Long Term Performance of a Submerged Coastal Control Structure: A Case Study of the Narrowneck Multi-Functional Artificial Reef

Conference Paper (PDF Available)inCoastal Engineering Proceedings 1(33) · July 2012with 128 Reads
DOI: 10.9753/icce.v33.structures.54
Conference: 33rd International Conference on Coastal Engineeering., At Santana, Spain
Abstract
In response to the increasing occurrences of beach erosion along Surfers Paradise and Main Beaches - Gold Coast, Australia, the Northern Gold Coast Beach Protection Strategy [NGCBPS] was developed to widen the beach by 20-30m as well as improving surfing conditions as a secondary objective. The strategy, implemented in 1999- 2000, involved large-scale beach nourishment and construction of a submerged breakwater “reef” to act as a control point at Narrowneck. Construction of the reef involved innovative filling and placement methods using very large sand filled geotextile containers coupled with significant advances with regards to design of the geotextile material and containers. In the 11 years since construction, there has been substantial monitoring of the project since its completion in late 2000 including: - video imaging using webcams; hydrographic and beach surveys; aerial and oblique photography; surf and surf safety observations and GPS surfing track plots; and geotextile container condition and stability. This paper presents an update on the performance of the reef over the last four years. In particular, the response of the structure and the shoreline to a series of major storm events in 2009 has been examined. The results have shown that the erosion caused by these major events was accommodated within the wider beach created in 1999. Over the next 2 years there was a gradual recovery in the lee of the reef with a subtle groyne effect resulting in an even larger increase in the width of the updrift beach. A detailed underwater condition survey was also undertaken in 2011, to determine changes in the condition of the geotextile containers. This revealed a number of containers missing or damaged, and that seaward containers were covered by sand. The marine habitat which has been a feature of the reef has been impacted by the increased coverage of sand, but still shows high abundance and biodiversity.
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LONG TERM PERFORMANCE OF A SUBMERGED COASTAL CONTROL
STRUCTURE: A CASE STUDY OF THE NARROWNECK MULTI-FUNCTIONAL
ARTIFICIAL REEF
Angus Jackson
1
, Rodger Tomlinson2, Bobbie Corbett1 and Darrell Strauss
2
In response to the increasing occurrences of beach erosion along Surfers Paradise and Main Beaches - Gold Coast,
Australia, the Northern Gold Coast Beach Protection Strategy [NGCBPS] was developed to widen the beach by 20-
30m as well as improving surfing conditions as a secondary objective. The strategy, implemented in 1999- 2000,
involved large-scale beach nourishment and construction of a submerged breakwater “reef” to act as a control point
at Narrowneck. Construction of the reef involved innovative filling and placement methods using very large sand
filled geotextile containers coupled with significant advances with regards to design of the geotextile material and
containers. In the 11 years since construction, there has been substantial monitoring of the project since its
completion in late 2000 including: - video imaging using webcams; hydrographic and beach surveys; aerial and
oblique photography; surf and surf safety observations and GPS surfing track plots; and geotextile container
condition and stability. This paper presents an update on the performance of the reef over the last four years. In
particular, the response of the structure and the shoreline to a series of major storm events in 2009 has been
examined. The results have shown that the erosion caused by these major events was accommodated within the
wider beach created in 1999. Over the next 2 years there was a gradual recovery in the lee of the reef with a subtle
groyne effect resulting in an even larger increase in the width of the updrift beach. A detailed underwater condition
survey was also undertaken in 2011, to determine changes in the condition of the geotextile containers. This revealed
a number of containers missing or damaged, and that seaward containers were covered by sand. The marine habitat
which has been a feature of the reef has been impacted by the increased coverage of sand, but still shows high
abundance and biodiversity.
Keywords: multi-functional artificial reef; geotextile containers; monitoring; salient
INTRODUCTION
Background
The Northern Gold Coast Beach Protection Strategy (Jackson et al., 1997) was developed in
response to the ongoing decrease in beach width of the Northern Gold Coast Beaches during the
1990’s. The large scale nourishment of 1.5Mm3, which had been placed on the beaches in 1974
following the devastating cyclones of the 1950’s and late 1960’s, was no longer sufficient to cover the
boulder wall at Narrowneck Beach.
Figure 1 shows the exposed boulder wall at Narrowneck following storms in 1996. This section of
the boulder wall is some 20m seaward of the general seawall alignment resulting in minimal beach
widths and potentially hazardous conditions. Widening of the beach by 30-50m was proposed to
provide a storm buffer for 1:50 year events.
The proposed strategy included the following short term elements:
1. Nourishment: a minimum of 1.5Mm3 to be pumped from various sources to widen Surfers
Paradise beach by 30-50m. Regular ongoing nourishment of at least 60,000m3/yr is necessary to
manage potential down-drift impacts. This quantity can at present be provided from maintenance
navigation dredging in the nearby Broadwater estuary and sand excavations from building sites.
Back-passing from the Seaway bypass system is another potential source.
2. Coastal Control Point: the control point is to be an artificial submerged (low crested) reef
breakwater designed to stabilize the nourishment and provide better and more consistent surfing
conditions. The reef should be constructed of mega- sand filled containers designed and fabricated
for the project to minimize the hazard to surfers, reduce costs and reduce construction impacts.
