Massey Documents by Type

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

Browse

Subject: search.filters.subject.Sediment transport

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Quantifying bed stability : the missing tool for establishing mechanistic hydrological limits : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Geography at Massey University, Palmerston North, New Zealand
    (Massey University, 2018) Neverman, Andrew J.
    Sediment transport processes are a key mechanism of ecological change in riverine systems, and certain levels of sediment flux are necessary for healthy ecosystem functioning. Altered flow regimes and sediment mobility are contributing to a global problem of higher substrate embeddedness reducing the frequency of substrate scour events and leading to increases in periphyton accrual. Excess periphyton accrual leads to fish and invertebrate kills from oxygen depletion, degraded ecological health, altered sediment dynamics, deterioration in water taste, and odour nuisance. In recent decades, reports of toxic periphyton proliferations have increased and are linked with health problems in humans including asthma, skin rashes, liver damage, and the death of domestic dogs. Excess periphyton accrual is prominent in impounded catchments where dams have a considerable impact on flow and sediment regimes. With at least 3,700 large dams currently under construction or in the planning phase the problem is set to increase in the foreseeable future. Hydrological limits are widely implemented by authorities in an attempt to manage periphyton accrual. Hydrological limits are frequently based on flow-ecology relationships but are often ineffective. Sediment transport thresholds have been found to have a better relationship with periphyton accrual than hydrological metrics. Flow-ecology relationships do not account for the mechanisms of periphyton removal (scour, abrasion, and molar action) which are likely to vary between sites at equivalent flows, and the species-specific resistance to each mechanism also likely varies. Abrasion and molar action result from transport of sediment. Improving the effectiveness of hydrological limits as a tool for river management therefore relies on setting flows with the aim of inducing sediment transport to initiate mechanisms of periphyton scour. This will require models which can accurately predict the flow required to induce different phases of sediment transport. The research presented in this thesis focuses on improving the estimation of gravel entrainment to advance entrainment models as a means of setting hydrological limits to induce molar action and improve the effectiveness of periphyton removal. A literature review of methods for estimating gravel particle entrainment thresholds in natural channels revealed a considerable gap in methods being available to quantify substrate characteristics to calculate resistance thresholds. The review also found significant challenges in identifying the onset of gravel transport in natural channels, and difficulty obtaining corresponding hydrodynamic data to identify entrainment thresholds. Further, the review found seepage was an important component of hydrodynamic forces for inducing particle entrainment in flumes, but seepage is not considered in conventional entrainment formulae, and is not measured alongside bedload transport data in the field. A suite of tools is identified and developed to improve the quantification of substrate structure and resistance, identification of incipient motion, and quantification of entrainment thresholds in natural gravel beds to advance the assessment of bed mobility. Optical and ranging techniques are compared to identify an optimal approach to remotely quantify substrate structure. Both approaches were found to produce a comparable quantification of surface roughness using point cloud elevations, but identified different trends in surface layer development. Quantification of surface layer development was found to be sensitive to the cell size used to grid the data, and this sensitivity increased with higher-order statistical moments which were used to describe armouring. Airborne optical sensors were found to be the most versatile method for remote characterisation of gravel-bed surface structure, with a larger range of metrics being derivable from the same dataset to quantify a wider range of substrate structural and textural characteristics. Whilst quantifying bed structure is critical for developing bed mobility models, measuring the resistive force of the bed created by the structural arrangement of particles is required for model calibration and empirical data collection. A protocol was developed to use a modified penetrometer to quantify the resistive force of the armour (active) layer in gravel-bed channels. The modifications made to the penetrometer made it sensitive to variations in armour layer compactness, and allowed for adaptive penetration depths enabling variations in armour layer thickness to be accounted for. The protocol and modified penetrometer provide a significant advancement in the ability to empirically quantify bed resistance and relate bed structure to potential bed mobility, and build on the remote sensing methods to provide a suite of bed resistance parameters for entrainment