influences of AR on the processes are concluded as follows: (1) AR significantly decreases the incident wave energy, and its dissipation effect differs for higher and lower harmonics under irregular wave climates; (2) AR changes the cross-shore patterns of hydrodynamic factors (significant wave height, wave skewness and asymmetry, and undertow), leading to the movement of shoaling and breaking zones; (3) the beach evolution is characterized by a sandbar and a scarp which respectively sit at a higher and lower location on the profile with AR than natural beach without AR; (4) the cross-shore morphological features indicate that AR can lead to beach state transformation toward reflective state; (5) the scarp retreat process can be described by a model where the scarp location depends linearly on the natural exponential of time with the fitting parameters determined by wave run-up reduced by AR. This study demonstrates cross-shore effects of AR as a beach protection structure that changes wave dynamics in surf and swash zone, reduces offshore sediment transport, and induces different morphological features.

Nonlinear wave propagation in a vegetated sandbar-lagoon system

“…Ten different experimental tests are given in Table 1. The length scale was confirmed as 1:10 according to the Shields, Rouse and Froude similitude scaling [5,20,21]. The still water depth of 0.55 m and five incident wave heights were considered.…”

“…In the past decades, considerable laboratory studies have been concentrated on the wave attenuation by rigid and flexible vegetation [2]. Ma et al [3][4][5] studied experimentally the effect of artificial reef on wave spectra induced by regular and irregular waves. This facilitates the identification of detailed wave decay mechanisms.…”

Assessment of the Performance of an Artificial Reef Made of Modular Elements through Small Scale Experiments

“…The construction of the structure alone means an interruption to the beach profile, that is, the depth of closure is arbitrarily fixed and with it, the length and shape of the profile. A first effect, given the low or null permeability of the base of the barrier is that it serves as a trap for the cross-shore sediment transport [14]. In a sense, this function could be sufficient in places where the beach is exposed to storms and the presence of the barrier facilitates the maintenance of the beach by having a fixed and protected site from where to take material to fill the beach recurrently.…”

Experimental Observation on Beach Evolution Process with Presence of Artificial Submerged Sand Bar and Reef

“…The density of the resin sand was 1.40-1.45 g/cm 3 with grain size ranging from 0.15 to 0.18 mm, which maintained the similitude of the hydrodynamic and sediment process by satisfying the Froude number, the Shields number, and the Rouse number under the geometric scale factor of 10 (prototype/model). The details of the scaling calculations can be found in [75].…”