Submarine groundwater discharge (SGD) from unconfined coastal aquifers to the ocean is common within a few hundred metres of the coast. It has also been observed to occur further offshore, associated with semi confined paleochannels that formed during the last glacial maximum. Fresh groundwater discharges from such paleochannels to the ocean occur between the Queensland coast and the Great Barrier Reef (GBR) where seafloor depths are typically greater than 20 m below sea level. These SGD points are known locally as “wonky holes” and are sought after for recreational fishing. Groundwater development higher in the catchment can change the quantity and quality of SGD which may detrimentally impact the surrounding ecosystems.
The overarching aim of this work was to establish the types of ecosystems that exist in areas of SGD and how they might be vulnerable to groundwater management. The objective was to identify where SGDs are likely to occur, what the dominant flow processes are and to establish the types of marine ecological environments (coral and/or seagrass) they are associated with.
The approach was to gather and collate information about the occurrence of SGD and ecosystem type from the literature and local knowledge and compare these to existing spatial datasets to see if any correlations exist and whether these can be used to provide evidence of where SGD is likely to occur on a broader scale.
Preliminary analysis of high-resolution bathymetry datasets show local depressions that coincide with known locations of wonky holes and indicate many other locations of potential SGD that have not yet been confirmed. Sea surface temperature anomalies also align with some suspected areas of SGD. RECOM (Relocatable Coastal Ocean Model) was used to establish under what conditions SGD would be likely to disperse rapidly or have a longer residence time, thus having a stronger influence on local ecological environments.
Preliminary outcomes show that several existing spatial datasets can provide multiple lines of evidence indicating where SGD is likely to occur.