3. Pipeline/Boosters: a permanent buried pipeline is required from the Spit to Narrowneck to
facilitate regular nourishment to the control structure to improve the beaches down-drift.
4. Management Policies: ongoing nourishment is required and operational procedures will need to be
developed. Present policies should be continued to ensure completion of an adequate and
continuous seawall and continued supply of additional sand from building sites to the beaches.”
Further investigations by Carley et al. (1998), GCCM and ICM (1998) confirmed that a 30m
widening would provide protection for a single storm event of greater severity than 100yr ARI and
adequate buffer for multiple storm events of similar severity to those of 1967”. To achieve the
necessary 30m minimum beach widening, the volume of sand required was calculated to be 1.3Mm3
(Tomlinson et al., 2007).
1
International Coastal Management Pty Ltd, PO Box 306. Main Beach, Queensland. 4216, Australia
2
Griffith Centre for Coastal Management, Gold Coast Campus, Griffith University, 4222, Queensland, Australia
COASTAL ENGINEERING 2012
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Figure 1. Narrowneck Beach, looking south
An allowance for ongoing nourishment to the north of the control structure to compensate for
accretion of the beach to the south and a sea level rise component (initially totalling 60,000-80,000
m3/yr and decreasing over time) was included in the strategy however has yet to be implemented.
Sources of these nourishment volumes were identified as available sand from building sites and from
channel maintenance dredging in the Broadwater. The proposed backpassing facility has also not been
implemented however further studies have since been undertaken (e.g. Patterson, 2007), and are
continuing.
A total of 1.3Mm3 of nourishment was applied between February 1999 and June 2000, primarily
obtained from dredging wider and deeper navigation channels in the Broadwater with some from
building sites. The artificial reef was constructed between August 1999 and December 2000. The
artificial reef was constructed between August 1999 and December 2000. Figure 1 shows the visible
beach at Narrowneck on 24th August 2011.
The complexity of the construction process in the surf zone and on the highly variable and mobile
seabed in the surf zone is noted below and highlights the need for continued monitoring and
maintenance of the beach and reef structure at Narrowneck.
“The nourishment and large storms prior to reef construction had created a very large storm bar (over 1 m high over
the back half of the reef). The bar would migrate shoreward with milder weather. As dredging to potential
maximum scour depth, or a scour mattress, were not viable economic options, and as the construction materials
allow for easy top-up, a sequenced construction schedule [at reduced cost] with top-up after initial settlement (as the
large storm bar migrated shoreward) was undertaken. As recommended, regular maintenance has been carried out.”
Tomlinson et al. (2007).
Monitoring Program
Due to the innovative nature of the reef breakwater and construction method a long term
monitoring program was established at the time of construction. The overall performance of the reef
has been presented previously by Jackson et al. (2003), Jackson et al. (2005), Jackson, Reichelt et al.
(2005), and Jackson et al. (2007). In addition there have been regular six-monthly reports on the
impact of the reef on the adjacent shoreline, for example: Blacka et al (2007) and Strauss et al (2012).
Data collection undertaken includes:
Dive inspections, including underwater imagery to examine the condition of the structure, identify
damaged or missing containers and report on the development of marine ecology
Aerial photographic inventory of the artificial reef
Bathymetric survey and contour maps
Side scanning images Video
Land and aerial oblique photography.
Surf parameter observations & testing.
REEF INTEGRITY
Several dive inspections have been undertaken since construction in order to evaluate the condition
of the reef structure. The purpose of these inspections in the early years after construction was
primarily to check on the condition of the geotextile, the developing reef ecology and evidence of
structural failure. The recent inspections have focused on locating damaged or missing containers and
providing a photographic record of ecological changes.
Reef design
The design criteria for the Narrowneck artificial reef were (Jackson et al, 1997):-
to act as a coastal control point to stabilize the nourished beaches to the south
1996
2011
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after the initial nourishment of 1.3Mm3 the maximum annual trapping capacity be 100,000m3/ yr
as this quantity of suitable sand can be provided from outside the active system
the reef be shaped to provide improved surfing conditions
the reef be constructed so as not to be hazardous to surfers
To achieve these objectives there has been a progressive evolution of the reef shape since the
major construction phase was completed in 2000. The final revised design (2004) is shown in Figure 2.
-2 -3 -4 -5 -6 -7 -8
-9
-10
Figure 2. Reef Levels Original and Revised Design
Construction was carried out using mega sand filled containers designed to fit in the hopper of the
contractors split hull hopper dredge. Rather than the usual practice of sewing the containers closed on
the dredger, they were prefabricated to the required size and filled from the dredge pump outlet filling
and discharging tail water through trunks that were sealed above water to avoid the need for underwater
diving work. Considerable development of high durability geotextile, seaming methods and inlet /
outlet trunk closing methods were developed. Accuracy of placement was sub 1m.
Previous Maintenance
Overall, some 450 containers have been placed to form the reef since 1999 (Figure 3). Of those, 42
have been placed in three maintenance campaigns as shown in Figure 4.
