Performance of submerged nearshore sand-filled geosystems for coastal protection

• Submerged nearshore sand-filled geosystems retard offshore sediment transport.
• Geosystems can replicate the natural protection of sandbars against coastal storms.
• Scour depth tends to be less than the incident unbroken wave-height.
• Scour predictors underestimate scour for structures placed landward in shorelines undergoing erosion.
• Maintenance of these structures on a regular basis is anticipated.

Nearshore submerged structures made of sand-filled geosystems are an interesting use for this type of coastal protection technology. These systems have an advantage over more traditional materials such as concrete units or rock, which is the limited and non-permanent impact on natural coastal processes. On top of that are also some important research achievements and improvements at the level of the materials. However, at more exposed hydraulic conditions under high wave energy its application is still hampered by the lack of knowledge about their performance. This paper describes research results based on a series of laboratory measurements of the hydrodynamic and morphodynamic change produced in the vicinity of submerged nearshore structures. An analysis of the different model outputs produced, with respect to sediment transport, wave reflection and wave-induced pressures, has been made and is discussed throughout the paper. Such a comparative analysis provides insights into the efficiency of each defence scheme in maintaining a beach and in protecting the shoreline. The sand-filled geosystems as nearshore submerged structures proved to be efficient in retarding the offshore movement of sediments and in maintaining the shoreline, even if instabilities due to elements' displacement and local scour have been observed.