Study of connectivity of open framework gravel facies in the Canterbury Plains aquifer using smoke as a tracer
Lee F. Burbery, Catherine R. Moore, Merren A. Jones, Phillip M. Abraham, Bronwyn L. Humphries, Murray E. Close, 2018. "Study of connectivity of open framework gravel facies in the Canterbury Plains aquifer using smoke as a tracer", Geology and Geomorphology of Alluvial and Fluvial Fans: Terrestrial and Planetary Perspectives, D. Ventra, L. E. Clarke
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Open framework gravels (OFGs) are an inherent textural component of alluvial gravel outwash deposited by braided river systems. Being exceptionally permeable, they play an important part in facilitating the transmission of water and contaminants through alluvial gravel aquifers. Understanding how connected OFG facies are is helpful in making informed predictions about groundwater flow and contaminant transport through such aquifer systems. This work examined a section of the Rakaia fan, Canterbury, New Zealand. A 3 × 3 grid of large diameter auger holes was drilled in close proximity to a sea cliff, which provided very good three-dimensional exposure of the fan architecture. A novel smoke tracing experiment and water tracing field tests were conducted to measure the dynamic connectivity of the OFG facies. Smoke proved to be an effective tracer for measuring the interconnectedness of OFGs over set distances of 5 m. The water tracing tests confirmed that OFGs are connected across much longer distances – in excess of 18 m. Results from both tests revealed how rapid, and non-uniform, aqueous transport can be through alluvial outwash materials. The connectivity information will be used to improve realizations of the heterogeneity of the Canterbury Plains aquifer and inform future hydrogeological modelling.
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Alluvial and fluvial fans are the most widespread depositional landform bordering the margins of highland regions and actively subsiding continental basins, across a broad spectrum of tectonic and climatic settings. They are significant to the local morphodynamics of mountain regions and also to the evolution of sediment-routing systems, affecting the propagation and preservation of stratigraphic signals of environmental change over vast areas.
The volume presents case studies discussing the geology and geomorphology of alluvial and fluvial fans from both active systems and ancient ones preserved in the stratigraphic record. It brings together case studies from a range of continents, climatic and tectonic settings, some introducing innovative monitoring and analysis techniques, and it provides an overview of current debates in the field.
This volume will be of particular interest to geologists, geomorphologists, sedimentologists and the general reader with an interest in Earth science.