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TALK ONE: Pablo Higuera
Composite modelling: Experiments and CFD combined for better design insights on coastal structures.
The design of coastal structures continues to rely heavily on physical experiments, either compiled into widely-used semi-empirical formulations or to produce ad hoc formulations for non-conventional structures. Numerical modelling, having been under development for some decades now, has the potential to disrupt the design methodology in coastal engineering by providing detailed insights, additional data impossible to measure in the laboratory or by informing about scale effects. The largest benefits can be obtained when applying composite modelling, i.e. physical and numerical modelling working together in a complementary way.
In this presentation we will introduce the methodology to establish a composite modelling framework, outlining the advantages that it can offer and the challenges associated to its implementation. We will also review several practical applications in which two- and three-dimensional CFD models have been applied to analyse the wave-induced forces on a structure or the overtopping over it.
TALK TWO: Giovanni Coco, Joao Albuquerque, Laura Cagigal
Storm surge and wave climate projections (2020-2100) for Aotearoa New Zealand
A collaborative project by the University of Auckland with University of Cantabria has generated a nationwide set of projections of nearshore wave and storm surge conditions. The projections look at the next 80 years and are obtained using an innovative “multi-model” approach, which combines dynamical modelling and statistical downscaling. IPCC emission scenarios and associated climate properties are used to drive these predictions of future wave and surge processes.
The projections are calculated at a scale of about 25 (storm surge) and 10 (waves) kilometres for the whole New Zealand coastline. Also for the first time, this data is now publicly available through a free-access web-based platform. The data, which includes also hindcasts of both storm surge and waves, can be downloaded here.
This work provides unprecedented access to vital information for decision-makers involved in coastal planning. Our data also provides robust evidence to understand both the present and future changes in coastal hazards associated to climate change.
TALK ONE: Anita Lewis
Baseline investigation of microplastic pollution in sediment and bivalves in the Tauranga Harbour (Tauranga Moana) and eastern coastline in the Bay of Plenty.
Microplastic pollutants are distributed globally in marine ecosystems and exert severe effects on biota. Microplastic pollutants contribute to additional cumulative anthropogenic stressors on vulnerable ecosystems and species. Here, the presence of microplastic particles were investigated in sediments and bivalve species; (Macomona liliana and Austrovenus stutchburyi), from Tauranga Harbour and the eastern coastline of the Bay of Plenty, New Zealand. Microplastic particles were identified and quantified into three categories; fragments, fibres and films. Microplastic particles were separated from the sediment using a saturated solution of NaCl as a buoyancy density separation process. Microplastic particles were extracted from bivalves using a homogenising technique with 10 % KOH. Microplastic particles from sediment and bivalves were identified using visual light stereomicroscopy using an Olympus EP50 camera. Significant numbers of fibres, as well as some fragments and films were found to be present in the sediment throughout sampling locations. The greatest number of microplastics per m² (2800.20) were extrapolated from the intertidal area at the Omanu Sewage Outfall. M. liliana demonstrated a statistically significant higher amount of microplastic particles ingested than A. stutchburyi. This research provides baseline data for ongoing studies in the greater Bay of Plenty area and New Zealand. Furthermore, this study contributes valuable microplastics data for two bivalve species with differentiated feeding modes and functional roles in the marine environment. The results of this study; expands our understanding of the impact and magnitude of microplastic pollution in the marine ecosystem.
