The Australian coast contains 10,685 beach systems, which occupy half the coast and can be classified into 15 beach types. These include six wave-dominated, three tide-modified, and four tide-dominated types which are a product of wave-tide and sediment conditions and two types which are influenced by intertidal rocks and fringing reefs. Wave-dominated beaches occupy the higher energy, microtidal southern coast exposed to persistent Southern Ocean swell. Tide-modified and tide-dominated beaches are most prevalent around the more tropical northern coast, which experiences meso-, macro-, and mega-tides and receives lower seas, as well as some sheltered and mesotidal southern locations. This article assesses the roles of waves, sediment, and tide range in contributing to beach type, particularly through the dimensionless fall velocity and relative tide range. It also describes their regional distribution, together with the occurrence of rip currents, multibar beach systems, and the influence of geological inheritance and marine biota.

Between 1974 and 1976, a series of east-coast cyclones in the western Tasman Sea resulted in extensive coastal erosion along southeastern Australia. In many beach compartments, the backshore and incipient foredune were completely removed, and the sea cut back into the swale and/or second dune ridge. This occurred at Moruya Beach, where a profile monitoring program had been established in 1972—a program that continues to this day. Here we report field evidence describing the initial condition of the beach, its subsequent erosion (such that the position of the initial backshore became the foreshore), and how this foreshore became reconstituted as a backshore ultimately developing into the present foredune. Critical to the formation of the frontal dune was the presence of a broad backshore berm at an elevation of 2.3 to 2.8 m above local mean sea level (MSL). Achievement of this elevation did not, by itself, guarantee foredune development. Rather, there is also a width threshold to the berm, which at Moruya is at least 30 m. While the berm reached either this elevation (2.3 to 2.8 m) or width (>30 m) on several occasions prior to the formation of the incipient foredune, it was only when both conditions were satisfied that the embryo foredune developed into an incipient foredune. This was in the late 1970s and early 1980s. Incremental vertical growth of the foredune took place over the next 15 years, from an elevation of ca. 3.0 m up to 5 m above MSL. Initially, the position of the newly accreted foredune was well seaward of its prestorm (1972) position, but in the last few years it has tended to migrate inland, though the geographic position of the mean and high water level intercepts have not migrated with it.

Remote sensing methods are increasingly being deployed to measure and investigate morphology and hydrodynamics in the littoral zone, across spatial scales ranging from centimetres to kilometres, and at time-scales ranging from seconds to years. In the past 5 years in Australia, the deployment of video-based coastal imaging systems has grown rapidly, and by 2004, some 32 cameras were operating at eight sites along the coasts of New South Wales and Queensland. Coastal imaging techniques are being applied to a range of coastline monitoring programs. Projects include large- and small-scale sand nourishment works, the construction of a nearshore artificial reef structure, and the ongoing management of sand bypassing operations. At the same time, the growing image databases are underpinning more fundamental coastal research. The focus of recent and current research includes rip current behaviour, climate impacts, nearshore bar dynamics, and the development of new image analysis methods to support future research.

A considerable portion of the sedimentary coast of northern Australia is dominated by ridge plains (beach ridges) where the ridges are composed of coarse-grained sands and/or sand and beds of marine shells that rise above the limits of normal (fair weather and noncyclonic storms) wave run-up. Elsewhere, there exist ridge plains composed of lithic gravel, coral shingle, shell (cheniers), and, in one location, a ridge of pumice. These ridge sequences also lie above the zone of normal wave (noncyclonic) processes. There is little doubt that these ridges are deposited by waves and it is likely that only tropical cyclone-generated marine inundations are able to cause the necessary ephemeral rise in sea level in order to emplace them.

Tropical cyclones also cause substantial erosion of the coast. When the marine inundation (surge tide wave set-up waves wave run-up) or just wave run-up alone overtops coastal dunes (eolian) or ridges where they are unconsolidated, those dunes are eroded vertically and removed. At times, this can result in the deposition of sand sheets that extend inland for several hundreds of meters and taper in thickness landward. The sedimentary coast of northern Australia is composed therefore of a mosaic of landforms that represent the constant interplay between high-intensity, low-frequency events and processes and high-frequency, lower energy processes. The presence of numerous coastal landforms generated by tropical cyclones highlights the importance of recognizing the role of these events in policies concerning the management of coastal landscapes and also the reduction of hazard risks in this region.

