Narrowneck Reef: review of seven years of monitoring

Abstract

The Narrowneck Artificial Reef is a large submerged structure constructed in 1999-2000 as a key component of the Northern Gold Coast Beach Protection Strategy (NGCBPS) implemented by Gold Coast City Council (GCCC). While primarily a coastal protection structure, its secondary objective was to improve surfing. Since its construction, comprehensive monitoring has been undertaken. To date, the reef has been a success in terms of retaining the wider nourished beach. The structural performance has been satisfactory, with ongoing improvements, and the geotextile has provided a surprisingly good substrate for development of a diverse marine community. In terms of surfing, the reef has achieved its goal and provides improved surfing conditions for a wide range of surf craft. Evaluation of the incidence of wave breaking shows that breaking is initiated on the reef for wave heights over 0.7 m to 2.0 m, depending on the tide. For an average year, waves break on the reef approximately 50% of the time. While waves tend to be more spilling than plunging in average conditions, larger swells, lower tides, and offshore winds have the potential to produce hollow, plunging breakers. The reef needs long period, clean swell to replicate the modeling. As Gold Coast wave conditions are usually bi-modal and often short-crested, there have only been a few examples where this has been the case. Bar formations around the salient also provide favorable conditions on the shore-break and the reef break often merges with the adjacent bar break to extend ride lengths. GPS data shows that recorded rides average 150 to 200 m, but have reached up to 260 to 270 m. Similarly, recorded ride times have reached up to 60 seconds. Despite being home to a number of regular and one-off surfing events, Narrowneck reef has not gained a widespread reputation as a great surf spot. Part of the reason for this appears to be that it is surrounded by world-class surfing breaks and typically these locations work in similar conditions as the reef. The fact that the takeoff area is 300 m offshore also seems to make the reef break less attractive to surfers. Media hype prior to reef construction led to unrealistically high expectations that the reef would perform in all conditions and press statements criticizing the reef before completion has also negatively impacted public perception of its success. While the objective of improved surfing has definitely been achieved, it was not well quantified. While the design has progressively evolved during maintenance works to improve surfing and safety, further improvements specifically improve surfing are not considered warranted.