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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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    The use of radon and complementary hydrochemistry tracers for the identification of groundwater - surface water interaction in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management at the Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand
    (Massey University, 2015) Martindale, Heather
    Understanding how surface waters and groundwaters interact is an integral component of managing the influence of nutrient inputs to water quality. Knowledge of the potential nutrient loads from discharging groundwater is essential for meeting the bottom line nutrient concentrations in surface waters. Radon-222 is an emerging tracer for measuring groundwater-surface water interaction which has been underexploited in New Zealand. The aim of this research was to establish the potential of using radon for measuring groundwater and river water interaction in the New Zealand environment. Low and high resolution radon surveys were carried out in two gravel-bed rivers, the Hutt and Mangatainoka Rivers, in lower North Island of New Zealand. To provide accurate measurements of radon concentrations in surface waters containing very little radon, the development of a cost and time effective, simple and reproducible high sensitivity radon measurement method was investigated. Furthermore, the study aimed to assess the potential of using radon measurements in combination with concurrent stream flow gauging and other hydrochemistry data for providing more detailed information on groundwater and river water interaction processes. Radon measurements were found very helpful to identify groundwater discharge and recharge locations in both the Hutt and Mangatainoka Rivers. Furthermore, a high sensitivity radon analysis method was developed with a lower limit of detection of 0.006 BqL-1, a vast improvement on the direct count method, and offering practical advancements over previously published methods. This high sensitivity method was used to establish radon concentration thresholds to identify locations of groundwater discharge, potential groundwater recharge and hyporheic exchange in NZ gravel-bed rivers. In both studied rivers the groundwater discharge and potential recharge patterns identified by radon were not always matched by the concurrent flow gauging surveys, highlighting the ambiguity surrounding the use of concurrent flow gauging in gravel-bed rivers for mapping river gains and losses. In some sections of the studied rivers the concurrent flow gauging data indicated areas of groundwater recharge or discharge where the radon data showed the opposite process to be occurring. This has led to the conclusion that underflow beneath the gravels and other parafluvial exchange processes can cause the interpretation of concurrent flow gauging results to be misleading. Flow gauging combined with radon sampling gives a more conclusive picture of the groundwater and river water interaction processes in the gravel-bed rivers.
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    Simplified modelling of pollutant transport in naturally-layered aquifers : a thesis submitted for the degree of Philosophiæ Doctor (PhD), 2015 February, Institute of Natural & Mathematical Sciences, Massey University
    (Massey University, 2015) Ali, Amjad
    Chemical species such as tracers or dissolved pollutants fl ow along with the slow-moving water as it makes its way through the complex porous structure of the aquifer; during this process they are dispersed in different directions. The rate of dispersion depends on the geometric characteristics of the porous structure and speed of the fl uid. Generally, groundwater systems have layered structures determined by different events in the geological processes that formed them. The layers in a system have di erent physical properties, and their thicknesses are not uniform. This naturally layered structure is used here to advantage by discretizing them into almost horizontal layers, where each may have different geometrical characteristics such as thickness permeability, dispersivitiy, porosity, etc. The system of advection-dispersion equations that model the uid and species transport then have coeffcients that depend mainly on depth, but with a layer composition that may change with horizontal distance. The mean dynamic pressure (or mean hydraulic head) may be assumed constant vertically at each horizontal point if it is not in the vicinity of a well or where there is very small vertical ow. In the vicinity of recharge or pumping wells, the mean dynamic pressures or hydraulic heads for each sub-layer of the aquifer may be allowed to have different values for each different sub-layer. Steady-state fl uid fl ow is considered in this thesis in both confined and phreatic (unconfined) aquifers.