Groundwater–Surface Water Interaction: Process Understanding, Conceptualization and Modelling (Proceedings of Symposium HS1002 at IUGG2007, Perugia, July 2007). IAHS Publ. 321, 2008, 5-10.

Surface water–groundwater interactions in pristine and cleared fractured rock catchments: Kangaroo Island, South Australia

Paul Shand^1,3, andrew love^2,3 & julianne james-smith³

1 CSIRO Land and Water, Adelaide, Australia

paul.shand@csiro.au

2 Flinders University of South Australia, Adelaide, Australia

3 Department of Water, Land and Biodiversity Conservation, Adelaide, Australia

Abstract The surface waters of Kangaroo Island, South Australia, display large changes in hydrochemistry, both spatially and temporally, reflecting complex sources, flow pathways and residence times. A comparison is made between a pristine catchment (Rocky River) and a cleared (Cygnet River) catchment on the island. Gaining and losing reaches in rivers were variable, largely related to the presence of thick sequences of fluvial deposits in the river channels. Natural stable isotope tracers provided evidence for evaporative signatures during the summer months, and Sr isotopes showed that there are both marine sources and non-marine-derived solutes from contrasting rock lithologies. Comparisons of river waters between the cleared and pristine catchments suggest that there is a link between land clearance and the dominant shallow flow pathways determining streamflow generation. Preliminary data in the Rocky River show that there are large stores of salt present at shallow depth. Despite this, the river water is remarkably fresh, and in places continues to flow throughout the year. It is suggested that flow via macropores, effectively by-passing the salt store, and lateral flow in regolith or bedrock, is an important pathway for flow to the river.

Key words surface water–groundwater interactions; kangaroo island; hydrochemistry; Sr isotopes; flow pathway