The greater Wellington region, New Zealand, is highly vulnerable to large earthquakes. While attention has been paid to the consequences of earthquake damage to road, electricity and water supply networks, the consequences of wastewater network damage for public health, environmental health and habitability of homes remain largely unknown for Wellington City. The Canterbury and Kaikōura earthquakes have highlighted the vulnerability of sewerage systems to disruption during a disaster. Management of human waste is one of the critical components of disaster planning to reduce faecal-oral transmission of disease and exposure to disease-bearing vectors. In Canterbury and Kaikōura, emergency sanitation involved a combination of Port-a-loos, chemical toilets and backyard long-drops. While many lessons may be learned from experiences in Canterbury earthquakes, it is important to note that isolation is likely to be a much greater factor for Wellington households, compared to Christchurch, due to the potential for widespread landslides in hill suburbs affecting road access. This in turn implies that human waste may have to be managed onsite, as options such as chemical toilets and Port-a-loos rely completely on road access for delivering chemicals and collecting waste. While some progress has been made on options such as emergency composting toilets, significant knowledge gaps remain on how to safely manage waste onsite. In order to bridge these gaps, laboratory tests will be conducted through the second half of 2019 to assess the pathogen die-off rates in the composting toilet system with variables being the type of carbon bulking material and the addition of a Bokashi composting activator.
For 150,000 Christchurch school students, the 12.51 pm earthquake of 22 February 2011 shattered their normal lunch time activities and thrust their teachers into the role of emergency first responders. Whether helping students (children) escape immediate danger, or identifying and managing the best strategies for keeping children safe, including provision of extended caregiving when parents were unable to return to school to retrieve their children, teachers had to manage their own fears and trauma reactions in order to appear calm and prevent further distress for the children in their care. Only then did teachers return to their families. Eighteen months later, twenty teachers from across Christchurch, were interviewed. At 12.51pm, the teachers were essentially first responders. Using their usual methods for presenting a calm and professional image, the teachers’ emotion regulation (ER) strategies for managing their immediate fears were similar to those of professional first responders, with similar potential for subsequent burnout and negative emotional effects. Teachers’ higher emotional exhaustion and burnout 18 months later, were associated with school relocation. Lower burnout was associated with more emotional awareness, ER and perceived support. Consistent with international research, teachers’ use of cognitive reappraisal (re-thinking a situation) was an effective ER strategy, but this may not prevent teachers’ emotional resources from eventually becoming depleted. Teachers fulfill an important role in supporting children’s psychosocial adjustment following a natural disaster. However, as also acknowledged in international research, we need to also focus on supporting the teachers themselves.
Sewerage systems convey sewage, or wastewater, from residential or commercial buildings through complex reticulation networks to treatment plants. During seismic events both transient ground motion and permanent ground deformation can induce physical damage to sewerage system components, limiting or impeding the operability of the whole system. The malfunction of municipal sewerage systems can result in the pollution of nearby waterways through discharge of untreated sewage, pose a public health threat by preventing the use of appropriate sanitation facilities, and cause serious inconvenience for rescuers and residents. Christchurch, the second largest city in New Zealand, was seriously affected by the Canterbury Earthquake Sequence (CES) in 2010-2011. The CES imposed widespread damage to the Christchurch sewerage system (CSS), causing a significant loss of functionality and serviceability to the system. The Christchurch City Council (CCC) relied heavily on temporary sewerage services for several months following the CES. The temporary services were supported by use of chemical and portable toilets to supplement the damaged wastewater system. The rebuild delivery agency -Stronger Christchurch Infrastructure Rebuild Team (SCIRT) was created to be responsible for repair of 85 % of the damaged horizontal infrastructure (i.e., water, wastewater, stormwater systems, and roads) in Christchurch. Numerous initiatives to create platforms/tools aiming to, on the one hand, support the understanding, management and mitigation of seismic risk for infrastructure prior to disasters, and on the other hand, to support the decision-making for post-disaster reconstruction and recovery, have been promoted worldwide. Despite this, the CES in New Zealand highlighted that none of the existing platforms/tools are either accessible and/or readable or usable by emergency managers and decision makers for restoring the CSS. Furthermore, the majority of existing tools have a sole focus on the engineering perspective, while the holistic process of formulating recovery decisions is based on system-wide approach, where a variety of factors in addition to technical considerations are involved. Lastly, there is a paucity of studies focused on the tools and frameworks for supporting decision-making specifically on sewerage system restoration after earthquakes. This thesis develops a decision support framework for sewerage pipe and system restoration after earthquakes, building on the experience and learning of the organisations involved in recovering the CSS following the CES in 2010-2011. The proposed decision support framework includes three modules: 1) Physical Damage Module (PDM); 2) Functional Impact Module (FIM); 3) Pipeline Restoration Module (PRM). The PDM provides seismic fragility matrices and functions for sewer gravity and pressure pipelines for predicting earthquake-induced physical damage, categorised by pipe materials and liquefaction zones. The FIM demonstrates a set of performance indicators that are categorised in five domains: structural, hydraulic, environmental, social and economic domains. These performance indicators are used to assess loss of wastewater system service and the induced functional impacts in three different phases: emergency response, short-term recovery and long-term restoration. Based on the knowledge of the physical and functional status-quo of the sewerage systems post-earthquake captured through the PDM and FIM, the PRM estimates restoration time of sewer networks by use of restoration models developed using a Random Forest technique and graphically represented in terms of restoration curves. The development of a decision support framework for sewer recovery after earthquakes enables decision makers to assess physical damage, evaluate functional impacts relating to hydraulic, environmental, structural, economic and social contexts, and to predict restoration time of sewerage systems. Furthermore, the decision support framework can be potentially employed to underpin system maintenance and upgrade by guiding system rehabilitation and to monitor system behaviours during business-as-usual time. In conjunction with expert judgement and best practices, this framework can be moreover applied to assist asset managers in targeting the inclusion of system resilience as part of asset maintenance programmes.
