Waterways Centre for Freshwater Management: Theses and Dissertations

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Open Access
Sustainability impact assessment of a proposed hydropower infrastructure project : a case study of the Lake Onslow Pumped Hydro Scheme, New Zealand.
(2022) Phetpasak, Khemaksone
In 2015, New Zealand and other UN Member States adopted the 2030 Agenda for Sustainable Development and the Paris Agreement. Central to the 2030 Agenda are the 17 Sustainable Development Goals (SDGs), whereby SDG7 ‘ensure access to affordable, reliable, sustainable and modern energy for all’ plays a significant role in achieving other SDGs and the Paris Agreement on climate change. Hydropower has been one of the popular renewable energy options pursued by many nations to achieve such goals. With more than 80% of its electricity supply already renewable, New Zealand seeks to fulfil its climate commitment by achieving a 100% renewable electricity system. The aims of this study were to examine the sustainability impact of the proposed Lake Onslow pumped hydropower project using the Hydropower Sustainability Assessment Protocol (HSAP) framework; to assess the applicability of the framework to this case; and to recommend how the framework might be improved to make it more suitable for assessing sustainability impacts of infrastructure projects in local contexts. Through a triangulated approach of data collection, drawing on: semi-structured interviews with local stakeholders and rūnanga, expert interviews, and analysis of published case studies of international hydropower projects, I examined a range of perspectives on the proposed project as a case study. The HSAP – Early Stage Assessment framework is helpful when assessing potential sustainability impacts of the Lake Onslow project, despite a need for further refinement. The study found that the Lake Onslow project, if carefully planned, could be a solution to addressing the ‘dry year’ energy security problem in New Zealand. However, several factors would need to be thoroughly investigated before a final decision could be made on whether to proceed with the Lake Onslow scheme. The natural environment, endemic species, trout fisheries, and downstream impacts need comprehensive investigation to understand how lake level variations will impact on these ecosystems. Social and cultural impacts, and indigenous values also need careful consideration. A strategic plan should be devised to manage disruption, safeguard ecological sites, and address compensation issues. Notably, ensuring benefits are equitably distributed across the community will be crucial. Ultimately, the sustainability impact of a project significantly depends on public acceptance and participation. New Zealand could benefit from the proposed Lake Onslow project to address the energy security challenge, while reducing carbon emissions if local perspectives and international lessons from past failures of hydropower projects are seriously considered.
Open Access
Characterising groundwater-surface water exchange in the Waikirikiri Selwyn River, using radon
(University of Canterbury, 2021) Robb, Linda
Quantifying groundwater–surface water interactions in braided rivers has considerable uncertainties, due to the dynamic nature of the river system and the heterogeneity of the sediments. The ability to quantify recharge rates to groundwater from these complex systems is of vital importance for freshwater management. Environmental tracers such as radon have proven to be useful tools to aid in characterising groundwater–surface water interactions in other settings. This research investigates the spatial variability of radon equilibrium concentrations in the braid plain sediments of the upper Waikirikiri Selwyn River, Canterbury, New Zealand. This is important because previous studies have assumed the radon concentration within the sediments is evenly distributed. Sediments were collected during the drilling of monitoring wells in the braid plain of the Waikirikiri Selwyn River. These monitoring wells were drilled through two geological formations, the Springston Formation (0–6 m) and the Burnham Formation (6-16 m). Grain size analysis was carried out on 32 sediment samples. Following this, 318 radon equilibrium experiments were carried out on samples from across the study site. Grain size fractions from one of the installed piezometers, Selwyn 5, were also used in the radon experiments. Analysis of sediment cores revealed a heterogeneous structure. The grain size analysis presented relatively consistent distribution curves showing a large range in grain size fractions. Hydraulic conductivity values were estimated from the grain sizes using a number of empirical formula and were found to vary vertically and spatially depending on the percentage of core recovery and formula used. The values ranged from ~ 80– >1,000 m/d. The calculated porosity ranged from 0.18 to 0.3 and bulk density values ranged from 1400 kg/m3 to 1700 kg/m3 and were similar to studies within the same region. Radon equilibrium concentrations of water samples were tested after the water had been in a sealed jar with the sediments for 30 days, until secular equilibrium was reached. It was evident from the 318 samples analysed that radon concentration varied with differing grain size. Specifically, the <63 μm fraction contained significantly more radon than the other grain size fractions sampled. When comparing the spatial variability with the Springston and Burnham formations it appears that the radon concentration increases with depth within both these formations. This study has provided baseline data within the research site on the radon equilibrium concentrations both spatially and within differing grain size fractions. The results suggest that radon concentrations in groundwater depend on the volume of silts and clays in the subsurface. Therefore, using radon as a tracer for groundwater–surface water interactions may be more complex than first thought.
Open Access
Groundwater discharge and hydrogeochemistry in a nutrient-rich coastal lagoon.
(University of Canterbury, 2021) Coluccio, K. M.
Coastal lagoons provide important wetland and aquatic habitat and food resources. These valuable cultural and recreational sites are also home to some of the world’s most developed coastal communities. Yet they are often significantly influenced by anthropogenic activities and face many pressures such as habitat degradation, eutrophication, draining and land development. Ongoing research has shown that groundwater discharge plays important roles in coastal biogeochemical processes and water quality. However, groundwater input to coastal water bodies has frequently been discounted as an important component of water and nutrient budgets, largely because groundwater seepage is difficult to measure. This thesis addresses this gap by investigating groundwater processes in a large, nutrient-rich coastal lagoon in New Zealand: Te Waihora (Lake Ellesmere). I first identified where discharge locations occur. Traditional conceptual models of groundwater seepage distribution place most seepage near the margins of lakes and lagoons. The first part of this thesis research set out to test the validity of this model in a geologically heterogeneous lagoon. I carried out an airborne thermal infrared imaging survey and spatial surveys (measuring 222Rn—a naturally occurring groundwater tracer and other physicochemical parameters) by boat in two seasons. The initial survey concentrated on the margins of the lagoon. I found evidence of diffuse seepage, as well as point-source seepage (i.e., springs) on mudflats and on the lagoon shore. Signs of groundwater seepage were concentrated on the northern and western sides of the lagoon. I later conducted a more comprehensive spatial survey with a high-density sampling grid to identify artesian aquifers discharging to the lagoon. However, I found no significant signs of freshwater inputs away from the lagoon shore. I did find new evidence of freshwater along the lagoon-barrier interface, which I hypothesised is either sourced from upwelling inland-sourced groundwater from underneath the lagoon or seepage from the surface aquifer on the mixed sand and gravel barrier. Previous work based on seepage meter measurements estimated that groundwater discharge to Te Waihora was a small component of the lagoon’s water budget. I built on earlier work using a method at a broader scale than seepage meters—radon mass balances. These models showed that groundwater seepage to the lagoon was 1-2 orders of magnitude greater than previous estimates. Groundwater discharge estimates to the lagoon ranged from 5.2 ± 5.8 m3/s to 18.7 ± 19.6 m3/s during summer and 0.9 ± 2.2 m3/s to 8.1 ± 10.5 m3/s during winter. Wind-driven radon degassing to the atmosphere was the most influential variable in the model. I carried out an in-depth uncertainty analysis and found that the most sensitive parameters in the model were radon degassing, as well as lagoon surface area and volume; the radon in groundwater endmember; and the average radon concentration in the lagoon surface water. Finally, I carried out a hydrogeochemistry survey to distinguish groundwater sources to Te Waihora and shed light on their contribution to nutrient transport to the lagoon. I analysed major ions, stable water isotopes, trace metals and nutrients in lagoon surface water, porewater (shallow nearshore groundwater), existing groundwater wells and springs. Groundwater seepage split into two groups: (1) Inland samples with low ion concentrations, dominated by Ca2+ and HCO - ions and more negative oxygen-18 and deuterium ratios, and (2) permeable barrier samples with higher ion concentrations, dominated by Na+ and Cl- ions and more positive oxygen-18 and deuterium ratios. The ion and stable isotope chemistry imply that inland seepage is sourced primarily from alpine river recharge and inland rainfall recharge, while barrier porewater is comprised of mainly mixing with lagoon surface water and localised rainfall recharge on the barrier. The study did not find evidence in the barrier porewater of freshwater inputs from upwelling artesian groundwater from under the lagoon. Analysis of porewater samples showed evidence of potential denitrification on the lagoon margins attenuating nitrogen inputs. In contrast, dissolved reactive phosphorus was elevated in porewater, suggesting phosphorus mobilisation in nearshore anoxic groundwater. Seepage-derived nitrogen inputs were only 3% of dissolved inorganic nitrogen river inputs, but the phosphorus groundwater load was 30% of river inputs. While previous studies assumed groundwater discharge played a minor role in the hydrology and water quality of Te Waihora, the results of this thesis highlight that groundwater is an important component of both the water and nutrient budget at this site. This research underscores that groundwater discharge in coastal environments should not be discounted. These results also highlight the value in studying lagoon types that do not feature as prominently in the international literature, such as those in temperate climates with gravel barriers and managed openings to the sea.