Figure 3. Container placement schedule
A significant modification was made to the original design in 2004 with the establishment of a
submerged weir between the two arms of the reef as well flared wings. The reason for the introduction
of a weir was to mitigate against wave penetration through the channel which was allowing the creation
of a double salient at times (the central channel was originally included in the design during modelling
but with lowered crest, the predicted high currents did not occur so the channel was not as necessary
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than originally envisaged). The flared wings were introduced primarily to improve the effectiveness of
the reef, and improve surf by improving the link from the reef break to the adjacent shore break.
Figure 4. Placement of Containers for Reef Maintenance
Bathymetric Survey
As part of the recent update of the performance of the reef, a survey of the Narrowneck reef was
undertaken by the Gold Coast City Council on 9th June 2011 (Figure 5) and an isopach comparing this
survey with another survey undertaken in 2008. It is noted that survey of this type of structure is very
useful but needs interpretation and verification since individual containers are unusual in shape and not
always well represented by the survey interpolation.
Figure 5.a) Reef Bathymetry (9/6/11), b) Isopach showing changes to surveyed levels between 2008 & 2011
An interpretation of the survey of critical crest areas showed that there are particular areas where
there would be sufficient height to place a mega-container and areas where the isopach indicates a
container has been lost since 2008. This has been overlaid with as-constructed survey of containers
placed as part of previous maintenance campaigns. This indicates that:
Maintenance of the structure is required as there are critical areas below design levels
Since 2008 (3 years), the isopach indicates some 10 containers have been compromised
Raising of seabed levels on outer reef since 2008 appears to have resulted in burial of seaward
containers
Raised seabed
Lower seabed
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Aerial Images
Aerial images of Narrowneck reef during calm conditions are occasionally clear enough to clearly
distinguish individual bags (Figure 6) and can be very useful for reviewing the condition of the reef
prior to direct inspection. Overlay of the most recent (July 2011) aerial photo with as-constructed
survey of containers placed as part of previous maintenance campaigns (Figure 7) indicates that:
Raising of the seabed levels on the outer reef has resulted in extensive burial of seaward
containers. It does not appear that these containers are missing, although their condition is
unknown and it is expected that there would be some damage in these outer areas.
Partial burial of containers used for design modification indicates that a change to crest levels
likely reflects settlement due to lack of foundation containers rather than damage or loss of the
containers themselves.
Figure 6. Aerial photographs taken in 2004 and 2011
Figure 7. Overlay of July 2011 Aerial Photo with containers placed during maintenance campaigns (ICM)
Inspection
On site verification of the survey and aerial information is necessary. As such, multiple
underwater inspections have been undertaken [in so far as this was possible given the extent of the
growth on the containers and the burial of large sections of reef].
The nearshore seabed is highly variable and a large proportion of the structure is presently buried
by a large storm bar and could not be inspected. Of those containers which could be inspected, the
majority appear to be in good condition and have retained their shape well. Despite being some 11
years since placement of many of the containers, visual inspection revealed:
Raised seabed
Burial of seaward
containers
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Raising of the seabed levels on outer reef has resulted in extensive burial of seaward containers. It
does not appear that these containers are missing, although their condition is unknown and it is
expected that there would be some damage due to anchors in these outer areas as it is a popular
fishing location.
No evidence of a general deterioration or wearing of the standard (ELCOMax 1200R) or
composite (ELCOMax 1209RP) geotextile on intact containers
At least one container with the unsuccessful trial polyurethane coating is still present and in good
condition, although several of these have failed (Figure 8). This coated geotextile was
discontinued usage during initial construction as it made the containers more rigid and stress
cracking was observed relatively quickly after placement. Progressive failure of these trial
containers was expected.
No evidence of diminished seam integrity, i.e. splitting or fraying. It was noted that seams of
failed containers also generally remained in good condition.
No evidence of failure of the complex closures developed during this project to cope with the
very large wave forces acting on the containers.
It is noted that the nominated guaranteed lifetime of the standard 1200R geotextile is 15 years and
the reinforced 1209 geotextile is 25 years, although this is primarily driven by the UV exposure and is
expected to be significantly lengthened by the presence of marine growth.
For containers placed as part of the original construction, there is not adequate as-constructed
survey of individual containers for effective container identification. This information is available for
the containers placed as part of maintenance campaigns and specific inspections of these containers
were undertaken. Of the 42 containers:
26 containers were inspected and found in good condition
6 containers were substantially buried
8 containers were either damaged or missing entirely
2 containers were known to have failed previously
Figure 8. Failed container with polyurethane coating
Settlement
In 2004 two containers were placed on the existing sandy seabed to create the weir across the
central channel between the northern and southern reefs. As such, there was no attempt to provide a
foundation to support the containers during periods where the seabed was eroded and this resulted in
lowering the container to scour level. This was expected and as dredging to possible scour level was
not as cost effective as the strategy of allowing settlement and topping up, initial placement heights
were approximately 0.5m above design levels to provide some initial compensation. Since placement,
these containers have experienced lowering of up to 2m, resulting in present levels some 1.5m below
design. Containers are predominantly buried at present (Figure 6).
Two containers were also placed to provide a widened, more flared crest. These containers have
also experienced settlement, although this is limited to 1 1.5m [and as a result present levels are
COASTAL ENGINEERING 2012
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within 1m of design levels]. Again, containers are predominantly buried during seabed conditions at
present (Figure 6).
