GEOCHEMISTRY OF DRAINS IN TILLEY SWAMP, UPPER SOUTH-EAST, SOUTH AUSTRALIA

INTRODUCTION To manage an expected increase in land area affected by dryland salinity and flooding in the upper South East of South Australia, an extensive system of drains has been constructed to intercept both saline ground water and fresher surface waters. Saline water is to be delivered to temporary storage in Morella Basin and nearby areas such as Tilley Swamp, or discharged to the Coorong. Fresher surface waters are expected to be directed to wetlands to improve environmental condition. Tilley Swamp is an interdune area running parallel to and just inland to the east of the Coorong. It trends approximately NNW-SSE and is approximately 40 km long and 4 km wide. A natural drainage course runs along the western side of the interdune. A drain that is about 2.5 to 3 m deep was constructed towards the eastern side of the interdune flat. It intercepts ground water and conveys saline waters from the extensive southern part of the network across the length of Tilley Swamp to Morella Basin. Vegetation of the area includes extensive areas of Melaleuca halmaturorum (coastal paperbark), pasture species, and Gahnia spp. (cutting grass) with samphire species in permanent saline areas along the natural drainage course.