An Artificial Reef to Protect Surfers Paradise Beach Developing ...

An Artificial Reef to Protect Surfers Paradise Beach 

Developing & Implementing the Science 

Mr L.A. Jackson CP Eng 

Managing Director, International Coastal Management, Southport, Australia. 

e-mail: jackson@onthenet.com.au 

Mr W.P. Hornsey Pr. Eng 

Development Engineer Coastal & Marine, Soil Filters Australia Pty Ltd, Southport Australia. 

e-mail: whornsey@soilfilters.com.au 

Introduction 

The large artificial submerged reef at Narrowneck is constructed only of sand and 

geotextile. This reef is an important element in the strategy funded by Gold 

Coast City Council to protect the world famous Surfers Paradise beaches from 

erosion during storms. It has provided a huge forward leap in geocontainer 

technology and represents the cutting edge of marine geocontainer manufacture 

and installation. The reef, although primarily for beach protection, also represents 

a major step forward in the dream to create artificial surf reefs from user friendly 

and cost effective materials. Monitoring of the reef also highlights the behaviour 

of geocontainers confirming the need for continued investigation and 

development of the science. This article will detail the lessons learned during the 

construction and monitoring period and identify areas of research needed in 

order to better understand this complex field. 

© Copyright 2003 Soil Filters Australia Pty Ltd 

Figure 1: Aerial View of Narrowneck Reef, 

created with submerged geotextile containers

Background 

The artificial reef is located at Narrowneck at the northern end of Surfers 

Paradise, on Australia’s Gold Coast. The Gold Coast is the major coastal holiday 

destination in Australia and the economy of the Gold Coast region is dependant 

on the tourism industry. In order to continue to attract tourist, it is important to 

maintain and protect the wide sandy beaches. 

The Gold Coast is in the cyclone belt and the wave buoy nearby has recorded 

waves of over 13m. The worst storm erosion occurred in 1967 when 7 cyclones 

affected this section of the east Australian coastline causing extensive damage to 

the Gold Coast beaches and beachfront developments (Figure 2) and resulted 

substantial loss in revenue to the tourist industry. 

Ongoing beach nourishment was implemented and has been effective but there 

were inadequate long-term sources of suitable sand to maintain the beaches 

even without the added effects of the predicted sea level rise. Prior to the 

implementation in 1997of the Northern Gold Coast Beach Protection Strategy 

(NGCBPS), the beaches were not wide enough to withstand storm erosion 

(Figure 3). 

Figure 2: Aftermath of the 1967 Cyclone – Surfers Paradise 

© Copyright 2003 Soil Filters Australia Pty Ltd

Objectives 

Figure 3: Storm erosion of Narrowneck in March 1996 

(taken at high tide before construction of the reef) 

The Gold Coast City Council commissioned International Coastal Management to 

determine and implement an appropriate proactive strategy to achieve the 

following objectives: - 

Primary objective:- 

• Widen the beach and dunes along the Surfer’s Paradise esplanade, 

Main Beach and Narrowneck Beach to accommodate storm erosion 

and retreat due to sea level rise. 

Secondary objective:- 

• Improve surfing conditions and beach amenities. 

Various schemes were investigated with the following design criteria:- 

• Not cause down drift erosion. 

• Have low visual impact. 

• Not restrict pedestrian flow. 

• Not create hazardous conditions. 

• Meet regulatory body requirements 


The preferred option was nourishment of the beach and dunal areas from 

navigation channel dredging, stabilised by a submerged reef structure. The ideal 

location for the reef was identified at Narrowneck, a short wide headland that 

protrudes seaward of the general alignment by approximately 35m and is prone 

to erosion. Not only was this site well located from a coastal management point 

of view but it also has very good parking and public access. 

A number of alternative construction materials, including rock &concrete, were 

investigated but it was decided to construct the reef using Geosynthetic sand 

filled containers for the following reasons: - 

• Cost: The Geosynthetic structure was approximately half the cost of a 

similar rock structure. 

• Safety/Public Liability: As the structure would be used by surfers it was 

therefore important that risk of injury to surfers be minimised. Also, using 

sand from the ocean on site for construction meant that the truck traffic 

hauling rock or concrete units would not cause a hazard to road or beach 

users. 

• Environmental: Transport of 45,000m 3 of rock from quarries along busy 

city roads would increase road traffic emissions into the air as well 

increasing the need for road maintenance. 

• Ease of removal: As the use of a submerged reef was untested and in 

effect a full scale model, approval conditions required that the structure be 

able to be removed or modified should there be any unforseen adverse 

impacts created by the structure. Rock and concrete would have been 

expensive if not impossible to remove. 