Open Access
Developing a numeric groundwater model to capture the interactions of the Selwyn River/Waikirikiri and local groundwater.
(University of Canterbury, 2021) Clark, Daniel
In recent years summer flows in the lower Selwyn River/Waikirikiri have dropped to very low levels and this has led to questions being raised about what is causing these low flows. When the Selwyn River at Coes Ford dried in February 2017, this was the first time that the lower Selwyn had not maintained permanent flow at this location since records began at the site in 1984. This dry period generated wide public interest in the river flows and the impacts of both climate and abstraction. As directly measuring the independent effects of climate and abstraction on flow was not possible in the Selwyn Catchment, a desktop study using existing data was undertaken. This study utilised conceptual understandings, analytical methods, and numeric modelling to better understand the drivers of low flows. As summer flows in the lower Selwyn River are spring- fed, the interactions between surface water and groundwater were a key component which needed to be captured in this study. To do this, a MODFLOW groundwater model was developed to simulate changes in groundwater levels and surface water flows. While model development and testing were the main area of focus, this was complemented by trend analysis carried out for rainfall and flow measurement sites within the study area. The GMS interface was used to implement the MODFLOW code, using a five-layer model and a uniform 1 km grid. Model parameters were adjusted to calibrate observed steady state (average) groundwater levels and lowland stream flows. Once calibrated, the model was used to test changes in recharge and abstraction. This indicated that both could influence groundwater levels, river flows and the extent of the dry reaches in the Selwyn and Irwell Rivers. By converting from a steady state to transient model, the daily changes in longitudinal flows were able to be simulated. Trend analysis was caried out using the Mann-Kendall test, which indicated that flows in the summer months (December- April) in the lower Selwyn River are showing significant declining trends. These declines are not observed in the upper Selwyn River, the other surrounding rivers, or in rainfall within the study area. While the trend analysis alone does not fully explain the causes of the declining flows, it does rule out rainfall within the catchment and inflows from the hills as being the drivers of the decreasing flows. The converging lines of evidence from the trend analysis and numeric modelling suggest that the changes in recharge drive the year-to-year variability but that the effects of abstraction are the likely cause of the longer-term declining trends. This means that the year-to-year variability is overlaid on a long-term declining trend. In more recent dry seasons, the flows in the lower Selwyn River are lower than the flows which would have occurred in historic dry seasons with lower levels of abstraction. Scenario testing also indicated that the decline in flows and extent of dry reaches could worsen if abstractors used a greater portion of their authorised volumes.
Open Access
Mechanisms of dissolved Zn and Cu retention by mussel shells in a rapid-flow stormwater treatment system.
(University of Canterbury, 2021) Skews, Rachel Anne
Dissolved zinc (Zndiss) and copper (Cudiss) are a threat to aquatic life, but continue to enter urban waterways largely via stormwater passing over the roofing and cladding materials ubiquitous in the urban environment. Typical stormwater treatment is aimed at removing particulates, so a retrofittable inline downpipe device was developed (the Storminator™) to remove dissolved metals from roof runoff prior to it reaching the stormwater network. The device with its waste seashell media inside had previously been shown to be effective at removing Zndiss and Cudiss (>80% removal for both metals), but the mechanisms of removal were unconfirmed. Research into metal retention mechanisms by biogenic calcium carbonate (CaCO3) such as seashells had so far been limited to higher metal concentration solutions and longer contact times than are relevant to the Storminator™ system. In addition to this, modelling to predict removal mechanisms carried out prior to this research was largely confined to mathematical correlation, with no basis in potential geochemical causal pathways. Therefore, this study aimed to determine the dominant Zn and Cu removal mechanisms occurring in a Storminator™ style system, using geochemical modelling to augment chemical and spectroscopic methods of analysis. Geochemical models, such as PHREEQC, can predict when a mineral will be oversaturated in a given solution, or adsorbed to a surface such as hydrous ferric oxide (HFO), by balancing known thermodynamic equations for their formation. Therefore, predictions of how much Zndiss or Cudiss could be removed from solution by those mechanisms were made using PHREEQC. These predictions were validated against Zndiss and Cudiss reductions measured in flow-through column experiments, and evidence of either mechanism was sought through analysis of used shells. Shells which had been exposed to high loads of Zn or Cu were subjected to a sequential extraction procedure (SEP), which is designed to release elements bound in one specific chemical phase at a time. The shells were also analysed by scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDS), to look for evidence of precipitates or adsorption by visual identification of particulates and elemental concentration mapping. Flow-through column results showed reductions of 73%–97% for Zndiss and 55%–82% for Cudiss, for concentrations typical of roof runoff, and that ranged over 2 orders of magnitude (Zndiss ≈ 0.3–3 mg/L, Cudiss ≈ 0.5–3 mg/L). PHREEQC geochemical modelling suggested that no stable Zn minerals were predicted to form at the measured pH, while Cudiss could have been reduced by up to 99% by precipitation of Cu hydroxide carbonate minerals. Further PHREEQC modelling suggests there was insufficient HFO present for adsorption onto this mineral to be a dominant removal mechanism for Zn or Cu. The sequential extraction of used seashell media released the largest proportions of Zn from the “carbonate” fraction. Cu was predominantly released from both the “carbonate” and “Fe oxides” fractions, though it appeared that larger proportions of Cu and Zn were released in the “Fe oxides” fractions when total Cu or Zn concentrations on the shell were low. SEM-EDS analyses of used media rarely highlighted ‘hotspots’ of high concentrations of Zn or Cu, instead generally showing low levels uniformly spread through the shell structures. The rare SEM-EDS analyses where Zn was concentrated in visible particles were of shells that had been exposed to high initial Zn concentrations (27 mg/L Zn), and these appeared to be either hydrozincite (a Zn hydroxycarbonate) or a Zn/Na/Al/Si based compound. Results suggest that adsorption to the calcium carbonate shell surface dominates removal mechanisms for Zn, and that the formation of surface precipitates is likely where influent Zn concentrations are high. The formation of Cu hydroxycarbonates is likely to be the dominant mechanism for Cudiss removal, though the relative importance of aqueous precipitation of such minerals, and their formation on the shell surface via adsorption to the CaCO3, was less clear. The role of adsorption to other surfaces, such as organic material, HFO and aluminosilicates, in the removal Zndiss and Cudiss appeared to increase in importance as dissolved Zn and Cu concentrations decreased. Implications for the optimisation of a Storminator™ type device include: maximising the shell surface area by minimising the shell fragment size, and increasing the runoff retention time within the device. However, these will be constrained by the hydraulic conductivity requirements of the inline system. Results suggest that the lifespan of the device is likely to be limited by operational factors rather than the availability of adsorption sites, so estimations of lifespan should be based on future field trials. Extension of the device lifespan may be possible by re-packing, or by regeneration of the media with EDTA or a low concentration weak acid, which should be investigated in further study.
