Designing a multifunctional artificial reef: studies on the influence of parameters with most influence in the vertical plane

Abstract

Multifunctional artificial reefs are submerged breakwaters that serve several purposes. As well as protecting the local coastline, they enhance surfing possibilities and/or increase the environmental value of the area where they are situated. Multifunctional artificial reefs (MFARs) have some promising new aspects, too: first, they provide an unimpaired visual amenity, and second, they can offer tourist and economic benefits by improving the surfing conditions. Regarding the functionality of an MFAR, much research has been carried out on surfability, i.e. whether a wave is good for surfers. However, no research has yet been done on the influence of the submergence and the length of the reef slope on the breaker type, even though this is important for the design of the reef in terms of surfability. A preliminary design was achieved step by step, making use of the theory and state of the art of multifunctional artificial reefs (Voorde et al. 2009a, 2009b). This reef geometry was then used as an initial design in physical and numerical tests. These were performed to ascertain the capacity of a multifunctional reef to serve as a submerged breakwater and so protect the local coastline of Leirosa, Portugal, and improve the local surfing possibilities. This paper describes the numerical study conducted to analyze the influences of the main relevant parameters in the vertical plane, namely: the height, the submergence, and the length and slope of the reef. The investigation was conducted using the COBRAS-UC numerical model in the vertical plane and the main results and conclusions are described and presented; a brief discussion and some recommendations for future work are also included.