The reef concept using sand filled geocontainers was considered a prototype for 

the design and construction of future reefs to protect other Gold Coast beaches 

against storm erosion and retreat due to sea level rise while improving the surfing 

amenity. However, it was recognised that the state of the art with respect to 

submerged breakwater design and the use of geocontainers would need to be 

developed. 

Design 

The need to provide a combination of coastal protection with improved surfing 

amenity without hazardous conditions made the design process to determine a 

suitable shape and location of the structure complex. Specialist consultants 

using physical and numerical modelling methods were used during the design 

process. The University of New South Wales, Water Research Laboratory 

conducted the physical modelling while the University of Waikato (New Zealand) 

conducted the numerical modelling. 


The design adopted consisted of a north reef and a south reef with a central 

“paddle” channel running perpendicular to the coastline (see figure 1) to avoid 

very high currents over the reef crest that were predicted in the numerical 

modelling. The Northern reef extends slightly closer in shore than the southern 

reef and this extension was designed to trap sand close to shore and prevent a 

natural bypassing channel from forming. The reef extends 400m offshore and is 

200m wide at its widest point (including “paddle” channel). The reef is 

constructed in water depths ranging from approximately 2m deep close to shore 

and 10.5m deep on the outside edge of the reef. The maximum tidal range is 

~2m and the reef crest was initially designed at approximately 0.5m below low 

water to optimise surfing. 

Geosynthetic Container Manufacture and placement 

The manufacture and filling of the large containers is one of the aspects that 

makes this project unique. Previously large containers were manufactured by 

placing a sheet of geotextile into a hopper barge filling the barge with material 

using an excavator, the edges of the container were then folded inwards and 

sewn together on site. Obviously this was not a simple task when the barge is 

moving due to the swell conditions and quality control is somewhat limited. 

Expressions of interest were called for geotextile suppliers interested in 

designing and supplying large geocontainers that could be filled to a 

predetermined size and would have at least a 25year design life. The 

successful supplier, Soil Filters Australia, recommended pre-manufacture of the 

containers in a controlled environment with filling and placement of the units by a 

split hull hopper. 

The Mega Sand containers used were constructed from heavy-duty UV stabilised 

polyester Terrafix ® nonwoven needle punched staple fibre geotextile. Quality 

assurance was identified as the key to the successful deployment and durability 

of the Sand Containers. The manufacture of the containers was carried out under 

strict supervision and complied with ISO 9001 standards. Specialist sewing 

techniques were developed specifically for this project and have proven 

themselves in extreme conditions. 

The containers were pre-manufactured, with inlet valves and exhaust vents the 

only items that requiring closure on board the hopper dredge. This ensures 

greater quality assurance as the amount of stitching required in board the moving 

vessel was minimised. Developments in the closure methods, such as the double 

seal closure, during construction ensured improved long-term durability and 

integrity of the closure system. 

Nearly 400, 20m long mega sand containers varying from 3.0 metres to 4.6 

metres in diameter, were placed using the split hulled, trailing suction hopper 

dredge, Faucon, fitted with computer interfaced DGPS. This purpose fitted out 

vessel, was again unique in that a single vessel was used to carry out all the 


functions required to construct the reef from filling the container to accurate 

location and placement. The containers were accurately filled utilising a 

calibrated flow density metre, ensuring repeatability and consistency of the 

construction. Containers were filled to 80% of maximum theoretical volume. The 

marine contractor McQuade Marine was required to work in very difficult 

conditions, which became progressively worse as the height of the structure was 

raised and increased swell heights above the structure (Figure 4). Not 

withstanding these difficult conditions the contractor was still able to manoeuvre 

his ship in such a way that containers were generally placed to an accuracy of 

0.5m. Figures 5 shows two containers placed alongside each other lengthwise 

with a gap of approximately 150mm between them. 

Placement of the containers was affected by a number of factors, namely: - 

Tides 

Swell size 

Swell direction 

Wind direction 

Extent of beach nourishment 

Timing of the beach nourishment had a significant effect on the construction. 

Unfortunately the timing of the contract was not ideal and the nourishment 

contract ran ahead of schedule, which meant that the expected large seabed 

movements would be increased. After examination of options it was decided to 

construct the reef on the seabed, allow settlement and then top up. The cost of 

dredging or installation of an effective scour mattresses for these conditions was 

excessive. 

Figure 4: Installation conditions and dredge, Faucon 


Figure 5: Placement Accuracy of ± 150mm between containers 

Construction commenced in May 1999 and monitoring of individual units and the 

total structure since this time has been carried out to determine the behaviour of 

the individual units and impacts of the structure. The seabed movements since 

commencement have resulted in lowering of the structure and this has provided 

data on the effect of crest height on erosion protection, safety and surfing. 

