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    The hydrogeology of the Pourewa sub-catchment, Rangitikei, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2020) Rees, Callum
    This story begins in the geologically young and active landscapes of the lower North Island of New Zealand, positioned astride the interface between the Pacific and Australian tectonic plates. The chosen field area is located within the onland Whanganui Basin, a Late Miocene-Quaternary marine basin that has undergone uplift, inversion and fluvial incision to form spectacular river valley exposures through the basin succession. The area contains one of the most complete records of Quaternary climate change exposed onland anywhere in the world. Our journey centres on a portion of this uplifted marine basin, characterised by the highly erodible, pastorally farmed hill country of the Rangitikei. The Pourewa Stream, a tributary of the Rangitikei River provides a cross section through rural landscapes of the lower North Island. The stream’s headwaters begin in steep Taihape sheep and beef country, before transitioning into a broad valley with a gentle gradient headed for Hunterville. The lower reaches step down across extensive Late Pleistocene river terraces, providing versatile arable cropping and dairy pasture, until finally joining the Rangitikei River 6 km east of Marton. Agriculture constitutes 90% of land use in the region, placing pressure on resources required for ongoing agricultural development and production. Recent concerns surrounding the long-term sustainability and potential contamination of freshwater resources have initiated research into the regions groundwater system. Previous studies have taken a broad approach examining large-scale issues surrounding classification, allocation, management and vulnerability of groundwater resources. This study takes a different approach by examining a single sub-catchment of the Rangitikei River, with the aim of developing a conceptual hydrogeological model for the Pourewa Stream area. The proposed model is underlain by a comprehensive stratigraphic investigation of the Quaternary succession in the central Rangitikei. Geological context is provided through the development of a 1:25 000 geological map series and accompanying structural interpretation. Hydrogeochemical datasets derived from targeted in situ and laboratory based analysis provide baseline information. The conceptual hydrogeological model is applied on a wider regional scale to investigate basin history and processes of landscape formation. The project aims to support policy makers, landowners and developers in achieving sustainable management of groundwater resources by the avoidance of over exploitation and contamination.
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    Characterisation and numerical simulation of the Lower Manawatu Catchment hydrogeological system : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Sciences at Massey University, Manawatu, New Zealand
    (Massey University, 2018) Zarour, Hisham Ibrahim Sabri
    The Lower Manawatu Catchment (LMC) hydrogeological system presents an example of extensive stratified heterogeneous aquifers. A conceptual model was developed for the system through systematic characterisation of its geology, soil, climate, hydrology, hydrogeology and hydrochemistry. Numerical groundwater flow modelling provided an effective integrated framework for the analysis. The developed knowledge and models are useful for the identification and comparison of land and water resources management options in the catchment. The research involved the development of a soil moisture balance modelling code to evaluate recharge. Stratigraphical modelling has been possible through incorporating imaginary lithological well logs and stratigraphical cross-sections in data-sparse areas. Geological material heterogeneity was represented in the groundwater flow model through hybridising zonal and pilot point calibration techniques. The developed soil moisture, geology and heterogeneity modelling techniques have universal applications. The study indicates that the LMC hydrogeological system is more suitably represented as a continuous groundwater flow system rather than a sequence of discrete aquifers and aquitards. Average groundwater recharge is estimated at about 25% of average rainfall. Average baseflow is estimated at about 10% of the average runoff, the equivalent to more than half the estimated average recharge. The LMC groundwater resource is mainly tapped at shallow depths, the locus where most of the interaction with surface water occurs. Catchment-scale steady-state numerical groundwater flow modelling suggests that in average groundwater abstraction may have been depleting overall surface water flow by about 5%. Groundwater levels in the LMC were found to be generally stable, implying sustainable resource development. Rising groundwater levels noted in the eastern and southern outskirts of Palmerston North may be related to prolonged practice of irrigation. No evidence of land use impacts on groundwater quality was found in the catchment. Nitrate concentrations are believed to have been kept at acceptable levels in groundwater due to denitrification stimulated by extensive organic content in some geological units. This thesis represents a one stop shop for information on groundwater in the LMC. The knowledge and tools developed through this research have immediate use in the LMC and elsewhere, and they provide solid basis for further work.
