Beaches and shorelines | Australia state of the environment 2021

Beaches and shorelines provide some of the most classic and striking images of the Australian coast. With a diversity of habitats that includes beaches and dunes, rocky shores, mudflats, and sandbars, the shore is a dynamic zone exposed to both land and marine forces (Short & Woodroffe 2009).

Australia boasts over 10,000 beaches (Short 2020), which are highly valued in Australian culture for their aesthetic qualities and recreational amenities. These dynamic sandy environments erode and accrete in response to ocean forces and sand movement, and vary widely in their shapes and structures, wave conditions, tidal regimes and sedimentology. They also vary greatly in their level of modification and human activity, which in most cases is driven by local population density.

The dune systems that sit behind beaches support native vegetation and provide a buffer against beach erosion, and their fresh watertables act as buffers to saltwater intrusion. However, despite their critical importance to beach ecology and beaches themselves, dune systems are typically undervalued by the public and are often degraded by human traffic or invasive species.

Mudflats and sandbars are areas of bedded sediment adjacent to the coast. They are heavily dependent on tides, exposed during low tide and submerged during high tide, and shift in position in response to sediment supply and physical forces. The main feature distinguishing these 2 habitats is the size of their sediment particles – mudflats consist of fine silt while sandbars generally consist of fairly coarse sand. The faunal communities inhabiting the sediments are critical for water column and interstitial (between-grain) water quality due to their role in nutrient cycling, and are important prey for shorebirds, crabs, prawns and fish. Protection of these habitats is essential for conserving the threatened shorebird populations that depend on them, both in Australia and overseas.

Beaches and shorelines have historical significance for all Aboriginal and Torres Strait Islander peoples, whether they are from saltwater Country or not (see the Country and connections section in the Indigenous chapter). Shorelines are places where culture was and is practised, knowledge was created, seasons and tides were understood, food was and is collected, and ceremonies took place. These habitats were also the place where first contact between the Traditional Owners and colonisers occurred. However, the connection to shorelines for Indigenous peoples has not been recorded in academic literature as prominently as for other habitats (Stronach et al. 2019). Middens are hugely important social sites, which not only provide historical information, but also provide a place of connection for Indigenous people who continue to use them. Impacts on these habitats are having and will continue to have an influence on Indigenous communities (see the Climate, Biodiversity, Extreme events, Indigenous and Marine chapters).

Assessment The condition of beaches and shorelines

2021

Limited confidence

Indigenous assessment

2021 Assessment graphic for an assessment conducted by Indigenous community members, showing the environment is in poor condition, resulting in diminished environmental values, but the trend is unclear.

Assessments of beaches and shorelines vary between good and poor, but all are deteriorating due to sea level rise and local factors related to human use of the coast. Ocean beaches are currently stable in position and are in relatively good condition away from urban centres, but beaches in urbanised estuaries and bays are exposed to numerous human pressures. Rocky shorelines, mudflats and sandbars are vulnerable to many threats, but monitoring of those habitats is rare. The Indigenous assessments for the state of beaches and shorelines found that 2 assets are good and 2 are poor, and that the trend is unclear for 2 assets and stable for 2. Local government assessments (see Approach) show that the condition of beaches and shorelines varies around Australia, but with no clear north–south or east–west pattern. Some shorelines are in worse condition near capital cities. Related to United Nations Sustainable Development Goal targets 14.2, 15.1, 15.5

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How was this assessment made

Assessment Ocean beaches and sand dunes

2021

Adequate confidence

2016

Most beaches are in a dynamic but stable position with little change in decadal-scale behaviour. They are exposed to extreme wave events that can damage legacy planning infrastructure, and are vulnerable to sea level rise. The Indigenous assessment for some regional areas was poor, with an unclear trend.

Assessment Beaches in estuaries and bays

2021

Limited confidence

Urban beaches in estuaries and bays continue to be subject to increased pressures including engineering interventions, urbanisation and sea level rise. The Indigenous assessment for some regional areas was poor, with an unclear trend.

Assessment Rocky shoreline

2021

Limited confidence

2016

Data are generally sparse, but heatwaves, harvesting, trampling, deteriorating water quality, urban development and sea level rise all threaten this habitat. The Indigenous assessment for some regional areas was good, with a stable trend.

Assessment Mudflats and sandbars

2021

Low confidence

2016

Sea level rise, river regulation and urbanisation are increasing pressures on mudflats and sandflats. However, studies documenting the resultant ecosystem change are lacking. The Indigenous assessment for some local areas was good, with a stable trend.

