Intermittent Swamps

Landscape

This unit differentiates the intermittent waterbodies, used for grazing and in some cases cropping, from the permanent waterbodies which are not agriculturally viable. Many of these swamps were not able to be delineated due to their close proximity to permanent waterbodies and have been mapped as a complex. Lunettes are common on the eastern side of swamps and in many cases have been mapped separately.

The water source of the intermittent swamps is mainly from local runoff or recharge from the surrounding dunes.

Due to the high perched watertable often present in the intermittent swamps, rushes commonly occur. In these cases the land use in summer is restricted to grazing.

Native Vegetation

Red Gum is the major tree species and a variety of rushes are the major grass species found on the wetter areas. On the edge of some swamps where cracking clay soils occur, Black Box and Lignum Bush can be found.

Soil Types

As the formation of the lakes are variable, there is a range of soil types occurring on the swamp floor. Grey clay soils are common and may crack on drying. The depth of sand above the clay is variable, ranging from less than 10 cm to greater that one metre. A high percentage of fine sand in the clay subsoil is common due to a combination of alluvial deposition and the sand falling through the cracks when the subsoil shrinks.

The clay tends to become greyer at depth where the soil is undergoing more anaerobic (lack of oxygen) conditions. The presence of a calcium carbonate layer, or at least pockets of carbonate, is common at depth.

During the winter months the perched watertable intersects with the surface which creates the intermittency of the swamps. During the summer months the watertable drops to varying depths. The perched watertable level can be as close as 50 cm from the surface and could create problems for deeper rooted plants.

Representative Soil Type for Land Element

Although two soil types have been described for this unit, Sites WW66 and WW67, the former is regarded as the most representative soil type.

Current Land Use

During the winter months when the perched watertable is at or close to the surface, grazing is often restricted to the outer edges or not at all. Pugging of the soil caused by grazing while wet, leads to problems including destruction of the soil structure and waterlogging.

Grazing of the swamps is common when the watertable recedes during the drier months. In some areas where the swamps have been drained or the perched watertable is lower than rooting depth, cropping can occur.