We present preliminary observations on three waters impacts from the Mw7.8 14th November 2016 Kaikōura Earthquake on wider metropolitan Wellington, urban and rural Marlborough, and in Kaikōura township. Three waters systems in these areas experienced widespread and significant transient ground deformation in response to seismic shaking, with localised permanent ground deformation via liquefaction and lateral spreading. In Wellington, potable water quality was impacted temporarily by increased turbidity, and significant water losses occurred due to damaged pipes at the port. The Seaview and Porirua wastewater treatment plants sustained damage to clarifier tanks from water seiching, and increased water infiltration to the wastewater system occurred. Most failure modes in urban Marlborough were similar to the 2010-2011 Canterbury Earthquake Sequence; however some rural water tanks experienced rotational and translational movements, highlighting importance of flexible pipe connections. In Kaikōura, damage to reservoirs and pipes led to loss of water supply and compromised firefighting capability. Wastewater damage led to environmental contamination, and necessitated restrictions on greywater entry into the system to minimise flows. Damage to these systems necessitated the importation of tankered and bottled water, boil water notices and chlorination of the system, and importation of portaloos and chemical toilets. Stormwater infrastructure such as road drainage channels was also damaged, which could compromise condition of underlying road materials. Good operational asset management practices (current and accurate information, renewals, appreciation of criticality, good system knowledge and practical contingency plans) helped improve system resilience, and having robust emergency management centres and accurate Geographic Information System data allowed effective response coordination. Minimal damage to the wider built environment facilitated system inspections. Note Future research will include detailed geospatial assessments of seismic demand on these systems and attendant modes of failure, levels of service restoration, and collaborative development of resilience measures.
Research on human behaviour during earthquake shaking has identified three main influences of behaviour: the environment the individual is located immediately before and during the earthquake, in terms of where the individual is and who the individual is with at the time of the earthquake; individual characteristics, such as age, gender, previous earthquake experience, and the intensity and duration of earthquake shaking. However, little research to date has systematically analysed the immediate observable human responses to earthquake shaking, mostly due to data constraints and/or ethical considerations. Research on human behaviour during earthquakes has relied on simulations or post-event, reflective interviews and questionnaire studies, often performed weeks to months or even years following the event. Such studies are therefore subject to limitations such as the quality of the participant's memory or (perceived) realism of a simulation. The aim of this research was to develop a robust coding scheme to analyse human behaviour during earthquake shaking using video footage captured during an earthquake event. This will allow systematic analysis of individuals during real earthquakes using a previously unutilized data source, thus help develop guidance on appropriate protective actions. The coding scheme was developed in a two-part process, combining a deductive and inductive approach. Previous research studies of human behavioral response during earthquake shaking provided the basis for the coding scheme. This was then iteratively refined by applying the coding scheme to a broad range of video footage of people exposed to strong shaking during the Canterbury earthquake sequence. The aim of this was to optimise coding scheme content and application across a broad range of scenarios, and to increase inter-coder reliability. The methodology to code data will enhance objective observation of video footage to allow cross-event analysis and explore (among others): reaction time, patterns of behaviour, and social, environmental and situational influences of behaviour. This can provide guidance for building configuration and design, and evidence-based recommendations for public education about injury-preventing behavioural responses during earthquake shaking.
After a disaster, cities experience profound social and environmental upheaval. Current research on disasters describes this social disruption along with collective community action to provide support. Pre-existing social capital is recognised as fundamental to this observed support. This research examines the relationship between sense of place for neighbourhood, social connectedness and resilience. Canterbury residents experienced considerable and continued disruption following a large and protracted sequence of earthquakes starting in September 2010. A major aftershock on 22 February 2011 caused significant loss of life, destruction of buildings and infrastructure. Following this earthquake some suburbs of Christchurch showed strong collective action. This research examines the features of the built environment that helped to form this cooperative support. Data were collected through semi-structured interviews with 20 key informants followed by 38 participants from four case study suburbs. The objectives were to describe the community response of suburbs, to identify the key features of the built environment and the role of social infrastructure in fostering social connectedness. The last objective was to contribute to future planning for community resilience. The findings from this research indicated that social capital and community competence are significant resources to be called upon after a disaster. Features of the local environment facilitated the formation of neighbourhood connections that enabled participants to cope, manage and to collectively solve problems. These features also strengthened a sense of belonging and attachment to the home territory. Propinquity was important; the bumping and gathering places such as schools, small local shops and parks provided the common ground for meaningful pre-existing local interaction. Well-defined geography, intimate street typology, access to quality natural space and social infrastructure helped to build the local social connections and develop a sense of place. Resourceful individuals and groups were also a factor, and many are drawn to live near the inner city or more natural places. The features are the same well understood attributes that contribute to health and wellbeing. The policy and planning framework needs to consider broader social outcomes, including resilience in new and existing urban developments. The socio-political structures that provide access to secure and stable housing and local education should also be recognised and incorporated into local planning for resilience and the everyday.
Background: There has been a psychopathology focus in disaster research examining adolescent mental health and wellbeing, but recently studies have begun to also examine wellbeing-related constructs. Although an increased risk of posttraumatic stress disorder has been established in disaster-exposed adolescents, comparatively little is known about how disasters impact adolescent wellbeing, nor how factors within the post-disaster environment interact to influence holistic adolescent mental health and wellbeing. Objective: The objective of this study was to describe the holistic mental health and wellbeing of adolescents living in an earthquake-struck city by considering a range of mental health and wellbeing indicators, as well as risk and protective factors hypothesised to influence mental health and wellbeing. The dual-factor model of mental health was used as a framework to guide this study. Method: A survey of Christchurch secondary school students was used to gather data about their subjective wellbeing, risk of low wellbeing, psychological distress, quality of life, exposure to Adverse Childhood Experiences, social support from friends and family, school connectedness, and expectations about future quality of life. Results: A slim majority of students reported good subjective wellbeing (52.3%) and high current quality of life (56.4%), whereas a larger majority reported low risk of psychological distress (79%). An equal proportion of students reported high and low risk of low wellbeing. There were no statistically significant differences in any of the variables measured between adolescents who did and did not live through the Christchurch earthquakes. Regression analyses identified that school connectedness, social support from friends and family, and future expectations of quality of life significantly predicted subjective wellbeing, risk of low wellbeing, risk of psychological distress, and current quality of life. The number of Adverse Childhood Experiences significantly predicted only risk of psychological distress when the effects of other variables were controlled for. Conclusion: The findings of this study indicate that there is a low mean level of wellbeing and quality of life in this sample of adolescents living in a severely earthquake- affected community. School connectedness, social support from family and friends, and expectations about future quality of life were shown to significantly predict variance in subjective wellbeing, quality of life, and psychological distress. This suggests that there are social and environmental factors that can be targeted to improve holistic mental health and wellbeing in disaster-affected adolescents who have experienced high levels of trauma. Conclusions in this study are limited by the representativeness of the sample, the cross- sectional nature of the study, and potential sampling bias.