Monitoring 

The extensive monitoring since construction commenced has included:- 

• Video “Argus” imaging using multiple cameras 

• Hydrographic and beach surveys. 

• Dive inspections. 

• Aerial oblique photography. 

• Surf parameter observations 

• Pressure sensors in and on individual units. 

The ARGUS coastal imaging system installed for the Council by the University of 

New South Wales is used to obtain hourly images from four video cameras and 

these are also available to the general public via the web. From the images, 

sophisticated digital image processing techniques are used to:- 

• assess beach width, 

• assess the three dimensional inter-tidal morphology, 

• compare wave breaking on the reef and adjacent offshore sand bars 

Settling of the reef has been evident but the reef has proven very robust in its 

protection of the beaches and improving the surf. Despite a number of storms 

very little erosion has been observed in the vicinity of the reef and the beach has 

maintained an additional ~40 m width relative to pre-nourishment conditions. 


Despite the initial settling, and lower than design crest level, in the analysis of the 

wave breaking data a strong trend towards increased wave breaking on the reef 

location has been found (see figure 6). The increase of wave breaking from 20% 

in January 2000 (during construction) to 60% - 80% from March 2000 to July 

2001 (post construction) can be seen quite clearly (1) . Also, the amount of wave 

breaking remains relatively constant from March 2000 to July 2001. The analysis 

does not consider the quality of the breaking waves for surfing, however the reef 

is now more popular with surfers. Not all surfers are happy yet due to over 

optimistic reporting by media who claimed that the reef would produce the perfect 

surf. The balancing between surfing and safety at this early stage has been a 

cautious. The monitoring backed by recent wave modelling of the effect of crest 

height, lead to a decision to leave the crest height a 0.5m lower during the first 

top up recently. This by no means the end of the surfers dream, in July 2001 

large 3m swell was recorded off Surfers Paradise and photos were taken to 

asses the quality of the wave breaking on the reef, figure 7 shows the left and 

right breaks off the reef and the paddle channel is clearly defined through the 

centre. 

reef breaking days per month 

wave breaking - reef only 

(normalised) 

wave breaking - hourly (daylight) images per month 

35 

30 

25 

20 

15 

10 

5 

0 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

300 

250 

200 

150 

100 

50 

0 

Pol ynomial fit 

Jan-00 Apr-00 Jul-00 Oct-00 

2000 

Jan-01 Apr-01 Jul-01 

Gold Coast Reef 

adjacent storm bar 

Figure 6: Reef Wave Breaking data indicate a trend toward increased wave 

breaking on the artificial reef 


Figure 7: Waves breaking on Narrowneck Reef 

The design team together with the geotextile container supplier carry out regular 

dives on the reef in order to assess the durability and stability of the containers. 

This monitoring confirms that the containers are not deforming beyond what was 

allowed for in the design of the structure. Back analysis of the geocontainers 

using the GeoCops program produced an expected shape of the container filled 

on dry land these dimensions are compared with field data obtained from the 

monitoring dives. Figure 8 shows the calculated shape as the dashed line while 

the solid line defines the actual shape of the container measured in place. 

2 100 mm 

4 600 mm 

4 950 mm 

1 800 mm 

2 300 mm 

Figure 8: Container Shape 

5 900 mm 

6 500 mm 

2 000 mm 

It is clear from the monitoring that the containers have deformed slightly when 

compared to the undisturbed dimensions. However this difference was expected 

as the containers are placed under considerable stress when exiting the hopper 

and in some cases fall though 8m of water before landing on the seabed. Up to 

20% reduction in height was allowed for in the design but the actual reduction in 

height is closer to the 15% mark. Continued monitoring of the containers has 

shown that the container shape has remained stable since installation. 


Lessons Learned 

The GCCC expressed concern over damage to containers due to surfboard fins, 

therefore various coatings were trialed in order to improve puncture resistance. 

These protective coatings trials showed that as the coatings became more rigid 

(less flexible), the greater the chance of damage. The most successful protection 

to the geotextile was achieved by producing a composite geotextile. This 

consisted of the primary geotextile (the geotextile which must withstand filling 

and placement stresses), with a secondary coarse staple fibre layer needled to 

the surface. The secondary layer adds no structural strength to the primary 

geotextile and does not reduce the high elongation characteristics but it does trap 

up to 5kg/m 2 of sand in the structure thereby significantly increasing the puncture 

resistance of the geotextile. The secondary layer also protects the primary 

geotextile from abrasion and UV degradation 

The shape of the containers is very important, no part of the container must be 

allowed to flap with the movement of the swell over the containers. This continual 

flapping motion causes fatigue in the geotextile and can lead to rupturing of the 

containers. 