The morphology of Como Beach in the Swan River Estuary, Western Australia, is described. Como Beach is in a microtidal estuarine environment in which modal wave conditions are extremely low and nontidal fluctuations in water level are principally determined by storm surges and low-frequency changes in ocean water levels. Detailed descriptions of sandy beaches in very sheltered locations, such as Como, are uncommon in the literature, although these beaches are a common feature of coastal environments. In contrast to beaches in wave-dominated environments, those in very sheltered, low-energy locations may support subtidal terraces and beach profiles that differ in form and scale from the bars and intertidal flats in wave- and tide-dominated environments. At Como, beach profiles are superimposed on a subtidal terrace rising steeply from waters several metres deep to −1.5 m (Australian Height Datum; AHD), then with a low gradient to approximately −0.3 m (AHD) at the shore. The profiles range from planar forms on which very small waves (H_b less than 0.1 m) are dissipated to curvilinear forms that reflect higher waves (H_b > 0.2 m) from the beachface. A transitional form with a segmented profile comprising a steep beachface and flat inshore occurs, particularly where littoral drift is apparent.

This article revisits the debate about the processes of coastal dune initiation in Australia. A review of the dates published so far on coastal dunes in Australia indicates that these belong to identifiable process regions. Those to the north and northeast seem to be largely derived from the deflation, at low sea levels, of exposed deltaic sediments, which are subsequently reworked by episodes of active transgressive dune development. In the southeast, the dunes, like other coastal depositional features, are largely derived from the alongshore sediment transport system, which is active along this coast at times of higher sea level. Apart from during glacial maxima, episodes of dune transgression, where a source is identifiable, seem to be initiated along the shoreline, strongly suggesting that marine disturbance is the trigger. Although, in many cases, these are also at times when climate is favourable to active transgressive dune development, the eastern Cape York dune fields make it clear that this is not a necessary condition.

Coastal evolution following the Holocene marine transgression in South Australia is examined under three contrasting coastal environments: the high-energy, microtidal southeast coast, and the Holocene barrier system of the Sir Richard and Younghusband peninsulas; the sandy deposits of the moderate-energy eastern Gulf St Vincent around the metropolitan Adelaide coastline; and the rapidly prograding sediments of the sheltered subtidal to supratidal gulf environments in the low-energy Upper Spencer Gulf. Although only the Upper Spencer Gulf case study provides detailed data on the Holocene sea level change, collectively, the three case studies illustrate differences in coastal evolution following the transgression, linked to factors such as regional variations in wave energy and wind regime, tidal range, and sediment availability.

This study addresses the mid- to late Holocene stratigraphy and sea level history of a macrotidal barrier and paleoestuary system located along the relatively unstudied northwest coast of Australia. Thirty-nine shallow cores were obtained from three transects perpendicular to the barrier and paleoestuary axis. Seven sedimentary facies were identified on the basis of sediment texture, carbonate content, and foraminifera assemblages: slope, upper intertidal mud, upper intertidal sand flat, lower intertidal sand flat, barrier, estuarine beach, and flood tide delta. The sedimentary infill reveals a fining upward succession of marine sediments up to 6 m thick, mostly along a regressive sequence. All facies are of Holocene age and started to be laid down when sea level was approximately 3 m below present elevation. A radiocarbon date from the topmost sedimentary facies (upper intertidal mud) indicates that relative sea level was at least 1 m higher than today by 2720 years BP. At this time, the estuary was at the final stages of sedimentary infill, with tidal inundation reduced to a minimum. Further evidence of a higher relative sea level during the Holocene is in the form of estuarine beach deposits found at the back of the paleoestuary at an elevation above the present day beach/dune interface. Net nearshore transport in the area, driven by tidal current asymmetry, is northward, and it is proposed that this has significantly influenced the alongshore component of the barrier progradation and evolution of the barrier estuary.

An aminostratigraphy of Lake Illawarra and St Georges Basin, two wave-dominated barrier estuaries in southeastern Australia, has been derived on the basis of the extent of aspartic acid racemisation in the Holocene fossil molluscs Anadara trapezia and Notospisula trigonella. Relative ages were also assigned to Late Pleistocene fossil molluscs on the basis of the extent of racemisation of the slower racemising amino acids valine, leucine, and proline. Aminostratigraphy indicates that remnant Last Interglacial deposits within both incised valleys form a substrate over which Holocene estuarine sediments have been deposited and form a core for the Holocene barrier. Results from this study also indicate that the early geomorphological evolution of wave-dominated barrier estuaries formed in broad and relatively shallow, incised valleys is different from previously published models of Holocene barrier estuary evolution that explain successions in narrow, drowned valleys. Divergence from previous models is seen with the deposition of a near-basinwide shell-rich transgressive sandsheet deposited as rising sea levels breached remnants of Last Interglacial barriers during the most recent postglacial marine transgression (PMT; ca. 12,000–7000 Cal BP). Subsequent development of the estuaries follows the previously developed models with the Holocene barrier and central mud basin accumulating over the initial transgressive sandsheet. The aminostratigraphic framework derived from this study will serve as a geochronological template for future studies in wave-dominated barrier estuaries on the southeast coast of Australia.

