Natural Hazards Update - No.3 2003
Lifelines - how prepared are we?
Wellington's "arteries". (Photo: Lloyd Homer, GNS)
Lifelines are the arteries and veins of our communities. They are either utility services, such as water, wastewater, power, gas, and telecommunications, or transportation networks including roading, rail, ports, and airports.
Rapid restoration of lifelines after a disaster is a key factor in how quickly an affected community can recover. Utility services and transportation networks can be restored rapidly if mitigation measures are well established and robust plans are already in place.
Over the past decade, Lifelines Projects have played an important role in helping individual utility organisations address mitigation and preparedness for regional-scale events. Lifelines Engineering was initiated in 1989 by the Centre for Advanced Engineering (University of Canterbury) with their lifelines study of Wellington City. There are now Lifelines Projects or Groups underway or planned in almost all regions of New Zealand.
The new Civil Defence Emergency Management Act requires Lifeline utilities to be able to function during an emergency and to actively participate in CDEM planning.
The focus of Lifelines Engineering is on regional-scale emergencies that are beyond the ability of individual organisations to respond to and control. However, responsibility ultimately remains with individual organisations. The process happens by getting all the utility and transportation network operators together within a region, with inputs from hazard researchers, emergency managers, insurers, and planners.
Hazard information needs to be expressed in equivalent terms across the range of regional-scale hazards (e.g., storm, flood, earthquake, volcanic, tsunami). There must also be an appreciation of the difference between hazards affecting a region and those specifically affecting lifelines. There have been few “real” disasters over the past decade, so an important step is to work in “virtual reality” mode to visualise impacts on utility networks by using well-described “what-if?” scenarios. Using this process, Lifelines Groups facilitate a collective risk management process that can then address the weak links.
No two Lifelines projects are the same. City projects differ widely from rural projects, where community dependence on lifelines varies and the resources to carry out a systematic rural district project are more limited.
The role of the National Lifelines Engineering Co-ordinator is to provide a resource person for each of the Lifelines Projects and Groups and to liaise between the Lifelines Groups, the national utilities, and the Ministry of Civil Defence and Emergency Management, who collectively fund the Co-ordination position.
Aerial laser scanning of coastal and river hazards
Hazard map of Charlottetown, Prince Edward Island, Canada
Hazard mapping has benefited greatly from ongoing advances in aerial remote sensing techniques, GIS, and computer models. The most common methods are aerial photogrammetry and a newer technique called lidar (light detection and ranging), also known as airborne laser scanning (ALS). The high-frequency laser is mounted under an aircraft and scans to and fro several hundred metres across the flight path, allowing large tracts of land, riverbeds, or beaches to be scanned in a matter of hours. Lidar has been around for over a decade, but initially cost was a major impediment. However, rapid technological advances, combined with the benefits of large-scale efficiencies and multiple uses of the data have seen lidar more widely used for resource management. Land heights can be measured to an accuracy of ±0.15 m, with complete horizontal coverage. An important step for a successful hazard map lies in the processing of the raw data through to a consistent digital topography that is “tied-back” to an appropriate land survey datum.
A case study was undertaken recently by Geological Survey of Canada to produce a coastal flooding risk map for Charlottetown (Prince Edward Island, Canada) as part of a climate-change adaptation study. A high-resolution lidar image of the land surface was integrated with municipal GIS data. Computer models of inundation at various flooding scenarios were applied against the digital terrain map to highlight areas and properties at risk from future flooding (blue areas on diagram).
Some regional councils and a hydroelectricity generator have (or are about to have) commissioned airborne laser scanning surveys to acquire high-resolution digital data of land surface, riverbed, and coastal topography. NIWA and GNS support these endeavours because the lack of good topographical coverage in low-lying areas in New Zealand has hampered the translation of hazard research and modelling into hazard maps.
Natural hazards in summer 2003 (December–February)
Landslides |
Weather extremes |
Coastal hazards |
Floods and droughts |
Earthquakes and volcanic activity |
Data sources for these maps: GeoNet, NIWA, MetService, Regional Councils
Tangiwai disaster
Rescue party beside wrecked carriage of the Wellington-Auckland express. (Photo: Alexander Turnbull Library, Morrie Peacock Collection 35/59. A14)
24 December 1953
The worst railway disaster in New Zealand’s history occurred on Christmas Eve 1953 when the Wellington-Auckland night express plunged into the flooded Whangaehu River just west of Tangiwai (near Waiouru). Tragically, 151 people were killed.