models. Measurement of bed mobility is also critical for calibrating entrainment models and relating ecological metrics to bed mobility thresholds. Both direct and indirect measurement of bed mobility have benefits for research and river management. Tick-box indices are frequently used in ecological studies to provide an indirect assessment of substrate (in)stability (i.e. bed mobility). These indices often provide a poor approximation of bed mobility, and do not relate well with biotic communities, but their low-cost and rapidity make them a valuable tool for research and management. An improved index is developed to provide rapid, low-cost assessment of bed mobility. This index improves on previous methods by focusing on objective measurements of parameters where low-cost approaches are available, or providing a framework for scoring parameters where visual assessment is required. The index scores correlated well with tracer particle data, and were found to relate to accrual of Phormidium biomass. This index therefore provides a means to rapidly and cost-effectively estimate bed mobility and predict periphyton accrual. Direct measurement of bed mobility is also required to provide an empirical dataset for the calibration of particle entrainment and transport models, and for the empirical derivation of hydrological limits. A multi-sensor system was developed to measure the onset of particle movement, and record corresponding hydrodynamic data, including bed seepage, to identify hydraulic entrainment thresholds in natural channels, and therefore address the challenges of identifying bedload entrainment thresholds identified in the literature review. A pilot study testing the system identified bed seepage and turbulence intensity as key predictors of particle entrainment, and discharge and mean velocity as the worst predictors. These findings challenge the use of discharge and mean velocity as the metrics used to set hydrological limits if mechanistic limits based on bed mobility-ecology relationships are to be established effectively. These tools provide a means for scientists to study bedload entrainment and transport, identify their thresholds, and relate the frequency and magnitude of these processes to benthic community dynamics. This research will form the basis for establishing the mechanisms required to achieve removal of excess periphyton and establish hydrological limits to ensure these mechanisms function and effective removal of periphyton is achieved to maintain ecosystem health.
  • Thumbnail Image
    Item
    The clay mineralogy and erosion of the Waipaoa River catchment, Gisborne, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Quaternary Science at Massey University
    (Massey University, 2002) D'Ath, Michele Annette
    The Waipaoa River Catchment lies N-NW of Gisborne, covering 2181 km2 it drains south into Poverty Bay 10 km SW of Gisborne. It carries approximately 15 million tonnes of suspended sediment annually, ranking it as one of the most sediment - laden rivers in the world. Deforestation in the early 1900's has led to severe landslide and gully erosion. To assist in catchment analysis and sediment budgeting, Landcare Research divided the Waipaoa River Catchment into 16 land systems, based on the Land Resource Inventory; principally rock type and erosion type and severity. Four of these land systems were chosen to test the hypothesis that clay mineralogy will influence whether landslide or gully erosion is dominant. And, if mineralogical signatures could be established for the different land systems, they could be traced downstream onto the floodplain and into the marine environment. There is no consistent mineralogical difference between the two chosen landslide dominated land systems and the two gully dominated systems. The Mangatu Land System is dominated by gully erosion. Samples taken from the Tarndale Gully complex within the Mangatu Land System for example, are dominated by quartz in the clay fraction, whereas gullies in the Waingaromia Land System are dominated by mica and smectite. The landslide dominated Te Arai Land System, like the Waingaromia Land System, is also primarily mica and smectite, while the clay minerals of the Mako Mako Land System consist of mica and the clay - sized mineral feldspar. It appears that tectonic influence of uplift and faulting, and its influence on headward erosion by streams, is most important in predisposition to gully erosion. The Mangatu Land System dominates the clay mineralogy of both the bedload and suspended sediment of the Waipaoa River at normal flow. However, dilution of this signature does occur at Te Karaka with the influence of the Waingaromia, Waikohu, and Waihora Rivers. In major flood events during high intensity storms, landsliding is more prevalent. Floodplain sediments are thus predominantly soil mantle materials derived from shallow landsliding and bare little resemblance to the dominant Mangatu Land System sediments. Whereas, the Poverty Bay marine core MD2122 sediment, representative of the annual Waipaoa River sediment yield, is produced by the continuous gully erosion. The effect of differential settling gives the core mineralogy a similar signal to that of the floodplain cores; however, sediment is considered to be predominantly Cretaceous material.
