Narrowneck Artificial Reef

Anna Cleary 				CEE514, 2007  

Background to the Project 


The long stretch of beach that makes up the Gold Coast of Queensland is subject to large amounts of longshore drift (partially due to the fine particle size
 of the white sand that makes up these beaches). The magnitude of this drift can be up to about 500,000 m3, in the northerly direction .   The other factor 
that contributes to the shift of sand is that historically the Gold Coast experiences about 1.4 cyclones a year on average   The Northern Gold Coast Beach 
Protection Strategy aims to maintain sufficient beach area for the sake of tourism and protection the coastline from large storm events  .  This outcome has
 been achieved in the past though beach nourishment (addition of sand from the dredging of other locations such as the Tweed River.  Another aspect of the 
Strategy was the construction of a submerged artificial reef to  be placed offshore of Narrowneck beach to act as shoreline protection.  This reef serves a 
secondary purpose in that it acts to improve the surfing conditions at Narrowneck.  The irony of this ‘artificially designed wavebreak’ is that the surf 
conditions achieved still do not rival some of the other breaks in the region such as Snapper Rocks. The boulder wall at narrowneck was frequently exposed 
leaving little beach at narrowneck.  

The purpose of the reef is to stabilize earlier beach nourishment.  

Design of the Reef Structure 

Sand-filled geotextile bags make up the reef (approximately 500).  The reef is 350 m ( in the direction of the shoreline) and 600m wide.  The water depths 
range from about 2-11m.   Sandbags were chosen as the most appropriate design choice to avoid adverse impacts (Jackson, 2002).
Modelling was undertaken by the University of Waikato (NZ) (2-d  and 3-d models including GENUIS, 3DD and POL 3DD) which was followed up with numerical 
modeling of the choosen reef shape. 


  
Surfability


The narrowneck artificial reef was one of the first reefs to be designed with the surfing conditions in mind.  The shape of the reef had to be adjusted from the traditional rectangular reefs running parallel to the shore.  
The design of the reef was aimed to optimized the surfing potential for this wave break.  The criteria for the quality of the surf break was taken from previous studies on this concept of surfability.  This addressed issues like the wave peel angle.  Peel is an important concept because it defines the rate at which the wave breaks.  A large wave peel will mean longer breaking time and hence a longer ride for the surfers.  This is related to peel angle; a small peel angle gives a large peel time.  One of the other aspects of surfability is the type of wave breaking that occupies.  Kerry Black, of the did a study which determined the types of waves preferred in various types of recreational activities.
The structure consists of two islands with a channel in between.  Kerry Black found that the ‘work class’ surfing breaks exist on headlands, so one of the aims in designing the shape of the narrowneck reef was to replicate a headland.  
The structure also had to be designed to allow for most of the sediment transport to continue – the design criteria was that 80% of the sediment should be still transported across thee ocean.  
Defined a number of components of a surfing reef (Mead and Black – field).

The final design crest was designed at about 1.5m below low tide (the original design had this crest at 0.5 m to optimize the surfing conditions for experts, but was considered too dangerous).  


Imaging used to compare the increased potential for surfing on the reef.  The criteria used to evaluate this was the occurrence of wave breaks on the reef as
 opposed to the adjacent areas (Turner, summer 2004).  
The parameters that define the character of a wave include: breaking wave height, breaker type (spilling, plunging, collapsing, surging), wave period, 
breaking wave celerity, peel angle, water depth at break point and velocity of the undertow at breakpoint (Jackson 2002).  Shallow submerge structures will 
decrease the magnitude of the waves, hence provided more coastal protection.  In the case of a surfing reef however, this could be dangerous if the reef 
becomes dry during certain tides (Jackson 2002).   

Monitoring of the reef 

ARGUS system originally used to design the system.  This system differs from a webcam in that in can provide qualitative data.  This system, consisting of a
 series of cameras,  is located 60m inland of the dune line at narroneck and approximately 100m above the average sea level.  A series of cameras take a 
number of pictures (varying from snapshots to ‘timex’ or time averaged shots).  The photos from the three angles are merged into one image and rectified to 
ensure that each pixel represents the same area on ground.  The result is a plan view of the beach which can be converted to real world map coordinates to 
allow for easy interpretation (Black etc all, 2007).  



Other Aspects of the Reef

It was not originally expected for the reef to act as a fish habitat (artificial reefs that are designed for this purpose have custom specific features to 
attract marine life), however many marine species have been observed on the reef, and have subsequently attracted fishermen and divers alike .  
The construction of the reef has been considered successful in increasing the usage of the narrowneck waters.  
There are many more surf craft observed on this reef than the surrounding sand banks, including shortboards,longboards, bodyboards, surfskis, jetskis and kayaks.  

Monitoring 



Bibliogragphy

Hutt J. Black, K & Mazeiraud 2001 “Improving the Surfing Climate of Narrowneck Beach” Australasian Coastal & Ocean Engineering Conference – Gold Coast, Australia, p114-119
http://www.surfline.com/mag/features/artificial_reef/html/text.html

Mead, S and Black, K “Field Studies Leading to the Bathymetric Classification of World-Class Surfing Brekas” Special Issue of the Journal of Coastal Research on Surfing 

Aarninkhof, S.G.J, Dronkers, T.D.T McGrath, J and Turner I L, (Summer 2004) CZM applications of Argus coastal imaging at the Gold Coast, Australia Journal of Coastal Research 20.3 (Summer 2004): p739(14).

Jackson L.A., Tomlinson, R. and D’Agata M. (2002), The challenge of combining coastal protection and improved surfing amenity, Proc littoral 2002, Porto, Portugal, 22-26 Sep, p257-263
Source Citation:Turner, Ian L., S.G.J. Aarninkhof, T.D.T. Dronkers, and J. McGrath. "CZM applications of Argus coastal imaging at the Gold Coast, Australia." Journal of Coastal Research 20.3 (Summer 2004): 739(14). Expanded Academic ASAP. Gale. University of Queensland. 13 Dec. 2007 
. 

Jackson, L.A, Tomlinson, R, Turner,I, Corbett, Bobbie  D’Agata, M and  McGrath, J (2005) “Narrowneck Artificial Reef, Results of 4 yrs of Monitoring and Modifications” Proceedings of the 4th International Surfing Reef Symposium  
Blacka, M.J, Anderson, D.J, and Turner, I.L (2007) Analysis of Shoreline Variability, Seasonality and Erosion/Accretion Trends August 2006 – January 2007  Technical Report, The University of New South Wales Water Research Laboratory 


Narrowneck Links 

Electronic Copies of the Monitoring Reports from the University of New South Wales Water Research Laboratory 
http://www.wrl.unsw.edu.au/coastalimaging/public/goldcst/

Surf Cams for Narrowneck
http://www.coastalwatch.com/camera/cameras_large.aspx?cam=1200&state=QLD&t=7:18:17%20AM&camName=Artificial%20Reef