Developing Kinematic Models of the Development of North West Shelf Basins to Quantify the Energy Resources

The Australian North West Shelf (NWS) has a complex geological history that has been affected by several phases of extension and rifting, creating features like the failed rift system in the Northern Carnarvon Basin (NCB). The NWS has been impacted by several regional tectonic events, most notably Gondwana’s dispersal and Australia’s collision with Southeast Asia. Such events created the various sub-basins of the Shelf and impacted the vertical and lateral – or kinematic – motions of these basins. To date, no studies have fully quantified the spatial and temporal distribution of these motions and their impacts on the region’s resource systems. This thesis proposes that accurate basin kinematic evolution models can reveal the time-dependent evolution of basins and how such evolution affects the development of resource systems in those basins. The NWS has a rich coverage of geological and geophysical datasets, hence an excellent location for building such models. I have built detailed kinematic evolution models of the Shelf basins using backstripping, decompaction and thermochronology techniques. The models extend vertical motion analysis from the traditional single-well analysis to accurate regional analysis by combining datasets from multiple wells and seismic sections. They also extend lateral motion analysis from traditional inter-plate analyses into intraplate settings to precisely reconstruct the pre-rift deformation of intracontinental rifts using novel methods. The thesis has modelled the spatial and temporal distribution of subsidence, rift-related lateral motions and exhumation in the NWS basins. The results reveal a northeast propagating rift in the NCB with rapid subsidence and sedimentation rates (up to 80 m/Ma) from the Jurassic to the Cretaceous. Based on this data, I developed a reconstruction model of this NCB rift system, which reveals multiphase anomalous rifting rates (8 mm/yr), correlating Gondwana dispersal events. The exhumation models reveal a complex multiphase Mesozoic-present exhumation of up to ~2.5 km across the NWS, likely caused by magmatic underplating, compression and depth-dependent extension. The exhumation impeded the development of various Jurassic-Cretaceous petroleum systems in the central Bonaparte Basin and the Exmouth Plateau, NCB. This thesis improves the understanding of the NWS basins’ evolution, considers the implications for CO2 and H2 storage locations, and has significant applications in resource exploration

Environmental tracers to evaluate groundwater residence times and water quality risk in shallow unconfined aquifers in sub Saharan Africa

In sub-Saharan Africa, shallow aquifer systems are relied on as the main safe and secure water resource available to rural communities. Information on the sustainability and vulnerability of groundwater abstraction is becoming increasingly important as groundwater development increases. As part of the UpGro Consortium Project- Hidden Crisis, 150 hand pumped boreholes (HPBs), ranging between 15 and 101 m depth were investigated to examine the resilience of aquifer systems in the Ethiopian Highlands, and the crystalline basement rocks of Uganda and Malawi. Environmental tracers (chlorofluorocarbons (CFCs), SF6, chloride and the stable isotopes of water), water quality indicators (nitrate and E. coli), and groundwater-level time series data were used to estimate groundwater residence time and recharge at a regional scale (100–10,000 km2) and investigate the risks to water quality and water supply over different timeframes, and geological and climatic environments. Average estimated recharge rates using three different techniques (CFCs, chloride mass balance, water table fluctuation method) were between 30 and 330, 27–110 and 30–170 mm y−1, for sites in Ethiopia, Uganda and Malawi, respectively. These estimates of recharge suggests abstraction from dispersed low-yielding HPBs is sustainable. Comparison of stable isotopes in rainfall and groundwater indicates that there is little evaporation prior to recharge, and recharge events are biased to months with greater rainfall and more intense rainfall events There was a weak correlation between nitrate and CFCs within all three countries, and no correlation between E. coli and CFCs within Ethiopia or Malawi. The presence of E. coli at a large proportion of the sites (Ethiopia = 38%, Uganda = 65% and Malawi = 47%) suggests rapid transit of contaminated surface water into the borehole and its presence in groundwater that has CFC-12 concentrations less than 75 pg kg−1 indicates mixing of very young water with water >40 years old. The rapid transit pathways are most likely associated with damaged HPB headworks and poor construction. In several monitored HPBs, daily drawdown due to pumping, drew the groundwater levels close to the base of the HPB, indicating that these HPBs were located in parts of the aquifer with low permeability, or were poorly designed, offering limited capacity for increased demand. Improved HPB siting and construction, coupled with groundwater level monitoring are required to capitalise on the more resilient groundwater within the shallow aquifers and safeguard adequate and good quality water supply for rural communities

Functionality and resilience of hand-pumped boreholes in sub-Saharan Africa

In sub-Saharan Africa as many as 184 million people rely on hand-pumps. Thus, hand-pumps are, and will remain, a crucial water source in a changing climate, although as many as one in three are non-functional at any time. Drawing on the results of three studies we demonstrate that hand-pumps are resilient and safe, and we examine the physical factors that determine hand-pump functionality. In the first study we analysed the performance of 5196 water points (hand-pumps, motorized boreholes, springs, open-sources) and the success of a proactive maintenance programme during the 2015-16 drought in Ethiopia. Water sources were visited every week for 12 weeks to gather data on access and functionality. The second study, again in Ethiopia, involved monitoring 51 groundwater points (hand-pumps, springs, hand-dug wells) over an 18-month period in 2016. Water sources were equipped with water level loggers and were tested monthly for thermo-tolerant coliforms. All sources were put under considerable strain during the drought. Most demand was placed on motorised boreholes in lowland areas. However, increases in functionality of motorised boreholes, as a result of the maintenance programme, lagged behind those of hand-pumps. Functionality was low for both sources at the on-set of the drought (65% and 75% respectively). Motorised boreholes had longer downtimes due to a lack of appropriate and/or accessible maintenance skills. Water level monitoring showed that hand-pumped boreholes recovered most quickly from daily abstractions. All sources were contaminated with thermo-tolerant coliforms during the rains marking drought cessation but hand-pumped boreholes were least affected. Our results show that hand-pumped boreholes are resilient and less prone to contamination than springs and hand-dug wells. However, like the other sources we studied, hand-pumps had low levels of functionality at the onset of the drought. To better understand the factors affecting functionality we systematically dismantled 150 hand-pumped boreholes in Ethiopia, Uganda and Malawi in 2017. We conducted detailed inspections of hand-pump components and borehole design. Water levels were measured and a pumping test was conducted to measure aquifer yield (transmissivity). In each country specific contextual factors influence functionality. In Ethiopia deep water levels (>60 m) strongly influence functionality. Many hand-pumps operate beyond lift limits (45 m). Aquifer yield is an order of magnitude larger for fully functional hand-pumps than partially functional hand-pumps in Ethiopia. In Uganda many hand-pumps are installed in aquifers with transmissivities close to the minimum required to sustain a hand-pump (c.1 m2/d). The use of galvanized steel components, along with corrosive groundwater, results in high rates of corrosion in Uganda. In all three countries hydrogeology, borehole design and pump condition interact to determine functionality outcomes. Our results reinforce the importance of appropriate borehole siting and design, on-going operation and maintenance and use of appropriate and good quality materials. When supported by responsive and proactive maintenance hand-pumped boreholes, which are less prone to contamination than other shallow groundwater sources, are a resilient water source in a changing climate and are capable of providing water continuously during drought