Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Filters

2018 - 20203

Settings

Subject: search.filters.subject.Hydrogeological modeling

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    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.
  • Thumbnail Image
    Item
    Accounting of nitrogen attenuation in agricultural catchments : 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, 2018) Elwan, Ahmed
    The transport and fate of the nitrate that leaches from the root zone of farms, via groundwaters, to receiving surface waters is poorly understood, particularly for New Zealand’s agricultural catchments. Monitoring nitrate concentrations in rivers clearly demonstrates that not all of the nitrate leached across the catchment enters the river. As nitrate moves from land to receiving waters there is potential for subsurface denitrification and hence the attenuation of the nitrate flux to receiving surface waters. A good understanding of the influence of catchment characteristics on the spatial variations of nitrate attenuation is essential for targeted and effective water quality outcomes across agricultural landscapes. This thesis analysed large datasets of geographical information (land use, soils and geology) and water quality records at 20 sites in two large agricultural catchments, the Tararua and Rangitikei, which are located in the lower parts of the North Island New Zealand. The results demonstrated that the influence of land use on river soluble inorganic nitrogen (SIN) concentrations in the Tararua catchment was outweighed by other catchment characteristics such as soil type and hydrological indices. A simple approach, that is not data-intensive, was developed and applied to quantify the capacity of a catchment to attenuate nitrogen. The nitrogen attenuation factor (AFN) is a key component of this approach. AFN is defined as the average annual land use nitrogen leaching losses minus the average annual river SIN river loads, divided by the average annual land use nitrogen leaching losses. AFN was determined for 5 and 15 sub-catchments in the Rangitikei and Tararua catchments, respectively, and was found to be highly spatially variable with values ranging from 0.14 to 0.94. To assess the uncertainty associated with AFN, the uncertainty in the average annual river SIN loads was evaluated. Five load calculation methods (global mean GM, rating curve RC, ratio estimator RE, flow-stratified FS, and flow-weighted FW) and four sampling frequencies (2 days, weekly, fortnightly, and monthly) were investigated to calculate average annual river loads at one of the long-term, representative water quality monitoring sites in the study catchment. The FS method using a monthly sampling frequency resulted in the lowest bias (0.9%) for average annual river SIN loads and therefore was used in the quantification of AFN across the study catchments. A robust uncertainty analysis of AFN showed two distinct groups of sub-catchments; sub-catchments with higher (>0.7) and less uncertain nitrogen attenuation factors, and sub-catchments with lower (<0.4) and more uncertain nitrogen attenuation factors. This supports the use and applicability of AFN as a sub-catchment descriptor of the capacity of a sub-catchment to attenuate nitrogen. AFN was positively related to poorly drained soils and mudstones, and negatively related to well-drained soils and gravels in the study catchments. A novel but simple hydrogeologic-based model was developed to evaluate the potential to use soil and rock indices to predict average annual river SIN loads from different land uses in a catchment. Four different versions of the model (uniform nitrogen attenuation, variable nitrogen attenuation based on soil indices only; variable nitrogen attenuation based on rock indices only; and variable nitrogen attenuation based on both soil and rock indices) were developed. Accounting for the spatial distribution of the nitrogen attenuation capacities of both soils and rocks resulted in markedly better predictions of river SIN loads in the Tararua and Rangitikei sub-catchments. The novel findings of this thesis clearly suggest that effective and targeted measures to improve water quality at a catchment scale should account not only for land use but also for other catchment characteristics, such as the subsurface nitrogen attenuation capacity. This new knowledge will be instrumental in the future development of the models and planning tools required to reduce the detrimental impacts of agriculture, by aligning spatially intensive land use practices with high nitrogen attenuation pathways in sensitive agricultural catchments.
  • Thumbnail Image
    Item
    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.