1.3. the Poverty Bay Flats
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http://researchcommons.waikato.ac.nz/ Research Commons at the University of Waikato Copyright Statement: The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). The thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: Any use you make of these documents or images must be for research or private study purposes only, and you may not make them available to any other person. Authors control the copyright of their thesis. You will recognise the author’s right to be identified as the author of the thesis, and due acknowledgement will be made to the author where appropriate. You will obtain the author’s permission before publishing any material from the thesis. Managed Aquifer Recharge in the Poverty Bay flats? A thesis submitted in fulfilment of the requirements for the degree of Master of Science in Earth Sciences at The University of Waikato by George Hampton 2015 Abstract Groundwater use within the Poverty Bay flats has increased over the past 35 years due to land use changes. As a result, groundwater levels within the Makauri and Matokitoki Gravel aquifers are declining at statistically significant rates. The GDC is investigating whether managed aquifer recharge (MAR) can be used to help achieve the sustainable management of groundwater resources within the Poverty Bay flats. The objective of this research is to identify whether an infiltration basin may be successfully used to artificially recharge the Makauri Gravel aquifer beneath the Poverty Bay flats. Trend analyses were undertaken to provide updated information as to the current state of groundwater resources. Groundwater levels within the Te Hapara Sands, Shallow Fluvial Deposits, and Waipaoa Gravel aquifers are typically stable. However, further monitoring is needed within these aquifers to increase the spatial coverage of the bores monitored. Groundwater levels within the Makauri and Matokitoki Gravel aquifers are declining at statistically significant rates. These declines are probably due to groundwater abstractions. Groundwater level changes as a result of rainfall event and associated changes in river stage were examined. Groundwater level changes in the Te Hapara Sands, Shallow Fluvial Deposits, and Waipaoa Gravel aquifer were all dependent on the location of each bore. Groundwater level increases in these aquifers were greatest in close proximity to the Waipaoa River. Groundwater level changes within the Makauri Gravel aquifer could be broken into two groups. In the northern and southern reaches of the Makauri Gravel aquifer groundwater levels increased and declined in conjunction with river stage, indicating little recharge occurs in these areas. In the middle reaches of the Makauri Gravel aquifer groundwater levels increased throughout the monitoring period, indicating that this area of the aquifer is subject to significant amounts of recharge. i A pumping test was undertaken to identify if a hydraulic connection existed between the Makauri Gravel aquifer and the overlying Waipaoa Gravel aquifer in the Caesar Road area. No hydraulic connection was identified. Further research is needed in this area to identify if a hydraulic connection does exist, and if so, to evaluate the vertical exchange of groundwater. Surface-groundwater interactions were analysed via concurrent Waipaoa River flow gaugings. No consistent gaining or losing reaches were identified. Further gaugings should be undertaken regularly to help characterise surface-groundwater interactions. Two sites were then identified within the Poverty Bay flats for MAR using infiltration basins using the “HIGGS Index”, which was developed to evaluate the MAR potential of an infiltration basin site. While the two sites showed initial promise via a desktop study, infiltrations tests at each site indicated low rates of saturated hydraulic conductivity due to the presence of sediments with low permeability. Subsequently, the MAR potential of both sites was low. Hydrogeological modelling was undertaken to ascertain whether an infiltration basin may be successfully used as a MAR technique to artificially recharge the Makauri Gravel aquifer. Modelling indicated that an infiltration basin would result in hydraulic head increases of up to 0.85 m within the Makauri Gravel aquifer. However, infiltration rates must not exceed 0.0425 m/day (10.625 m3/day) to avoid inundation at the ground surface in close proximity to the infiltration basin. Therefore, given the low infiltration rates it is questionable whether the benefits of establishing and operating an infiltration basin within the Poverty Bay flats would outweigh the costs. ii Acknowledgements This thesis could not have been completed without contributions from the following people: Associate Professor Earl Bardsley (primary supervisor, University of Waikato) for proposing and agreeing to supervise this project. Your advice throughout the duration of my research was invaluable. Paul White (secondary supervisor, GNS) for sharing your knowledge of the groundwater system within the Poverty Bay flats. Your expertise and advice throughout the duration of this project was much appreciated. Dennis Crone, Paul Murphy, Greg Hall, and Peter Hancock (Gisborne District Council). Without your input and help along the way I could not have completed this project. It has been an enjoyable experience working with you. I hope that this thesis is in some manner beneficial to you. Clare Houlbrooke, Bob Bower, and Brett Sinclair (Golder Associates) for the providing advice and generously allowing me to use some of your infiltrometer. To the landowners who gave me access to their bores and in some cases allowed me to dig up their land. I appreciate your generosity. My family and friends for encouraging me to chase my dreams. Your support is valued. Kelsey for your unwavering support for which I am incredibly grateful to have. Lastly, this project was not possible without the generous financial support provided by the University of Waikato Masters Research Scholarship, the Broad Memorial Fund, and the New Zealand Hydrological Society Project Fund grant. Thank you for thinking I was worthy of your funding. iii Table of Contents Abstract ............................................................................................................................ i Acknowledgements ................................................................................................... iii Table of Contents ........................................................................................................ iv List of Figures .............................................................................................................. vii List of Tables ..................................................................................................................x Chapter 1 – Introduction ........................................................................................... 1 1.1. Groundwater in New Zealand .................................................................................. 1 1.2. Groundwater Management ....................................................................................... 2 1.3. The Poverty Bay flats .................................................................................................. 3 1.4. Research Objective ...................................................................................................... 4 1.5. Thesis Structure ............................................................................................................ 4 Chapter 2 – Theoretical Review ............................................................................. 5 2.1. Introduction ................................................................................................................... 5 2.2. Groundwater .................................................................................................................. 5 2.2.1 Groundwater & aquifer properties .............................................................................. 5 2.2.2 Groundwater recharge & discharge ......................................................................... 10 2.2.3 Groundwater flow ............................................................................................................ 11 2.3 Groundwater management in New Zealand ..................................................... 15 2.4 Managed aquifer recharge ...................................................................................... 16 2.4.1 Managed aquifer recharge methods ......................................................................... 17 2.4.2 Infiltration basins ............................................................................................................. 19 2.4.3. Case Study – Roys Hill artificial recharge scheme ............................................. 20 Chapter 3 – The Poverty Bay Flats ....................................................................... 24 3.1 Introduction ................................................................................................................. 24 3.2 Geology ........................................................................................................................... 26 3.3 Groundwater system ................................................................................................. 27 3.3.1 Te Hapara Sands ..............................................................................................................