BEACHES, DUNES AND BLOWOUTS – USING GPR TO RELATE COASTAL FEATURES AND CLIMATES, COORONG LAGOON, SOUTH AUSTRALIA

Monitoring sea level and shoreline changes has become crucial in the past several years due to increasing global sea levels. As Australia is a coastal based society, it will be greatly impacted in the future as rising sea level and increasing erosion rates affect the country’s infrastructure. The need to understand the coastal systems; including variables such as long and short term sea level, rates of sea level change, erosion rates, and dynamics of the system, is becoming a vital step in understanding how the coastal zone will respond in the future. Coastal dune fields and beaches are critical environments that require detailed studies and increased understanding. GPR, satellite imaging, and coring are frequently used to elucidate the spatial and temporal relationship of paleoshorelines and past dune fields with current environments. These techniques were used on the coast of South Australia at 42 Mile Crossing, located at the southern tip of the Coroong Lagoon. The area hosts landward migrating Holocene dunes, relict Quaternary coastal dunes and an active beach system. The area is currently experiencing erosion of the coastal barrier beach and foredunes.

High-resolution GPR was acquired using a MALA GX system with 450 MHz and 160 MHz antennas. The system was paired with a RTK GPS for precise location measurements. The 160 MHz antenna was used to locate the most recent paleoshoreline system under the current dune field, while the 450 MHz antenna was used to understand the three-dimensional morphology of active blowouts. Over 50 GPR lines were obtained; the majority within active and buried blowouts.

In the initial processing of the lines several features clearly stand out, particularly within the higher frequency transects. The blowout erosional surface and infill of the blowout are easily seen in many lines. Deeper sections reveal former shoreface environments. The data will aid in understanding the coastal system, specifically the erosion and sea level rates and changes throughout the recent geologic past. The images will be analyzed, processed to a further extent, connected, and interpreted on the full feature and ultimately related to paleoclimates.