Considerations in Using Bragg Reflection for Storm Erosion Protection

Abstract

It has been suggested that Bragg reflection, the combined coherent wave reflection from a few low-lying shore-parallel bars, might be used to protect a beach against storm-wave attack. Numerical models are used to examine two issues relating to the feasibility of this concept: the degree of erosion protection provided by reflecting a portion of the incident wave energy, and the degree of wave reflection that can be generated by a bar field of varying geometry. The results show that a Bragg-reflection bar field must reflect about one-quarter of the incident wave energy to provide a significant measure of storm erosion protection. Bar fields with uniform spacing are capable of producing the required magnitude of wave reflection, but lack sufficient bandwidth. Bandwidth can be increased by staggering the spacings between bars, however, this produces a concurrent decrease in wave-reflection magnitude. Bragg-reflection bar fields appear capable of providing a limited measure of storm erosion protection along U.S. Gulf Coast and Atlantic Coast beaches, but their bandwidth may be too limited for use along Pacific Coast beaches.

Wave reflection and vortex evolution in Bragg scattering in real fluids

“…Their experimental results show the limitation of both the theory of Miles (1981) and extended mildslope equation of Kirby (1986). Bailard et al (1992) also observed the feasibility of the Bragg reflection of artificial bars placed offshore on a natural beach. They reported that the Bragg reflection of artificial bars may be an encouraging method for reducing beach erosion in some cases.…”

Experiments on standing waves in a rectangular tank with a corrugated bed

“…Some time later, Kirby (1993) elucidated numerically the reflection of linear surface waves by sinusoidal bars in the case when the incident wave frequency is not necessarily close to resonance. Using Mei's asymptotic method, Yu & Mei (2000a,b) extended the work of Bailard, DeVries & Kirby (1992) to investigate waves passing over a periodic array of sandbars and then (partially) reflecting from a beach or seawall. They demonstrated that the resulting partially standing waves over the periodic bed depended sensitively on the effective position of the shore reflection with respect to the phase of the bed corrugations, at least when the incident waves had a length near twice the sandbar spacing.…”

The Feasibility and Effectiveness of using Bragg Breakwaters in the Shoreline Wave Climate for East Taiwan Ocean Energy

“…Kirby and Anton [5] applied previous theories for Bragg reflection of surface waves by parallel bars to the case of artificial bars placed discretely on the seabed. Bailard et al [6] explored the feasibility of the Bragg reflection of artificial bars placed offshore on a natural beach. Their results concluded that the Bragg reflection of artificial bars may have merits as an appropriate shore protection method.…”

“…The Bragg breakwaters could be used to protect coast and constructions in the sea. The Bragg breakwaters can be effective and feasible to be used to increase wave energy in the sea [5,6,10,11]. Therefore, the study of the impact of energy absorption by wave farms on the nearshore wave climate and specially the influence of the incident wave conditions and the number and position of the farms, on the near-shore wave characteristics has been performed and discussed in this paper.…”