Through the application of downhole logging techniques an innovative assessment of density dependent groundwater flow has been undertaken that highlights the limitations of water level measurements for assessing groundwater flow in coastal environments. The method utilises an EM39 bulk conductivity log to calculate fluid conductivity/fluid density that was then used to convert measured point water head to freshwater head/environmental head to improve the understanding of groundwater flow at the creek. This method of assessing density dependent flow is unique and has not previously been demonstrated. The converted water levels showed that interpretation of groundwater flow is critically dependent on a detailed knowledge of both head and density. An assessment of the potential error in the conversion process indicated that, for the low gradients at the study site, misinterpretation of flow could occur due to errors inherent in the process. As a result, it is recommended that pressure transducers and loggers be used to monitor pressure in variable density systems so that Darcy???s equation can be used directly to calculate groundwater flow and direction. The thesis also presents the results of high-resolution geophysical mapping of the distribution of saline groundwater beneath a tidal creek. The mapping was used to develop a detailed conceptual model of the salinity distribution at a tidal creek that included: the presence of saline intrusion beneath the creek; saline groundwater overlying fresh groundwater due to surface flooding in extreme tide events; concentrated discharge of groundwater (comprised of brackish water due to mixing in the aquifer) at the creek banks; and, significant changes in the distribution of saline groundwater according to rainfall events and only minor changes over a tidal cycle. The conceptual model, geophysical site assessment, water level analysis and numerical modelling represents a multi-disciplinary approach to the assessment of the interaction of saline and fresh groundwater that has not previously been undertaken. Significant anisotropy was inferred from geophysical observations that indicated vertical flow in the borehole annulus. This observation is particularly significant and implies that even relatively short (1.0 to 2.0 m) screened wells may not yield accurate fluid conductivity and head values in variable density systems.
| Identifer | oai:union.ndltd.org:ADTP/272871 |
| Date | January 2010 |
| Creators | Dasey, Gregory R, Civil & Environmental Engineering, Faculty of Engineering, UNSW |
| Publisher | Awarded by:University of New South Wales. Civil & Environmental Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Dasey Gregory R., http://unsworks.unsw.edu.au/copyright |
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