Open Access
The Ōtūkaikino River : factors contributing to apparent macroinvertebrate loss.
(University of Canterbury, 2020) Painter, Ariana
In recent years the Ōtūkaikino River catchment has had some of best water quality and stream health of all Christchurch rivers. However, the absence of stoneflies from macroinvertebrate surveys in 2017 indicates that all may not be well with the catchment. Given stoneflies are typically associated with high habitat and water quality, their decline or disappearance may signal stream health challenges that require further attention. A 12-month monitoring programme was created for the Ōtūkaikino River catchment to determine potential sources of pollution and habitat limitation related to this apparent decline. A range of physical, chemical and biological parameters were investigated across ten sites in the catchment in 2019 and 2020. The moderately pollution sensitive cased caddisfly Pycnocentria was a dominating taxon at many sites, though pollution tolerant Potamopurgus snails and pollution sensitive Deleatidium mayflies were also typically in high numbers. Four Zelandobius stoneflies were identified in catchment monitoring surveys in 2019, indicating that the catchment is still able to support populations of stoneflies, despite the apparent decline between 2008 and 2017. Metrics for ecological health generally increased downstream towards the middle reaches. Site scores ranged from poor ecological health (upper Waimakariri South Branch) to excellent (middle reaches). This differed to the generally good-excellent ecological health reported in 2017. Low concentrations of trace elements suggested they were generally not a key contributor to changes in ecosystem health in the Ōtūkaikino River catchment. Key exceptions were dissolved arsenic, chromium, copper and zinc at some sites. In sediment, metal concentrations were generally low, except for two headwater sites of the Waimakariri South Branch. These two sites recorded high levels of most parameters analysed, with lead and copper exceeding ANZECC (2000) interim sediment quality guidelines. Most other water quality parameters were within ANZECC (2000) water quality guidelines for ecosystem protection, with a few key exceptions. Dissolved oxygen reached low concentrations at several sites. Elevated levels of faecal coliforms were recorded in some samples, though E. coli was comparatively low. While nitrate-nitrogen concentrations were low, DRP (dissolved reactive phosphorus) was consistently elevated above ANZECC (2000) water quality guidelines at one site, as was ammoniacal nitrogen at several sites. The main factors identified in this study that contributed to this variation in macroinvertebrate community health and water quality were differences in riparian and canopy cover. They were typically highest in the middle reaches, though there were some other areas of thick vegetation. In particular, much of the upper reaches had limited mature shading plants and sediment filtering plants. Localised inputs, such as trace elements in two Waimakariri South Branch sites, were also potential contributors. Substantial planting efforts have occurred in the catchment in the last couple of decades. This study recommends that these efforts continue, with a focus on intercepting sediment and shading the waterway. Further monitoring and research in the vicinity of the two sites where high levels of trace elements were recorded is also recommended.
Open Access
Resilient shorelines : earthquake effects on sea levels and their implications for conservation and climate change.
(University of Canterbury, 2020) Orchard, Shane
Coastal margins are exposed to rising sea levels that present challenging circumstances for natural resource management. This study investigates a rare example of tectonic displacement caused by earthquakes that generated rapid sea-level change in a tidal lagoon system typical of many worldwide. This thesis begins by evaluating the coastal squeeze effects caused by interactions between relative sea-level (RSL) rise and the built environment of Christchurch, New Zealand, and also examples of release from similar effects in areas of uplift where land reclamations were already present. Quantification of area gains and losses demonstrated the importance of natural lagoon expansion into areas of suitable elevation under conditions of RSL rise and showed that they may be necessary to offset coastal squeeze losses experienced elsewhere. Implications of these spatial effects include the need to provide accommodation space for natural ecosystems under RSL rise, yet other land-uses are likely to be present in the areas required. Consequently, the resilience of these environments depends on facilitating transitions between human land-uses either proactively or in response to disaster events. Principles illustrated by co-seismic sea-level change are generally applicable to climate change adaptation due to the similarity of inundation effects. Furthermore, they highlight the potential role of non-climatic factors in determining the overall trajectory of change. Chapter 2 quantifies impacts on riparian wetland ecosystems over an eight year period post- quake. Coastal wetlands were overwhelmed by RSL rise and recovery trajectories were surprisingly slow. Four risk factors were identified from the observed changes: 1) the encroachment of anthropogenic land-uses, 2) connectivity losses between areas of suitable elevation, 3) the disproportionate effect of larger wetland vulnerabilities, and 4) the need to protect new areas to address the future movement of ecosystems. Chapter 3 evaluates the unique context of shoreline management on a barrier sandspit under sea-level rise. A linked scenario approach was used to evaluate changes on the open coast and estuarine shorelines simultaneously and consider combined effects. The results show dune loss from a third of the study area using a sea-level rise scenario of 1 m over 100 years and with continuation of current land-uses. Increased exposure to natural hazards and accompanying demand for seawalls is a likely consequence unless natural alternatives can be progressed. In contrast, an example of managed retreat following earthquake-induced subsidence of the backshore presents a new opportunity to restart saltmarsh accretion processes seaward of coastal defences with the potential to reverse decades of degradation and build sea-level rise resilience. Considering both shorelines simultaneously highlights the existence of pinch-points from opposing forces that result in small land volumes above the tidal range. Societal adaptation is delicately poised between the paradigms of resisting or accommodating nature and challenged by the long perimeter and confined nature of the sandspit feature. The remaining chapters address the potential for salinity effects caused by tidal prism changes with a focus on the conservation of īnanga (Galaxias maculatus), a culturally important fish that supports New Zealand‘s whitebait fishery. Methodologies were developed to test the hypothesis that RSL changes would drive a shift in the distribution of spawning sites with implications for their management. Chapter 4 describes a new practical methodology for quantifying the total productivity and spatiotemporal variability of spawning sites at catchment scale. Chapter 5 describes the novel use of artificial habitats as a detection tools to help overcome field survey limitations in degraded environments where egg mortality can be high. The results showed that RSL changes resulted in major shifts in spawning locations and these were associated with new patterns of vulnerability due to the continuation of pre-disturbance land-uses. Unexpected findings includes an improved understanding of the spatial relationship between salinity and spawning habitat, and identification of an invasive plant species as important spawning habitat, both with practical management implications. To conclude, the design of legal protection mechanisms was evaluated in relation to the observed habitat shifts and with a focus on two new planning initiatives that identified relatively large protected areas (PAs) in the lower river corridors. Although the larger PAs were better able to accommodate the observed habitat shifts inefficiencies were also apparent due to spatial disparities between PA boundaries and the values requiring protection. To reduce unnecessary trade-offs with other land-uses, PAs of sufficient size to cover the observable spatiotemporal variability and coupled with adaptive capacity to address future change may offer a high effectiveness from a network of smaller PAs. The latter may be informed by both monitoring and modelling of future shifts and these are expected to include upstream habitat migration driven by the identified salinity relationships and eustatic sea-level rise. The thesis concludes with a summary of the knowledge gained from this research that can assist the development of a new paradigm of environmental sustainability incorporating conservation and climate change adaptation. Several promising directions for future research identified within this project are also discussed.