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    Hydrogeological investigations of the Palmerston North region : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science with Honours in Earth Science at Massey University
    (Massey University, 1990) Lieffering, Robert Ewout
    The Lower Manawatu River Valley and its major tributary the Pohangina River Valley are incised within the marine strata of the South Wanganui Basin. Lining each valley are a flight of both aggradational and degradational terraces. Three aggradational terraces are identified and correlated with the Ohakea, Rata, and Porewa terraces of the Rangitikei River Valley which aggraded during stadial periods of the Last (Otiran) Glaciation. The distribution of these terraces in the Lower Manawatu River Valley is discussed and their cover beds described. Previous river channels of the Manawatu River are identified by means of bore-log information. The nature and history of the Manawatu River has resulted in a sequence of clay, silt, sand, and gravel deposits which is exceedingly complex in detail. Cross-sections are presented which show this complexity. This has been the main factor influencing the distribution and nature of the aquifers in the region. Water is normally extracted from the coarsest deposits with 75% of the bores in the region obtaining water from gravel layers, 15% from sand layers, and 10% from sand/gravel mixtures. The aquifer system is considered to be "leaky" due to the complex arrangement of lithologies allowing water to flow both vertically and horizontally without much impedance. Depth ranges of 0-60 m, 60-120 m, and > 120 m below the ground surface are considered to be the closest resemblance to separate aquifers. Piezometric contour maps are presented which show an overall groundwater flow direction for all the depth ranges from east to west along the Manawatu River Valley with additional water influx from the Pohangina and Oroua River catchments. Transmisivities of the aquifer system ranges between 150-2000 m2/day and storativity between 1.1 × 19-4 and 3.2 × 10-4. Static water levels and discharge rates increase with depth and decrease from east to west. Nearly all the bores in the area are naturally flowing artesian, making the entire area a discharge zone. Recharge of the aquifer system is from two sources. Firstly, direct percolation of atmospheric precipitation, the main source areas being the Tararua Range, the Ruahine Range, and both the eastern and western flanks of the Pohangina Anticline, and secondly, river recharge. There is a significant loss (6,500 1/s) of water as the Manawatu River flows through the Manawatu Gorge which is identified as occurring in the vicinity of White Horse Rapids. This water loss is attributed to groundwater river recharge of shallow aquifers. Groundwater accounts for nearly 90% of total water use within this area and the estimated water extraction from the aquifer system is 120,000 m3/day (43 × 106 m3/year.) The hydrochemistry of the area is presented by way of isoconcentration contour maps. Total alkalinity, calcium, magnesium, chloride, electrical conductivity, potassium, manganese, sodium, and total dissolved solids increase from east to west within the research area. Free carbon dioxide, fluorine, and iron show no trend but have local "highs". Only sulphate shows an increase from west to east. The average concentrations for the various chemical parameters are: total alkalinity - 157 ppm, Ca - 104 ppm, Cl - 36 ppm, free CO2 - 11 ppm, conductivity - 43 mS/m, F - 0.16 ppm, Fe-2.1 ppm, Fe-2.1 ppm, Mg - 55 ppm, Mn - 0.38 ppm, nitrate - 0.02 ppm, Na - 23 ppm, SO42- - 10 ppm, and total dissolved solids - 256 ppm. Concentrations increase with depth for all the chemical parameters. Conductivity diagrams are presented which show extremely good linear relationships when plotted against all the major cations and anions. These diagrams have practical significance because conductivity is easy to measure in the field.
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    The role of substrate hydrogeology and surface hydrology in the construction of phreatomagmatic volcanoes on an active monogenetic field (Auckland, New Zealand) : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2015) Agustín Flores, Javier
    Phreatomagmatic activity is pervasive in the Auckland Volcanic Field (AVF) with more than two thirds of the erupted volcanoes showing this type of activity at different degrees, dominantly at the onset of their eruptive histories. In general, the volcanoes built in the northern AVF rest on Late Miocene Waitemata Group rocks (turbiditic siltstone and sandstone succession), whereas in the southern AVF the Waitemata rocks are overlain by tens of metres of Plio-Pleistocene, water-saturated sediments (Tauranga Group and Kaawa Formation). Identifying the control exerted by the type of substrate in the eruption dynamics of the phreatomagmatic phases of three volcanoes in the AVF is the objective of this study. The stratigraphic, sedimentary, and pyroclast characteristics of the phreatomagmatic sequences of Maungataketake, Motukorea, and North Head volcanoes, together with supplementary information on the geology and hydrogeology of the area, were investigated to solve the problem. Three phreatomagmatic eruptive scenarios were outlined. Scenario 1 (Maungataketake eruption) and Scenario 2 (Motukorea eruption) depict the formation of maar-diatreme volcanoes in the southern and northern AVF, respectively. The dominant presence of lithics from the upper part of the substrate in their tephra rings suggests the construction of their tephra rings from shallow-seated explosions. Due to the water-saturated sediments filling the diatreme in Scenario 1, the eruption appears to have remained relatively wet throughout. Conversely, the drier Waitemata rocks involved in Scenario 2 promoted a progressive drying of the eruption. Scenario 3 (North Head eruption) represents a Surtseyan eruption scenario in which the rising magma erupted to the shallow sea floor (a few metres-water depth), promoting rapid chilling and explosive fragmentation. This study shows that the characterization of lithics within the tephra ring and the geological and hydrogeological information provide valuable clues to envisage the degree of influence of the substrate in the phreatomagmatic eruption dynamics. Other studies in the AVF appear to confirm this view. It is proposed that any future phreatomagmatic eruption in the AVF will be strongly influenced by the substrate hydrogeology and geology, as well as the surface hydrological conditions.
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    Mio/Pliocene phreatomagmatic volcanism in the Western Pannonian Basin
    (Massey University., 2004-01-01) Martin, Ulrike; Nemeth, Karoly
    No abstract available