Tephra clean-up in Auckland City, New Zealand : quantitative impact assessment and response planning.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Tephra impacts urban communities by disrupting transport systems, damaging buildings and infrastructure, and affecting human health. Impacts can be exac- erbated by remobilisation of tephra by wind and water processes, and human activ- ities. Therefore, prompt and effective tephra clean-up measures are a fundamental component of the societal response to tephra fall. However, planning for tephra clean-up operations is rare which increases losses and prolongs recovery. To support effective planning knowledge gaps need filling, such as determining tephra volumes requiring removal, methods of clean-up, and potential disposal sites.
The objectives of this thesis are to build an evidence base of tephra clean-up opera- tions which can be used to inform an assessment of the potential impacts of tephra clean-up operations in Auckland, New Zealand. To achieve this, I have reviewed case studies of tephra clean-up operations spanning 50 years and from around the world. This forms the most comprehensive existing evidence base for tephra clean- up operations. This review can inform impact assessments and response planning by documenting methods involved in tephra clean-up and by assessing a range of empirical relationships between tephra accumulation and clean-up metrics such as collected tephra volume, costs, and the duration of operations. Large variation is seen between communities that have little or no prior tephra clean-up experience, which indicates that relatively simple tephra accumulation-cost relationships are unlikely to provide sufficient results for impact assessments. Clean-up experiences and costs are context specific and depend on many community-specific attributes. However, one relationship consistent across all case studies describes the percentage volume of tephra collected related to tephra fall accumulation in the urban area. Urban areas which experienced low tephra accumulation (1,000 m³/km² or 1mm thickness) only remove 1% of the total deposit, whereas urban areas which experienced large accumulations (>50,000 m³/km² or 50 mm thickness) remove up to 80% of the deposit. This relationship can inform impact assessments by providing an estimate of the likely response for a given tephra fall. This information, used in conjunction with community specific characteristics, allows communities to create more robust plans for tephra fall clean-up activities.
Using the compiled evidence base as a guide, I have developed a tephra clean- up model using geospatial analysis and monte carlo simulation methods to assess duration and costs of tephra clean-up in Auckland after distal and proximal volcanic eruptions. The model suggests that clean-up duration could take weeks to months to clean-up tephra fall deposits, and potentially years to clean-up areas impacted by pyroclastic flows. Costs will range from a few hundred thousand dollars to implement street sweeping clean-up operations of road surfaces to hundreds of millions of dollars to clean-up areas impacted by pyroclastic flows. These results have implications for response (e.g. resource requirements, disposal site locations) and recovery (e.g. restoration of land for use, retirement of land) planning as part of disaster risk reduction in Auckland.