Beach changes along Kirra
Since 2002, there has been a build up of sand along the Kirra Beach to North Kirra Beach stretch of coast. This can be seen in the Tweed River Entrance Sand Bypassing Project's Kirra Point Beach and Miles Street photo albums.
The sand build up has occurred during almost a decade of calmer than expected storm seasons. Especially notable during the 2000s has been the lack of ocean storms approaching from the North East, such as cyclones, which are the storms that generally cause the most significant coastal impacts along the southern Gold Coast. Large volumes of sand supplied by the sand bypassing system to rebuild severely depleted beaches in the early years of the TRESBP also contributed to the build up.
However, over the past few years sand dispersal has been occurring from the Kirra area and the sand build up has been reducing as sand is moved to the north by natural waves and currents.
Sand reduction at Kirra due to the autumn 2009 storms
Sand dispersal at Kirra was most rapid over 2008/09, primarily as a result of the autumn 2009 storms. During this time there was a loss of more than 200,000 cubic metres of sand from the upper beach and offshore area between the Kirra Point groyne and the Miles Street groyne (August 2008 to August 2009). About 60,000 cubic metres of this sand was lost from the beach above the water line, and about 160,000 cubic metres was lost in shallow waters out to about 6 metres depth. Central Kirra Beach (between Miles Street groyne and the Coolangatta Creek stormwater culvert) also lost an approximate 90,000 m3 during this period. By mid 2009, seabed levels in the nearshore area had reduced by up to about 2 metres and Kirra Reef became more exposed.
Sand Changes at Kirra after the autumn 2009 storms
In addition to natural sand movements, Gold Coast City Council carried out beach scraping and dune works at Kirra in July and December 2009 and November 2010. These works formed part of the Queensland Government's $1.5 million contribution towards the restoration of Kirra Beach and involved relocating a total of 136,000 m3 of sand from the intertidal zone to form a low profile backbeach dune. These works were successful in further reducing beach widths at Kirra.
Overall sand volumes at Kirra have continued to naturally fluctuate after the autumn 2009 storms. Between August 2009 and April 2012 there has been a further loss of approximately 30,000 m3 at Kirra and 75,000 m3 at Central Kirra.
Between August 2009 and March 2011, approximately 400,000 m3 of sand was lost from Coolangatta Bay between Point Danger and Kirra Point groyne (Figure 2). As the sand moved northwards out of Coolangatta Bay, it flowed around Kirra Point during 2010, and in March 2011was evident in the build up of the Kirra Point groyne offshore bar (Figure 3).
Almost all of this new sand flowing around Kirra Point groyne from Coolangatta Bay continued to travel northwards beyond North Kirra, offsetting the inshore and upper beach losses. Further losses both above the water line on the beach, and below the water line were seen at Kirra for the remainder of 2011. In particular, there was a loss of sand from the Kirra Point groyne offshore bar with slight accretion along the nearshore bar, closer to the shoreline.
The most recent seabed mapping in April 2012 revealed a decrease in the amount of sand both on the beach and nearshore bar, and an increase in sand along the Kirra Point groyne offshore bar. This recent build up is most likely due to a pulse of sand that was eroded from Point Danger and Duranbah in the latter part of 2011 (due to strong and persistent south easterly wave conditions), which moved through Coolangatta Bay in late 2011 and is only just appearing at Kirra. In a similar way to what occurred over a year ago in March 2011, it is expected that this sand will continue to move further north under typical wave conditions.
Table 1 and Figure 4 show the further reduction of just over 100,000 m3 at Kirra and Central Kirra between August 2009 and April 2012. The majority of these losses occurred in the nearshore zone which extends from just below the shoreline to ten metres water depth.
The changes in sand movement in the overall Kirra area since the autumn 2009 storms reflect the seasonal variation of sand flow into Coolangatta Bay, around Kirra Point groyne and through Kirra and Central Kirra Beach areas. Severe storm activity can significantly alter sand movement patterns in Coolangatta Bay. In a similar way to what occurred after the Autumn 2009 storms, sand that is currently sitting in the storm bar offshore of Rainbow Bay due to the June 2012 storms should begin to move through Greenmount and Coolangatta, temporarily building the Kirra Point groyne offshore bar before moving further north.
The combination of beach scraping and natural sand dispersion has contributed to greatly reduced beach widths along Kirra Beach in the last three years. Sand dispersal from Coolangatta Bay is discussed on the Coolangatta Bay sand volumes page. Most of the sand dispersal from Kirra occurred during and after the autumn 2009 storms, particularly during and after the most severe storm of the season that occurred in May 2009. Rocks between Kirra Point groyne and the Kirra Surf Club that had been covered by sand were seen for the first time in at least nine years soon after the May 2009 storm.
Although Kirra Beach had been nourished with 300,000 cubic metres of dredged sand in 1995, a large number of cyclones during the 1990s left Kirra in an eroded and vulnerable condition.
Fewer storms during the 2000s allowed nourishment sand to build up at Kirra Beach, though the autumn 2009 storms significantly reduced sand volumes and beach widths at Kirra.
Shoreline position monitoring carried out by the University of New South Wales on behalf of the TRESBP shows that the width of the beach in front of the Kirra Surf Club can advance and retreat by in excess of 40 metres over six month periods. The beach width in front of the Kirra Surf Club has reduced by about 120 metres from September 2008 to March 2011, at an average rate of about 50 metres per year. Over the same period, at Central Kirra the beach width reduced by about 60 metres and at North Kirra there has been some advance of 15 metres, as sand is reworked northwards. Beach widths over the last year from March 2011 to April 2012 have continued to show natural variation.
Looking north from Kirra Hill, September 2008
Looking north from Kirra Hill, May 2012
The sand that has dispersed from Kirra and Central Kirra over the last few years has now reached the stretch of coast from the North Kirra Surf Club to the Tugun Surf Club. There are no obstructive features such as headlands or groynes along this stretch of coast so the sand has been able to spread out more evenly instead of travelling as a large mass of the kind that has filled in the beaches from Rainbow Bay to North Kirra in the early years of TRESBP operations.
As a result of the spreading out of sand, the beaches to the north of the North Kirra should not become as wide as the beaches from Rainbow Bay to North Kirra were in the early 2000's, but they will receive some much needed nourishing sand. This sand will provide additional protection against storm erosion for these beaches.