Kirra Point Groyne Coastal Impact Study

In March 2010 the Tweed River Entrance Sand Bypassing Project (TRESBP) commissioned the Kirra Point Groyne Effects Study. The purpose of the study was to undertake a desktop investigation of the expected impacts of Kirra Point groyne on the shapes and widths of Kirra, Coolangatta and Greenmount beaches, and on the exposure of Kirra Reef now the project is delivering natural quantities of littoral drift sand to Queensland. In addition, potential changes to sand movements and possible inundation effects on Kirra Reef were investigated in response to two hypothetical scenarios: 1) adjustments to the length of Kirra Point groyne (including both lengthening and shortening the groyne); and 2) the complete removal of the groyne.

The Effects Study used a qualitative approach based primarily on the analysis of aerial photography to describe sand movements during three time periods. These periods included: pre-1960s (prior to both the construction of Kirra Point groyne and the extension of the Tweed River training walls); 1972-2001 (after both the construction of Kirra Point groyne and the extension of the Tweed River training walls); and 2009 onwards (after approximately eight years of operation of the TRESBP).

A copy of the Effects Study can be viewed here (PDF 3.79MB) and a summary table is presented below. In addition, the project has compiled a history of vertical aerial photography for the Kirra Point region taken from the 1930's through to 2011, although available historical aerial photography from the 1930s to the 1960s is very limited in extent. A summary of the aerial photography relevant to discussions presented in the Kirra Point Groyne Effects Study can be viewed here (PDF 3.3mb).

As indicated above, the Kirra Point Groyne Effects Study was prepared using a desktop approach and historical data. The findings of the report should be regularly verified against observed behaviour and as the TRESBP continues to deliver sand to match the natural littoral drift rate there may be an opportunity to review the outcomes of the Impact Study in the future.

It is also important to note that the Kirra Point Groyne Effects Study does not form part of a management strategy for Kirra Point Groyne. Decisions regarding the groyne are the responsibility of Gold Coast City Council (GCCC) and the Queensland Department of Environment and Resource Management (DERM).

Kirra Point Locality–Beach and Reef Exposure Changes Summary Table

(Adapted from the Kirra Point Groyne Effects Study)

Physical Aspect	Pre 1960s Pre Tweed Breakwater Extension (Natural Condition)	1972–2001 Post Kirra Point Groyne Construction Pre TRESBP Operations (Depleted Sand Supply Condition)	2009 onwards Post TRESBP Operations (Restoring Natural TRESBP-Sand Supply Conditions)
Sand movements Point #1: Beach conditions are a result of wave conditions (such as ocean storms), sand transport rates and the impact of the headland and/or Kirra Point groyne on sand movement. Point #2: The locations of shorelines around offshorhe bars have varied over time in response to changing sand movements and wave conditions.	Kirra Point was an exposed rocky reef and small headland that naturally retained sand on Coolangatta Beach. A thin band of sand close to the base of the headland fed sand from Coolangatta Beach to Kirra Beach (Figure 5), with supplies increasing when Coolangatta Beach grew in width. Sand movement past Kirra Point also occurred via an offshore beach bar. The width of Kirra Beach varied but was typically about 100 m.	Sand accreted (or built up) against the groyne on Coolangatta Beach, at the expense of downdrift beaches and particularly Kirra Beach (Figure 7a). Offshore profiles were lowered. On the wider Coolangatta side of the groyne the offshore bar moved further seaward. The path of the offshore bar around Kirra Point varied relative to water depth, wave height and wave direction.	After an initial period of beach expansion following the initiation of sand by-passing there was an observable reduction in beach widths by April 2009. This reduction was reinforced by a series of severe storms that occurred in May 2009 and promoted beach retreat (Figure 11b).
4 January 1955 5 April 2010		6 May 1982
Reef Exposure Point #3: Exposure of Kirra Reef is strongly linked to beach widths, littoral zone widths and offshore seabed levels. Point #4: All of these aspects are, in turn, affected by variations in the volumes of sand being transported along the coast. Point #5: The presence of Kirra Point groyne also has the potential to affect sand coverage on Kirra Reef.	In the 1930s (Figure 20a) the outer western reef was visible, as was the offshore end of the eastern reef. The inner western reef was mostly covered by sand. Partial sand coverage of Kirra Reef would have been a normaloccurrance under naturally fluctuating sand supplies.	Increased exposure of the reef occurred in association with a lowering of the offshore seabed (Figures 20b-c). This lowering accompanied general sand supply reductions resulting from the extension of the Tweed River training walls. Kirra Point groyne trapped sand on Coolangatta Beach but, because of the limited sand supplies moving around it, this did not affect reef exposure.	Kirra Beach alignment approximates the pre-1960s condition with more sand coverage of the inner reefs compared to the 1970s-1990s. Coolangatta Beach is much wider than the pre-1960s condition due to the accumulation of sand updrift of Kirra Point groyne. Wave conditions and the volume of sand coming through the transport system generally dictate beach alignments and are the main determinants of Reef coverage. There is potential for Kirra Point groyne to impact on the coverage of the eastern reef during high energy conditions. This may occur because the storm beach bar is located further seaward when the groyne is in place.
2 April 1946 12 October 2009		24 July 1996
Effect of Kirra Point groyne on sand movements and reef exposure Point #6: Generally, the groyne affects the positioning of the updrift(Coolangatta–Greenmount) beach system, including the beach bar that extends between Coolangatta Beach and Kirra Beach.	Not Applicable	Both the offshore bar and the shoreline retreat (Figure 24). Greater exposure of Kirra Reef occurs as offshore seabed levels are lowered and Kirra Point groyne holds sand on Coolangatta Beach, with small volumes of sand 'leaking' through to Kirra Beach.	The presence of Kirra Point groyne results in the relocation of the beach storm bar further offshore than when compared with the 'no groyne' situation. Under higher swell conditions sand may travel as a pulse in a more northerly direction towards the inner Kirra Reef—potentially covering parts of the reef. Under low swell and sand transport conditions sand will generally travel closer inshore with less potential to move across the reef zone.
Effect of extending Kirra Point groyne Point #7: Generally, the updrift (Coolangatta–Greenmount) beach system, including the nearshore bar, moves offshore	Not Applicable	Not Applicable	Groyne extension moves the beach and bar system further offshore. Both Coolangatta and Greenmount Beaches widen. Under higher swell conditions strong sand movements may travel as 'pulses' in a more northerly direction towards the inner Kirra Reef—potentially covering parts of the reef with sand. Under low swell conditions small volumes of sand will generally travel closer inshore with less potential to move across the reef zone.
Effect of removing/shortening Kirra Point groyne Point #8: Generally, the updrift (Coolangatta–Greenmount) beach system, including the offshore bar, moves onshore.	Not Applicable	Not Applicable	Both Coolangatta and Greenmount Beaches generally narrow. The offshore bar moves closer to the shoreline. Surfing conditions and peel angle in the take-off zone change, developing a shorter transition that is similar to the pre-1960's condition. The increase in peel angle results in waves that are less suited to the advanced surfer. Coverage of Kirra Reef with sand is likely to be reduced as sand transport pathways move offshore.