Coastal and subcoastal non-floodplain sand lake—Perched
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Perched lakes are formed when sand is cemented together with decomposed organic matter (such as leaves, bark and dead plants) and aluminium and iron, creating a relatively impermeable layer well above sea level.
This cemented (or indurated) layer, known as ‘coffee rock’, tends to slow water from percolating down to the regional aquifer, holding rainwater in a depression, forming a lake (and associated swamp habitat). The geomorphology of perched lakes can be quite diverse and complex. The wetland environment that develops can depend on the topography, depth of the coffee rock, degree of cementation (induration), as well as its organic matter and metal content. The perched lake’s position in the landscape (e.g. in a deflation dune or a backswamp) also plays an important role in the formation and functioning of the perched lake. Commonly they are formed in saucer-shaped depressions in the dune surface with their own local water table that sits well above the large lens-shaped aquifer that may be associated with the greater sandmass system. However, further research is required to better understand these wetlands.
Last updated: 22 March 2013
This page should be cited as:
Coastal and subcoastal non-floodplain sand lake—Perched – Geomorphology, WetlandInfo, Department of Environment and Science, Queensland, viewed 31 January 2020, .