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Intertidal substrate below HAT with indeterminate tidal influence

Short description

Terrestrial and freshwater ecosystems below Highest Astronomical Tide.

Disclaimer: Ecosystem type descriptions are based on biophysical attributes identified in Central Queensland through expert advice and supported by scientific literature. Not all ecosystem types are mapped based on current inventory, and many of the ecosystems described here may also occur in other parts of Queensland.

Townsville Town Common Conservation Park. Photo by Jonathan Burcher, Queensland Government

Classification categories

Select from the links below to view related ecosystem type categories

Long description

Rubyanna Creek. Photo by Maria Zann, Queensland Government

Terrestrial and freshwater ecosystems (e.g. groundwater dependent ecosystems, GDEs) below the mapped level of Highest Astronomical Tide (HAT) and potentially subject to tidal influence. There are two main sub-types.

  1. Remnant Regional Ecosystems (REs) and in the Queensland Wetlands mapping on Land Zones 2 (sand masses) and 3 (alluvium). In swales behind beach ridges where saline seawater influence is moderated by freshwater/groundwater from the dunes, and in the upper reaches of groundwater-fed estuaries. Tidal influence may be pushing the height of the water in these wetlands up and down, but the water itself is fresh as freshwater floats on top of seawater.
  2. A separate and different sub-ecosystem from these are the modified non-remnant agricultural land that is below the mapped level of HAT, but has been hydrologically altered either by bunding, artificial canal drains, or levelling and filling and are often irrigated systems. Where irrigation is derived from groundwater and close to the sea, these systems may be subject to saline ingress, (i.e. have saline groundwater influence).

Special values

Where remnant ecosystems exist, these are important areas of hydrological connectivity between land and sea and protect brackish to fresh habitat for fish in the upper estuaries of streams. Diadromous fish need these areas for fish passage.

Can be important to shorebird feeding, as outlined within the Aquatic Conservation Assessment (ACA). Many shorebirds Environment Protection and Biodiversity Conservation Act 1999-listed species (EPBC).

Diagnostic attributes

Inundation ‘Intertidal – indeterminate’

Structural macrobiota ‘Unknown’

Energy magnitude (wave) ‘Low’, ‘Very low’

Sediment texture ‘MUD’, ‘gravelly MUD’, ‘muddy SAND’, ‘(slightly gravelly) sandy MUD’, ‘(slightly gravelly) MUD’, ‘sandy MUD’, ‘SAND’, ‘(slightly gravelly) SAND’, ‘gravelly muddy SAND’, ‘gravelly SAND’, ‘(slightly gravelly) muddy SAND’, ‘GRAVEL’, ‘muddy GRAVEL’, ‘sandy GRAVEL’, ‘muddy sandy GRAVEL’, Unknown’ (note that the dominant grain size is capitalised)

Benthic depth ‘Intertidal (>0m)’


Sub-type ii (non-remnant) includes modified Naturalness agricultural land as mapped by Queensland Land Use Mapping Program (QLUMP) mapping. Modified Terrain morphology including cut channels, bunds etc. have altered the hydrology of agricultural land such that its tidal influence is minimal. However, irrigated areas may be subject to saline ingress and the groundwater may be salty. Although unmapped, Period and Trend qualifiers are also relevant as the Energy magnitude may also vary seasonally and episodically with respect to wave action and with respect to inundation, as remnant wetland areas may be seasonally inundated with freshwater but then the tidal influence returns with the drying out of the substrate.


Relatively common in developed parts of the state, although typically small areas in between the landwards edge of the mangrove/saltmarsh/grass/sedge complex and terrestrial vegetation. Freshwater vegetation subject to indeterminate tidal vegetation is frequently in deltas and mouths of river systems, or in swales adjoining estuaries.

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

  • Large areas mapped in Central Queensland including sub-type i (remnant) as the freshwater systems below HAT associated with dune swale wetlands south of Baffle Creek to the Kolan, Susan River wetlands and tributaries, Burrum River National Park dune swales and tributaries of the Burrum River, and sub-type ii (non-remnant) as the Burnett River floodplain below Bundaberg to Moore Park.


Other relevant attributes can include Freshwater input volume, Freshwater input source, Tidal range, Terrain relative relief, Terrain morphology, Terrain slope, Terrain pattern and Sediment composition (applied as Sediment texture typology).

Refer to freshwater wetlands mapping and Regional Ecosystem mapping for remnant vegetation.

Additional Information

Wetland Maps - WetlandInfo

Groundwater Dependent Ecosystems - WetlandInfo

Land zone definitions - Queensland Government

Regional ecosystems - Queensland Government

Queensland Land Use Mapping Program (QLUMP) - Queensland Government

Last updated: 22 July 2019

This page should be cited as:

Department of Environment, Science and Innovation, Queensland (2019) Intertidal substrate below HAT with indeterminate tidal influence, WetlandInfo website, accessed 1 February 2024. Available at:

Queensland Government
WetlandInfo   —   Department of Environment, Science and Innovation