Morphological changes associated with saltwater intrusion of a small salt-affected floodplain in the vicinity of the mouth of the East Alligator River were examined through interpretation of aerial photography and ground surveys. The floodplain, in the Alligator Rivers Region of the Northern Territory, Australia, includes mudflats, tidal creeks, upper and lower floodplains, and a freshwater basin impounded by cheniers. Significant morphological change has occurred since 1950, with the tidal creek extending 4 km inland. By 2000, bare saline mudflats on the coastal plain had undergone a ninefold increase, and 64% of Melaleuca spp. forest had been lost.

Saltwater intrusion and associated morphological change over time appears to have been driven by drier-than-average monsoonal conditions, low-frequency and low-intensity cyclonic events, and above-average ocean water levels experienced since 1950 and particularly since the mid-1980s. Loss of vegetation on the lower coastal plain was facilitated by expansion of the tidal creek. As a result, deflation of sediment followed sediment desiccation in the dry seasons. Arguably, the deflation contributes to basin formation and promotes favourable conditions for continuation of tidal-creek development. In turn, this promotes favourable conditions for subsequent retention of floodwater and continuation of tidal-creek development. There is interplay between the two processes. Historical records and field observations indicate that the floodplains may grow in elevation, responding to slight rise in sea level, through alternation of their freshwater and saltwater states. In sequence, the change occurs as a result of shallow basin formation by aeolian processes, saltwater intrusion by tidal creeks, basin infilling by tidal creeks and river deposition, and reestablishment of the freshwater body at a slightly higher level.

Several modes of coral reef growth are found along the edge of Australia's Great Barrier Reef (GBR), determined by the morphology and slope of the shelf edge, especially between −50 m and −100 m, and the velocity of tidal currents near the surface. The simplest forms are the flood tide deltaic reefs and ribbon reefs of the far north. The shelf margin of the central GBR is characterized by lines of submerged reefs that continue on the ocean (northeastern) side of the Pompey Reefs, which are the largest and most complex in the entire GBR. Combining interpretations of reef evolution from the simpler marginal reefs with data collected from the Pompey Complex, a model of evolution on a stepped continental shelf margin is developed, involving initiation as ribbon reefs, formation of both ebb and flood tide deltas (which have formed the foundation for further reef growth), and incorporation of at least one line of previously submerged reefs on the open ocean side by progradation of the deltaic structures to form large lagoonal reefs. Although the reefs cover a smaller area than the extensive reefs of the continental shelf, which could have grown only at higher Quaternary sea levels, the smaller area of shelf-marginal reefs may contain a longer record of coral growth than that of the better-known shelf reefs.

The Holocene growth of fringing and nearshore reefs on the GBR is examined. A review of data from 21 reefs indicates that most grow upon Pleistocene reef, boulder, and gravel, or sand and clay substrates, with no cored examples growing directly over rocky headlands or shores. Dated microatolls and material from shallow reef-flat cores indicate that fringing and nearshore reefs have experienced several critical growth phases since the mid-Holocene: (1) from initiation to 5500 YBP, optimum conditions for reef and reef-flat growth prevailed; (2) from 5500–4800 YBP, reef-flat progradation stalls in almost 50% of the reefs examined; (3) of reefs prograding post-4800 YBP, approximately half ceased active progradation around 3000–2500 YBP; (4) reefs prograding to present do so at rates well below mid-Holocene rates; (5) a group of nearshore reefs has established since 3000 YBP, in conditions traditionally considered poor for reef establishment and growth. Importantly, many of the reefs that appear to have grown little for several millennia are veneered by well-developed coral communities. Although local conditions no doubt exert some influence over these growth patterns, the apparent synchronicity of these growth and quiescent phases over wide geographical areas suggests the involvement of broader scale influences, such as climate and sea-level change. Recognition and understanding these phases of active and moribund reef growth provides a useful longer term context in which to evaluate reported current declines in fringing and nearshore reef condition.