Four containers showed significantly lowered levels on the isopach survey (Figure 5) although
visual inspection indicates that the crest containers are in good condition and it appears likely that the
slumping is the result of failure of lower containers (Figure 9).
Figure 9. Conceptual sketch showing slumping
Damaged Containers
Visual identification and inspection of containers placed as part of maintenance works was
undertaken and damaged or missing containers were identified as shown in Table 1.
During inspections it is often difficult to definitively identify the cause of damage because the
initial cause of failure is masked by the damage suffered during cyclic flapping and deflation of the
container. After the container is fully deflated, weather events can often result in complete removal of
the remaining material, leaving no evidence as to potential cause of failure. The reef is a very popular
fishing area and there has previously been clear evidence of instances where damage has been the result
of:
Propeller damage
Anchor damage
Vandalism and spears from spear guns
Table 1. Maintenance Containers Damaged Since 2006
Date
Placed
Type **
Size
Status in 2011
Comments
2002
½ Standard
½ Composite
T2
Container not
evident
Previous anchor damage repaired on 9/11/2002
2002
½ Standard
½ Composite
T1
Container not
evident.
2002
Standard
T4
Container not
evident.
2006
Standard
T4
Failed
Container.
2006
Standard
T4
Container not
evident.
2006
½ Standard
½ Composite
T2
Container not
evident.
High container vulnerable to damage.
Trunk cover damage repaired in April 2007
2006
Standard
T4
Container not
evident.
2006
Standard
T2
Failed
Container.
Ear evident upon placement.
Repaired trunk cover May 2006.
** Standard is ELCOMax 1200R ; Composite is ELCOMax 1209RP
During the 2011 inspection, one container was almost fully deflated and showed clear evidence of
propeller damage (Figure 10). The slumping on the north reef due to damage of base containers would
indicate potential damage due to anchors. As a result, it seems clear that damage to the structure as a
result of vessels is ongoing.
The fact that the majority of the damaged containers were of the standard 1200R geotextile would
indicate that the reinforced 1209RP geotextile (developed specifically for this project) is in fact proving
to be more robust and anchor resistant. Continued usage would be expected to reduce ongoing
maintenance requirements.
Where there was no indication of previous damage, 4 of the 5 containers were standard T4
containers. Given previous observations indicating that these size containers tended not to be as well
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filled as smaller containers and tended to develop ‘ears’, it is possible that these containers may be
more vulnerable to flapping during large events. It is noted, however, that these containers are located
in deeper water, which also makes them more vulnerable to anchor damage.
Figure 9. Container with evidence of propeller damage
ECOLOGICAL ASPECTS
A full ecological inventory was reported on in Jackson et al. (2007). For the current update, dive
inspections were carried out to evaluate and photograph the reef to assess any qualitative ecological
changes.
Observations
During the dive inspections, observations were also made of the marine species present on the reef.
While this is not a comprehensive assessment, it provides a qualitative indication of changes. Critical
changes identified during 2011 monitoring include:
Diversity of shallow containers has increased. During previous monitoring these containers were
dominated by macro algae / sea grasses. The more diverse growth was limited to the deeper
sections of the reef. Crest layer containers now support a wider range of species (Figure 11),
including kelp and sponges as well as a range of brown algae and red algae.
Some containers show evidence of growth in the early stages of development and it is expected
that these containers have recently been exposed after a period of burial
Growth on deep containers has likely been eliminated due to extended burial beneath the well-
developed storm bar. It is expected that these regions will develop quickly as they become
exposed once more.
Containers placed in 2005/06 are diversifying at a much greater rate, likely due to increased
recruitment of marine life from existing reef.
Areas of high diversity remain concentrated on vertical faces and areas where the reef’s structural
complexity is high.
Pelagic fish remain dominated by yellowtail scad, although the population of these pelagic species
is likely variable.
Major species, including turtles, wobbegongs and stingray are still resident on the reef.
PROPELLOR DAMAGE
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Figure 11. Marine Species Present on the Reef
BEACH WIDTH
The exposed boulder wall (Figure 1) that was visible prior to the nourishment and reef construction
has remained completely covered despite the occurrence of several large storms and a significantly
wider beach has been evident since 1996. Wave conditions experienced in 2009 were considered to be
the stormiest for more than 20 years. Seven storms with significant wave height exceeding 3m
impacted the coast between February and May 2009 causing significant erosion (Figure 12). The last
and largest was caused by an “East Coast Low” which persisted from 19 -25 May. The storm recorded a
peak significant wave height of 6.2m and a maximum wave height of 10.6m. Peak periods reached 14s
and wave direction was predominantly easterly (shore-normal to the coast) (Figure 11). The combined
storm surge and high energy waves, which persisted above 2m from May 19th to May 25th (Figure 13),
resulted in widespread erosion of beaches. The maximum significant wave height of 6.1m corresponds
to a 1:10 year event according to the extreme wave analysis of Allen and Callaghan (2000) (Table 2).
The April to October 2009 six month average shoreline position decreased by 20m in the vicinity
of Narrowneck Reef with respect to the previous six month period, primarily in response to the May
2009 storm event (Splinter et al, 2009). The average beach width along the CoastalCOMS monitored
area of the northern beaches at the end of May 2009 and for the six months to October 2009 was 60m
(Figure 14).