Ocean beaches and sand dunes

Australia has 10,685 beaches, which occupy 14,686 kilometres (km) or 49.1% of the open coast, backed by sand dunes along 12,175 km (39.6%) of coast (Short & Woodroffe 2009). Together they constitute a major and iconic component of our national coastal zone, recreation and culture. Sand dunes are also important to coastal Indigenous people.

Our beaches and sand dunes are sensitive to current and future changes in atmospheric and ocean climate, especially sea level rise and ocean acidification (see Sea level rise) (see the Marine chapter). For example, around 50% of coastal sediment, such as sand, comes from marine carbonates (e.g. shellfish), and ocean acidification may threaten the future of these sediments because it will reduce the formation of shells and other carbonate structures (Simeone et al. 2018).

Most beaches and dunes currently have erosion and recovery cycles that vary around a stable mean shoreline position, while some shorelines are eroding and a few shores are building seaward, despite a sea level rise of around 10 centimetres (cm) over the past few decades. A recent nationwide study found that since 1988 78% of the beaches have remained stable, with 11% receding and 11% accreting (Table 2) (Bishop-Taylor et al. 2020).

Coastal sand dunes cover an area of 23,455 square kilometres (km²), of which 2,765 km² (11.7%) was bare and unstable in 2010 (Figures 5 and 6) (Short 2010). Recent global research has found generally warmer and wetter climates are leading to a ‘greening’ of coastal dunes worldwide (Jackson et al. 2019), and this has occurred in some parts of Australia (see Dune vegetation). In Australia’s case, however, most of the ‘greening’ can be attributed to increasing dune management, recovery after fire, the spread of exotic plant species, and removal of rabbits and grazing animals.

Beach and dune management and monitoring

Human pressures on the coast include increasing development, pollution, modification of coastal systems and climate change. These are generally managed by local and state or territory coastal management programs, which mostly focus on the protection of beaches at greenfield (newly developed) sites. All states and the Northern Territory have locations where shoreline protection works have been constructed to defend beachfront properties at risk from storm waves, but these only protect a small proportion of coastline and many beaches remain exposed. Beach nourishment and scraping has been used at some locations to maintain beach width and protect coastal property (Cooke et al. 2012); however, such practices can impact sandy beach flora and fauna through smothering and potential changes in sediment properties such as grain size (Schlacher et al. 2012, Cooke et al. 2020).

Beach systems have been monitored to some degree in all states and the Northern Territory using various techniques, including traditional land-based survey and satellite technology. Some states and regions (e.g. Queensland’s Gold Coast, New South Wales, South Australia) have been monitoring beaches since the late 1960s and early 1970s, enabling insight into decadal-scale trends in shoreline behaviour as well as extreme event erosion. Monitoring of Collaroy–Narrabeen Beach (Sydney, New South Wales) dates back to 1976 – an example of long-term monitoring, spanning more than 40 years, over which monitoring methods have evolved with technical innovations (Harley et al. 2015, Splinter et al. 2018). Other monitoring programs are more recent, such as Victoria’s Coastal Monitoring Program that commenced in 2017 (DEWLP 2020) and uses drone surveys and 3D-modelling of historical aerial imagery to predict long-term trends. In 2020, Geoscience Australia released its Digital Earth Australia Coastlines dataset (Bishop-Taylor et al. 2020) which maps shoreline changes around the entire coast since the 1980s and identifies areas of concern (see case study: Digital Earth Australia Coastlines – monitoring coastal change in Australia using freely available satellite data). Citizen science programs of beach monitoring (e.g. CoastSnap) are also contributing data and generating public awareness, and now have national and international coverage.

In 2018, a new national approach to understanding the behaviour of our beach systems was developed based on coastal sediment compartments, which are discrete spatial units of coast within which sediments behave similarly (Thom et al. 2018). Characteristics and status of all 354 secondary compartments, covering the entire coast, are mapped and summarised on the Shoreline Explorer website (NCCARF 2020) and described in more detail by Short (2010). Different beach systems have markedly different sediment budgets (net gain or loss of sediment), which influences their susceptibility to present and future change (Figure 5). ‘Leaky’ beach compartments are dominated by longshore sand transport, in which a potential sand budget deficit could lead to gradual beach recession, as along the northern New South Wales and south-east Queensland coast. In an embayed or ‘closed’ compartment – typical of the central-southern New South Wales coast – sand transport is predominately onshore-offshore, with little if any net shoreline change.

Wave climates are predicted to change all across southern Australia, particularly due to enhanced southern ocean wave energy (Morim et al. 2019), which is likely to alter sediment transport pathways across Australia. For example, predicted changes in Tasman Sea wave climate (Mortlock & Goodwin 2015) could result in a decrease in northerly sand transport and southerly beach rotation, both of which would also impact the stability and behaviour of the New South Wales – south-east Queensland shoreline.

