Intertidal low energy over sand

Long description

Intertidal low to very low energy over sand, including: beaches, banks, flats and plains subject to little or no wave action (i.e. the wave climate generally consists of 0.5 – 0.8m swells).

The majority of low energy sandy beaches are influenced by a combination of tidal and wave energy. Intertidal sandy ecosystems occur on a variety of different terrain morphologies and usually have a gentle Terrain slope in contrast to high energy sandy beaches. A slightly steeper slope is present above mean sea level, tapering out to broad very gradually sloping sand flats that may extend 50 – 500m offshore, some with a scattering of sparse mangroves. Tidal flats may extend out from creeks and estuaries as tidal deltas[6].

May include burrowing infauna such as: crustaceans, molluscs, polychaete worms and a variety of other worms (including filter-feeders). These invertebrates provide a productive food source for migratory and resident shorebirds.

Special values

Critical to turtle nesting and shorebird feeding[3]. Marine turtles and many shorebirds are Environment Protection and Biodiversity Conservation Act 1999-listed species (EPBC).

Groundwater influence in some places, seeping out of the large sand masses.

These areas are likely to contain unmapped areas of seagrass, which are potential habitat for dugong and green turtles.

Diagnostic attributes

Inundation 'Intertidal – Lower low', 'Intertidal – Mid low', 'Intertidal – Upper low', 'Intertidal – Low undifferentiated', 'Intertidal – Lower medium', 'Intertidal – Upper-medium', 'Intertidal – Medium undifferentiated', 'Intertidal – High', 'Intertidal – Undifferentiated', 'Intertidal – High undifferentiated'

Sediment texture 'Sand (slightly gravelly)', 'Sand', 'Gravelly muddy sand', Gravelly sand', '(slightly gravelly) muddy sand'

Energy magnitude (wave) 'Low', 'Very low'

Qualifiers

Period and Trend qualifiers are relevant here as normally low wave energy can be amplified during storm events (such as cyclones and east coast lows) and during floods, transporting sand away from the higher shoreline. Seasonal variations in wave energy and direction may contribute to changes in beach form and mobility. Riverine energy during flood events can re-shape shorelines, especially at the mouth of estuaries. Entire river systems can be re-shaped and new entrances created. The Naturalness qualifier is relevant on sandy beaches that have been armoured in an attempt to prevent property loss (e.g. buildings). There may be hardened structures nearby that will change wave and current energy and may potentially move sand away from the shoreline rather than accreting sand. The grain size of sands is particularly important for their retention in the intertidal area[2][1].

For thousands of years, Traditional Owners caught and ate large numbers of shellfish species in and around the Queensland coast. Often they would cook the meat and use the shells for a number of purposes, or dispose of shells in large dump sites called shell middens. Shell middens have provided important information and clues about Traditional Owners and the environment they lived in. The middens tell the story of the Traditional Owners’ diet, food sources and species available and the impact of environmental changes on biodiversity and marine ecosystems[5]. Burrowing molluscs such as pipis (eugaris), cockles and ark shells are an important food source for Traditional Owners, and likely to be a component of neighbouring middens. Baler shells were also often seen as important ornamental shells[4].

Distribution

Large areas up and down protected waters of the Queensland coast in central to northern Queensland[6].The northern-most limit of high energy shorelines along the Queensland coast are K'gari and Double Island Point. Inside the Great Barrier Reef lagoon is mostly low wave energy. K'gari and the Great Barrier Reef form a barrier to wave energy and provide for this low energy ecosystem.

The following relates to distribution of this ecosystem type detailed in the Central Queensland mapping area:

• This is a very extensive ecosystem over much of the mapping area, which extend into the subtidal also see types 104 (subtidal high energy over sand) and 105 (subtidal low energy over sand). Very broad sand flats occur along the shores of Hervey Bay from Point Vernon to Burrum Heads.

Comments

Relevant attributes include Terrain morphology, crests and peaks can form part of dunes and channels and depressions may correlate to swales, whereas planes are the flat areas between. Further delineation of dunes and swales may be possible by including the Terrain slope. Factors influencing beaches include Sediment texture, Energy source (wave, current or riverine) and magnitude (see Ozcoasts conceptual models for further information) and Tidal range[6].

The former Beach Protection Authority produced detailed studies on the geology, underlying hydrological and geomorphological processes for Hervey Bay and Capricorn Coast beaches, identifying issues and locations where coastal erosion was problematic.

Additional Information

Coastal sand masses (beach ridges) - WetlandInfo

Understanding coastal erosion on beaches

References

1. ^ Beach Protection Authority of Queensland (1979), Capricorn Coast beaches: a detailed study of coastline behaviour along the Capricorn Coast of Queensland, Australia, Beach Protection Authority, Brisbane.
2. ^ Beach Protection Authority of Queensland & Beach Protection Authority (1989), Hervey Bay beaches, Beach Protection Authority, Queensland, Queensland, Australia.
3. ^ Department of Environment and Science, QG (2019f), Assessment of Common Conservation Values - Intertidal and Subtidal Environs of the Baffle to Fitzroy Coast, Version 1.1., Department of Environment and Science, Queensland Government., Brisbane, Queensland.
4. ^ McNiven, I (1997), Aboriginal Archaeology of the Corroboree Beach Dune Field, Fraser Island: Re-survey and Re-assessment, pp. 1-22.
5. ^ Queensland Museum Network, 'Indigenous Science: Shell middens and fish traps', The Queensland Museum Network Blog. [online] Available at: https://blog.qm.qld.gov.au/2012/10/08/indigenous-science-shell-middens-and-fish-traps/.
6. ^ a b c Short, AD (2006), 'Australian beach systems-nature and distribution', Journal of Coastal Research, pp. 11-27.

Last updated: 22 July 2019