HOLOBREAK: Homogeneous low-crested structures to protect beaches and regenerate coral reefs

The retreat of coral reefs during decades, and their progressive degradation, is a clear indicator of the poor health of coastal ecosystems, which in turn affects the stability of nearby beaches protected by these reefs. In addition to their importance in the resilience of coastal ecosystems, coral reefs also produce on average 1,000 m³/km² of biogenic sediment per year, which is key for the long-term stability of neighbouring sandy beaches. Sea-sand-sun tourism is critical for the social and economic development of many coastal communities worldwide and often this is directly related to the quality of the natural resources. The focus of the HOLOBREAK Project is the study of Homogeneous Low-Crested Structures (HLCS), a new type of coastal structure composed of large rocks or pre-cast concrete units. These are similar to low-crested structures (LCS) but without a core, mimicking the protection provided by coral reefs to adjacent beaches. HLCS also provide an increased porous substrate that allows colonization of the structure by local species. The placement grid of the HLCS is significant in economic, logistic and functional perspectives; affecting the feasibility of construction, the costs involved and its effectiveness as beach protection. In this study, various placement grids were analysed. The results of the physical 3D tests were calibrated and validated against numerical placement tests, based on a Bullet Physical Engine (BPE). Good agreement was found, with a global mean relative error of 2.75%, indicating that the BPE model is a valuable tool for the feasibility analysis of different placement grids.