Background: There has been a psychopathology focus in disaster research examining adolescent mental health and wellbeing, but recently studies have begun to also examine wellbeing-related constructs. Although an increased risk of posttraumatic stress disorder has been established in disaster-exposed adolescents, comparatively little is known about how disasters impact adolescent wellbeing, nor how factors within the post-disaster environment interact to influence holistic adolescent mental health and wellbeing. Objective: The objective of this study was to describe the holistic mental health and wellbeing of adolescents living in an earthquake-struck city by considering a range of mental health and wellbeing indicators, as well as risk and protective factors hypothesised to influence mental health and wellbeing. The dual-factor model of mental health was used as a framework to guide this study. Method: A survey of Christchurch secondary school students was used to gather data about their subjective wellbeing, risk of low wellbeing, psychological distress, quality of life, exposure to Adverse Childhood Experiences, social support from friends and family, school connectedness, and expectations about future quality of life. Results: A slim majority of students reported good subjective wellbeing (52.3%) and high current quality of life (56.4%), whereas a larger majority reported low risk of psychological distress (79%). An equal proportion of students reported high and low risk of low wellbeing. There were no statistically significant differences in any of the variables measured between adolescents who did and did not live through the Christchurch earthquakes. Regression analyses identified that school connectedness, social support from friends and family, and future expectations of quality of life significantly predicted subjective wellbeing, risk of low wellbeing, risk of psychological distress, and current quality of life. The number of Adverse Childhood Experiences significantly predicted only risk of psychological distress when the effects of other variables were controlled for. Conclusion: The findings of this study indicate that there is a low mean level of wellbeing and quality of life in this sample of adolescents living in a severely earthquake-affected community. School connectedness, social support from family and friends, and expectations about future quality of life were shown to significantly predict variance in subjective wellbeing, quality of life, and psychological distress. This suggests that there are social and environmental factors that can be targeted to improve holistic mental health and wellbeing in disaster-affected adolescents who have experienced high levels of trauma. Conclusions in this study are limited by the representativeness of the sample, the cross-sectional nature of the study, and potential sampling bias.
Background: There has been a psychopathology focus in disaster research examining adolescent mental health and wellbeing, but recently studies have begun to also examine wellbeing-related constructs. Although an increased risk of posttraumatic stress disorder has been established in disaster-exposed adolescents, comparatively little is known about how disasters impact adolescent wellbeing, nor how factors within the post-disaster environment interact to influence holistic adolescent mental health and wellbeing. Objective: The objective of this study was to describe the holistic mental health and wellbeing of adolescents living in an earthquake-struck city by considering a range of mental health and wellbeing indicators, as well as risk and protective factors hypothesised to influence mental health and wellbeing. The dual-factor model of mental health was used as a framework to guide this study. Method: A survey of Christchurch secondary school students was used to gather data about their subjective wellbeing, risk of low wellbeing, psychological distress, quality of life, exposure to Adverse Childhood Experiences, social support from friends and family, school connectedness, and expectations about future quality of life. Results: A slim majority of students reported good subjective wellbeing (52.3%) and high current quality of life (56.4%), whereas a larger majority reported low risk of psychological distress (79%). An equal proportion of students reported high and low risk of low wellbeing. There were no statistically significant differences in any of the variables measured between adolescents who did and did not live through the Christchurch earthquakes. Regression analyses identified that school connectedness, social support from friends and family, and future expectations of quality of life significantly predicted subjective wellbeing, risk of low wellbeing, risk of psychological distress, and current quality of life. The number of Adverse Childhood Experiences significantly predicted only risk of psychological distress when the effects of other variables were controlled for. Conclusion: The findings of this study indicate that there is a low mean level of wellbeing and quality of life in this sample of adolescents living in a severely earthquake- affected community. School connectedness, social support from family and friends, and expectations about future quality of life were shown to significantly predict variance in subjective wellbeing, quality of life, and psychological distress. This suggests that there are social and environmental factors that can be targeted to improve holistic mental health and wellbeing in disaster-affected adolescents who have experienced high levels of trauma. Conclusions in this study are limited by the representativeness of the sample, the cross- sectional nature of the study, and potential sampling bias.
Organisations play a vital role in assisting communities to recover from disasters. They are the key providers of goods and services needed in both response and recovery efforts. They provide the employment which both anchors people to place and supports the taxation base to allow for necessary recovery spending. Finally, organisations are an integral part of much day to day functioning contributing immensely to people’s sense of ‘normality’ and psychological wellbeing. Yet, despite their overall importance in the recovery process, there are significant gaps in our existing knowledge with regard to how organisations respond and recover following disaster. This research fills one part of this gap by examining collaboration as an adaptive strategy enacted by organisations in the Canterbury region of New Zealand, which was heavily impacted by a series of major earthquakes, occurring in 2010 and 2011. Collaboration has been extensively investigated in a variety of settings and from numerous disciplinary perspectives. However, there are few studies that investigate the role of collaborative approaches to support post-disaster business recovery. This study investigates the type of collaborations that have occurred and how they evolved as organisations reacted to the resource and environmental change caused by the disaster. Using data collected through semi-structured interviews, survey and document analysis, a rich and detailed picture of the recovery journey is created for 26 Canterbury organisations including 14 collaborators, six non-traders, five continued traders and one new business. Collaborations included two or more individual businesses collaborating along with two multi-party, place based projects. Comparative analysis of the organisations’ experiences enabled the assessment of decisions, processes and outcomes of collaboration, as well as insight into the overall process of business recovery. This research adopted a primarily inductive, qualitative approach, drawing from both grounded theory and case study methodologies in order to generate theory from this rich and contextually situated data. Important findings include the importance of creating an enabling context which allows organisations to lead their own recovery, the creation of a framework for effective post-disaster collaboration and the importance of considering both economic and other outcomes. Collaboration is found to be an effective strategy enabling resumption of trade at a time when there seemed few other options available. While solving this need, many collaborators have discovered significant and unexpected benefits not just in terms of long term strategy but also with regard to wellbeing. Economic outcomes were less clear-cut. However, with approximately 70% of the Central Business District demolished and rebuilding only gaining momentum in late 2014, many organisations are still in a transition stage moving towards a new ‘normal’.
