A dynamic habitat mudflat model for the Coorong, South Australia

Abstract

The Coorong is a 2-3 km wide lagoon running parallel to the coast for approximately 100 km from the Murray Mouth in South Australia. It provides an important habitat for a wide range of bird species, and in particular has been listed as a Ramsar wetland due to its exceptional importance for migratory waterbirds. Using an extensive dataset of high resolution bathymetry data with the outputs of a CSIRO hydrodynamic model detailing hourly water level and salinity along the Coorong for given flow scenarios, we developed a dynamic habitat model for key bird species. The GIS-based model predicts the availability and viability of mudflats, defined as soft sediment areas that are either immersed or covered by no more than 12 cm of water, where most waterbird foraging occurs. Mudflat availability varies spatially and temporarily along the Coorong, and is influenced by tide, wind, rainfall and evaporation, some of which are dependent on the distance from the Murray Mouth and are affected by seasonal variation. The modelling of mudflats at different water levels suggests that an average water level of 0.12 m AHD gives the maximum average mudflat area across the majority of the Coorong. We present a model that can be run for any given flow scenario over any time period for any site along the Coorong. However, this model can be easily modified for use in different environments where water level-habitat interactions are important. For the Coorong, it is important for managers to understand the influence of both water level and salinity on mudflat habitats as well as the aquatic habitats for fish, macrophyte and infauna. The spatial model developed for this study allows managers to readily quantify these habitats for specified flow scenarios, and supports informed decisions on the amount and frequency of barrage outflows from the Lower Lakes when excess water is available for environmental improvement and maintenance of the Coorong.