Decision support framework for post-earthquake restoration of sewerage pip…

Research papers, University of Canterbury Library

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.

Coexistence, dynamics and disturbance history of mixed conifer, beech, and…

Research papers, Lincoln University

Mixed conifer, beech and hardwood forests are relatively common in Aotearoa/New Zealand, but are not well studied. This thesis investigates the coexistence, regeneration dynamics and disturbance history of a mixed species forest across an environmental gradient of drainage and soil development in north Westland. The aim was to investigate whether conifers, beech and non-beech hardwood species were able to coexist on surfaces that differed in their underlying edaphic conditions, and if so to understand the mechanisms that influenced their regeneration on both poorly drained and well drained soils. The site selected was an area of high tree species diversity on a lowland 0.8 km² post-glacial terrace at the base of Mount Harata in the Grey River Valley. My approach was to use forest stand history reconstruction at two spatial scales: an intensive within-plot study of stand dynamics (chapter 1) and a whole-landform approach (chapter 2) that examined whether the dynamics identified at the smaller within-plot scale reflected larger patterns across the terrace. In chapter 1, three large permanent plots (0.3-0.7 ha) were placed at different points along the drainage gradient, one plot situated in each of the mainly well-drained, poorly drained and very poorly drained areas along the terrace. Information was gathered on species age and size structures, spatial distributions of tree ages, species interactions, microsite establishment preferences, patterns of stand mortality, and disturbance history in each plot. There were differences in stand structure, composition and relative abundance of species found between the well drained plot and the two poorer drained plots. On the well drained site conifers were scarce, the beeches Nothofagus fusca and N. menziesii dominated the canopy, and in the subcanopy the hardwood species Weinmannia racemosa and Quintinia acutifolia were abundant. As drainage became progressively poorer, the conifers Dacrydium cupressinum and Dacrycarpus dacrydioides became more abundant and occupied the emergent tier over a beech canopy. The hardwoods W. racemosa and Q. acutifolia became gradually less abundant in the subcanopy, whereas the hardwood Elaeocarpus hookerianus became more so. In the well drained plot, gap partitioning for light between beeches and hardwoods enabled coexistence in response to a range of different sized openings resulting from disturbances of different extent. In the two more poorly drained plots, species also coexisted by partitioning microsite establishment sites according to drainage. There were several distinct periods where synchronous establishment of different species occurred in different plots, suggesting there were large disturbances: c. 100yrs, 190-200 yrs, 275-300 yrs and 375-425 yrs ago. Generally after the same disturbance, different species regenerated in different plots reflecting the underlying drainage gradient. However, at the same site after different disturbances, different sets of species regenerated, suggesting the type and extent of disturbances and the conditions left behind influenced species regeneration at some times but not others. The regeneration of some species (e.g., N. fusca in the well-drained plot, and Dacrydium in the poorer drained plots) was periodic and appeared to be closely linked to these events. In the intervals between these disturbances, less extensive disturbances resulted in the more frequent N. menziesii and especially hardwood regeneration. The type of tree death caused by different disturbances favoured different species, with dead standing tree death favouring the more shade-tolerant N. menziesii and hardwoods, whereas uprooting created a mosaic of microsite conditions and larger gap sizes that enabled Dacrycarpus, N. fusca and E. hookerianus to maintain themselves in the poorly drained areas. In chapter 2, 10 circular plots (c. 0.12 ha) were placed in well drained areas and 10 circular plots (c. 0.2 ha) in poorly drained plots to collect information on species population structures and microsite preferences. The aims were to reconstruct species' regeneration responses to a range of disturbances of different type and extent across the whole terrace, and to examine whether there were important differences in the effects of these disturbances. At this landform scale, the composition and relative abundances of species across the drainage gradient reflected those found in chapter 1. There were few scattered conifers in well drained areas, despite many potential regeneration opportunities created from a range of different stand destroying and smaller scale disturbances. Three of the four periods identified in chapter 1 reflected distinct terrace-wide periods of regeneration 75-100 yrs, 200-275 yrs and 350-450 yrs ago, providing strong evidence of periodic large, infrequent disturbances that occurred at intervals of 100-200 yrs. These large, infrequent disturbances have had a substantial influence in determining forest history, and have had long term effects on forest structure and successional processes. Different large, infrequent disturbances had different effects across the terrace, with the variability in conditions that resulted enabling different species to regenerate at different times. For example, the regeneration of distinct even-aged Dacrydium cohorts in poorly drained areas was linked to historical Alpine Fault earthquakes, but not to more recent storms. The variation in the intensity of different large, infrequent disturbances at different points along the environmental drainage gradient, was a key factor influencing the scale of impacts. In effect, the underlying edaphic conditions influenced species composition along the drainage gradient and disturbance history regulated the relative abundances of species. The results presented here further emphasise the importance of large scale disturbances as a mechanism that allows coexistence of different tree species in mixed forest, in particular for the conifers Dacrydium, Dacrycarpus and the beech N. fusca, by creating much of the environmental variation to which these species responded. This study adds to our understanding of the effects of historical earthquakes in the relatively complex forests of north Westland, and further illustrates their importance in the Westland forest landscape as the major influential disturbance on forest pattern and history. These results also further develop the 'two-component' model used to describe conifer/angiosperm dynamics, by identifying qualitative differences in the impacts of different large, infrequent disturbances across an environmental gradient that allowed for coexistence of different species. In poorer drained areas, these forests may even be thought of as 'three-component' systems with conifers, beeches and hardwoods exhibiting key differences in their regeneration patterns after disturbances of different type and extent, and in their microsite preferences.