The Sendai Framework for Disaster Risk Reduction 2015-2030 finds that, despite progress in disaster risk reduction over the last decade “evidence indicates that exposure of persons and assets in all countries has increased faster than vulnerability has decreased, thus generating new risk and a steady rise in disaster losses” (p.4, UNISDR 2015). Fostering cooperation among relevant stakeholders and policy makers to “facilitate a science-policy interface for effective decisionmaking in disaster risk management” is required to achieve two priority areas for action, understanding disaster risk and enhancing disaster preparedness (p. 13, p. 23, UNISDR 2015). In other topic areas, the term science-policy interface is used interchangeably with the term boundary organisation. Both terms are usually used refer to systematic collaborative arrangements used to manage the intersection, or boundary, between science and policy domains, with the aim of facilitating the joint construction of knowledge to inform decision-making. Informed by complexity theory, and a constructivist focus on the functions and processes that minimize inevitable tensions between domains, this conceptual framework has become well established in fields where large complex issues have significant economic and political consequences, including environmental management, biodiversity, sustainable development, climate change and public health. To date, however, there has been little application of this framework in the disaster risk reduction field. In this doctoral project the boundary management framework informs an analysis of the research response to the 2010-2011 Canterbury Earthquake Sequence, focusing on the coordination role of New Zealand’s national Natural Hazards Research Platform. The project has two aims. It uses this framework to tell the nuanced story of the way this research coordination role evolved in response to both the complexity of the unfolding post-disaster environment, and to national policy and research developments. Lessons are drawn from this analysis for those planning and implementing arrangements across the science-policy boundary to manage research support for disaster risk reduction decision-making, particularly after disasters. The second aim is to use this case study to test the utility of the boundary management framework in the disaster risk reduction context. This requires that terminology and concepts are explained and translated in terms that make this analysis as accessible as possible across the disciplines, domains and sectors involved in disaster risk reduction. Key findings are that the focus on balance, both within organisations, and between organisations and domains, and the emphasis on systemic effects, patterns and trends, offer an effective and productive alternative to the more traditional focus on individual or organisational performance. Lessons are drawn concerning the application of this framework when planning and implementing boundary organisations in the hazard and disaster risk management context.
Land cover change information in urban areas supports decision makers in dealing with public policy planning and resource management. Remote sensing has been demonstrated as an efficient and accurate way to monitor land cover change over large extents. The Canterbury Earthquake Sequence (CES) caused massive damage in Christchurch, New Zealand and resulted in significant land cover change over a short time period. This study combined two types of remote sensing data, aerial imagery (RGB) and LiDAR, as the basis for quantifying land cover change in Christchurch between 2011 – 2015, a period corresponding to the five years immediately following the 22 February 2011 earthquake, which was part of the CES. An object based image analysis (OBIA) approach was adopted to classify the aerial imagery and LiDAR data into seven land cover types (bare land, building, grass, shadow, tree and water). The OBIA approach consisted of two steps, image segmentation and object classification. For the first step, this study used multi-level segmentation to better segment objects. For the second step, the random forest (RF) classifier was used to assign a land cover type to each object defined by the segmentation. Overall classification accuracies for 2011 and 2015 were 94.0% and 94.32%, respectively. Based on the classification result, land cover changes between 2011 and 2015 were then analysed. Significant increases were found in road and tree cover, while the land cover types that decreased were bare land, grass, roof, water. To better understand the reasons for those changes, land cover transitions were calculated. Canopy growth, seasonal differences and forest plantation establishment were the main reasons for tree cover increase. Redevelopment after the earthquake was the main reason for road area growth. By comparing the spatial distribution of these transitions, this study also identified Halswell and Wigram as the fastest developing suburbs in Christchurch. These results provided quantitative information for the effects of CES, with respect to land cover change. They allow for a better understanding for the current land cover status of Christchurch. Among those land cover changes, the significant increase in tree cover aroused particularly interest as urban forests benefit citizens via ecosystem services, including health, social, economic, and environmental benefits. Therefore, this study firstly calculated the percentages of tree cover in Christchurch’s fifteen wards in order to provide a general idea of tree cover change in the city extent. Following this, an automatic individual tree detection and crown delineation (ITCD) was undertaken to determine the feasibility of automated tree counting. The accuracies of the proposed approach ranged between 56.47% and 92.11% in thirty different sample plots, with an overall accuracy of 75.60%. Such varied accuracies were later found to be caused by the fixed tree detection window size and misclassifications from the land cover classification that affected the boundary of the CHM. Due to the large variability in accuracy, tree counting was not undertaken city-wide for both time periods. However, directions for further study for ITCD in Christchurch could be exploring ITCD approaches with variable window size or optimizing the classification approach to focus more on producing highly accurate CHMs.
Timber has experienced renewed interests as a sustainable building material in recent times. Although traditionally it has been the prime choice for residential construction in New Zealand and some other parts of the world, its use can be increased significantly in the future through a wider range of applications, particularly when adopting engineered wood material, Research has been started on the development of innovative solutions for multi-storey non-residential timber buildings in recent years and this study is part of that initiative. Application of timber in commercial and office spaces posed some challenges with requirements of large column-free spaces. The current construction practice with timber is not properly suited for structures with the aforementioned required characteristics and new type of structures has to be developed for this type of applications. Any new structural system has to have adequate capacity for carry the gravity and lateral loads due to occupancy and the environmental effects. Along with wind loading, one of the major sources of lateral loads is earthquakes. New Zealand, being located in a seismically active region, has significant risk of earthquake hazard specially in the central region of the country and any structure has be designed for the seismic loading appropriate for the locality. There have been some significant developments in precast concrete in terms of solutions for earthquake resistant structures in the last decade. The “Hybrid” concept combining post-tensioning and energy dissipating elements with structural members has been introduced in the late 1990s by the precast concrete industry to achieve moment-resistant connections based on dry jointed ductile connections. Recent research at the University of Canterbury has shown that the concept can be adopted for timber for similar applications. Hybrid timber frames using post-tensioned beams and dissipaters have the potential to allow longer spans and smaller cross sections than other forms of solid timber frames. Buildings with post-tensioned frames and walls can have larger column-free spaces which is a particular advantage for non-residential applications. While other researchers are focusing on whole structural systems, this research concentrated on the analysis and design of individual members and connections between members or between member and foundation. This thesis extends existing knowledge on the seismic behaviour and response of post-tensioned single walls, columns under uni-direction loads and small scale beam-column joint connections into the response and design of post-tensioned coupled walls, columns under bi-directional loading and full-scale beam-column joints, as well as to generate further insight into practical applications of the design concept for subassemblies. Extensive experimental investigation of walls, column and beam-column joints provided valuable confirmation of the satisfactory performance of these systems. In general, they all exhibited almost complete re-centering capacity and significant energy dissipation, without resulting into structural damage. The different configurations tested also demonstrated the flexibility in design and possibilities for applications in practical structures. Based on the experimental results, numerical models were developed and refined from previous literature in precast concrete jointed ductile connections to predict the behaviour of post-tensioned timber subassemblies. The calibrated models also suggest the values of relevant parameters for applications in further analysis and design. Section analyses involving those parameters are performed to develop procedures to calculate moment capacities of the subassemblies. The typical features and geometric configurations the different types of subassemblies are similar with the only major difference in the connection interfaces. With adoption of appropriate values representing the corresponding connection interface and incorporation of the details of geometry and configurations, moment capacities of all the subassemblies can be calculated with the same scheme. That is found to be true for both post-tensioned-only and hybrid specimens and also applied for both uni-directional and bi-directional loading. The common section analysis and moment capacity calculation procedure is applied in the general design approach for subassemblies.