The latest analysis of beach width at Narrowneck derived from the CoastalCOMS monitoring
system reveals a monthly average beach width varying from 50 to 100m along the section of coastline
covered by the analysis shown in Figure 15. Much of this increase may be due to onshore movement of
nourishment sand placed offshore. This sand was dredged from the Gold Coast Seaway and has
provided nourishment to the active profile depths of around 6-9m offshore of Surfers Paradise. The
nourishment volume was approximately 170,000 m3.
Impact of reef on shoreline
The analysis of beach width trends conducted in 2007 (Blacka et al, 2007) suggested that the beach
had achieved an equilibrium state following the completion of nourishment in mid-2000. Seasonal
variability of ~40m in shoreline position is consistent with the impact of the May 2009 storm event and
recovery. The beach width from Narrowneck to Surfers Paradise was fairly uniform at around 50-60m
in May 2009 whereas the latest monitoring (October 2011, Figure 15) displays beach width of around
Kelp
Brown Algae
Red Algae
Wobbegong Shark
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70m at Narrowneck increasing to 100m at Surfers Paradise. This is indicative of the reef providing a
minor groyne effect and acting to widen the beach updrift as per the original design. However, the
absence of a long term salient on the shoreline suggests that for some wave conditions there is
sufficient long shore transport occurring shoreward of the reef to inhibit the formation a permanent
salient.
Figure 12. Narrowneck beach looking south June 2, 2009
Figure 13. Wave height measured at the Gold Coast Seaway wave rider buoy (DERM).
Table 2. Extreme wave statistics for Southeast Queensland (Allen and Callaghan,
2000)
Average return
Interval (year)
East Coast Lows
Hsig (m)
Tropical cyclones
Hsig (m)
Combined
Hsig(m)
2
4.85
3.89
5.02
5
5.67
4.60
5.83
10
6.10
5.20
6.29
20
6.47
5.83
6.71
50
6.90
6.7
7.28
100
7.2
3
7.75
Wave Height (Gold Coast Wave Buoy)
0
2
4
6
8
10
12
18/05/09 19/05/09 20/05/09 21/05/09 22/05/09 23/05/09 24/05/09 25/05/09 26/05/09 27/05/09
Wave Height (m)
GC Buoy Hs GC Buoy Hmax
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Figure 14. Northern Gold Coast beach width (400 to -2200m), May 2009 (from top to bottom): (a) Beach width
relative to current 6 month mean, (b) Beach width relative to previous 6 month mean (c) Change in beach
width from previous month, (d) Mean beach width, (e) Monthly average shoreline position (CoastalCOMS).
Furthermore, the anticipated need for maintenance nourishment of the shoreline north of the reef
(downdrift) due to groyne effects has not yet been required. A distinct salient in the lee of the reef is
not continuously present but is a recurring feature which can be clearly identified in time exposure
images such as in Figure 16.
Other Observations
The reef structure has generally produced a salient as predicted by physical and numerical
modelling; however the location of the salient is offset by 100m from the centreline of the reef. The
continuing evolution of a marine habitat on the reef has resulted in it becoming a very popular fishing
and, to a lesser extent, dive location.
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Figure 15. Northern Gold Coast beach width (400 to -2200m), October 2011 (from top to bottom): (a) Beach
width relative to current 6 month mean, (b) Beach width relative to previous 6 month mean (c) Change in
beach width from previous month, (d) Mean beach width, (e) Monthly average shoreline position
(CoastalCOMS).
The reef structure has generally produced a salient as predicted by physical and numerical
modelling, however the location of the salient is offset by 100m from the centreline of the reef. The
continuing evolution of a marine habitat on the reef has resulted in it becoming a very popular fishing
and, to a lesser extent, dive location.
In terms of detailed aspects of the container structure, the trunk covers have proven successful in
avoiding vandalism to the inlet and outlets closures. However, anchors from vessels over about 8m
length have caused considerable damage. A “no anchoring zone” was implemented but this was not
maintained. As a result major maintenance has been required as set up above, with further maintenance
placement being required.
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In terms of safety and recreational usage, no injuries have been reported on the reef. The crest
height of about 1 1.5m below low tide has proven to be suitable for prevention of injuries but has not
optimised the surf quality (Corbett et al 2005).
Figure 16. Salient in lee of Narrowneck Reef on May 20th, 2010
ACKNOWLEDGEMENTS
The work presented here was undertaken as part of the Gold Coast Shoreline Management Plan
Implementation funded by the Gold Coast City Council. Shoreline position analysis was undertaken in
partnership with CoastalCOMS Pty Ltd under contract to the Gold Coast City Council.
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Tomlinson, R. B., Jackson, L.A. & Corbett, B., (2007). Baseline Data Assessment Volume 5: Summary
of Narrowneck Reef Monitoring to May 2007. GCCM Research Report No. 63.
  • ... Although not prescribing a definitive obligation, this clearly advocates sensitive engineering design that can deliver secondary benefits above and beyond the primary purpose of developments – in the context of this study, coastal protection. To date, there are few examples of truly and purposefully-designed multi-functional coastal defences around the world (but see [52,59,73,74,87,94,98] ). Single-purpose artificial reefs have been implemented to provide habitat for commercial fish species [93,97], to enhance marine biodiversity [5,7], and to provide amenity functions such as surfing [91], diving [103] and sea angling [104]. ...