Open Access
Assessing the use of geochemical modelling in supporting mine site remediation.
(University of Canterbury, 2019) Fairgray, Marlese Elizabeth
The extraction of minerals through mining activities often results in the generation of acid mine drainage (AMD) due to the exposure of sulfidic minerals to oxygen and water at a rate faster than would have occurred naturally. In order to operate at best practice, the effects of mining and AMD on the natural environment need to be mitigated or prevented. In this thesis water and sediment chemistry of three historic mine sites at various stages in the post- closure process in New Zealand were assessed. Changes in water and sediment chemistry due to the precipitation of Fe, Mn and Al precipitates and the adsorption of trace elements to freshly formed precipitates were modelled in PHREEQC. The modelled results were compared to measured results in order to evaluate the effectiveness of PHREEQC in modelling post-remediation water and sediment chemistry at mining sites. The remedial works carried out at Tui Mine have resulted in an increased pH and decreased concentration of dissolved trace elements (Fe, Cu, Pb, Zn, Cd, As) in Tui Stream and in Tunakohoia Stream. The remedial works have been more effective in mitigating the effects of AMD in Tui Stream than in Tunakohoia Stream due to the difference in the pre-remediation pH of these two streams. PHREEQC was used to show that the concentrations of Zn²⁺ and Cd²⁺ remain above ecologically relevant guidelines even after remedial works have been completed. PHREEQC was also used to show that the addition of limestone to these streams is unlikely to reduce the concentration of these two elements by either formation of mineral precipitates or adsorption to Fe (oxy)hydroxide precipitates to a concentration suitable for supporting healthy ecosystem function in the streams draining Tui Mine. The use of Tui Mine to assess the reliability of PHREEQC modelling found that it is possible to use PHREEQC to reliably model a system where the elements of concern are cationic metals such as Cu, Pb, Zn and Cd. In fact, it is possible that the remediation works carried out between 2010 and 2013 could have achieved a better outcome had PHREEQC been used to model the post-remediation water chemistry expected in the Tui and Tunakohoia Streams following the addition of limestone to the tailings dam and mine adits at Tui Mine. However, adsorption of Pb to HFO was underestimated and adsorption of As to HFO was overestimated by PHREEQC. Historic mining operations to produce mercury, the surfacing of roads with aggregate containing Hg and As and the presence of sinter outcrops containing Hg and As have resulted in elevated concentrations of sediment-bound Hg and As, above ISQG-high guidelines, in the streams draining the Puhipuhi area. This has led to depauperate macroinvertebrate communities at the sites higher up in this catchment where sediment-bound Fe and Hg is greatest. Additionally, this has also lead to the bioaccumulation of Hg in eels which is of concern to human health, should these be consumed as part of a regular diet and the cultural value of eel harvesting for consumption. PHREEQC could be used to reliably model the speciation of cationic trace elements (Cu, Zn and Ni), the formation of Fe (oxy)hydroxides and the consequent adsorption of Cu, Zn and Ni to Fe (oxy)hydroxides. However, these elements were not the elements of concern in this catchment. PHREEQC could not be used to reliably model the speciation of dissolved Hg and the formation of methylmercury, the form of Hg which bioaccumulates, because the process of methylation is outside the capacity of the PHREEQC model. It could not be used to reliably predict the adsorption of Hg and As to Fe (oxy)hydroxides and it could not be used to model the stability of HgS found within the quartz sinter matrix as this mineral consists of components not able to be measured in natural waters and therefore cannot be input into PHREEQC. Arsenic was associated with residual FeS₂ for which the stability again could not be reliably predicted in PHREEQC due to S²⁻ not being present in natural waters and therefore it was not able to be input into PHREEQC. Therefore, it is not recommended that PHREEQC be used to model systems where Hg and As are the elements of most environmental concern as the thermodynamic data required by PHREEQC to make accurate predictions of the behaviour of these elements is not yet known and the adsorption of As to HFO is not reliably predicted by PHREEQC. The water chemistry of Cannel Creek prior to and following the installation of a sulfate-reducing bioreactor treatment system at Bellvue Mine was measured. The treatment system resulted in >80% less Fe, Al and Ni and a 66% less of Zn on average in Cannel Creek downstream of the AMD discharge point. Additionally, the treatment system increased the pH of AMD entering Cannel Creek sufficiently that Fe- and Al-rich precipitates were able to form and adsorption of trace elements to HFO became favourable. PHREEQC was used to develop a model predicting water chemistry in Cannel Creek following the installation of the treatment system and was validated by comparing the predicted water quality to measured water quality. The model that was developed predicted water quality in the upper reaches of the stream very well but the measured concentrations of dissolved Fe and Al deviated from those predicted in the lower reaches of the stream as there had not been sufficient time for the Fe (oxy)hydroxysulfates and Al oxides to precipitate out of solution in between sampling sites. PHREEQC is a geochemical modelling program suitable for predicting the speciation of trace elements in AMD solutions and the attenuation of trace elements by mineral formation and adsorption to HFO. However, there are certain situations where PHREEQC cannot reliably predict trace element attenuation quantifiably. These include adsorption of dissolved Cd to HFO where solution pH is in the range of greatest change for the Cu adsorption edge, adsorption of Pb and As to HFO and methylation of Hg. In these situations PHREEQC models can provide guidance as to what processes are likely to occur but should not be depended on to set remediation targets for water quality.
Open Access
Quantification of the probable environmental effects of the Hinds Managed Aquifer Recharge trial using mathematical modelling and advanced uncertainty techniques.