The Avon-Heathcote Estuary, located in Christchurch, New Zealand, experienced coseismic deformation as a result of the February 22nd 2011 Christchurch Earthquake. The deformation is reflected as subsidence in the northern area and uplift in the southern area of the Estuary, in addition to sand volcanoes which forced up sediment throughout the floor of the Estuary altering estuary bed height and tidal flow. The first part of the research involved quantifying the change in the modern benthic foraminifera distribution as a result of the coseismic deformation caused by the February 22nd 2011 earthquake. By analysing the taxa present immediately post deformation and then the taxa present 2 years post deformation a comparison of the benthic foraminifera distribution can be made of the pre and post deformation. Both the northern and the southern areas of the Estuary were sampled to establish whether foraminifera faunas migrated landward or seaward as a result of subsidence and uplift experienced in different areas. There was no statistical change in overall species distribution in the two year time period since the coseismic deformation occurred, however, there were some noticeable changes in foraminifera distribution at BSNS-Z3 showing a landward migration of taxa. The changes that were predicted to occur as a result of the deformation of the Estuary are taking longer than expected to show up in the foraminiferal record and a longer time period is needed to establish these changes. The second stage involved establishing the modern distribution of foraminifera at Settlers Reserve in the southern area of the Avon-Heathcote Estuary by detailed sampling along a 160 m transect. Foraminifera are sensitive to environmental parameters, tidal height, grainsize, pH and salinity were recorded to evaluate the effect these parameters have on distribution. Bray-Curtis two-way cluster analysis was primarily used to assess the distribution pattern of foraminifera. The modern foraminifera distribution is comparable to that of the modern day New Zealand brackish-water benthic foraminifera distribution and includes species not yet found in other studies of the Avon-Heathcote Estuary. Differences in sampling techniques and the restricted intertidal marshland area where the transect samples were collected account for some of the differences seen between this model and past foraminifera studies. xiii The final stage involved sampling a 2.20 m core collected from Settlers Reserve and using the modern foraminiferal distribution to establish a foraminiferal history of Settlers Reserve. As foraminifera are sensitive to tidal height they may record past coseismic deformation events and the core was used to ascertain whether record of past coseismic deformation is preserved in Settlers Reserve sediments. Sampling the core for foraminifera, grainsize, trace metals and carbon material helped to build a story of estuary development. Using the modern foraminiferal distribution and the tidal height information collected, a down core model of past tidal heights was established to determine past rates of change. Foraminifera are not well preserved throughout the core, however, a sudden relative rise in sea level is recorded between 0.25 m and 0.85 m. Using trace metal and isotope analysis to develop an age profile, this sea level rise is interpreted to record coseismic subsidence associated with a palaeoseismic event in the early 1900’s. Overall, although the Avon-Heathcote Estuary experienced clear coseismic deformation as a result of the 22nd of February 2011 earthquake, modern changes in foraminiferal distribution cannot yet be tracked, however, past seismic deformation is identified in a core. The modern transect describes the foraminifera distribution which identifies species that have not been identified in the Avon-Heathcote Estuary before. This thesis enhances the current knowledge of the Avon-Heathcote Estuary and is a baseline for future studies.
The increase of the world's population located near areas prone to natural disasters has given rise to new ‘mega risks’; the rebuild after disasters will test the governments’ capabilities to provide appropriate responses to protect the people and businesses. During the aftermath of the Christchurch earthquakes (2010-2012) that destroyed much of the inner city, the government of New Zealand set up a new partnership between the public and private sector to rebuild the city’s infrastructure. The new alliance, called SCIRT, used traditional risk management methods in the many construction projects. And, in hindsight, this was seen as one of the causes for some of the unanticipated problems. This study investigated the risk management practices in the post-disaster recovery to produce a specific risk management model that can be used effectively during future post-disaster situations. The aim was to develop a risk management guideline for more integrated risk management and fill the gap that arises when the traditional risk management framework is used in post-disaster situations. The study used the SCIRT alliance as a case study. The findings of the study are based on time and financial data from 100 rebuild projects, and from surveying and interviewing risk management professionals connected to the infrastructure recovery programme. The study focussed on post-disaster risk management in construction as a whole. It took into consideration the changes that happened to the people, the work and the environment due to the disaster. System thinking, and system dynamics techniques have been used due to the complexity of the recovery and to minimise the effect of unforeseen consequences. Based on an extensive literature review, the following methods were used to produce the model. The analytical hierarchical process and the relative importance index have been used to identify the critical risks inside the recovery project. System theory methods and quantitative graph theory have been used to investigate the dynamics of risks between the different management levels. Qualitative comparative analysis has been used to explore the critical success factors. And finally, causal loop diagrams combined with the grounded theory approach has been used to develop the model itself. The study identified that inexperienced staff, low management competency, poor communication, scope uncertainty, and non-alignment of the timing of strategic decisions with schedule demands, were the key risk factors in recovery projects. Among the critical risk groups, it was found that at a strategic management level, financial risks attracted the highest level of interest, as the client needs to secure funding. At both alliance-management and alliance-execution levels, the safety and environmental risks were given top priority due to a combination of high levels of emotional, reputational and media stresses. Risks arising from a lack of resources combined with the high volume of work and the concern that the cost could go out of control, alongside the aforementioned funding issues encouraged the client to create the recovery alliance model with large reputable construction organisations to lock in the recovery cost, at a time when the scope was still uncertain. This study found that building trust between all parties, clearer communication and a constant interactive flow of information, established a more working environment. Competent and clear allocation of risk management responsibilities, cultural shift, risk prioritisation, and staff training were crucial factors. Finally, the post-disaster risk management (PDRM) model can be described as an integrated risk management model that considers how the changes which happened to the environment, the people and their work, caused them to think differently to ease the complexity of the recovery projects. The model should be used as a guideline for recovery systems, especially after an earthquake, looking in detail at all the attributes and the concepts, which influence the risk management for more effective PDRM. The PDRM model is represented in Causal Loops Diagrams (CLD) in Figure 8.31 and based on 10 principles (Figure 8.32) and 26 concepts (Table 8.1) with its attributes.