    ... [12,35,39,67,87]) as well as to investigate multi-functional designs for new developments (e.g. [20,28,39,59,86,87,94,95]). Some Delphi panel members commented that the legislative framework , communication between sectors and awareness of multi-functional structures all exist, despite these being perceived as barriers by others. ...
    Article
    Full-text available
    To fulfil international conservation commitments, governments have begun to recognise the need for more proactive marine planning policies, advocating sensitive engineering design that can deliver secondary benefits above and beyond the primary purpose of developments. In response, there is growing scientific interest in novel multi-functional coastal defence structures with built-in secondary ecological and/or socio-economic benefits. To ensure research efforts are invested effectively, it is first necessary to determine what secondary benefits can potentially be built-in to engineered coastal defence structures, and further, which of these benefits would be most desirable. It is unlikely that secondary benefits are perceived in the same way across different stakeholder groups. Further, their order of priority when evaluating different options is unlikely to be consistent, since each option will present a suite of compromises and trade-offs. The aim of this study was to investigate stakeholder attitudes towards multi-functional coastal defence developments across different sector groups. A preliminary questionnaire indicated unanimous support for implementing multi-functional structures in place of traditional single-purpose ones. This preliminary survey informed the design of a Delphi-like study, which revealed a more nuanced and caveated level of support from a panel of experts and practitioners. The study also elicited a degree of consensus that the most desirable secondary benefits that could be built-in to developments would be ecological ones – prioritised over social, economic and technical benefits. This paper synthesises these findings, discusses the perceived barriers that remain, and proposes a stepwise approach to effective implementation of multi-functional coastal defence developments.
  • ... Narrowneck and increased to 100 m at Surfers Paradise ( Jackson et al., 2012). ...
    Article
    The efforts made to reduce the causes and mitigate the effects of global climate change continue to be critical in coastal areas. Many adaptation strategies implemented in coastal areas remain inadequate or ineffective. Using primarily events and interventions carried out along the Portuguese Atlantic coast, this work aims to show the paradigm shift that has occurred in Portugal since the last century (the 1990s) within the scope of the National Coastal Zone Management Strategy, taking into account the new guidelines for the implementation of coastal defence works. In this context, this paper also aims to assist coastal communities in carrying out operational coastal management by presenting and discussing management tools and primary options that should be considered in any adaptation programme that is to be implemented. Both nonstructural and structural measures are considered. Action plans, warning systems, emergency plans, and evacuation plans belong to the first category. Education and training are also considered, because they play a key role in the sustainability of coastal areas, especially in the coming generations. Structural measures are adaptation options that are designed to increase the safety of people and reduce risks. They are discussed and grouped into categories that include accommodation, protection, and retreat. Recent cases of successful accommodation and protection measures implemented along the Portuguese coast are also presented and discussed.
  • ... In the lee of the reef, an additional 30 m had been maintained ( Jackson et al., 2005). The beach was fairly uniform, with a width of approximately 50 to 60 m in May 2009, whereas the monitoring carried out in October 2011 displayed a beach width of approximately 70 m at Narrowneck and increased to 100 m at Surfers Paradise ( Jackson et al., 2012). ...
    Article
    Full-text available
    Antunes do Carmo, J.S., 2018. Climate change, adaptation measures, and integrated coastal zone management: The new protection paradigm for the Portuguese coastal zone. Journal of Coastal Research, 34(3), 687-703. Coconut Creek (Florida), ISSN 0749-0208. The efforts made to reduce the causes and mitigate the effects of global climate change continue to be critical in coastal areas. Many adaptation strategies implemented in coastal areas remain inadequate or ineffective. Using primarily events and interventions carried out along the Portuguese Atlantic coast, this work aims to show the paradigm shift that has occurred in Portugal since the last century (the 1990s) within the scope of the National Coastal Zone Management Strategy, taking into account the new guidelines for the implementation of coastal defence works. In this context, this paper also aims to assist coastal communities in carrying out operational coastal management by presenting and discussing management tools and primary options that should be considered in any adaptation programme that is to be implemented. Both nonstructural and structural measures are considered. Action plans, warning systems, emergency plans, and evacuation plans belong to the first category. Education and training are also considered, because they play a key role in the sustainability of coastal areas, especially in the coming generations. Structural measures are adaptation options that are designed to increase the safety of people and reduce risks. They are discussed and grouped into categories that include accommodation, protection, and retreat. Recent cases of successful accommodation and protection measures implemented along the Portuguese coast are also presented and discussed. ADDITIONAL INDEX WORDS: Storms, multifunctional options, management tools, public participation.
  • Chapter
    Full-text available
    Due to the combined action of several natural phenomena such as waves, tides, currents, wind, sedimentary movements and extreme weather events including storms, the coast is constantly changing. However, ongoing climate change, including human action, has been changing natural patterns and profoundly affecting coastal ecosystems, as they are particularly sensitive to rising sea surface temperatures, ocean acidification, salt intrusion, rise in groundwater levels, and changes in flow patterns. The significant increase in vulnerabilities and risks witnessed in coastal areas, especially since the middle of the last century, is also a consequence of the combined action of all these phenomena. Accordingly, the sustainability of these areas depends on the success of an integrated adaptation capable of promoting the system’s resilience, taking into account climate change, human action and other factors. Bearing in mind the vulnerabilities on the Portuguese coast, this work begins with a brief introduction about guidelines for possible forms of intervention. Some examples of adaptation and other natural protection solutions are discussed. After a brief reference to collaborative management procedures, the need to invest in the creation of an advanced national marine science and technology program is highlighted.