Seismic performance assessment and improvement of unitized glazing systems

Research papers, University of Canterbury Library

Recent seismic events, such as the 2010-2011 Canterbury earthquakes and the 2016 Kaikōura earthquakes, have shed light on issues with the seismic performance of glazing systems. This is attributed to the limited amount of research and consideration of glazing systems in design and assessments. Previous research and evidence from post-earthquake reconnaissance have shown that glazing systems pose a hazard due to falling glass. As such, it is vital to ensure that glazing systems are designed with the necessary levels of seismic performance. Furthermore, the post-earthquake repair of glass facades can be costly and time-consuming. Some previous research has been conducted to highlight the seismic performance and fragility of glazing systems. However, most prior research only focussed on life-safety issues of glazing systems and rarely on the serviceability of glazing systems. The serviceability of glazing systems, such as water-tightness, is a vital aspect of glazing systems as a low serviceability capacity will increase the likelihood of further damage which will increase economic losses. This is the aim of this research, to provide insight towards the seismic performance of glazing systems considering both the serviceability and ultimate limit state by generating insight into the behaviour of glazing systems and developing tools for the consideration of glazing systems in design and assessment. This will allow a value proposition for seismic detailing of glazing to be evaluated. In order to provide insight into the behaviour of glazing systems and a means for evaluating their seismic performance, this research firstly develops an applicable experimental testing procedure that allows for serviceability limit state tests on glazing units. This experimental testing procedure is used to obtain data on the vulnerability of general New Zealand glazing systems’ performance, specifically unitised glazing systems that are commonly used as commercial shopfront glazing system types. These glazing systems typically realised using aluminium framing with gaskets connecting the frame to the glass. After the experimental testing, numerical analyses calibrated to the experimental testing results are conducted to enable robust analyses of glazing systems’ fragility. Finally, a value proposition for glazing systems with seismic detailing is made by comparing the performance of glazing systems with seismic detailing and conventional glazing systems. This comparison is done using the PEER-PBEE method and the economic implications of each glazing system is shown. Suggestions for designers and stakeholders aimed at reducing costs related to the seismic performance of glazing systems is also shown. Using the novel experimental method developed in this research, three different full-scale glazing systems were tested. A total of 10 unitised glazing specimens were tested; three with standard detailing, three with seismic detailing and four that were structurally glazed. These tests evaluated three damage states (DS): loss of water-tightness (DS1), gasket damage (DS2), and glass or framing failure (DS3). The experimental method that was adopted is considered to be more desirable than the optional procedures set out in New Zealand glazing standards. The method does not require high-speed testing equipment and is easy to replicate by the industry. The test results show that water-tightness was lost at low drift levels, with the first leakage occurring at just 0.15% drift for one specimen, while a standard glazing system had a median drift capacity of 0.35%. In contrast, seismic glazing systems detailed to better accommodate in-plane movements, demonstrated a significantly higher median drift capacity of 1.88%. The numerical approach proposed in this research has shown that it is possible to numerically model the glazing-gasket interaction to conservatively predict the water-leakage drift (damage state 1). The modelling approach still needs further development if it were to be used for damage states DS2 and DS3. The last part of the research considered the value proposition for seismic glazing systems. This was achieved by applying the FEMA P-58 performance assessment framework to a number of case study buldings that are typical of New Zealand design. The results suggest that it may not be economically worthwhile to use well-detailed seismic glazing systems despite the considerably larger drift capacity they possess relative to standard systems. However, as the cost of seismic glazing systems reduces, and more information on repair costs for different damage states is obtained, the value proposition may change.