Geologic phenomena produced by earthquake shaking, including rockfalls and liquefaction features, provide important information on the intensity and spatiotemporal distribution of earthquake ground motions. The study of rockfall and liquefaction features produced in contemporary well- instrumented earthquakes increases our knowledge of how natural and anthropogenic environments respond to earthquakes and improves our ability to deduce seismologic information from analogous pre-contemporary (paleo-) geologic features. The study of contemporary and paleo- rockfall and liquefaction features enables improved forecasting of environmental responses to future earthquakes. In this thesis I utilize a combination of field and imagery-based mapping, trenching, stratigraphy, and numerical dating techniques to understand the nature and timing of rockfalls (and hillslope sedimentation) and liquefaction in the eastern South Island of New Zealand, and to examine the influence that anthropogenic activity has had on the geologic expressions of earthquake phenomena. At Rapaki (Banks Peninsula, NZ), field and imagery-based mapping, statistical analysis and numerical modeling was conducted on rockfall boulders triggered by the fatal 2011 Christchurch earthquakes (n=285) and compared with newly identified prehistoric (Holocene and Pleistocene) boulders (n=1049) deposited on the same hillslope. A significant population of modern boulders (n=26) travelled farther downslope (>150 m) than their most-travelled prehistoric counterparts, causing extensive damage to residential dwellings at the foot of the hillslope. Replication of prehistoric boulder distributions using 3-dimensional rigid body numerical models requires the application of a drag-coefficient, attributed to moderate to dense slope vegetation, to account for their spatial distribution. Radiocarbon dating provides evidence for 17th to early 20th century deforestation at the study site during Polynesian and European colonization and after emplacement of prehistoric rockfalls. Anthropocene deforestation enabled modern rockfalls to exceed the limits of their prehistoric predecessors, highlighting a shift in the geologic expression of rockfalls due to anthropogenic activity. Optical and radiocarbon dating of loessic hillslope sediments in New Zealand’s South Island is used to constrain the timing of prehistoric rockfalls and associated seismic events, and quantify spatial and temporal patterns of hillslope sedimentation including responses to seismic and anthropogenic forcing. Luminescence ages from loessic sediments constrain timing of boulder emplacement to between ~3.0 and ~12.5 ka, well before the arrival of Polynesians (ca AD 1280) and Europeans (ca AD 1800) in New Zealand, and suggest loess accumulation was continuing at the study site until 12-13 ka. Large (>5 m3) prehistoric rockfall boulders preserve an important record of Holocene hillslope sedimentation by creating local traps for sediment aggradation and upbuilding soil formation. Sediment accumulation rates increased considerably (>~10 factor increase) following human arrival and associated anthropogenic burning of hillslope vegetation. New numerical ages are presented to place the evolution of loess-mantled hillslopes in New Zealand’s South Island into a longer temporal framework and highlight the roles of earthquakes and humans on hillslope surface process. Extensive field mapping and characterization for 1733 individual prehistoric rockfall boulders was conducted at Rapaki and another Banks Peninsula site, Purau, to understand their origin, frequency, and spatial and volumetric distributions. Boulder characteristics and distributions were compared to 421 boulders deposited at the same sites during the 2010-2011 Canterbury earthquake sequence. Prehistoric boulders at Rapaki and Purau are comprised of two dominant lithofacies types: volcanic breccia and massive (coherent) lava basalt. Volcanic breccia boulders are found in greatest abundance (64-73% of total mapped rockfall) and volume (~90-96% of total rockfall) at both locations and exclusively comprise the largest boulders with the longest runout distances that pose the greatest hazard to life and property. This study highlights the primary influence that volcanic lithofacies architecture has on rockfall hazard. The influence of anthropogenic modifications on the surface and subsurface geologic expression of contemporary liquefaction created during the 2010-2011 Canterbury earthquake sequence (CES) in eastern Christchurch is examined. Trench observations indicate that anthropogenic fill layer boundaries and the composition/texture of discretely placed fill layers play an important role in absorbing fluidized sand/silt and controlling the subsurface architecture of preserved liquefaction features. Surface liquefaction morphologies (i.e. sand blows and linear sand blow arrays) display alignment with existing utility lines and utility excavations (and perforated pipes) provided conduits for liquefaction ejecta during the CES. No evidence of pre-CES liquefaction was identified within the anthropogenic fill layers or underlying native sediment. Radiocarbon dating of charcoal within the youngest native sediment suggests liquefaction has not occurred at the study site for at least the past 750-800 years. The importance of systematically examining the impact of buried infrastructure on channelizing and influencing surface and subsurface liquefaction morphologies is demonstrated. This thesis highlights the importance of using a multi-technique approach for understanding prehistoric and contemporary earthquake phenomena and emphasizes the critical role that humans play in shaping the geologic record and Earth’s surface processes.
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.
