The Gippsland Lakes, Victoria : a geomorphological study

Abstract

The Gippsland Lakes are a group of coastal lagoons in eastern Victoria, fed by rivers and cut off from the sea (Bass Strait) by sandy coastal barriers bearing dune topography. The lakes originated when a coastal embayment formed by Postglacial submergence and extended by Recent tectonic subsidence was sealed off by the successive formation of barriers. The pattern and growth of the coastal barriers has been determined by wave action, notably by the constructive action of ocean swell approaching from Bass Strait. Successively-formed parallel foredunes show stages in podzolisation accompanied by a vegetation succession from dune grasses and scrub to woodland and heath. The foredunes were partly rearranged into parabolic dunes in a mid-Recent phase of drier conditions. Contemporary erosion and the initiation of blowouts along the outer shore of the coastal barriers (the Ninety Mile Beach) are related to a contemporary rise in sea level. The development of the lakes has been influenced by three processes, segmentation, alluviation, and encroachmento Segmentation is a process by which a long narrow lagoon is divided into smaller rounded lagoons separated by strips of depositional land, and is the outcome of erosion and accretion around the lake shores by wave action. Waves formed on the lakes are related entirely to local winds, and segmentation began as soon as the coastal barriers effectively excluded ocean swell from the embayment. The submerged valleys have been partly reclaimed by alluviation, and the larger rivers have built deltaic silt jetties protruding into the lakes. Swamps have been built up around the lake shores by means of encroachment by reeds, followed by swamp scrub vegetation. The growth of the silt jetties and the encroachment of swamps depend on the presence of a shoreline reed vegetation (Phragmites), for in the eastern half of the lakes where the reed fringe has disappeared the silt jetties and lake-shore swamps are being eroded. The disappearance of the reed fringe is correlated with increasing salinity since the opening of an artificial entrance near the eastern end of the lakes in 1889. The salinity of much of the lakes is now above the limit of tolerance for Phragmites. Previously the barriers largely excluded sea water and the lakes were freshened by rain and rivers; shoreline vegetation initiated delta growth and swamp encroachment, and impeded wave action so that segmentation was reduced. Now shoreline erosion is widespread and segmentation has revived. The problem of shoreline erosion is discussed in terms of these conclusions 0 It is thought that the introduction of a halophytic vegetation (possibly Spartina townsendii) to the lake shores will arrest erosion and revive encroachment .