TALK TWO: Laura Robichaux
Evaluation of the Implementation Gap in Coastal Risk Management
Over the past century, urban development along the coast has exposed communities to flooding, erosion and inundation hazards. These risks are often exacerbated by both long-term municipal planning decisions. and environmental perturbations associated with sea level rise and climatic variability. Consequently, there is growing need to increase resilience through adoption of management strategies to mitigate the impacts of coastal hazards on communities while also avoiding overreliance on hard engineering structures. Some calls for implemented risk management solutions are tinged with frustration following decades of studies and promises and limited action. Within coastal management and climate change literature, there is acknowledgement of this “implementation gap” or “adaptation deficit” between proposed and executed projects and strategies to manage risk or adapt to climate change. Project progression from conceptualization to implementation is influenced by several social, financial and institutional factors. To examine the factors influencing each phase of the project life cycle, fuzzy cognitive maps (FCMs) were constructed to improve resolution of the networks influencing project development. We have identified patterns in enabling or constraining factors when comparing different types of projects: defend, adapt or retreat. These varied strategy types sit within existing institutions differently and typically provoke different reactions from communities. We critically evaluate how various project types from two distinct locations sit within socio-political environments within the project life cycle to better understand the implementation gap.
Kaituna Re-diversion Project
Since at least 1979, people have been calling for the Kaituna River to be re-diverted back into the estuary to address the environmental degradation. That journey began in earnest in 2009 with finalisation of a joint strategy for the Kaituna River and Maketu Estuary that included the goal of rediverting the Kaituna River and creating 100 ha of wetland. Approximately ten years later the next stage of the journey has begun with water rediverted, the estuary starting to recover and wetland projects underway.
Analysis of extreme storm-tide and skew-surge events around the coastline of New Zealand
We set out to understand the things contributing to the highest sea levels we get in New Zealand and whether there are patterns and if they are likely to occur in multiple places at once, or if they occur in close succession. These are issues that are important for emergency managers and insurance companies. We examined the spatial and temporal clustering of these extreme storm-tide and skew-surge events and identify typical storm-tracks and weather types associated with the spatial clusters of extreme events, from 85 extreme sea level and 135 extreme skew-surge events recorded in NZ since 1900. In this talk we explain how tides combine with storm surge, how the spring–neap tidal cycle prevents storm-tide events in close succession, the typical weather systems associated with extreme sea-levels and which areas of NZ they strike, and the surprising high sensitivity to the quite small mean sea level anomaly.
Aerial drones and their application within coastal zones for data collection
Most coastal investigations are expensive and complex to implement leading to the reliance on assumptions during the initial stages of projects. The presentation covers measuring currents in the surf zone using drones as well as other notable coastal features which were encountered during testing; this is to provide examples of where aerial drones can be applied to coastal applications to provide a cost effective and easily accessible means for data collection.
PART ONE: Marta Ribo
Human impact on shallow marine environments in Aotearoa
For decades, shallow marine environments in New Zealand have been subject to human impact associated with changes in land-use, resource extraction and modification of the coastline. This has led to dramatic declines of benthic habitat, changes in seafloor geomorphology, variations of sedimentation patterns and introduction of foreign materials/chemicals (e.g., plastics) into the marine environment. We present a detailed study of the seafloor geomorphology and anthropogenic footprint within Queen Charlotte Sound/Tōtaranui (QCS), located in the Marlborough Sounds, north- east of the South Island of New Zealand. For this we use a very high-resolution (50 cm) bathymetric data, from coastline to ~350 m water depth, combined with backscatter and Automatic Identification System (AIS) data. Our results show that cumulative physical anthropogenic seafloor footprint (6.4 km 2 ) represents ~1.5% of the total QCS seafloor area, predominantly related to marine infrastructure (marine farms, cables/pipelines and wharves) and maritime activities (mooring blocks, anchor drag marks and shipwrecks). 47.5% of the entire physical anthropogenic footprint observed is produced by the anchor drag marks. We have observed that these marks excavate the seafloor up to 0.5 m, which is enough to destroy soft sediment habitats and potentially put seafloor infrastructures at risk. It is also likely that the anthropogenic impact within the QCS extends well beyond physical disturbance to the seafloor, and probably includes the introduction of pollutants (e.g., microplastics).