Multi-scale influences of abiotic factors on alpine treelines

Research papers, Lincoln University

Globally, the maximum elevations at which treelines are observed to occur coincide with a 6.4 °C soil isotherm. However, when observed at finer scales, treelines display a considerable degree of spatial complexity in their patterns across the landscape and are often found occurring at lower elevations than expected relative to the global-scale pattern. There is still a lack of understanding of how the abiotic environment imposes constraints on treeline patterns, the scales at which different effects are acting, and how these effects vary over large spatial extents. In this thesis, I examined abrupt Nothofagus treelines across seven degrees of latitude in New Zealand in order to investigate two broad questions: (1) What is the nature and extent of spatial variability in Nothofagus treelines across the country? (2) How is this variation associated with abiotic variation at different spatial scales? A range of GIS, statistical, and atmospheric modelling methods were applied to address these two questions. First, I characterised Nothofagus treeline patterns at a 15x15km scale across New Zealand using a set of seven, GIS-derived, quantitative metrics that describe different aspects of treeline position, shape, spatial configuration, and relationships with adjacent vegetation. Multivariate clustering of these metrics revealed distinct treeline types that showed strong spatial aggregation across the country. This suggests a strong spatial structuring of the abiotic environment which, in turn, drives treeline patterns. About half of the multivariate treeline metric variation was explained by patterns of climate, substrate, topographic and disturbance variability; on the whole, climatic and disturbance factors were most influential. Second, I developed a conceptual model that describes how treeline elevation may vary at different scales according to three categories of effects: thermal modifying effects, physiological stressors, and disturbance effects. I tested the relevance of this model for Nothofagus treelines by investigating treeline elevation variation at five nested scales (regional to local) using a hierarchical design based on nested river catchments. Hierarchical linear modelling revealed that the majority of the variation in treeline elevation resided at the broadest, regional scale, which was best explained by the thermal modifying effects of solar radiation, mountain mass, and differences in the potential for cold air ponding. Nonetheless, at finer scales, physiological and disturbance effects were important and acted to modify the regional trend at these scales. These results suggest that variation in abrupt treeline elevations are due to both broad-scale temperature-based growth limitation processes and finer-scale stress- and disturbance-related effects on seedling establishment. Third, I explored the applicability of a meso-scale atmospheric model, The Air Pollution Model (TAPM), for generating 200 m resolution, hourly topoclimatic data for temperature, incoming and outgoing radiation, relative humidity, and wind speeds. Initial assessments of TAPM outputs against data from two climate station locations over seven years showed that the model could generate predictions with a consistent level of accuracy for both sites, and which agreed with other evaluations in the literature. TAPM was then used to generate data at 28, 7x7 km Nothofagus treeline zones across New Zealand for January (summer) and July (winter) 2002. Using mixed-effects linear models, I determined that both site-level factors (mean growing season temperature, mountain mass, precipitation, earthquake intensity) and local-level landform (slope and convexity) and topoclimatic factors (solar radiation, photoinhibition index, frost index, desiccation index) were influential in explaining variation in treeline elevation within and among these sites. Treelines were generally closer to their site-level maxima in regions with higher mean growing season temperatures, larger mountains, and lower levels of precipitation. Within sites, higher treelines were associated with higher solar radiation, and lower photoinhibition and desiccation index values, in January, and lower desiccation index values in July. Higher treelines were also significantly associated with steeper, more convex landforms. Overall, this thesis shows that investigating treelines across extensive areas at multiple study scales enables the development of a more comprehensive understanding of treeline variability and underlying environmental constraints. These results can be used to formulate new hypotheses regarding the mechanisms driving treeline formation and to guide the optimal choice of field sites at which to test these hypotheses.