We all love our beaches on the Central Coast, and we are fortunate to have so many to enjoy, but have you ever thought about how our beaches were formed or how they have evolved in such a highly dynamic environment?

Did you know that around 120,000 years ago the sea level was a few metres higher than today? The waves moved large volumes of sand along the coastline forming our beaches and sand dunes. During the last Ice Age, around 21,000 years ago, sea levels dropped to approximately 130 metres below the present level! Most of the NSW coastline was tens of kilometres further east than where we see it today.  With the melting of the ice and glaciers the sea level rose again until about 6,500 years ago when it reached the current level. Around 2,000 years ago the transport of sand from the continental shelf pretty much ceased. There is now little supply of sand to form our beaches and dunes making them a very precious resource indeed.  

The waves and surf zone currents are responsible for the cycle of erosion and deposition along the NSW coastline. Sand accretion (deposition) on the shore comes from the movement of waves, tides and longshore currents. Once deposited and dried out, sand is blown further onto the beach by onshore winds. Erosion of this sand happens during storms and when there is large surf. 

In New South Wales a typical undisturbed beach will have a series of foredunes and hind dunes and may have incipient foredunes during prolonged accretionary phases:

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Image source: NSW Department of Land and Water Conservation 2001, Coastal Dune Management: A Manual of Coastal Dune Management and Rehabilitation Techniques, Coastal Unit, DLWC, Newcastle.

Incipient dunes are typically low undulating rises which support low spreading plants such as spinifex (Spinifex sericiea), purple fan flower (Scaevola calendulacea) and pigface (Carpobrotus glaucescens). Foredunes support vegetation which is slightly taller (about 1m) such as coastal wattle (Acacia longifolia subsp. sophorae), while hind dunes contain a significantly taller (2m+) and more diverse range of species such as coastal banksia (Banksia integrifolia) and coastal tea tree (Leptospermum laevigatum).

A healthy, natural dune system along the coastline serves a defensive role, protecting the land behind from the ravages of salt spray, storm activity and high tides, particularly now with the changing climate and associated forecast sea level rises.

Unfortunately, many of our dune systems have seen historical disturbance in one form or another, from weed incursion to their total destruction. These disturbances continue to this day through the impacts of urban and industrial developments and recreational activities like walking and fishing, horseriding and 4WDing (to name a few).  

Many Central Coast beaches were mined in the 1950’s and 60’s for rutile and other minerals, from Budgewoi in the north to Killcare in the south. This activity saw the natural dune systems levelled and minerals and nutrients removed, along with the soil seed bank and associated mycorrhizae (soil fungi). Following these mining activities only a stark landscape remained! Rather than rehabilitation efforts using native plant species, exotic plant species, including Bitou bush (Chrysanthemoides monilifera subsp.. rotundata) from South Africa, were planted to stabilise the mined beach and dune areas.   

Under favourable conditions Bitou bush plants can begin producing seed from as young as 6 months of age. Plants can go on to live for many years, with mature plants producing in excess of 48,000 seeds annually. Not only does Bitou bush spread quickly but, as it establishes, the wind blows sand from around the plants inward creating hummocks thereby increasing erosion. Bitou bush has been recorded along approximately 900km, or 80%, of the NSW coastline and is the dominant plant species for 400km of this range. It is recognised as posing a significant threat to over 150 native plant species and 24 different coastal vegetation communities.

The absence of native vegetation on our coastal dunes allowed other exotic species in the form of garden escapes such as Asparagus Fern (Asparagus aethiopicus) and Turkey rhubarb (Rumex sagittatus) to become established. Our native fauna helped with the spread of these exotic plants as they consumed and distributed the readily available fruit and seed, alternative food sources that replaced their diet from native plant species. Pest animal species, such as European red foxes, similarly contributed to this spread. As this was happening above the ground, the soil below lacked many of the different mycorrhizal associations essential for the successful root development of native species.

It is not surprising that we have 22 environmental volunteer groups involved in caring for our Central Coast dunes. The Dunecare and Coastcare groups work from our northernmost beaches at Budgewoi Beach and Hargraves Beach to our southernmost at Pearl Beach and Patonga, truly spanning the entire length of the Central Coast. Collectively these volunteer groups have spent many tens of thousands of hours working on their sites, with some individuals and groups having over 25 years of on-ground experience. Over this time treatments have been tried and tested, lessons learned, best practices established and knowledge has been shared. Much like the dunes themselves, dune conservation and management is a dynamic and ever changing discipline. 

Everyone benefits from the dedication of our Dunecare and Coastcare volunteers in protecting our beloved beaches and dunes. It is so encouraging to see that we have members from our community who dedicate their time and put in so much hard work in helping to protect these very beautiful and special places. Thank you all so very, very much for all of your dedication and hard work. 
 

References:

NSW Department of Land and Water Conservation 2001, Coastal Dune Management : A Manual of Coastal Dune Management and Rehabilitation Techniques, Coastal Unit, DLWC, Newcastle

Winkler, MA, Cherry, H and Downey, PO (eds) (2008). Bitou bush Management Manual: current management and control options for bitou bush (Chrysanthemoides monilifera ssp. rotundata) in Australia. Department of Environment and Climate Change (NSW), Sydney

This article was written by Penny Pinkess, retired Environmental Volunteer Officer and Nick Carson, Environmental Education Officer