Figure 5 Examples of contrasting Australian beach systems and sediment budgets

Source: Thom et al. (2018)

Note: Reprinted from Ocean & Coastal Management 154, BG Thom, I Eliot, M Eliot, N Harvey, D Rissik, C Sharples, AD Short & CD Woodroffe, National sediment compartment framework for Australian coastal management, 103–120, Copyright (2018), with permission from Elsevier.

Figure 6 Coastal dunes depend on beaches for sand supply and stability (Towterer Beach, south-west Tasmania)

Source: Thom et al. (2018)

Beaches in estuaries and bays

Most of Australia’s largest population hubs are located on or near estuaries and bays. Beaches in estuaries and bays (BEBs) are a critical natural asset for recreation for over 10 million Australians, especially in providing safe swimming havens for young children (Largier & Taggart 2006). BEBs also provide habitat and feeding areas for marine and terrestrial flora and fauna, and play a role in coastal protection.

BEBs are exposed to highly variable wave energy environments (Rahbani et al. 2022) and present highly variable morphologies. They are usually sheltered from ocean waves, so currents and other sources of wave energy (e.g. locally generated wind waves and infragravity waves) play a larger role for BEBs than they do for open-coast beaches (Vila-Concejo et al. 2020). Boat wakes can also be an important source of waves in estuaries and bays.

Pressures on BEBs include climate-change-related sea level rise and storms, and pressures related to urbanisation, such as coastal structures and land reclamation. These pressures can directly result in losses of BEBs, as well as indirectly modify them through changes in waves and sediment transport. Many BEBs around Australia have seawalls erected and properties built within the current beach hazard zone, with little consideration for current or future climatic scenarios. Engineering interventions, such as dredging or construction of groynes, jetties or reefs, also change wave propagation patterns, exposure of estuarine shores to waves and estuarine circulation patterns, and consequently modify sediment transport.

Recent studies have highlighted the vulnerability of BEBs in Australia (Kennedy 2002, Vila-Concejo et al. 2010, Lowe & Kennedy 2016). The east coast storm in June 2016 caused severe damage in Pittwater and Kamay (Botany Bay). The entire subaerial beach was eroded during the storm, and only 5 of the 29 beaches studied had recovered to their pre-storm condition 3 years later (Gallop et al. 2020).

Beach type and the estuarine sedimentary features (e.g. flood-tide shoals or channels) adjacent to BEBs are important factors determining beach recovery after storms, and different types of BEBs respond differently to storm events (Fellowes et al. 2021):

Quasi-stable BEBs include swell-exposed beaches near the entrance and recover after storms at rates comparable with open-coast beaches.
Prograding BEBs are resilient to storm erosion and are typically far from the entrance where a combination of fluvial, tidal and wind-wave processes may dominate.
Retreating or relict beaches include those that only recover partially or not at all after storms.

As beach management is underpinned by models developed for open-coast beaches, millions of dollars are spent annually on managing urban BEBs without understanding their long-term evolution or short-term responses to changes in wave energy (Lowe & Kennedy 2016). Recently, ecosystem restoration approaches have become more popular, but these commonly do not consider the spatial and temporal scales on which BEBs operate, potentially increasing the long-term climate change vulnerability of these systems. Research on the bio-eco-morphodynamics of BEBs is needed to secure the future of the important ecosystem services provided by these critical landform systems.

Rocky shoreline

Rocky shores are found along most of Australia’s coast and provide habitat for a highly diverse mix of species adapted to particularly harsh environmental conditions, such as wave action and strong environmental gradients in temperature and desiccation. Rocky shorelines provide goods and services to humans, such as shellfish and seaweeds that have provided subsistence foods since prehistory, as well as natural coastal defence and recreational opportunities. They are important feeding areas for birds and fish. Many of the species in these habitats are endemic (found only in that region), particularly on Australia’s southern coast.

Rocky shorelines are focal areas for human activities, with threats from both landward and seaward directions. Rocky shorelines near population centres are threatened by trampling, harvesting, bait collecting, artificial light pollution and poor water quality. They are one of the habitats most affected by urbanisation, which causes loss and fragmentation of habitats. Regulated closures, such as marine parks, offer some protection, but poaching threatens their effectiveness. Pollutants can enter rocky shores as waterborne or land-based contaminants, potentially causing toxicity to some organisms. Urban and stormwater run-off, and bushfires and associated run-off, may all have negative impacts, but these are likely to be localised.

