Intertidal sand boils within springs

Author: Marianna Ramirez Lagunas

Ramirez Lagunas, Marianna, 2024 Intertidal sand boils within springs, Flinders University, College of Science and Engineering

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This Master by Research thesis presents the results of a study aimed at characterising the hydrogeophysical properties and sediment characteristics of intertidal sand boils within springs at Sellicks Beach, South Australia. The study was conducted to describe the temporal and spatial variability of these sand boils and to gain a better understanding of their role in groundwater flow dynamics.

Chapter 1 introduces the physical processes of coastal groundwater discharge and focused on the characterisation of discrete discharge features that including springs and sand boils.

In Chapter 2, the study area at Sellicks Beach in the southwest of the Willunga Basin is described. This includes a detailed description of sediment transport at a micro-tidal environment with a dissipative beach profile and the impact of waves, tidal currents, and wind.

Chapter 3 details a hydrogeophysical characterisation of intertidal sand boils. The survey methods included thermal infrared imaging, electromagnetic geophysics, and environmental tracers (stable isotopes of water and salinity). The results showed that the sand boils exhibited significant spatial and temporal variability in their hydraulic conductivity and salinity. The thermal infrared imagery survey revealed that sand boils have higher temperatures than the surrounding areas, indicating greater water flow. The electromagnetic survey showed that the sand boils have lower bulk electrical conductivity, and defined the spatial extent of the boils within the intertidal zone. The water sampling showed differences in salinity and stable isotope composition between the sand boils and the surrounding area, indicating differences in water source and flow paths.

Chapter 4 focuses on the sediment characteristics of the sand boils and the surrounding area. The sediment analysis showed that the sand boils contain mainly pebble-sized grains, in contrast to the surrounding area where sediments range from fine to medium sands. This suggests that the sand boils are fed by a different source of sediment, possibly related to the geology of the area.

Overall, the study highlights the importance of intertidal sand boils as part of coastal groundwater discharge processes and the mechanisms that control their spatial extent and temporal dynamics. The results suggest that sand boils have higher hydraulic conductivity and are more permeable than the surrounding sediments, which may impact the distribution and quality of groundwater. The sediment analysis also suggests that the sand boils may have a distinct sediment source, which could be relevant to understanding the hydrogeological context of the area.

In conclusion, this thesis provides valuable insights into the hydrogeophysical and sediment characteristics of intertidal sand boils within beach springs. The findings have implications for understanding the dynamics of groundwater flow in the area, which may be relevant for water management and environmental planning. The study also highlights the importance of considering sediment characteristics in hydrogeological studies, as these can provide valuable information about groundwater flow pathways and sources.

Keywords: intertidal zone

Subject: Earth Sciences thesis

Thesis type: Masters
Completed: 2024
School: College of Science and Engineering
Supervisor: Ilka Wallis