(University of Canterbury, 2019) Durney, Kim Patrick
Internationally, Managed Aquifer Recharge (MAR) has gained recognition as a mechanism to address environmental degradation. Investigations into its effectiveness in the New Zealand setting are ongoing and started with a five-year trial near Hinds, mid-Canterbury. The Hinds MAR trial aimed to raise groundwater levels, improve lowland streamflow and improve both ground and surface water quality. This research used advanced numerical modelling techniques such as null space Monte Carlo to assess the probable effectiveness of the Hinds MAR trial. Use of numerical uncertainty analysis to understand the probable effects of MAR programmes is both recommended and noted as a gap in international literature. Secondly, this research investigates the usefulness of various modelling approaches for quantifying the effects of MAR on the receiving environment. The water resources of the Hinds Plains, mid-Canterbury, have been degraded by decades of high- intensity agriculture. The effects are seen as lowered groundwater levels, reduced spring-fed stream flows and high nitrate-nitrogen concentrations in both surface and groundwater. The Hinds MAR trial sought to introduce 500 l/s recharge into the groundwater system. The original evaluations of the trials probable effectiveness are based on this rate of recharge. However, due to in-situ conditions, the design recharge rate was never realised. Using the model code MODFLOW-NWT and advanced uncertainty analysis, this research investigated the probable response to the long-term achievable recharge rate of approximately 110 l/s after the trial completion. This research investigated the effectiveness of a range of modelling approaches, from simple analytical and homogenous parameter numerical models to highly parameterised, spatially variable numerical models. It ultimately settles on highly parameterised numerical modelling as the most effective approach to assess the effects of the MAR trial. Like previous international studies, this research demonstrates the importance of calibrating numerical models to both quantity and quality, especially if useful results are to be obtained for water quality outcomes. For instance, initial uncertainty analysis used a model that was only calibrated to quantity, and despite a suite of 100 calibration constrained simulations it was not possible to reproduce observed water quality changes in response to the trial. Failure to capture the hydraulic conductivity field that represented the observed water quality changes was possibly caused by the model calibration being biased towards a local calibration optima, something highlighted in international literature as a possible unwanted outcome with calibration constrained uncertainty analysis. Recalibration of the flow model with the inclusion of concentration targets as calibration criteria produced more reasonable approximations of the observed and expected water quality changes. The final suite of null space Monte-Carlo simulations suggest the Hinds MAR trial will successfully raise groundwater levels across a large area and increase stream flows. Further, the trial will improve water quality in groundwater, though it will probably not influence surface water quality. Transport modelling suggests water quality improvements can be expected for several kilometres down-gradient of the trial site, though they are unlikely to propagate as far as the lowland streams. In terms of the appropriateness of the various modelling techniques investigated, analytical modelling is likely sufficient to estimate the mounding effects in the immediate vicinity of the trial. However, once the area of interest extends beyond the immediate trial site, numerical modelling should be applied. Water quality observations should be included in the calibration targets, and flow and transport calibrated simultaneously. Uncertainty analysis was useful for providing confidence in modelled outcomes and should be employed if the risks (whether financial or environmental) associated with MAR programmes need to be considered.
Open Access
Understanding Eiffelton Irrigation’s targeted stream augmentation.
(University of Canterbury, 2019) Calder-Steele, Nicole
Eiffelton Community Group Irrigation Scheme (ECGIS) is a small owner-operated irrigation scheme located near the Ashburton Coast of Canterbury. ECGIS is bisected by a number of drainage channels which serve to lower the water table and keep the land suited for agriculture. ECGIS provides water to its members by targeted stream augmentation. This is where groundwater is pumped from bores into the drainage channels which transports the water to members to enable take for irrigation. Despite the length of operation of ECGIS, little is known about it beyond this conceptual understanding establish in consent documents. Thus, the aim of this investigation was to understand operation and operational effects of ECGIS. This was achieved by meeting four objectives. The first objective was to document the operation of ECGIS and how operational decisions were made. This was achieved by undertaking semi-structured interviews with ECGIS members. ECGIS consists of 4,000 ha of land, 58 km of drains, and 20 production bores. ECGIS pumps water from the production bores into Deals, Windermere and Home Paddock drains to convey water for irrigation to its members. Bores are pumped into the closest drain, except HP1 which is pumped into Windermere Drain. Diversion gates allow transfer of water between these drains to enable the most cost-efficient use of water. Member access to water is proportional to their relative share of land within the ECGIS footprint. More water can be abstracted from the drains than can be supplied by ECGIS production bores, but each drain has a minimum flow rate which must be complied with whenever an ECGIS member is irrigating. The Race Manager and Assistant Race Manager are responsible for the day-to-day operation of ECGIS. Both are ECGIS members. ECGIS management make decisions on which production bores to use and how much flow to divert between the drains based on their understanding of ECGIS; capacity of the production bores, requirements of each irrigator, and the hydrology of the ECGIS area. Management operates to a 20 L/s surplus in provided water to prevent non-compliance. Management recognises that some bores have better yield than others, while some have higher operating costs. Because of these factors, there is no set order in which production bores are used. The second objective was to understand the hydrological setting of ECGIS and how scheme operation impacts measured parameters. This was addressed by undertaking field investigation on the largest and centremost drain utilised by ECGIS; Windermere Drain. Gauging results showed Windermere Drain increased in flow towards the coast across 2018, while in 2019 flows increased to Surveyors Road and again fell. Highest nitrate-N concentrations were found at the top of ECGIS and in drain water. E. Coli detections were lowest at the top of ECGIS and increased in drain water down-gradient. Data from the top of ECGIS suggests that Windermere Drain gains in its upper to mid reaches, but loses flow from its mid reaches, with rate increasing towards the coast. When predicting the flow in Windermere Drain over the irrigation period in the absence of targeted stream augmentation and without irrigation abstraction there were significant periods of no flow. This suggests ECGIS ensures flow in Windermere Drain where it may otherwise be dry. Water quality parameters were considered relative to the 2018/19 irrigation season. Targeted stream augmentation by ECGIS is understood to have contributed to lower dissolved oxygen, lower electrical conductivity, and lower nitrate-N concentrations in Windermere Drain and shallow groundwater across the 2018/19 irrigation season. The third objective was to identify values associated with the Hinds Drains, of which the drains used by ECGIS are a part. This was achieved by conducting semi-structured interviews with ECGIS members and individuals that have been involved in Ashburton water management. The most common value associated with the Hinds Drains by ECGIS members was their function as drains and keeping their land farmable. This likely reflected the fact that most interviewees lived within the Hinds Drains area and so benefitted directly from this primary function of the drains. Recreation (e.g. swimming, fishing) was the value most associated with the Hinds Drains by other interviewees. Presence of introduced and native fish was equally valued by ECGIS Members, but introduced fish were less valued by other interviewees. Interviewees were asked what they would like to see the Hinds Drains used for in a ‘perfect world’. Most interviewees identified restoration to provide for native fish. Many interviewees commented that while it would be nice to see greater biodiversity in the area, developing the drainage network to support such things should not come at the expense of their drainage function. The final objective was to determine how values could be met using an integrated framework. This was achieved by incorporating information obtained to address the previous three. Integrated water management was selected to identify opportunities to enhance drainage and native fish habitat. It was considered that to address both or either of these that efforts should be made to better understand and optimise existing drainage, and to improve riparian management along Windermere Drain.
Open Access
Increasing the uptake of building-scale water sensitive urban design stormwater management options in Christchurch, New Zealand
(University of Canterbury, 2019) Southworth, Vicky
Christchurch Ōtautahi, New Zealand, is a city of myriad waterways and springs. Māori, the indigenous people of New Zealand, have water quality at the core of their cultural values. The city’s rivers include the Avon/Ōtākaro, central to the city centre’s aesthetic appeal since early settlement, and the Heathcote/Ōpāwaho. Both have been degraded with increasing urbanisation. The destructive earthquake sequence that occurred during 2010/11 presented an opportunity to rebuild significant areas of the city. Public consultation identified enthusiasm to rebuild a sustainable city. A sustainable water sensitive city is one where development is constructed with the water environment in mind. Water sensitive urban design applies at all scales and is a holistic concept. In Christchurch larger-scale multi-value stormwater management solutions were incorporated into rapidly developed greenfield sites on the city’s outskirts and in satellite towns, as they had been pre-earthquake. Individual properties on greenfield sites and within the city, however, continued to be constructed without water sensitive features such as rainwater tanks or living roofs. This research uses semi-structured interviews, policy analysis, and findings from local and international studies to investigate the benefits of building-scale WSUD and the barriers that have resulted in their absence. Although several inter-related barriers became apparent, cost, commonly cited as a barrier to sustainable development in general, was strongly represented. However, it is argued that the issue is one of mindset rather than cost. Solutions are proposed, based on international and national experience, that will demonstrate the benefits of adopting water sensitive urban design principles including at the building scale, and thereby build public and political support. The research is timely - there is still much development to occur, and increasing pressures from urban densification, population growth and climate change to mitigate.