Climate change also poses a threat to these rocky shoreline habitats. Increased air and sea temperatures are likely to change the species inhabiting rocky shores, and heatwave conditions can lead to significant species mortality (Starko et al. 2019). Climate-related storm activity is likely to mobilise sediments, which may abrade or bury some species. Finally, sea level rise threatens to reduce suitable habitat as the platforms of many rocky shores are inundated.

Deficiencies in the availability of data, particularly long-term datasets, make it difficult to assess impacts. One study compared modern species distributions on the eastern coast of Australia to historical records and found little change over the past 50 years (Poloczanska et al. 2011). However, more detailed monitoring is required to increase confidence in trends. Baseline data from around 40 sites have been established in New South Wales and will aid in detecting change in the future. Climate-related impacts on some key habitat-forming species of rocky shores are still unclear, but some studies have examined climate effects on Hormosira (algae) (Clark et al. 2013, Clark et al. 2018b, Miller et al. 2020) and on oysters (McAfee et al. 2017). Experimental examination of the effect of ocean warming and acidification on all life stages of habitat-forming species is urgently needed, as well as studies of how these changes affect ecological interactions between species. Additionally, lack of taxonomic expertise is a continued threat to understanding and appreciating much of Australia’s marine biodiversity.

Further, stressors generally do not act in isolation and synergies among stressors, including contaminants, may be particularly harmful (Holan et al. 2019). Emerging technologies, such as drones (Gomes et al. 2018, Castellanos-Galindo et al. 2019) and other forms of aerial surveillance (Adams et al. 2020a), offer an opportunity to gather high-resolution information over broad spatial and temporal scales at modest cost.

Case Study Digital Earth Australia Coastlines – monitoring coastal change in Australia using freely available satellite data

The ability to map shorelines through time provides valuable insights into whether changes to Australia’s coastline are the result of specific events or actions, or processes of more gradual change over time. This information can enable scientists, managers and policy-makers to assess the effects of the drivers impacting our coastlines, and potentially aid planning and forecasting for future scenarios.

Digital Earth Australia (DEA) Coastlines (GA 2021) is a continental dataset that includes annual shorelines and rates of coastal change along the entire Australian coastline from 1988 to the present. DEA Coastlines combines satellite data from Geoscience Australia’s DEA program (Dhu et al. 2017, Lewis et al. 2017) with tidal modelling to map the dominant position of the shoreline at mean sea level tide each year. DEA Coastlines allows trends of coastal erosion and growth to be examined at both local and continental scales, and for patterns of coastal change to be mapped historically and updated regularly as data continues to be acquired. This allows current rates of coastal change to be compared with those observed in previous years or decades.

The 33-year DEA Coastlines record provides new insights into patterns and processes of coastal change across the entire Australian coastline. At a national scale, 22% of Australia’s nonrocky coastlines have retreated or grown significantly since 1988, with 78% remaining net stable over this time (Table 2) (Bishop-Taylor et al. 2021). Trends of retreat and growth were closely balanced across Australia over the past 3 decades, despite strong regional variability and extreme local hotspots of coastal change – for example, point 1 in Figure 7.

At a local scale, DEA Coastlines can be used to better understand the complex coastal processes occurring at these hotspots of coastal change. For example, on Australia’s wave-dominated coasts, coastal barriers and lagoons are threatened by the influence of relative sea level rise, altered storm systems and other climatic effects (Nanson et al. 2022). Barrier responses are likely to vary between regions, and detailed analyses of historical barrier dynamics can help to inform their management.

Figure 8 presents 2 examples of how DEA Coastlines can provide insights into historical erosion impacting coastal lagoon barriers. Figure 8a shows that that changes at Southport Lagoon are all negative, indicating sand loss, with losses of around 2 m being most common, apart from 0 m. Figure 8b shows the lagoon; the area in the white box is shown in more detail in Figure 8c. Figure 8d traces the barrier width over time, measured along the white dotted line in Figure 8c. Figures 8e–h give similar results for Bribie Island – again, the barrier is thinning.

These long-term insights can be used to aid management of these affected ecosystems and population centres, complementing coastal monitoring data from existing state and local government programs.