PART TWO: Arnaud Valcarcel
Measuring turbulent ocean mixing in the tidally driven energetic flows of Cook Strait
The ocean stores 90% of the heat received by the Earth from solar radiation. Understanding how this input is redistributed in the ocean interior and exchanged with the atmosphere is critical to make tangible forecasts for our climate system. Turbulent ocean mixing is a key process responsible for this redistribution. However, due to its highly variable strength and efficiency numerical models still fail to capture the full complexity of turbulence. Thus field observations are essential to improve our knowledge on its characteristics and how it impacts exchanges of heat, momentum, and tracers in geophysical flows. Project CookieMonster utilizes the very fast and deep tidal flows of Cook Strait (Aotearoa - New Zealand) as a “full scale” laboratory to study intense turbulent mixing. Previous work in the Strait on measuring both the mean state of the flow and the turbulent kinetic energy dissipation rates has shown high levels of turbulence with large overturn sizes in a seasonally stratified water column. In our new work we explore new ways of collecting continuous data using microstructure packages mounted on autonomous underwater vehicles, to investigate the intricate interplay between high winds and fast flows that generates extreme turbulent mixing in the strait.
PART THREE: Wagner Costa
Satellite derived intertidal bathymetry, study case: Tauranga Harbour
Bathymetric data are a key parameter to assess shallow-water hydrodynamic processes. In-situ surveys provide high data quality; however, surveys are expensive and cover a limited spatial extent. To fill this gap, over recent years, the Satellite Derived Bathymetry (SDB) techniques have been developed. The present work aims to elaborate a technique to estimate bathymetric data from satellite images for intertidal zones. The method applied in this work is composed of 6 steps: (1) image querying and pre-processing is done through Google Earth Engine application (API) using Copernicus Sentinel 2A and B, product type 2A. (2) Identification of the intertidal zone for the study area by temporal variability of the Normalized Difference Water Index (NDWI). (3) Recognition of the waterline in each image by the use of an adaptive threshold technique; and assignment of the elevation for each detected waterline based on local observed tide heights. (4) Validation of the estimated bathymetry by comparison with LiDAR measurements. (5) Implementation of a SDB correction: numerical and/or statistical and, (6) assessment of the validity of SDB for hydrodynamic modelling. The SDB technique was applied to 4 different estuaries in New Zealand: Maketu, Ohiwa, Whitianga and Tauranga Harbour showing similar or better estimations in comparison to previous works using optical or synthetic aperture radar (SAR). For Tauranga Harbour, results from the statistical and dynamical corrections showed that the major error source is due to the image optical properties and environmental conditions when the image was acquired (35%). However, the tidal propagation can significantly decrease the SDB accuracy (13%). Finally, the use of the SDB in numerical simulations does not present huge differences in the predicted waterlevels in comparison to the use of survey bathymetry, showing that SDB could be potentially used for coastal flooding simulations.
TALK ONE: Jamie Boyle
Thames-Coromandel Shoreline Management Plans – From ad-hoc to Holistic Coastal Management in the Face of Climate Change
Previously, coastal management in the Thames-Coromandel district has been reactionary and ad hoc, with several isolated hard structures doted around the coast put in place either as emergency works or as temporary mitigation. This approach has placed a significant strain on the ability to accurately fund mitigation measures for coastal hazards within long-term planning, created additional coastal issues by not appropriately considering the wider mechanisms of coastal change, and caused angst among some communities on how these measures have been implemented. In 2018, a significant storm event hit the Thames coast causing millions of dollars’ worth of damage and rattled several communities’ cages. After this final nail in the coastal management coffin, Thames-Coromandel District Council’s Shoreline Management Plan project was initiated to define coastal hazard risk across the district for the next 100 plus years and to enable empowered and resilient coastal communities to direct these action plans based on how they value the coast and what risks are acceptable or not. This presentation will take you through this journey leading up to the present day, highlight where we are at and what is next and cover off some learnings we have uncovered.
TALK TWO: Tom Simons-Smith
St Clair – St Kilda Coastal Plan: The Community Engagement Journey
In 2019, Dunedin City Council (DCC) began its journey to develop an adaptive management plan for the city’s most popular beach, St. Clair to St. Kilda. Through this process the team sought to draw in a broad range of community groups to support in the development of a community-oriented vision for the coast. To achieve this, a range of innovative and accessible engagement activities were offered to encourage participation by those groups and individuals that otherwise find it difficult to get involved.