Geosynthetic reinforced soil (GRS) walls involve the use of geosynthetic reinforcement (polymer material) within the retained backfill, forming a reinforced soil block where transmission of overturning and sliding forces on the wall to the backfill occurs. Key advantages of GRS systems include the reduced need for large foundations, cost reduction (up to 50%), lower environmental costs, faster construction and significantly improved seismic performance as observed in previous earthquakes. Design methods in New Zealand have not been well established and as a result, GRS structures do not have a uniform level of seismic and static resistance; hence involve different risks of failure. Further research is required to better understand the seismic behaviour of GRS structures to advance design practices. The experimental study of this research involved a series of twelve 1-g shake table tests on reduced-scale (1:5) GRS wall models using the University of Canterbury shake-table. The seismic excitation of the models was unidirectional sinusoidal input motion with a predominant frequency of 5Hz and 10s duration. Seismic excitation of the model commenced at an acceleration amplitude level of 0.1g and was incrementally increased by 0.1g in subsequent excitation levels up to failure (excessive displacement of the wall panel). The wall models were 900mm high with a full-height rigid facing panel and five layers of Microgird reinforcement (reinforcement spacing of 150mm). The wall panel toe was founded on a rigid foundation and was free to slide. The backfill deposit was constructed from dry Albany sand to a backfill relative density, Dr = 85% or 50% through model vibration. The influence of GRS wall parameters such as reinforcement length and layout, backfill density and application of a 3kPa surcharge on the backfill surface was investigated in the testing sequence. Through extensive instrumentation of the wall models, the wall facing displacements, backfill accelerations, earth pressures and reinforcement loads were recorded at the varying levels of model excitation. Additionally, backfill deformation was also measured through high-speed imaging and Geotechnical Particle Image Velocimetry (GeoPIV) analysis. The GeoPIV analysis enabled the identification of the evolution of shear strains and volumetric strains within the backfill at low strain levels before failure of the wall thus allowing interpretations to be made regarding the strain development and shear band progression within the retained backfill. Rotation about the wall toe was the predominant failure mechanism in all excitation level with sliding only significant in the last two excitation levels, resulting in a bi-linear displacement acceleration curve. An increase in acceleration amplification with increasing excitation was observed with amplification factors of up to 1.5 recorded. Maximum seismic and static horizontal earth pressures were recorded at failure and were recorded at the wall toe. The highest reinforcement load was recorded at the lowest (deepest in the backfill) reinforcement layer with a decrease in peak load observed at failure, possibly due to pullout failure of the reinforcement layer. Conversely, peak reinforcement load was recorded at failure for the top reinforcement layer. The staggered reinforcement models exhibited greater wall stability than the uniform reinforcement models of L/H=0.75. However, similar critical accelerations were determined for the two wall models due to the coarseness of excitation level increments of 0.1g. The extended top reinforcements were found to restrict the rotational component of displacement and prevented the development of a preliminary shear band at the middle reinforcement layer, contributing positively to wall stability. Lower acceleration amplification factors were determined for the longer uniform reinforcement length models due to reduced model deformation. A greater distribution of reinforcement load towards the top two extended reinforcement layers was also observed in the staggered wall models. An increase in model backfill density was observed to result in greater wall stability than an increase in uniform reinforcement length. Greater acceleration amplification was observed in looser backfill models due to their lower model stiffness. Due to greater confinement of the reinforcement layers, greater reinforcement loads were developed in higher density wall models with less wall movement required to engage the reinforcement layers and mobilise their resistance. The application of surcharge on the backfill was observed to initially increase the wall stability due to greater normal stresses within the backfill but at greater excitation levels, the surcharge contribution to wall destabilising inertial forces outweighs its contribution to wall stability. As a result, no clear influence of surcharge on the critical acceleration of the wall models was observed. Lower acceleration amplification factors were observed for the surcharged models as the surcharge acts as a damper during excitation. The application of the surcharge also increases the magnitude of reinforcement load developed due to greater confinement and increased wall destabilising forces. The rotation of the wall panel resulted in the progressive development of shears surface with depth that extended from the backfill surface to the ends of the reinforcement (edge of the reinforced soil block). The resultant failure plane would have extended from the backfill surface to the lowest reinforcement layer before developing at the toe of the wall, forming a two-wedge failure mechanism. This is confirmed by development of failure planes at the lowest reinforcement layer (deepest with the backfill) and at the wall toe observed at the critical acceleration level. Key observations of the effect of different wall parameters from the GeoPIV results are found to be in good agreement with conclusions developed from the other forms of instrumentation. Further research is required to achieve the goal of developing seismic guidelines for GRS walls in geotechnical structures in New Zealand. This includes developing and testing wall models with a different facing type (segmental or wrap-around facing), load cell instrumentation of all reinforcement layers, dynamic loading on the wall panel and the use of local soils as the backfill material. Lastly, the limitations of the experimental procedure and wall models should be understood.
As a global phenomenon, many cities are undergoing urban renewal to accommodate rapid growth in urban population. However, urban renewal can struggle to balance social, economic, and environmental outcomes, whereby economic outcomes are often primarily considered by developers. This has important implications for urban forests, which have previously been shown to be negatively affected by development activities. Urban forests serve the purpose of providing ecosystem services and thus are beneficial to human wellbeing. Better understanding the effect of urban renewal on city trees may help improve urban forest outcomes via effective management and policy strategies, thereby maximising ecosystem service provision and human wellbeing. Though the relationship between certain aspects of development and urban forests has received consideration in previous literature, little research has focused on how the complete property redevelopment cycle affects urban forest dynamics over time. This research provides an opportunity to gain a comprehensive understanding of the effect of residential property redevelopment on urban forest dynamics, at a range of spatial scales, in Christchurch, New Zealand following a series of major earthquakes which occurred in 2010 – 2011. One consequence of the earthquakes is the redevelopment of thousands of properties over a relatively short time-frame. The research quantifies changes in canopy cover city-wide, as well as, tree removal, retention, and planting on individual residential properties. Moreover, the research identifies the underlying reasons for these dynamics, by exploring the roles of socio-economic and demographic factors, the spatial relationships between trees and other infrastructure, and finally, the attitudes of residential property owners. To quantify the effect of property redevelopment on canopy cover change in Christchurch, this research delineated tree canopy cover city-wide in 2011 and again in 2015. An object-based image analysis (OBIA) technique was applied to aerial imagery and LiDAR data acquired at both time steps, in order to estimate city-wide canopy cover for 2011 and 2015. Changes in tree canopy cover between 2011 and 2015 were then spatially quantified. Tree canopy cover change was also calculated for all meshblocks (a relatively fine-scale geographic boundary) in Christchurch. The results show a relatively small magnitude of tree canopy cover loss, city-wide, from 10.8% to 10.3% between 2011 and 2015, but a statistically significant change in mean tree canopy cover across all the meshblocks. Tree canopy cover losses were more likely to occur in meshblocks containing properties that underwent a complete redevelopment cycle, but the loss was insensitive to the density of redevelopment within meshblocks. To explore property-scale individual tree dynamics, a mixed-methods approach was used, combining questionnaire data and remote sensing analysis. A mail-based questionnaire was delivered to residential properties to collect resident and household data; 450 residential properties (321 redeveloped, 129 non- redeveloped) returned valid questionnaires and were identified as analysis subjects. Subsequently, 2,422 tree removals and 4,544 tree retentions were identified within the 450 properties; this was done by manually delineating individual tree crowns, based on aerial imagery and LiDAR data, and visually comparing the presence or absence of these trees between 2011 and 2015. The tree removal rate on redeveloped properties (44.0%) was over three times greater than on non-redeveloped properties (13.5%) and the average canopy cover loss on redeveloped properties (52.2%) was significantly greater than on non-redeveloped properties (18.8%). A classification tree (CT) analysis was used to model individual tree dynamics (i.e. tree removal, tree retention) and candidate explanatory variables (i.e. resident and household, economic, land cover, and spatial variables). The results indicate that the model including land cover, spatial, and economic variables had the best predicting ability for individual tree dynamics (accuracy = 73.4%). Relatively small trees were more likely to be removed, while trees with large crowns were more likely to be retained. Trees were most likely to be removed from redeveloped properties with capital values lower than NZ$1,060,000 if they were within 1.4 m of the boundary of a redeveloped building. Conversely, trees were most likely to be retained if they were on a property that was not redeveloped. The analysis suggested that the resident and household factors included as potential explanatory variables did not influence tree removal or retention. To conduct a further exploration of the relationship between resident attitudes and actions towards trees on redeveloped versus non-redeveloped properties, this research also asked the landowners from the 450 properties that returned mail questionnaires to indicate their attitudes towards tree management (i.e. tree removal, tree retention, and tree planting) on their properties. The results show that residents from redeveloped properties were more likely to remove and/or plant trees, while residents from non- redeveloped properties were more likely to retain existing trees. A principal component analysis (PCA) was used to explore resident attitudes towards tree management. The results of the PCA show that residents identified ecosystem disservices (e.g. leaf litter, root damage to infrastructure) as common reasons for tree removal; however, they also noted ecosystem services as important reasons for both tree planting and tree retention on their properties. Moreover, the reasons for tree removal and tree planting varied based on whether residents’ property had been redeveloped. Most tree removal occurred on redeveloped properties because trees were in conflict with redevelopment, but occurred on non- redeveloped properties because of perceived poor tree health. Residents from redeveloped properties were more likely to plant trees due to being aesthetically pleasing or to replace trees removed during redevelopment. Overall, this research adds to, and complements, the existing literature on the effects of residential property redevelopment on urban forest dynamics. The findings of this research provide empirical support for developing specific legislation or policies about urban forest management during residential property redevelopment. The results also imply that urban foresters should enhance public education on the ecosystem services provided by urban forests and thus minimise the potential for tree removal when undertaking property redevelopment.