Figure 7 Three decades of coastal change across Australia based on the satellite-derived Digital Earth Australia Coastlines dataset

Source: Bishop-Taylor et al. (2021)

Figure 8 Evolution of width of sand features at Southport Lagoon (Tasmania) and Bribie Island (Queensland), 1988 to 2018

Source: Nanson et al. (2022)

Table 2 Coastal change across Australia by major coastal region; net stable coastlines showed no long-term trends of coastal change since 1988, whereas dynamic coastlines include trends of long-term growth or retreat

Coastal change	Continentally (%)	Western Coasts (%)	North-western Coasts (%)	Southern Coasts (%)	Carpentaria Gulf Coasts (%)	North-eastern Coasts (%)	South-eastern Coasts (%)
Net stable (no long-term trend)	77.9	73.7	81.3	77.5	72.6	76.3	76.6
Dynamic	22.1	26.3	18.7	22.6	27.4	23.7	23.4
Retreat	11.1	16.5	10.9	9.0	11.9	11.3	10.6
Growth	11.0	9.8	7.8	13.5	15.5	12.4	12.8

Source: Adapted from Bishop-Taylor et al. (2021)

Mudflats and sandbars

Mudflats and sandbars are important intertidal environments. Generally, mudflats are formed from fine sediments supplied by rivers while sandbars are formed from coarser sediments supplied by the ocean, but the nature and extent of habitats also depends on tidal range and geomorphic setting. Sediments in mudflats and sandbars support dense and diverse communities of invertebrates, which are an important prey resource for large mobile invertebrates and fish at high tide, and shorebirds at low tide. Both habitats, but especially mudflats, often contain great amounts of organic material from terrestrial sources, which is either buried or processed by invertebrates and microbes (Snelgrove et al. 2014). Thus, these habitats help maintain clean water through their nutrient cycling processes, and can be important carbon sinks when organic matter is buried within the sediment.

Trends in the extent and distribution of mudflats and sandbars are uncertain. Tides, floods and storms may cause shifts in the distributions of mudflats and sandbars within channels, but few studies have been of sufficient duration or spatial extent to adequately assess long-term changes in their area and distribution. Bare mudflats of the Rocky Dam Creek/Cape Palmerston National Park region (central Queensland) displayed a 5.5% decline in area over 2004–17 (Chamberlain et al. 2020b), possibly due to climatic factors such as enhanced cyclonic activity and sea level rise. However, due to the scarcity of monitoring in other areas, it is difficult to know how general this trend is. Furthermore, because most studies of mudflats have used remote-sensing methods (as in Murray et al. (2019)), they have been unable to assess ecological impacts of changes in sediment conditions (but seeDittmann et al. (2019b), Dittmann et al. (2019a)).

Changes in the condition of benthic communities in mudflats are rarely studied, and trends appear to be variable through space and time. Studies of mudflats in the Gulf St Vincent have detected little change, or scattered changes, in benthic communities over time (Dittmann et al. 2019b), contrasting with a 10-year study in the Kimberley region that found dramatic declines in species abundance in the first 5 years, followed by recovery in the next 5 years (de Goeij et al. 2008). However, pronounced changes in the condition of benthic communities in mudflats are likely in response to changes in drought and flood cycles and water management of river systems draining into the estuaries.

Besides climate change, key stressors to mudflats and sandbars include:

disruptions to sediment flow – water regulation is pervasive in Australia, and structures such as dams, culverts, weirs and breakwaters can impede sediment transport from rivers to estuaries and along coasts (Kingsford 2016)
disruptions to water flow – dams and weirs keep water inland, starving estuaries of freshwater inflows, which causes hypersalinity and associated declines in benthic mudflat communities, as well as in fish that are sensitive to high salinities or unable to complete diadromous migrations in their life cycles
displacement by built structures, land reclamation, marine construction, and coastal armouring with seawalls and other protective structures – these result in direct loss of sedimentary habitats, and cause indirect loss by exacerbating erosion and squeezing these habitats between rising sea levels and development (Heery et al. 2017)
contamination – sediments are sinks for contaminants such as nutrients, heavy metals and polyaromatic hydrocarbons, which are introduced through urbanisation, agriculture and industry (Birch 2000); these contaminants can hinder nutrient cycling and render sediments uninhabitable for many invertebrates
disturbance by human recreational activities – harvest of some species, such as burrowing shrimp, for bait can result in large changes to sediment conditions and ecological communities, particularly where the harvested species are important oxygenators and/or bio-irrigators of sediments (Winberg & Davis 2014). Boating can disrupt sediment habitats through sediment resuspension, and physical disturbance by boats anchoring and running aground, and by modifying the behaviour of fish and invertebrates that live and feed in these habitats (Burgin & Hardiman 2011).

Nature-based management strategies that replace hard engineering, such as stream naturalisation and nature-based coastal defence, can reinstate natural sediment flows and partially mitigate local-scale impacts of urbanisation and land-use change on mudflats and sandbars. Nevertheless, given the projected growth in the human population of Australia, sea level rise and increases in storm frequency, particularly in the tropics, overall pressures on mudflats and sandbars are predicted to increase.