The containers are placed in a highly abrasive environment and only the most 

abrasion resistant geotextiles should be used in this type of application. Any 

geotextile proposed for use in this application should undergo vigorous testing. 

The German “Baudesanstalt fur Wasserbau” (2) rotating drum test method is 

recommended, as it best replicates abrasive near shore surf environment. 

In order to ensure a quality finished product containers must be manufactured in 

a controlled environment not on site. Specialised stitching methods and 

configurations should be applied when manufacturing the containers as the 

stitching is placed under repeated severe stress during the filling and placement 

operation. The seam strength becomes more important as the geotextile 

becomes more rigid (lower elongation) as the stresses appear to become 

concentrated on the seams rather than dissipated throughout the geotextile. 

The on site inlet and exhaust valve closures are the only areas in the container, 

which are not carried out under any quality assurance system. Conditions under 

which theses closures are made are far from ideal, particularly during rough seas 

and should therefore include a failsafe mechanism. The failsafe mechanism used 

in this project was a double seal configuration, which made use of two 

independent systems to close the valve. This meant that should there be a failure 

of one of the seals that the second seal would not be affected by the failure of the 

first and maintains the integrity of the closure. This will in increase container 

factor of safety significantly. Compromising a small detail such as this can lead to 

the failure of the container as a whole. 


Some damage to the containers is inevitable, be it during the placement 

operation or from pleasure boats anchoring on the reef, however underwater 

repairs to containers is possible. Patching devices and techniques were 

developed during the contract, which will allow ongoing maintenance to 

submerged geotextile containers. Although patching was never considered 

during the adjudication of tenders it should be considered in future projects. 

As with any other construction material placed on the seabed, some settlement 

of the containers into the seabed must be expected. However if containers are 

placed on a newly nourished and unconsolidated seabed significant settlement of 

the structure can be expected. 

The open structure of the geotextile provides an ideal platform for the 

colonisation of marine life. Marine algae begins to grow on the containers as 

soon as they are placed and are generally completely covered in up to 300mm 

long growth within 3 months. It also appears as if the composite geotextile 

provides a better substrate for the colonisation of marine life than say epoxycoated 

geotextiles. The reef has now become a favourite fishing and diving spot 

as well as for surfing. 

Conclusion 

Construction of the Narrowneck Reef using thick nonwoven needle punched 

staple fibre geotextiles has proved their effectiveness in marine conditions 

beyond doubt. The nourished and stabilised beach is now wide and able to 

withstand storm wave attack (Figure 9), both figure 3 and figure 9 taken a high 

tide. 

While a great deal is yet to be learnt about the use of geocontainers in artificial 

reefs, this project has pushed the boundaries of geocontainer use to new levels 

and raised new questions. The reef has provided a full scale model to measure 

and observe raising questions such as “why is there little turbulence around the 

containers?” and “why is settlement into the seabed minimal?” – note: rocks have 

an expensive habit of disappearing into large scour holes that form around rock. 

International Coastal Management and Soil Filters Australia are involved with 

ongoing research to answer these and other questions. Pressure transducers 

inserted into a bag have already helped understand the way in which the sand 

filled containers actually absorb wave energy. However, further research into 

areas such as stability, durability, energy absorption and the best layouts for 

surfing is still to be completed. 


Figure 9: Narrowneck after storms in March 2001 (c/f figure3) 

The monitoring of the Narrowneck prototype has provided extensive “real world” 

data that has influenced the design of the Noosa and Palm Beach reefs 

programmed for commencement in 2002-03. 

The success of this project has been possible due to the close working 

relationship involving ongoing Research and Development between Client, 

Engineer, Geosynthetic Supplier and Contactor. 

References 

1. Turner, I.L., Dronkers, T.D.T., Roman, C., Aarninkhof, S.G.J., McGrath, J., 

2001. The application of Video Imaging at the Gold Coast to Quantify Beach 

Response to Sand Nourishment and Construction of an Artificial Reef. 

Proceedings, 8 th Australian Port and Harbour Conference, Surfers Paradise, 

Australia, 55-60. 

2. Federal Waterways Engineering & Research Institute, 1994. Guidelines for 

testing of geotextiles in hydraulic engineering applications. 

Acknowledgements 

Dr I Turner, University of New South Wales, Water Research Laboratory for the 

latest wave breaking data. 

Mr J McGrath, Gold Coast City Council, for the 1967 storm damage photo. 

The authors supplied all other photo’s.

An Artificial Reef to Protect Surfers Paradise Beach Developing ...

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