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Tidal inundation

The tide, as defined by the Australian Hydrographic Service glossary, is the periodic rise and fall of the water of oceans, seas, bays, etc., caused mainly by the gravitational interactions between the Earth, Moon and Sun. The tidal inundation regime is the frequency of tidal inundation and is a fundamental driver of wetland function.

Saltpan, Hervey Bay. Photo by Maria Zann

Quick facts

Inundation from the tides
is reflected by the patterns of fauna and flora of the intertidal area.

Tidal inundation defines and delineates intertidal and subtidal areas. The intertidal area is between the highest astronomical tide (HAT) and the lowest astronomical tide (LAT) and experiences fluctuating inundation and exposure to air. The subtidal area is below LAT and experiences permanent inundation. 

The duration and frequency of inundation (e.g. diurnal, weekly, fortnightly, monthly, annual, decadal, episodic) and the spatial extent is important as it may affect desiccation and stress. 

   
Diurnal tidal planes. Image by Maritime Safety Queensland, 2018
   
Semidiurnal tidal planes. Image by Maritime Safety Queensland, 2018

Over a lunar month, the highest tides and lowest tides occur roughly every 14 days, at the new and full moons, when the gravitational pull of the moon and the sun are in line and are termed spring tides which align to higher and lower tidal planes.

The terms “tidal planes”, “tidal datums”, and “tidal levels” may be used interchangeably, although some draw a distinction - for example, a “plane” implies a two-dimensional surface extending over a given region[5]. A tidal datum plane is a plane of reference for elevations, determined from the rise and fall of the tides. Various tidal planes may be derived, and each is designated by a definite name, as, for example, the plane of mean high water, the plane of half-tide level, the plane of lower low water[4].

Tidal planes are a product of and response to topography. Currently tidal planes are almost impossible to predict at the habitat scale; they are best applied at seascape scales and above.

The duration of the tidal cycle changes along the Queensland coast for example, south from Lindeman Island tidal planes are semidiurnal (i.e. usually two high and two low tides each day), whereas in the Torres Strait and the Gulf of Carpentaria tidal planes are diurnal (usually one high and one low tide per day)[7][5].

Although tidal planes can be important legal boundaries, the mapping is often based on models. Biotic patterns are often better indicators of tidal inundation, because inundation determines a range of water and sediment chemical properties that influence biota, e.g. salinity[1] and oxidation-reduction (redox)[2].

Patterns of marine plants can approximate some of the tidal planes. For example, marine plant ecosystems grow below HAT and are mapped as ‘Estuarine’ by the state wetland mapping and as occurring on Land Zone 1 (tidal flats and beaches) in Regional Ecosystem (RE) mapping. Mangroves generally grow above mean sea level (MSL) and species such as marine couch (Sporobolus virginicus) often help to identify the upper tidal limit or Highest Astronomical Tide (HAT). However freshwater influence (either groundwater or riverine) can modify patterns, especially at the upper tidal limits[3]

High tides, storm surges, floods and run-off events periodically connect wetland pools with estuaries, creating important nurseries for fish[10]– see figure below[9].

Tidal influence may also be independent of water salinity as the tidal water moving up and down in the upper estuary (including areas of riverine flow) or in groundwater influenced ecosystems may be fresh water. It may be difficult to determine whether such areas are being tidally influenced or not and for the purposes of classification these areas are categorised as ‘indeterminate’ until otherwise confirmed in the field.

OzCoasts Conceptual Model - Hyrdological Processes. Image by OzCoasts, 2013

Queensland Intertidal and Subtidal Classification Scheme

Inundation falls under the 'Hydrology' theme of attributes for the Intertidal and Subtidal Classification Scheme and represents the tidal inundation regime.

Modelled HAT surfaces are based on LiDAR.

Inundation frequency are based on multiple imagery time series[8]. The spectral bands of light attenuate through the water column exponentially but at different rates depending on the depth or presence of land (various products derive from a 30 year Landsat series of 30m pixel size – seascape scale – produced by: Geosciences Australia[6]; various commercial remote sensing companies).

