Hanging swamp

Posted by Thew Wise One on January 27, 2004

In Reply to: Hanging swamp posted by Lotg on January 26, 2004

: In a large basin at the bottom of our property, at the base of some cliffs is a substantial area of hanging swamp.

: This term is something I've heard all my life and never questioned. I've always known that a hanging swamp is a shallow swamp with such a mass of plant-life as to make it appear from above to be solid ground.

: However, when I was showing guests the other day, one asked me "why is it called a 'hanging' swamp". Pretty fair question and I have no idea. Can anyone help?

What is a Hanging Swamp?
The Environmental Study for the Blue Mountains Environmental Management Plan: 1989 (EMP) explains as follows: "Hanging swamps are an important part of the character of the upper and central Blue Mountains. There are two broad types of hanging swamp - sedge swamp and shrub swamp. Sedge swamps are a common vegetation community occurring in a broad band from Bell east through all townships to Woodford. Shrub swamps generally occur in the Bell through to Leura areas, where they are locally common. In some situations, particularly in the upper mountains, the two types intergrade".

"Hanging swamps develop at moderate to high altitudes on sloping rock faces composed of Narrabeen Sandstone which are subject to a constant supply of water - especially groundwater but also surface runoff. Rainfall infiltrates the sandy soils and the permeable sandstone below. At intervals in the sandstone are narrow layers of claystone, or tightly cemented sandstone which are impervious to groundwater. The water then travels laterally on top of this impervious barrier until it reaches the edge of the impervious layer, which has been exposed by geological erosion. The groundwater then seeps out over the broad sandstone rock face below the impervious layer. These rock faces are in effect the foundations of the swamp structure and are often many hectares in area. Slopes vary widely but commonly exceed 1 in 3 (33%). The condition of constant moisture allows a range of plant species to gradually colonise these bare-rock sites over long periods of time....." Common species are Button Grass Gymnoschoenus sphaerocephalus, Lepidosperma limicola, Xyris ustulata and Baeckea linifolia.

"The constant saturation creates anaerobic (oxygen starved) conditions in the soil, which inhibit the microbial breakdown and decomposition of dead plant material. This organic matter accumulates in a partly decomposed state as peat. Peat has an extraordinary ability to absorb water, and so the swamp soil acts as a sponge, retaining much rainwater for later slow release."

"Streams fed by hanging swamps will continue to run for weeks after rainfall. These assured water supplies maintain the flow in creeks and the numerous escarpment waterfalls"

For more info see: www.zipworld.com.au/~aabr/info/seminars/seminar01.html from which the quote above was cut and pasted.