  • Conference Paper
    INTRODUCTION Globally, the use of rock in coastal design and construction projects has been common practice. This is largely due to the availability of material, relative cost and extensive research and development in rock design. Formulated equations, such as the ‘Hudson’ or ‘van Der Meer’ are used to produce standardized breakwaters, groynes, revetments and offshore reefs, however the structures are typically ‘over designed’, using larger volumes of material than necessarily required for site conditions. With the increase in rock costs globally and specifically in the UAE, this year of 7.00AED/tonne for trucks traveling in the Emirates of Ras Al Khamiah and Fujairah (Shabaan, 2016) coastal projects are becoming increasingly costly and designs should consider more site-specific alternatives with the integration of alternative construction materials, specifically geotextile containers. HISTORY OF GEOTEXTILES IN COASTAL DESIGN There has been significant development of geotextiles in coastal design since their beginning in the 1960’s. International Coastal Management (ICM) has been at the forefront of material and construction methodology development since the early 90’s with the completion of various, successful global coastal projects. Some notable (ICM) projects, utilizing site-specific design and construction methodologies include the following: 1. Narrowneck Artificial Reef, Gold Coast, Australia. Development of new in-situ filling techniques using split hull barge and material strengths for extended durability (15 years since installation). 2. Maroochydore Groyne, Sunshine Coast, Australia. Development of geotextile containers and filling frame for onsite constructability of innovative design. 3. Nearshore Berms, Ullal, India. Development of construction apparatus for efficient methodology. 4. Private Submerged Seawall, Ajman, UAE. Design and construction methodology for the installation of sand filled geotextile containers for emergency erosion protection. Figure 1 Various geotextile containers and methodologies developed by ICM on international projects WHEN TO USE ROCK vs. GEOTEXTILE CONTAINERS Coastal sites vary greatly from location to location and therefore it is highly unlikely that a standardised or ‘textbook’ type solution will be the most site-effective. In some locations the use of both rock and geotextile containers will be more cost/end user efficient, as per recent works in Ajman, UAE (ICM). Some key factors when applying site-specific designs are:  Site Weather Conditions (Wind, Waves, Tides, etc.)  Site Accessibility for Construction  End User Requirements (Beach access, Visual Impact, Environmental Impact, etc.)  Material Supply Costs  Expected Structure Duration Use  Capital vs. Maintenance Costs In some cases, capital costs and construction times can be greatly reduced using temporary geotextile structures to provide an agile coastal solution which can be easily updated/extended/removed etc. as the site requirements and/or coastal processes in the location change. In other cases, rock may be better suited; this may occur when integration into existing structures, greater durability or visual consistency is required. SITE-EFFECTIVE DESIGN As mentioned, there has been significant advancement in the design and construction methodologies of geotextile containers for coastal stabilization. Each site is however unique and requires site-effective design to achieve the most cost and outcome efficient results. Agile designing can enhance and stabilise a coastal location for low capital costs, allowing the site/structure(s) to develop over time as site requirements/conditions change. REFERENCES Shabaan, A. (2016, January 27), Trucks to pay Dh7 for a tonne of rock, Khajeel Times, pp. 7
  • Conference Paper
    Full-text available
    Natural environments generally have a limited capacity to support a level of sustainable use. Therefore, as use levels increase, natural systems can no longer sustain man's impacts without management. The Gold Coast is Australia's premier tourist destination and offers some of the best and most popular surfing beaches in Australia. Tourism is the Gold Coast's largest industry however it is at risk of significant losses due to storm events. As a major beachfront tourism area, Gold Coast City Council has recognised the need to provide infrastructure that enhances the natural capacity of the environment (IENCE) to support, manage and protect the beaches which form the base of the tourism industry. The Northern Gold Coast Beach Protection Strategy (NGCBPS) has been developed to provide a sustainable long term coastal management solution for the Northern Gold Coast. While the oceanfront boulder wall has been successful in stopping buildings from being lost into the ocean in severe erosion events it does not protect the beach. The need for post storm nourishment, is not efficient in terms of cost or preserving the tourist industry from erosion induced slumps. A case study is presented that shows how the Gold Coast City Council is investing in infrastructure that enhances the natural capacity of the environment (IENCE) to support the local tourist economy. The Northern Gold Coast Beach Protection Strategy (NGCBPS) aims to decrease the magnitude of economic loss following storm events by increasing the volume of sand within the storm buffer seaward of the oceanfront boulder wall. The NGCBPS has the dual objectives of increasing the sand volume within the dunal buffer through beach nourishment and improving surf quality through the establishment of an artificial surfing reef. The project will cost a total of $8.8 million dollars and is expected to yield benefit- cost ratios of over 60 to 1.