Lord Howe Island is a volcanic island, rising to over 800 m, draped with Late Quaternary submarine and subaerial carbonate sediments. The island and neighbouring islets lie within a chain of seamounts and is presently at or close to the latitudinal limit to coral reef growth. Lord Howe Island and adjacent Balls Pyramid, composed of the basalts erupted around 6 million years ago, sit near the middle of broad shelves on separate peaks of one major volcanic edifice. The central part of the Lord Howe Island is covered by calcarenite that was deposited primarily as dunes (eolianite), but with isolated beach units. Uranium-series, amino acid racemisation, and thermoluminescence dating indicate that many of these were deposited during marine oxygen isotope stage 5. Eolianite units stratigraphically below the beach deposits are of penultimate interglacial, or in places perhaps older, age. Different suites of erosional landforms are associated with different lithologies. Towering plunging cliffs characterise the resistant Mount Lidgbird Basalt, in some cases fringed with large talus slopes. On less resistant lithologies or where nearshore topography means greater wave force as a result of waves breaking, there are shore platforms. Slumping cliffs abut broad erosional platforms on the poorly lithified calcarenite. A fringing reef on the western side of Lord Howe Island, the southernmost coral reef in the Pacific, is dominated by coral and coralline algae. Carbonate sediments veneering the shelf around the islands contain a more temperate biota. Located at the southern limit of reef-forming seas, but apparently having undergone erosion for much of its history outside of reef seas, Lord Howe Island provides insights into marine planation of volcanic islands close to what has been termed the Darwin Point. It represents the initial stages of fringing reef development on a volcanic island. Middleton and Elizabeth Reefs, north of Lord Howe Island, have the morphology of coral atolls and appear to be gradually subsiding. The Darwinian sequence, fringing reef to atoll, appears particularly compressed in this chain of islands. However, a fossil reef in water depths of around 30 m on the shelf around Lord Howe Island, of unknown age, implies a more complex history.

The distinctive blue hole terrains of the Houtman Abrolhos reef complex have been previously interpreted as the result of karst processes controlling Holocene reef growth and morphology. The apparent intensity of karst modification, indicated by the abundance and density of blue holes, steered the general perception of the reef complex as one that was stressed and marginal for Holocene coral growth. This view is commensurate with the high-latitude location (28°–29° S) of the reefs. Through an investigation of the reef morphology, litho and seismic stratigraphy, and the growth chronology of these reef complexes, we demonstrate that the blue hole terrains of the Houtman Abrolhos are not karst features but are growth forms that are characteristic of these reefs.

Australian reef flats on the Cocos (Keeling) Islands atoll, Indian Ocean; Warraber Reef, Torres Strait; and Lady Elliot Island, Great Barrier Reef vary greatly in morphology (width, elevation) and hydrodynamic setting (wave and tidal regime). This study describes results from detailed wave and current measurements, under nonstorm conditions, along five reef flat transects on these reef systems and examines implications for surface geomorphic processes. Results show that wave frequency and transformation varies between reefs in a consistent manner dependent on tidal elevation, reef elevation, and reef width. A nondimensional reef energy window index (Ψ) is developed that incorporates these critical factors (water depth at spring high tide and reef width). A statistically significant relation (95% confidence interval) between Ψ and the proportion of time that wave energy propagates across reefs illustrates the index ability to characterise the wave process regime of reef flats and provide a physically meaningful descriptor of the efficacy of geomorphic processes on reefs. High values of Ψ indicate narrow and low-elevation reef flats, which are exposed to high wave energy and are geomorphically active. Low values reflect wide and high-elevation reef flats associated with less active wave and geomorphic processes. Results show that while incident energy is undoubtedly an important factor for reef geomorphology, the nature of wave modification across reef flats is equally important in governing levels of geomorphic activity that control development of surface geomorphic features on reef platforms.

This study determined whether a previous laboratory finding relating platform elevation to rock strength could be verified when tested in the field. Testing took place along the Otway coast in southeastern Australia. Fourteen platforms were profiled using a total station while rock strength tests were performed with a type L Schmidt hammer. Results established that higher mean platform elevation correlated with increased rock strength (r = 0.661, p < 0.05). This confirmed that a relation exists between elevation and rock strength when tested in the field. This finding has implications for the interpretation of shore platforms and marine terrace elevations in relation to sea level.

Management of uncertainty in model predictions of long-term coastal change begins by admitting uncertainty. In the case of geometric mass-balance models, the first step is to relax restrictive assumptions to allow for open sediment budgets, time-dependent morphology, effects of mixed sediment sizes, and variable resistance in substrate material. These refinements introduce new uncertainty regarding the choice of parameter values. The next step is to actively manage uncertainty using techniques readily available from information science. The final step requires a shift in coastal management culture to accept decision making based on risk-management protocols.

Stochastic simulation was applied to manage predictive uncertainty in cases involving complications resulting from open sediment budgets, rock reefs, and seawalls. In these examples, the respective effects caused between 20% and 60% difference from conventional predictions based solely on equilibrium assumptions and substrates comprised entirely of sand.

Stochastic simulation makes it possible to establish confidence limits and determine the statistical significance of differences caused by varying effects such as substrate resistance and shoreface geometry. It also enables the likelihood of critical impacts to be specified in terms of probability. Moreover, probabilistic forecasts provide a transparent basis for coastal management decisions by revealing the consequences if quantitative estimates prove to be wrong.