Open Access
Constraining factors in water resources management and planning in the Plain of Reeds, Vietnam
(University of Canterbury, 2019) Nguyen, Khiem
The research explores current water uses in the Plain of Reeds (Dong Thap Muoi) sub-region in Vietnam and identifies key constraints facing water resources management and planning. With increasing upstream demands on water resources, and shifting weather and rainfall patterns linked to climate change, there is an urgent need for effective water governance. Integrative approaches my help to achieve coordination and cooperation among the various authorities and territories engaged in water management in the sub-region. Commitment at the national level to principles of Integrated Water Resource Management (IWRM), is evident in several key legal and policy documents in Vietnam, but it is unclear how far such principles have been translated to and implemented at the local levels. A multi-level governance perspective was applied to identify the connections, gaps and evolving interdependencies across policy areas and between agencies and levels of government engaged in water resource management in the Plain of Reeds. Field research involved focus group discussions with local communities, and key informant interviews with representatives from government agencies, NGOs, and research institutes at three administrative levels (commune, district and provincial). Together with the results of an analysis of key government policies, the findings show how water resource management and planning are constrained by a variety of factors. These factors are (1) a lack of transboundary collaboration among state actors across the study areas; (2) inadequate organizational capacity within responsible agencies; (3) a lack of water resources awareness in local communities and among officials; (4) the absence of inter-agency information sharing mechanisms; and (5) intensive investment and expansion in the agriculture sector. The study produces recommendations for policymakers and other relevant actors to promote greater inter-provincial collaboration and cross-border cooperation in water management in the area.
Open Access
Traditional and Western knowledge integration in water governance and its implications for rural livelihoods in Esigodini, Zimbabwe.
(University of Canterbury, 2019) Ncube, Xolile
Globally, the quality and quantity of water resources continue to decline, and there has been a realisation that water governance systems based solely on Western science, are not providing adequate solutions to the world’s water challenges. This has seen an increased interest in the integration of traditional and Western-based knowledge systems for efficient water management from the 1980s. Proponents of the notion, however, argue that although Western science and traditional knowledge are different, they can complement each other and improve the manner in which the world’s water resources are managed. In Zimbabwe, 70% of the population resides in rural areas, and 50% of the total population lives on communal lands, and utilises traditional knowledge on a daily basis to manage water. A plural legal system exists in the country, however, water statutory instruments do not recognise Indigenous knowledge systems. There are no provisions in water legislation and policy for improved access to water for the expansion of subsistence agriculture, which is mainly practised on communal lands. This qualitative study draws on fieldwork in Esigodini, Zimbabwe, to explore the different traditional water management practices of the Ndebele group. It identifies the opportunities and challenges of establishing a system that integrates traditional and Western-based water management, and considers how such a system can impact rural livelihoods. The research finds that small-scale agriculture is the main livelihood practised in Esigodini Village, and the villagers have, over time, developed traditional water management systems to support this livelihood. The local knowledge systems have, however, evolved over the years to address current water challenges including climate variability, and increased water demand. The study concludes that traditional water management systems practised in Esigodini, encourage the sustainable use of water. A water governance system that integrates traditional and Western-based knowledge can support improved and diversified rural livelihoods and reduce donor dependency in the village. Challenges such as local communities losing faith in government-initiated collaborative processes, have impelled the study to recommend that a third space be established. This space will allow for cross learning and formulation of information that contributes to decision making, legislation, and policy. A monitoring framework that is based on traditional and Western ways of knowing will need to be developed to monitor the outcomes of the implementation of the integrated system. All stakeholders need to participate with respect for each way of knowing and in good faith, in order for the collaborative process to have positive outcomes for rural livelihoods in Esigodini Village.
Open Access
A water quality study of Barkers Creek, South Canterbury.
(University of Canterbury, 2019) Graham, H. J.
Diffuse nitrogen and phosphorus pollution from farming practices is a water resource management issue throughout New Zealand. Efficient management of diffuse pollutants requires a conceptual understanding of the relationship between groundwater and surface water in the catchment being investigated. With this knowledge, transfer pathways and “hot-spots” can be identified. Barkers Creek is a small sub-catchment of the Waihi River, in South Canterbury. Diffuse pollution is causing water quality issues within the Barkers Creek catchment that propagate to Waihi River. There were three key components to this study. First, to characterise the hydrology, hydrogeology and hydrochemistry of Barkers Creek catchment. Then, to determine the main transfer pathways that nitrogen, phosphorus and sediment are entering Barkers Creek. Lastly, to understand temporal dynamics of nitrogen, phosphorus and sediment, and in particular the role storm flows have on these dynamics. A field campaign was conducted to intensively monitor the surface water and groundwater regime in Barkers Creek over the year 2016-2017. Data collection occurred at different temporal resolutions, with parameters measured at all sites bimonthly intervals and a subset of sites measured at fortnightly and 5-minute intervals. About of 44% of the flow in Barkers Creek is attributed to groundwater seepage occurring from the lower catchment, between McKeown Road (5.2 km upstream of the confluence) and the confluence with the Waihi River. Flow paths and residence times between the recharge and discharge zones for groundwater appear to be short. There is evidence of anthropogenic influence, particularly on shallow groundwater, with elevated nitrate-nitrogen concentrations observed throughout much of the lower catchment. Nitrate-nitrogen and dissolved reactive phosphorus concentrations are typically higher in groundwater and some of the spring-fed drains than what is observed in Barkers Creek. There is also evidence of a natural phosphorus source in the catchment. Of the nitrate-nitrogen load exported from the Barkers Creek catchment to the Waihi River, 20% is from diffuse groundwater seepage into the creek, 11% is from the Barkers Creek catchment upstream of McKeown Road and the remainder is from drain systems in the lower catchment, most of which are spring-fed. 56% of the total nitrate-nitrogen load is from the 3 (of 10) spring-fed drains in the lower catchment and can be considered the “hot-spots”. Nitrate-nitrogen loads during storm events do not differ significantly from loads during baseflow conditions and the spring-fed drains are a significant transfer pathway under all flow regimes. Minimal DRP load in Barkers Creek comes from diffuse groundwater seepage. Barkers Creek upstream of McKeown Road contributed 13% of the total load export with the remainder attributable to export via spring-fed drains. The hotspots for DRP are 4 (of 10) spring-fed drains in the lower catchment. Export of phosphorus and sediment is sensitive to flow regime, with storm events being the major time of transport from Barkers Creek to the Waihi River.
Open Access
A habitat template of Stuckenia Pectinata in Te Waihora (Lake Ellesmere).
