Performance of steel-wire mesh pebble/rock cells in coastal erosion and flooding control: a physical modelling study

Abstract

With a total coast length of approximately 30,000 km, UK coastlines experience significant coastal erosion annually and therefore substantial resources are allocated for their maintenance and rehabilitation. According to various sources, approximately 18% of UK coastlines are protected with defense works. This shows the enormous size of the sector and highlights the importance of introducing innovations to reduce the costs of coastal defense. Traditionally, various ways were applied for coastal erosion and flooding control including rock/concrete/wood revetments, sea walls, dykes, breakwaters, groynes, beach nourishment and recycling, and sand dunes/bags. Among these methods, revetment is possibly the most popular solution that can be constructed by various materials such as rock, concrete, gabions, and wood. While concrete revetments offer convenient access to the coast and require minimum maintenance relative to rock revetments, they are more expensive and are less effective in controlling wave runup and overtopping. On the other hand, rock revetments are a more cost-effective option and provide significant wave disputation, but they occupy large spaces at the coast, require continuous maintenance and undermine the aesthetic value of beaches.An alternate middle approach is to apply steel-wire mesh pebble/rock cells that carry the advantages of both concrete and rock revetments and minimize their drawbacks. The diamond mesh has an 8.3 cm unit width and 14.3 cm unit height, and are composed of relatively uniform rock/pebble units with diameters in the range of 20 – 25 cm. The cells are normally made to the thickness of 75 cm, but can be altered to withstand the different coastal conditions. Unlike gabions, the cells are more porous resulting in higher wave energy absorption and minimizing wave runup and overtopping. The inclusion of strong tension cables between each cell compartment when tensioned do not allow any movement in the rocks within the cells, enforcing the structure, providing stability and structural integrity making it robust for the most critical conditions.The purpose of this research is to test the hydrodynamic performance of the system through physical modelling. In this study, we focus on a particular type of cell called the TECCO CELL®manufactured by Geobrugg Inc. which offers marine grade stainless wire with high tensile strength steel. Such wire materials would ensure long-term durability of the system. This innovative coastal defense system was applied in Beesands (southwest England) in 2016 and yielded satisfactory performance in the past few years by the environmental bodies and the townsfolks for stopping the coastal erosion. We make 1/10 scaled models of the steel-wire mesh pebble/rock cells in the laboratory and study the interaction between the cells and incident waves by measuring various hydrodynamic performance criteria such as wave runup, transmission, overtopping and reflection. Based on our findings, we make recommendation on maximizing the hydrodynamic performance of steel-wire mesh pebble/rock cell revetments.