Attribute category table - Inundation

Habitat Seascape Subregion Region
Unknown Unknown Unknown [Not applied]
Subtidal (below LAT) Subtidal (below LAT) Subtidal (below LAT)
Lower Low (LAT to MLWS) Lower Low (LAT to MLWS) Low (LAT to MSL)
Mid-Low (MLWS to MLWN) Mid-Low (MLWS to MLWN)
Upper Low (MLWN to MSL) Upper Low (MLWN to MSL)
Low - undifferentiated Low - undifferentiated
Lower Medium (MSL to MHWN) Lower Medium (MSL to MHWN) Medium (MSL to MHWS)
Upper-Medium (MHWN to MHWS) Upper-Medium (MHWN to MHWS)
Medium - undifferentiated Medium - undifferentiated
High (MHWS to HAT) High (MHWS to HAT) High (MHWS to HAT)
Intertidal - undifferentiated Intertidal - undifferentiated Intertidal - undifferentiated
Indeterminate Indeterminate Indeterminate

Guide to abbreviations above (e.g. HAT)

Additional Information


References

  1. ^ Cowardin, LewisM, Carter, Virginia, Golet, FrancisC & LaRoe, EdwardT 1979, Classification of wetlands and deepwater habitats of the United States, Fish and Wildlife Service, US Department of the Interior Washington, DC, <https://www.fws.gov/wetlands/Documents/Classification-of-Wetlands-and-Deepwater-Habitats-of-the-United-States.pdf>.
  2. ^ Department of Environment and Heritage Protection, Water processes, WetlandInfo, viewed 24 November 2014, <https://wetlandinfo.des.qld.gov.au/wetlands/ecology/processes-systems/water/>.
  3. ^ Dowling, R & Stephens, K 2001, Coastal Wetlands of South East Queensland. mapping and Survey, February 2001., vol. 1, Queensland Government Environmental Protection Agency, Brisbane.
  4. ^ H. A. Marmer, Tidal datum planes, U. S. DEPARTMENT OF COMMERCE, viewed 15 July 2019, <https://www.govinfo.gov/content/pkg/CZIC-qc809-e2-m37-1951/html/CZIC-qc809-e2-m37-1951.htm>.
  5. ^ a b Intergovernmental Committee on Surveying and Mapping 2007, Australian Tides Manual - Special Publication No. 9, viewed 23 November 2014, <http://www.icsm.gov.au/tides/SP9_Australian_Tides_Manual_V4.1.pdf>.
  6. ^ Lewis, Adam, Oliver, Simon, Lymburner, Leo, Evans, Ben, Wyborn, Lesley, Mueller, Norman, Raevksi, Gregory, Hooke, Jeremy, Woodcock, Rob, Sixsmith, Joshua, Wu, Wenjun, Tan, Peter, Li, Fuqin, Killough, Brian, Minchin, Stuart, Roberts, Dale, Ayers, Damien, Bala, Biswajit, Dwyer, John, Dekker, Arnold, Dhu, Trevor, Hicks, Andrew, Ip, Alex, Purss, Matt, Richards, Clare, Sagar, Stephen, Trenham, Claire, Wang, Peter & Wang, Lan-Wei, 'The Australian Geoscience Data Cube — Foundations and lessons learned', Remote Sensing of Environment, <http://www.sciencedirect.com/science/article/pii/S0034425717301086>.
  7. ^ Maritime Safety Queensland, Notes and definitions, viewed 23 November 2014, <http://www.msq.qld.gov.au/Tides/Notes-and-definitions.aspx>.
  8. ^ Murray, NicholasJ, Clemens, RobertS, Phinn, StuartR, Possingham, HughP & Fuller, RichardA 2014, 'Tracking the rapid loss of tidal wetlands in the Yellow Sea', Frontiers in Ecology and the Environment, Eco Soc America.
  9. ^ OzCoasts Conceptual model: Hydrological processes 2013, Geosciences Australia, viewed 23 November 2014, <http://www.ozcoasts.gov.au/conceptual_mods/processes/hydrological.jsp>.
  10. ^ Sheaves, Marcus & Johnston, Ross 2008, 'Influence of marine and freshwater connectivity on the dynamics of subtropical estuarine wetland fish metapopulations', Marine Ecology Progress Series, vol. 357, pp. 225-243, Inter-Research.

Last updated: 16 July 2019

This page should be cited as:

Tidal inundation, WetlandInfo 2019, Department of Environment and Science, Queensland, viewed 6 August 2019, <https://wetlandinfo.des.qld.gov.au/wetlands/ecology/aquatic-ecosystems-natural/estuarine-marine/attributes/inundation/>.

Queensland Government
WetlandInfo   —   Department of Environment and Science