(University of Canterbury, 2018) Qian, Hu
Te Waihora (Lake Ellesmere) is a shallow coastal lagoon located on the east coast of the South Island of New Zealand. An extensive macrophyte bed (primarily Stuckenia pectinata and Ruppia spp.) once existed around the lake margins. It disappeared after a storm event in 1968 and never returns. Now the lake is highly turbid and water column attenuates light rapidly through depth. The lake is periodically open to the sea, and salinity in the lake fluctuates as a result of the lake opening activities, and varies with distance to the lake opening. The aim of this study is to define a habitat template, a set of environmental factors (light attenuation, water depth, salinity) that allows S. pectinata to grow and persist indefinitely. A series of experiments were conducted to investigate: 1) the morphological and leaf photosynthetic physiological acclimation to low light conditions; 2) the leaf demography and leaf photosynthesis in direct and stepwise exposures to a gradient of salinity; 3) the interaction of light acclimation and salinity on leaf photosynthesis. At low irradiance, primary shoots of S. pectinata grew taller, produced longer and lighter leaves and senesced leaves more quickly than at high irradiance. Salinity stress induced early leaf senescence and leaf production rate decreased with increasing salinity level. Plants did not tolerate salinity exceeding 20 ppt. Leaves at low irradiance havd higher chlorophylls per fresh weight (per photosynthetic leaf area), suggesting enhanced light harvesting (capture of photon energy) efficiency per unit leaf area. Leaves at high irradiance had fewer chlorophyll per fresh weight but higher photosynthetic rate per unit chlorophyll, indicating higher light utilization (utilization of captured photon energy) efficiency. High salinity (=> 12 ppt) reduced photosynthetic rate per unit chlorophyll-a in leaves acclimated to high irradiance (340 μmol/m2/s) but not to lower irradiances (110 and 50 μmol/m2/s), suggesting salinity would reduce light utilization efficiency of surface reaching leaves but not submerged leaves in the turbid water column. To conclude, turbidity and salinity synergistically limit the growth of S. pectinata in the lake: 1) both low-light stress in the water column and salinity reduce the number of leaves, therefore, less photosynthetic leaf area; 2) the photosynthetic rate per unit chlorophyll-a is either constrained by low-light stress in the water column or by salinity at or near the water surface. The knowledge of light and salinity limitation on growth of S. pectinata seems to well explain the dynamic of a population of S. pectinata in Te Waihora monitored over two consecutive growing seasons. In the end, a habitat template with defined ranges of water depth, light attenuation coefficient, and salinity was constructed for S.pectinata to grow in Te Waihora.
Open Access
Negotiating gross national happiness as community economy : a case study of the Thimphu River.
(University of Canterbury, 2018) Pem, Sonam
In recent years, the ecological health of the Thimphu River in Bhutan has been deteriorating. This leads to questions about the values that are ingrained in the Government’s development philosophy, known as gross national happiness. This study presents how the physical status of the Thimphu River and people’s behaviours around the river are influenced by modern, materialistic approaches, which challenge traditional, spiritual and cultural values. The objective is to understand local communities’ connections with the river, which foster perceptions of its worth, and thus frame behaviours towards the river. I used semi-structured interviews and group discussions with adults and students to gather data. I also performed a participatory rapid appraisal with local nuns, and I made direct field observations. I found that the Thimphu River has been exploited by local residents and communities living near it, resulting in its degradation. A disconnect from traditional spiritual and cultural values is evident in the waterways’ degraded state. Herein, I explore a new management approach, which could lead to sustainable river use. I explore new approaches to river management fostered by reconnecting to traditional, spiritual values, which are the core foundations of gross national happiness. I suggest re-negotiating Bhutan’s gross national happiness as a community economy, with particular reference to the ethics of taking care of a common resource belonging to all and fostering ethical behaviours through the ethical concern of encountering others.
Open Access
Examining the use of coral sand for the treatment of domestic effluent in Kiribati.
(University of Canterbury, 2018) Humphries, Bronwyn Louise
Laboratory based, unsaturated drainage experiments were undertaken using worked Bikenibeu beach coral sand from South Tarawa in Kiribati, to examine its drainage and effective microbial removal properties. Bacterial and viral indicators (E. coli J6-2, E. faecalis and MS2 phage) along with viral pathogens (adenovirus; echovirus; norovirus; rotavirus) were drained under gravity through coral sand-packed columns, serving as physical models of a domestic effluent drainage field. Experiments using clean coral sand and coral sand which were conditioned with Dissolved Organic Carbon (DOC), in the form of domestic effluent, were investigated. The results show that coral sand has a higher affinity for attenuating viruses than bacteria. All organisms examined showed removal efficiencies over 4-Log Removal Values (LRVs) which is equivalent to a 99.99 % reduction in the target microorganisms. Attenuation mechanisms such as absorption and to a lesser extent physical straining likely play a major role in the ability of coral sand to attenuate the microbial tracers used in this study. The application of DOC in the form of domestic effluent may have provided additional binding sites on the surface of the coral sand and increased the adsorption rate of viruses but the bacterial indicators (E. coli J6-2, E. faecalis) did not appear to be influenced by DOC. It was also found that changes in ionic strength, such as rainfall, increased the mobilisation of microorgansims within coral sand. Long term field scale studies are required to verify the laboratory results as well as incorporating the effects of kind tide events, fluctuations in groundwater, effects of prolonged rainfall and examining microbial transport within coral sand under saturated conditions. These findings could have important implications for the use of locally available materials, such as coral sand, to improve household onsite wastewater treatment in Kiribati and offer enhanced protection of groundwater resources and reduce diarrheal disease.
Open Access
Urban impact assessment and emergency response to flooding in Buenos Aires, Argentina.
(University of Canterbury, 2018) Ferligoj, Yanina
The determination of urban resilience and community response to flooding are significant aspects of hazard management and disaster risk reduction. Anticipating hazard impacts is vital to the development of flood mitigation strategies and emergency response planning. Argentina is an emerging economy with high flood hazard exposure, and its capital, Buenos Aires, is one of the most affected areas. Inappropriate disaster response could therefore affect food supply chains, telecommunications and transport systems nationwide. Flood risk areas in Buenos Aires City have been geographically identified. However, flood impacts have not been well considered, and the emergency response capacity of the city has not been evaluated. This research examined flood impacts in Buenos Aires on infrastructure lifelines and critical facilities, as well as on the wider commercial and residential built environment under current conditions, and accounting for projected impacts of climate change. Evacuation dynamics were explored through characterising spatiotemporal population exposure, modelling evacuation routes, and analysing emergency service response areas. Analyses of different sea-level rise and storm return interval scenarios showed clear trends in increasing impacts under increasing hazard intensities; these impacts were ameliorated when flood warnings were applied. Spatiotemporal population exposures developed for evacuation analyses showed increasing impacts under increasing sea-level rise scenarios. Dynamic evacuation analyses highlighted inadequacies in current welfare facilities to shelter evacuees, however modelling suggests that shelter and emergency response can both be improved by increasing the number of facilities. This research contributes to the quantification of impacts on the built environment and associated economic losses, and helps inform disaster response and management. The methodological approach presented here provides an analytical framework for flood impact analyses and evacuation dynamics that can inform other flood-exposed cities globally.
Open Access
Phormidium accrual cycles in Canterbury rivers: the effects of nutrients and flow
(University of Canterbury, 2018) McAllister, T. G.
