THE NEED FOR INTERVENTION

...seawall alignment

Increased occurrence of beach erosion...&

TOPIC CHRONOLOGY OF KEY EVENTSDate Key Event1923 Timber seawall constructed at Narrowneck (up to 35m seaward of the general seawall

alignment) to protect the highway1974 Beach nourishment (Main Beach to southern Surfers Paradise) (1.5Mm3)

1990’s Decrease in beach width; exposure of boulder wall at Narrowneck

1993 Proposal - Artificial headland (75m) for Narrow Neck1997 Northern Gold Coast Beach Protection Strategy (NGCBPS)1998 Design studies – Investigation of the reef design for: sediment transport (including

sedimentation patterns, net littoral sediment drift, effects on adjacent beaches); surfing amenity; and the field measurement program

1999 Design studies – Physical model study (1:50 scale model)

1999 (Feb - Jun) Sand nourishment works (Narrowneck)1999 (Aug - Dec) Construction - Artificial reef

2000 (to Dec) Sand nourishment works (Surfers Paradise)2002 Container ‘top-up’ & replacement2004 Container ‘top-up’ & replacement2006 Container ‘top-up’ & replacement2009 Significant storms (1:10 ARI)2011 Underwater condition survey2013

THE NORTHERN GOLD COAST

BEACH PROTECTION STRATEGY

Includes Recommendations:

� To widen and maintain beaches between Burleigh Heads and the Seaway, to provide an increased storm buffer to withstand a 1:50 year storm/sea level rise without exposing the seawall, and to provide additional open space.

� To complete a sand nourishment of 1.5Mm3, in order to achieve a beach widening of 30-50m at Surfers Paradise.

� To construct a submerged reef breakwater as a “coastal control point”, in order to stabilise the sand nourishment, and to provide improved surfing amenity.

� To undertake a regular nourishment of up to 80,000m3/year, in order to manage potential down-drift impacts (with the sand source as a combination of maintenance dredging from The Broadwater and sand from development sites).

THE DESIGN FOR AN ARTIFICIAL REEF

NumericalModelling Study

Under “Average” wave conditions:• No clear salient attached to the

beach• No sedimentation on the reef crest• No evidence of an

emerged/submerged sand bank to join the long arm to the shoreline

Under “Constant” wave conditions:• A salient with amplitude predicted to be

78m, with a gap remaining between the reef and the shoreline

THE DESIGN FOR AN ARTIFICIAL REEF

PhysicalModelling Study

…a fixed bed scale model, with a light-weight tracer to represent nourished areas…

Testing:Primary scenarioOther scenarios

THE DESIGN FOR AN ARTIFICIAL REEF

PhysicalModelling Study

Study Recommendations:

1. Nourish the beach in the lee of the reef at the time of reef construction, to provide the additional 30-40m, and avoid the erosion of the beach on the down-drift (northern) side.

2. Regular monitoring over a minimum 3 year period, of the beach in the lee of the reef; regular monitoring of the erosion on the beach to the north, with additional nourishment during the period as the shoreline adjusts.

3. If equilibrium state is not attained within 3 years, to shorten the inshore northern arm of the reef.

[Note: Northern arm was constructed the same length as the southern arm, and the down-drift erosion was not as severe.]

REEF CONSTRUCTION

REEF CONSTRUCTION

1999 / 2000

The ‘Faucon’ Hopper

Approx. 400 geo-bags

Each is 20m x 4.5m & 300 tonnes

Placement accuracy 1m

Reef footprint 450m (l) x 205m (w)

ONGOING OPERATIONAL ACTIVITIES

Damage has been caused by anchors from vessels over about 8m length, and propellors.

“Trunk” covers have proven successful in avoiding vandalism to the inlet and outlets closures.

SHORELINE MONITORING 2001-2008 � ARGUS Video imaging (WRL, UNSW)� Monitors shoreline variability from weeks to years� Assess shoreline response to storm impacts and recovery� Characteristics of bar morphology

MONITORING SHORELINE RESPONSE

“salient”-effect

“groyne”-effect

SHORELINE MONITORING 2008-2013

RECENT SHORELINE DATA

LONG TERM COASTAL EVOLUTION

SUMMARY

� Evidence of stabilising sand on the up-drift beaches to the south (Surfers Paradise), through measurements of Beach Volume.

� Evidence of the localised formation of the salient feature at Narrowneck, through shoreline monitoring.

� Evidence of additional beach width being maintained at Narrowneck, through measurements of time-averaged shoreline position.

� Evidence that use of modified geotextile materials has reduced the frequency of maintenance campaigns.

The decadal-scale datasets should now allow researchers to move to further address and quantify the long-term benefits of the reef.

SHORELINE MONITORING 2010-2014Camera View:Centre

SHORELINE MONITORING 2010-2014Camera View:Left