Artificial surf reef design Dutch swell conditions

for their enthusiasm, support and advice during the realization of this thesis. Furthermore I would like to thank the staff members of the Fluid Mechanics Laboratory of Delft University of Technology for their assistance while building the experimental setup and their support during the data processing. I would also like to thank Martijn Henriquez for his overall advice. Abstract Artificial surf reefs (ASRs) are structures specifically aimed at modifying the near-shore wave field transformation to improve surfing conditions or 'surfability'. With the increasing popularity of surfing, the demand for such artificial reefs is ever growing. Thus far, three ASRs have been realized over the last decade (see e.g. Black & Mead 2001) and many more are planned to be constructed in the near future. ASRs are planned to be constructed in big wave pools for indoor surfing. Nevertheless, artificial surf reef design is often done fairly ad hoc and there remains great uncertainty as to what the optimal dimensions of the artificial surf reef should be. Henriquez (2004) investigated, through a combination of numerical and experimental modelling, how ASR design affects the resulting surfability. The quality of a surf break is generally expressed in three measurable parameters: breaker height, peel angle and breaker shape. Together these parameters determine the surfability of the wave. In particular, the peel angle (a measure related to the rate at which the wave breaks along its crest) is an important measure that plays a dominant role in ASR design. The numerical modelling (Henriquez, 2004) was done without taking into account wave-driven currents. The experimental modelling by Henriquez showed that, approximately 20% of the wave ride was negatively affected by rip currents driven by wave breaking over the ASR. The waves in the rip current were breaking in sections, irregular and with a rough water surface, in other words: unsuitable for surfing. Through combination of numerical and experimental modelling this study aims at: 1) Gaining insight in reef properties that influence the wave-driven currents over the reef and associated effects on the surfability parameters; 2) Designing a reef shape optimized for surfing purposes, taking into account both waves and effects of wave-driven currents by means of numerical wave and wave-current models;3) Verification of design (and thus numerical predictions) by means of a laboratory experiment, specifically designed to obtain measurements of currents and surfability parameters. The models applied in the numerical study are: 1) a spectral wave …