Over the last two decades there has been a marked increase in the intensity and frequency of proliferations of the benthic, mat-forming cyanobacterial genus Phormidium in rivers worldwide. This has raised concerns because species of Phormidium are known to produce a variety of cyanotoxins, including; anatoxin-a, homoanatoxin-a, dihydro-anatoxin-a and dihydro-homoanatoxin-a. Phormidium has already been implicated in animal toxicosis events in France, the Netherlands, Scotland, Switzerland and the United States of America. In New Zealand, there have been over 100 dog deaths attributed to ingestion of Phormidium since the early 2000’s. Concern over increasing Phormidium proliferations has led to a series of investigations into the underlying cause, but to date there is a limited understanding of the physicochemical factors which enhance growth. Previous observational studies have allowed inferences to be drawn that nutrients and river flow may play roles in determining Phormidium cover, however experimental evidence to test these inferences was limited. To address this gap, I have undertaken a series of observations and experiments investigating the relationship between Phormidium growth, nutrients and water velocity. Initially, I explored correlations between physicochemical variables and Phormidium cover and toxin concentrations in the Canterbury region (New Zealand), using an observational survey with high temporal resolution. A series of experiments followed that used novel field and mesocosm-based methods that allowed an in-depth analysis of how nutrients and flow affect different phases of the accrual cycle of Phormidium mats. These provided new insights into conditions under which proliferations are likely. The observational-based field study was undertaken in eight rivers and involved weekly sampling over eight months. A variety of physicochemical variables including nutrients, dissolved metals, substrate size and stability, conductivity and temperature was measured as well as benthic Phormidium coverage and the associated toxin concentrations. Both Phormidium cover and anatoxin concentrations were highly variable spatially and temporally. Phormidium proliferations were documented under a wide range of water-column nutrient concentrations, including nitrogen concentrations suggested too low to support bloom formation in previous studies (dissolved inorganic nitrogen (DIN): <0.02 mg L-1) and also at low dissolved reactive phosphorus (DRP) concentrations (0.006 mg L-1). This survey used generalised additive mixed models to identify variables associated with Phormidium cover. High Phormidium cover was correlated with increasing conductivity and decreasing river flow. However, despite including a wide range of environmental and water quality variables, site was identified as an important factor in predicting cover, suggesting that a site-specific, timeindependent factor not included in analyses influences Phormidium cover. Higher anatoxin concentrations were measured between November and February and when DRP was less than 0.02 mg L-1. However, mats are a mixture of non-toxic and toxic genotypes and information of the relative abundance of these would allow more conclusive inferences to be drawn on influence of physicochemical factors on toxin concentrations. Previous research has shown that Phormidium mats may access sediment-bound phosphorus trapped within mat matrices, allowing them to grow partially independent of river water nutrient supply, and the occurrence of proliferations at low DIN concentrations, led to the development of the hypothesis that nitrogen-fixing bacteria are present in Phormidium mats and could contribute to the nitrogen requirements for growth. I investigated this hypothesis using molecular techniques (i.e., high-throughput sequencing) and showed that 16 operational taxonomic units containing genes for nitrogen-fixation were present in mats, and that their diversity increased with increasing water-column nitrogen concentrations, rather than decreased as hypothesized. The potential for nitrogen fixation within mats may therefore explain a weak dependence on water-column DIN, though the rates of fixation relative to nitrogen demand were not investigated. A stream-side mesocosm experiment was then conducted to elucidate links between Phormidium accrual and velocity and nitrate. Two velocity treatments; slow (0.1 m s-1) and fast (0.2 m s-1), were crossed with three nitrate treatments; ambient (0.02 mg L-1), medium (0.1 mg L-1) and high (0.4 mg L-1) and growth as areal expansion, biovolume, chlorophyll a and phycoerythrin was followed for 16 days. Due to the random nature of Phormidium colonisation in mesocosms, it was standardised by inoculating clean cobbles with a constant volume of homogenised Phormidium mats. High velocity resulted in significantly higher Phormidium biomass by the end of experiments, but did not affect expansion rates. Patches in slow velocity treatments detached significantly earlier compared to patches in high velocity treatments, due to autogenic detachment. Nitrate concentrations had no effect on Phormidium biovolume, chlorophyll a concentrations or mat expansion, although under high velocity and high nitrate treatments an increase in phycoerythrin concentrations over other treatments was evident. In order to further investigate the effects of site and velocity on Phormidium accrual, I then undertook an in-stream experiment across a velocity gradient in three south Canterbury rivers, again using pre-inoculated cobbles to eliminate colonisation effects. Phormidium expansion rates and biomass (chlorophyll a and phycoerythrin concentrations and biovolumes) were measured, along with near-bed velocity, nutrients, macroinvertebrate communities and shear stress. Velocity determined mat morphology, expansion rate and patch longevity. Patches in low-medium velocity (i.e., pools and runs) habitats spread relatively quickly laterally, at least initially, whereas mats from the high-velocity riffles expanded at a slower rate, but increased in thickness. The optimal near-bed velocity for Phormidium rate of accrual, as patch size, was 0.25 to 0.45 m s-1, which in these rivers represented run habitats. Patches in riffles, though expanding more slowly, persisted throughout the experiment and this persistence may explain the tendency for riffles to have higher Phormidium cover. Patches from pools expanded rapidly but were also removed quickly, presumably due to high grazing pressure. Under similar velocities, differences in accrual were still evident among sites, which was partially attributed to differences in shear stress and macroinvertebrate communities. Lastly, a synthesis of new knowledge gained through this thesis, together with recently published literature is presented, which develops a new paradigm for understanding the dynamics of Phormidium proliferation that is based on the factors influencing various phases of the accrual cycle. Of particular importance is the complex interactions between accrual, persistence and velocity, and perhaps nutrients. My research suggests that a nuanced interpretation of what governs Phormidium colonisation, growth and persistence needs to be developed that is sensitive to the demands of different phases of the accrual cycle. Future directions for research are also suggested, which aim to build upon the research presented in this thesis and further advance understanding of the physicochemical drivers of Phormidium proliferations.
Open Access
A comparison of methods for estimating groundwater-surface water interactions in braided rivers
(University of Canterbury, 2018) Coluccio, Katie
Understanding how groundwater and surface water bodies interact is an important component of freshwater management. The direction and quantity of the flow between these two systems can vary in time and space, and these processes play various hydrological and ecological roles. The exchange of groundwater and surface water impacts water quantity, nutrient cycling, contaminant transport, and temperature regulation in surface water bodies for aquatic organisms. The interactions between these two systems can be difficult to measure and is often a poorly understood component of water budgets. Characterising these exchanges in gravel-bed braided rivers and their surrounding aquifers can be more difficult than in other environments due to their highly heterogeneous substrate; very permeable streambeds and subsurface material; dynamic geomorphology and flow levels; and difficulty installing direct measurement equipment into the coarse-gravel riverbeds. In this study, mini-piezometers and vertical temperature probes were installed, and physicochemical analysis was carried out on the Hakatere/Ashburton River on the South Island of New Zealand. The methods were used to identify the direction of flow between groundwater and the river and quantify the rate of seepage through the streambed. Results from the methods were compared to assess their effectiveness for use in a braided river system. From a practical perspective, the purpose-built mini-piezometers and vertical temperature probes proved effective in this dynamic coarse-gravel environment. Results across the methods provided a complex picture of groundwater-surface water processes at the study sites, revealing areas of upwelling and downwelling through the streambed. The results reinforce the benefits of multi-method studies for investigating exchanges in groundwater and surface water, as they may better capture temporal and spatial variations in these flows, while providing robust study designs that allow for comparison of results across methods and redundancy in case of equipment or data collection failure.