  • Thumbnail Image
    Item
    Downstream fining in the Waipaoa River : an aggrading, gravel-bed river, East Coast, New Zealand : thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Quaternary Geology at Massey University
    (Massey University, 1997) Rosser, Brenda J
    The Waipaoa River, East Cape, New Zealand, drains a catchment from the Raukumara Ranges into Poverty Bay, near Gisborne. Conversion of the catchment from indigenous forest to pasture, between 1880-1920, initiated a phase of intense erosion in the hill country. The underlying geology consists of crushed and sheared sandstone, siltstone, argillite, and mudstone of Cretaceous and Tertiary age. Channel aggradation occurred in response to the influx of bed material load. Suspended sediment yields in headwater catchments are as high as 7 000 – 17 000 t km. For the period 1948 to 1988, aggradation in the upper reaches was > 5 m, while in the lower reaches it was ~0.5 m. The Waipaoa River is a gravel-bed river. Its morphology changes from a braided to a meandering configuration in the downstream direction. A bed material survey of the Waipaoa River in 1995/6 investigated the fluvial transfer of coarse bed material through the river system. Bed material samples were collected at 1 km intervals along the mainstem, as well as from major tributaries, near their confluence with the Waipaoa River. Surface and subsurface samples were systematically collected between the coast and 104 km upstream. The results of this survey were compared with earlier bed material surveys undertaken in 1950, 1956, and 1960. Results of the 1996 bed material survey indicate that the bed material in the Waipaoa River is polymodal. The gravel-sand transition occurs approximately 8 km upriver from the coast. Over the remaining 96 km reach, the median particle size declined from 5 mm in the headwaters, to 2 mm near the coast. The coarser particle size fractions exhibited a greater rate of downstream fining, and, over the same distance, the coarsest 10% declined from 48 mm to 6 mm. The bed material is dominated by fine sediment, which is illustrated by the fine median particle size over the length of the river, as well as the low fining coefficients for the finer particle size fractions . No downstream change in the proportion of each main pebble lithology was observed, and each pebble lithology exhibited a similar rate of downstream fining. No downstream alteration in particle shape was observed, although particle roundness did increase downstream. Close relationships were observed between the bed slope and particle size. The highest degree of correlation was observed between slope and the coarsest particle size fractions, representing the limiting condition of channel competence. Selective transport is the dominant process that produces downstream fining in the Waipaoa River, however, particle fragmentation, sediment supply or abrasion may be important processes within specific reaches. The rate of downstream fining was consistent for the period 1948 to 1996.
  • Thumbnail Image
    Item
    A DEM based investigation of mass movement sediment delivery : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Soil Science, Massey University
    (Massey University, 1998) Lovell, Leyton Richard
    Environmental legislation in New Zealand has required local and regional government to place a greater emphasis upon the external effects of land use. For New Zealand hill country this means a quantitative understanding of accelerated soil erosion in terms of its effects upon downstream sedimentation and subsequent flood events. This study was an investigation into the spatial distribution of soil slip erosion (NZLRI) for the Waipaoa River Catchment (~2204km2), East Cape, New Zealand. A combined Remote Sensing and GIS approach using orthorectified aerial photographs and digital elevation models was employed to investigate the topographic attributes influencing the spatial pattern of erosion, utilising a series of classified erosion maps. Of the variables examined, slope, aspect, elevation, and the soil moisture index (SMI) were quantitatively reaffirmed as controlling influences upon mass movement. The erosion maps in conjunction with hydrological flow accumulation images were also found to objectively determine thresholds for identifying stream channel networks from the DEM. The erosion maps when combined with historical data were used to construct sediment delivery ratios and sediment budgets for each landsystem investigated. The most significant influences upon landsliding were combined in a data driven model to assign a probability of landsliding for each pixel, which can later be used to create landslide susceptibility maps and assist in the allocation of soil conservation resources. Keywords: ORTHORECTIFIED AERIAL PHOTOGRAPHS, DEMs, SOIL SLIP EROSION, SEDIMENT DELIVERY RATIOS, SEDIMENT BUDGETS