  • Conference Paper
    Full-text available
    A large reef has been constructed offshore from Narrowneck on the Gold Coast, Queensland, Australia. The reef provides a submerged, low visual impact, coastal control point to stabilize the nourished northern Gold Coast beaches. As the reef is in a popular tourist and surfing area, it has also been designed and constructed to enhance recreational amenity. For safety and cost efficiency, the reef has been constructed of very large sand filled geotextile units. Experience with the design and construction of such structures is limited and the inclusion of improved surfing as secondary design criteria increases the complexity. To facilitate evaluation and modifications to the reef there is a comprehensive monitoring program, which includes the use of ARGUS video imagery to assess the changes in the shoreline related to wave conditions at the wave rider buoy nearby. Divers are studying the physical performance of the sand filled geotextile containers, as well as the extent and diversity of the marine ecosystem which has exceeded expectations. There have been a number of storm wave events during the monitoring period. The data obtained from the monitoring is being used to modify the long term Narrowneck reef shape, and to design other proposed reefs in the area.
  • Conference Paper
    Full-text available
    The Narrowneck Artificial Reef [Gold Coast, Australia] was constructed in 1999/2000 out of large sand-filled geotextile containers. It quickly became evident that the containers provided an excellent substrate for marine flora and the development of a diverse ecosystem. As a result, the reef has become popular with locals for fishing, diving, snorkeling and spearfishing. In the years since it was constructed, monitoring of the ecological aspects of the reef has been undertaken. While macroalgae and pelagic fish dominate the reef, it is also home to a wide variety of benthos, fish and other marine fauna. Influenced by the East Australia Current and wave action from the Pacific Ocean, driven by the South East Trade Winds, the reef exhibits a different community structure in comparison to other natural reefs of the Gold Coast. The popularity of the Narrowneck Reef has clearly shown that enhancing the ecological environment and improving recreational amenity have potential benefits on eco-tourism as well as local biodiversity. No Yes
  • Article
    Full-text available
    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. Yes Yes
  • Conference Paper
    Full-text available
    Submerged artificial reef breakwaters in the nearshore coastal zone can create the potential for a range of recreational activities as well as beach protection. As such, safety is an important issue when considering the design and construction of these types of structures. Investigations have been carried out for the proposed Palm Beach reefs and this paper provides an overview of the potential safety hazards and litigation threats presented by an artificial submerged structure to all potential users. Investigations into the safety aspects of these structures has incorporated: - extensive monitoring of the Narrowneck artificial reef [Gold Coast, Australia] - observations of natural reefs and beach breaks - physical model testing of a 1:10 sale submerged reef constructed of sand-filled geotextile containers at the Deagon Hydraulics Laboratory. The studies assessed the effect of a number of design parameters, including water depth above crest, roughness of the slope and truncation of the toe, on these safety aspects. The paper also covers the impact of achievable tolerances on the design, performance and safety of these structures and provides a number of guidelines for the design, management and maintenance of these structures in order to provide an acceptable level of risk. Yes Yes
  • Extreme wave conditions for the South East Queensland coastal region Analysis of Shoreline Variability, Seasonality and Erosion / Accretion Trends Numerical Modelling Sand Nourishment Profiles
    • M Allen
    • J M J Callaghan
    • D J Anderson
    • I L Cunningham
    Allen, M. and Callaghan, J. (2000) Extreme wave conditions for the South East Queensland coastal region. Environment Technical Report 32. Brisbane: Environmental Protection Agency Blacka, M.J., Anderson, D.J. and Cunningham, I.L., (2007). Analysis of Shoreline Variability, Seasonality and Erosion / Accretion Trends: February 2007 -July 2007. Report 16: Northern Gold Coast Coastal Imaging System. Water Research Laboratory Technical Report 2007/34, UNSW. Carley, J.T. Couriel, E.D. & Cox D.R., (1998). Numerical Modelling Sand Nourishment Profiles / Quantities and Beach Erosion Due to Storms and Sea Level Rise. University of New south Wales Water Research laboratory prepared for Gold Coast City Council.
  • Narrowneck Reef: Results of 4 years monitoring and modifications " 4 th Int Surfing Reef Symposium
    • L A Jackson
    • R B Tomlinson
    • I Turner
    • B Corbett
    • M Agata
    • J Mcgrath
    Jackson, L.A., Tomlinson, R.B., Turner, I., Corbett, B., D'Agata, M. and McGrath, J., (2005) " Narrowneck Reef: Results of 4 years monitoring and modifications " 4 th Int Surfing Reef Symposium, Los Angeles, January 2005.
  • Coastal Imaging – Palm Beach and Northern Beaches, Gold Coast
    • K Splinter
    • M Elliott-Smith
    • C Lane
    • R Tomlinson
    Splinter, K., Elliott-Smith, M., Lane, C. and Tomlinson, R., (2009). Coastal Imaging – Palm Beach and Northern Beaches, Gold Coast. May 2009 to October 2009. Griffith Centre for Coastal Management Research Report No. 97-02
  • Coastal Imaging – Palm Beach
    • D Strauss
    • T Murray
    • E Volep
    • C Lane
    • R Tomlinson
    Strauss, D., Murray, T., Volep, E., Lane, C. and Tomlinson, R., (2012). Coastal Imaging – Palm Beach