The team has followed the process outlined in the 2017 Ministry for the Environment Guidance for local government on preparing for climate change. The approach has been adapted to meet the needs of the project and the community. To date, the focus has been on receiving feedback on what people value – objective setting.
The St Clair – St Kilda Coastal Plan is DCC’s effort to establish a basis for change, a holistic and community-oriented plan that sets out practical steps for transition and the establishment of a vision for this much-loved coast. Dunedin City Council is proud of the community and stakeholder uptake achieved so far and is excited to have the opportunity to share a plan that has been centred around early, ongoing and honest engagement. This talk will focus on the engagement component of this work, the methods used, lessons learned and outcomes to date.
TALK ONE: Zhanchao Shao
Using satellite-derived optical properties to extract the true coastal water colour in Tauranga Harbour
In order to monitor estuarine health, a wide range of monitoring strategies are applied, including in situ water sampling, sediment bed level monitoring, observations of sediment properties, etc. However, these traditional ground-based surveys are expensive and labour-intensive. Therefore, remote sensing imagery like Sentinel-2 or Landsat-8 is widely used to monitor large-scale regions due to their high temporal and spatial resolutions. However, for the Case II water, the water surface reflectance is easily affected by the water bottom substrate reflectance. This may result in the greater errors in true water colour detection when the water depth gets shallower.
The proposed paper aims to detect true water colour from Sentinel-2 imagery for Tauranga Harbour and relate the water colour to other ecological factors. Here we develop and test a new methodology to extract the dominant wavelength of water from Sentinel-2 while removing the errors from the seabed and seagrass reflectance in shallow water and intertidal regions. The new methodology is based on estimating water bottom reflectance at the subtidal regions and the regression between seabed particle sizes and their reflectance. Our results show the high feasibility of this methodology to be used in large-scale true water colour extraction in the coastal regions. The extracted true water colour of Tauranga Harbour reflects the seasonal fluctuations and strong correlations with chlorophyll-a, suspended sediments and oloured metal ions. Future work will be directed to applying this methodology to all the coastal water in New Zealand and interpreting the colour dynamics in terms of ecological changes.
TALK TWO: Inigo Zabarte
Sediment-effects on seagrass Zostera muelleri in New Zealand
New Zealand’s seagrass meadows have declined substantially in the last 50 years, notably in estuaries affected by human activities. This is also a trend that is evident globally. The sole New Zealand species, Zostera muelleri, has a national threat status of “at risk – declining”. Globally, different factors are implicated in causing the decline of seagrass ecosystems. In New Zealand, fine sediment is considered to be the most pervasive stressor of estuarine environments and the most likely cause of seagrass decline in these systems. To increase our understanding of this threat-response issue, our research aims to determine acute and chronic fine sediment-effect thresholds for Zostera muelleri in terms of light attenuation, smothering and biogeochemical alteration of substrate. The research was based primarily in Pāuatahanui Inlet, North Island, New Zealand, where approximately 40% of seagrass meadows have been lost since the 1980s, primarily from the upper estuary. Both field surveys and experiments were used to explore the research aims. Previous investigations in the harbour have suggested that alteration to substrate biogeochemistry and/or smothering of plants is probably responsible for seagrass loss rather than sediment effects on the water column light climate. Thus, our research addressed the complex and multi-faceted effects of fine sediment inputs on the seagrass growing environment.
TALK ONE: Nina Murphy
Wharekawa Coast 2120
TALK TWO: Jose Beya
Learnings from the concept design for short-term pathways
Clifton to Tangoio 2120 Coastal Strategy
TALK ONE: Richard Reinen-Hamill
Natural and Nature Based Coastal Design
TALK TWO: Curtis Marsh
Computational fluid dynamics application for seawall forces