The geographical location of New Zealand to the south west of the ‘Pacific Ring of Fire’ and in the ‘Roaring Forties’ of the Pacific Ocean exposes national infrastructure networks across the country to a range of natural hazards. Despite this, studies of built environment resilience to natural hazards in New Zealand, have historically focused on the robustness of individual physical assets, with less emphasis on the performance of infrastructure networks at a national level. This is particularly true for the stopbank (levee) network. Until recently, stopbanks have often been considered at regional scales and to varying degrees depending on what information has been catalogued, and the level of interest / requirements and local expertise available at the time.
We present the findings of a preliminary national level natural hazard exposure assessment of New Zealand’s stopbank network by adopting the newly developed New Zealand Inventory of Stopbanks (NZIS). Geospatial seismic hazard data from recent modelling is used as a case study to demonstrate how understanding the exposure of stopbanks in NZIS can inform multi-hazard risk and resilience assessments. Four seismic and co- seismic hazard metrics are considered in our stopbank network exposure assessment: surface rupture (through proximity to known active faults), the strength of ground shaking (i.e. probabilistic estimates of peak ground accelerations and velocities), and liquefaction and landslide susceptibility.
With over 20% of current catalogued NZIS stopbank length and a relatively high seismic hazard exposure (active fault proximity and liquefaction susceptibility) in Southland, the likelihood of stopbank failure or breaching due to seismic activity appears to be relatively high in this region of New Zealand. Large sections of the stopbank network in other regions including Manawatu-Wanganui, Wellington and Hawkes Bay are also particularly exposed to large seismic hazards in our preliminary assessment. However, further work is required to more appropriately understand stopbank attributes including design and safety considerations.
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Estimation of the potential economic consequences of dam failure is becoming an issue of increasing importance in the Australian dams industry. As a result of the ongoing investment in dam safety upgrades, societal risk profiles for many dams are generally reducing. Additionally, there is evidence of the potential magnitude of economic and financial costs from recent overseas dam incidents. Whilst there is a well established framework for estimation of economic consequences, based on concepts of direct/indirect and tangible/intangible damages, there is a dearth of recent literature on the application of modern unit cost rates for various asset classes. This is particularly important in cases where direct, tangible damages are an important component of economic consequences.
Currently, unit cost rates used to estimate direct tangible economic consequences in Australia are typically taken from older sources such as the floodplain Rapid Assessment Method (RAM). The appropriate cost rates are then factored by CPI to represent ‘current day’ estimates of these costs. However, since the time when the RAM was first developed, there have been changes to the categorisations used to identify economic assets such as businesses in common databases such as the census. Additionally, there have been a number of large, recent flood events in Australia which provide very useful data to assist in deriving updated unit cost estimates.
This paper presents proposed unit rates for damaged and destroyed residential and commercial structures (including stage-damage curves) consistent with the Australian Bureau of Statistics categorisations used in the census data, agricultural land and assets such as roads. These rates have been derived based on a range of sources. The purpose of producing these unit rates is to promote ease-of-use and consistency, especially for large consequence assessment studies where numerous assets are impacted. A case study is presented showing the application of these unit cost rates and highlighting the variability in direct, tangible damages in different circumstances
Dam spillway gate collapse may have fatal consequences and cause severe structural damage due to flooding, additionally the dam owner will suffer substantial business losses. The repair work required to put a gate back in service can be time consuming, challenging, dangerous and costly. To ensure the reliability of radial gate operation, and depending on the type of trunnion bearing and the structural capacity of the gate arms, the bearing friction should be carefully monitored and gate performance evaluated to confirm the gate’s ability to withstand increases in friction over time. The frequency of monitoring requires careful consideration.
Radial gate arms are normally designed to withstand bending moments from nominal bearing friction. An inappropriate bearing, or a bearing in poor condition, might have friction sufficiently high to cause a gate arm to fail due to the excessive bending moment during gate operation.
An easy and non-invasive way of analysing the condition of the bearing, to ensure safe operation of radial gates where the arms might be prone to increased bending moment, is through friction measurement with the use of strain gauges. This paper briefly presents common radial gate design and some failure modes as a consequence of increased bearing friction, and a method of determining the bearing friction coefficient through strain gauge measurements and experience from the field is presented.
It is inevitable that, sooner or later, most dams will fill with sediment. It is simply a matter of time.
When the sediment reaches the power intakes of a hydro dam, there is a risk of the turbines being destroyed and the power station being abandoned. If this happens the spillway will need to operate continuously and this may lead to spillway failure possibly followed by failure of the dam.
Spillways are likely to fail because they are not designed for continuously discharging large amounts of sediment. The concrete and fixed parts will soon be damaged and need to be repaired. Repair is possible only if the spillway is segregated into two or more chutes so that one chute can be isolated and the flow passed down the other chute(s).
Reservoir sedimentation is a serious long-term problem that threatens the long-term viability of storage hydropower schemes. In 2010 global storage capacity was estimated at 6,000,000 km³ but it is projected that 4,000,000 km³ will be lost to sedimentation by 2050.1 Storage loss occurs worldwide at a rate of about 0.8 percent per year, but the sedimentation rate in many regions such as Asia is much higher.
Many reservoirs will fill with sediment within the next 100 years or so but some will fill up in a much
shorter timeframe. The sediment builds up at the head of the lake and a wall of sediment moves slowly down the lake until it reaches the dam and, eventually, the power intakes.
This paper is intended to draw attention to the problem and to emphasise the need to mitigate or solve the problem by providing a scour intake beneath the turbine intakes.
The major problem is designing the upstream gate to operate reliably when finally needed after, possibly, many years with little or no maintenance. A solution is suggested but it is recognised that better ones may be found: the objective of this paper is to encourage designers and developers to consider a wide range of solutions and to examine the potential of modern materials to help solve this very serious problem.
The majority of Australian tailings dams over the last 100 years have been successfully built using upstream construction. However, recent major tailings dam failures in some countries have led to a global industry wide review of the design and management of tailings storage facilities, with a focus on the upstream raise method as a common factor for some failures. As a reaction to the recent failures, there is the potential for regulations to become more restrictive and the potential for unjustified pressure on existing and new mines to rule out upstream raising due to possible safety and failure risks.
This paper looks at whether it is the upstream construction method or other more fundamental issues that have led to these failures and examines whether such issues are equally relevant in Australia. Does Australia have a specific advantage in being able to successfully use upstream tailings dam construction or are we fooling ourselves?
The topic of upstream tailings storage is a subject of broad and current interest and the lessons learned from historic failures are rightfully leading to improvements. Implementation of good practice starts with the overall management structure that guides how tailings dams are designed, constructed, operated and closed.
Critical design practice involves understanding the unique site conditions, properties of the tailings and management of tailings placement, as the tailings form part of the overall retaining structure. Good practice during operation of upstream tailings dams is key to reducing the risk of tailings dam failures and the success of safe and sustainable closure.
This paper presents key features of both good and bad practice for the upstream raising of tailings dams and discusses how the design and operation can be made more resilient to ensure the safety of the community and infrastructure. It concludes that upstream raising can be a safe and economical method of tailings disposal if designed, constructed and operated correctly.
Failure modes of seepage and internal erosion have been identified as one of the key issues for the
ongoing safety of dams and canals in New Zealand. Accordingly, many dams and canals have had
improvement works carried out to mitigate this issue. This paper examines the long-term performance of these measures including three case studies. It is concluded that the performance of these measures has been variable, but ongoing monitoring and periodic review has identified deterioration in performance. There are a number of technical areas where uncertainties on long-term performance may still remain, such as geotextiles in important filter functions and waterstops of various types.