Environmental stress and disturbance can affect the structure and functioning of marine ecosystems by altering their physical, chemical and biological features. In estuaries, benthic invertebrate communities play important roles in structuring sediments, influencing primary production and biogeochemical flux, and occupying key food web positions. Stress and disturbance can reduce species diversity, richness and abundance, with ecological theory predicting that biodiversity will be at its lowest soon after a disturbance with assemblages dominated by opportunistic species. The Avon-Heathcote Estuary in Christchurch New Zealand has provided a novel opportunity to examine the effects of stress, in the form of eutrophication, and disturbance, in the form of cataclysmic earthquake events, on the structure and functioning of an estuarine ecosystem. For more than 50 years, large quantities (up to 500,000m3/day) of treated wastewater were released into this estuary but in March 2010 this was diverted to an ocean outfall, thereby reducing the nutrient loading by around 90% to the estuary. This study was therefore initially focussed on the reversal of eutrophication and consequent effects on food web structure in the estuary as it responded to lower nutrients. In 2011, however, Christchurch was struck with a series of large earthquakes that greatly changed the estuary. Massive amounts of liquefied sediments, covering up to 65% of the estuary floor, were forced up from deep below the estuary, the estuary was tilted by up to a 50cm rise on one side and a corresponding drop on the other, and large quantities of raw sewage from broken wastewater infrastructure entered the estuary for up to nine months. This study was therefore a test of the potentially synergistic effects of nutrient reduction and earthquake disturbance on invertebrate communities, associated habitats and food web dynamics. Because there was considerable site-to-site heterogeneity in the estuary, the sites in this study were selected to represent a eutrophication gradient from relatively “clean” (where the influence of tidal flows was high) to highly impacted (near the historical discharge site). The study was structured around these sites, with components before the wastewater diversion, after the diversion but before the earthquakes, and after the earthquakes. The eutrophication gradient was reflected in the composition and isotopic chemistry of primary producer and invertebrate communities and the characteristics of sediments across the sample sites. Sites closest to the former wastewater discharge pipe were the most eutrophic and had cohesive organic -rich, fine sediments and relatively depauperate communities dominated by the opportunistic taxa Capitellidae. The less-impacted sites had coarser, sandier sediments with fewer pollutants and far less organic matter than at the eutrophic sites, relatively high diversity and lower abundances of micro- and macro-algae. Sewage-derived nitrogen had became incorporated into the estuarine food web at the eutrophic sites, starting at the base of the food chain with benthic microalgae (BMA), which were found to use mostly sediment-derived nitrogen. Stable isotopic analysis showed that δ13C and δ15N values of most food sources and consumers varied spatially, temporally and in relation to the diversion of wastewater, whereas the earthquakes did not appear to affect the overall estuarine food web structure. This was seen particularly at the most eutrophic site, where isotopic signatures became more similar to the cleaner sites over two-and-a-half years after the diversion. New sediments (liquefaction) produced by the earthquakes were found to be coarser, have lower concentrations of heavy metals and less organic matter than old (existing) sediments. They also had fewer macroinvertebrate inhabitants initially after the earthquakes but most areas recovered to pre-earthquake abundance and diversity within two years. Field experiments showed that there were higher amounts of primary production and lower amounts of nutrient efflux from new sediments at the eutrophic sites after the earthquakes. Primary production was highest in new sediments due to the increased photosynthetic efficiency of BMA resulting from the increased permeability of new sediments allowing increased light penetration, enhanced vertical migration of BMA and the enhanced transport of oxygen and nutrients. The reduced efflux of NH4-N in new sediments indicated that the capping of a large portion of eutrophic old sediments with new sediments had reduced the release of legacy nutrients (originating from the historical discharge) from the sediments to the overlying water. Laboratory experiments using an array of species and old and new sediments showed that invertebrates altered levels of primary production and nutrient flux but effects varied among species. The mud snail Amphibola crenata and mud crab Austrohelice crassa were found to reduce primary production and BMA biomass through the consumption of BMA (both species) and its burial from bioturbation and the construction of burrows (Austrohelice). In contrast, the cockle Austrovenus stutchburyi did not significantly affect primary production and BMA biomass. These results show that changes in the structure of invertebrate communities resulting from disturbances can also have consequences for the functioning of the system. The major conclusions of this study were that the wastewater diversion had a major effect on food web dynamics and that the large quantities of clean and unpolluted new sediments introduced to the estuary during the earthquakes altered the recovery trajectory of the estuary, accelerating it at least throughout the duration of this study. This was largely through the ‘capping’ effect of the new liquefied, coarser-grained sediments as they dissipated across the estuary and covered much of the old organic-rich eutrophic sediments. For all aspects of this study, the largest changes occurred at the most eutrophic sites; however, the surrounding habitats were important as they provided the context for recovery of the estuary, particularly because of the very strong influence of sediments, their biogeochemistry, microalgal and macroalgal dynamics. There have been few studies documenting system level responses to eutrophication amelioration and to the best on my knowledge there are no other published studies examining the impacts of large earthquakes on benthic communities in an estuarine ecosystem. This research gives valuable insight and advancements in the scientific understanding of the effects that eutrophication recovery and large-scale disturbances can have on the ecology of a soft-sediment ecosystem.