The disaster was precipitated by a sudden release of water, rocks, and ash (lahar) from Crater Lake on Mt Ruapehu that surged as a torrent down the Whangaehu River gathering boulders, mud, ash, and debris. After the 1995–96 eruptions, about 6 m of weak material dammed the lake outlet, increasing the risk of a lahar.
Planning for a managed response to a predicted lahar down the Whangaehu Valley is now well advanced with DoC, the local authorities, and MCDEM taking lead roles. GNS has been working with these agencies on aspects of the risk assessment, warnings system, and response planning.
Earthquake risk
Building damage in the 1995 Kobe earthquake. (Photo: GNS)
Earthquake risk modelling is needed for insurance purposes and for risk planning. For many years seismologists have been addressing the problem of assessing earthquake hazard (that is, estimating how often, and how badly, any given location is likely to be shaken). The results of these studies are important for engineering design and vulnerability assessment. Structural engineers know the strength and flexibility of a building, or a large structure such as a hydro dam, so information about the motion of that structure in an earthquake, and how likely it is to survive or fail, is needed for public safety considerations.
Studies of earthquake risk take this a little further by including knowledge of the strength of buildings or other assets to estimate the likely cost of damage, and how often it will be sustained. So, earthquake risk studies bring together a number of areas of research: where and how often earthquakes occur, and their magnitude; the severity of shaking at any given place, due to an earthquake of known magnitude elsewhere; the amount of damage that is likely when structures of known type and characteristics are subjected to damaging ground motion.
Figure 1. Loss curve for a group of Wellington buildings in millions of dollars for different return periods.
For a particular group of buildings in Wellington the likely cost of damage is shown as it increases with the earthquake return period (Figure 1). The return period is the likelihood that an event will occur. Thus, something that happens once in 100 years, on average, has a 100-year return period. It doesn’t happen at regular intervals of 100 years, but that is the average interval between events of that magnitude. Alternatively, we could say that the annual probability of occurrence is 1 in 100 or 1% chance each year. Figure 1 shows how the likely cost of building damage increases for the bigger events with longer return periods.
A “catalogue” of likely earthquakes in New Zealand for 50 000 years has been constructed by computer simulation, and the total cost of damage to today’s housing stock has been calculated (Figure 2). Every square symbol represents the housing loss from one damaging earthquake, given location; cost of replacement; and where earthquakes are most likely to occur, how often, and of what magnitude. The maximum cost for any one event could be about NZ$5 billion damage to domestic houses.
Figure 2. Squares are losses to NZ housing stock from 50 000 years of simulated earthquakes in NZ.
Yellow squares in Figure 2 represent damaging earthquakes where the simulation recorded an event on one of the four main Wellington faults. Purple squares represent damaging earthquakes for the rest of the country. The immediate and dramatic conclusion is that almost all earthquake disasters costing more than $1.5 billion occur in the Wellington area. This is because no other part of the country has the coincidence of active faults and housing. The Alpine Fault in the South Island, for instance, is very active and capable of very large earthquakes, but it is 150 km from Christchurch, so the damage could be quite different.
It is important to note that Figure 2 only refers to damage to houses. There will be many other contributions to the total damage bill in large earthquakes, in particular damage to commercial buildings, infrastructure, and lifelines (like roads, airports, power lines, water mains, and gas pipelines) and business interruption losses. These important aspects of risk could also be modelled in a similar way to help plan for such events and for insurance risk assessments.
Long waves and ships
Ships at open-coast ports are prey to long waves. (Photo: Port of Lavaca, Texas)
When long waves at around 7 to 11 minute intervals turn up on our east coast they are the bane of port operators and ship owners at open-coast ports like Timaru, Napier, and Gisborne. These waves can accentuate vessel motions and cause hawsers to break, damage wharf structures, and lead to unsafe working conditions.
Recently, NIWA has been on the hunt to learn why and how often these long waves turn up, with a view to providing more informed warning procedures. Sea-level recorders from Timaru and Napier have been set at fast 1-minute sampling intervals to capture these events, which are barely discernable by eye because of their longer length (unlike waves at the beach).
An analysis of the past 15-months of 1-minute data from Timaru has unearthed six “long-wave” events, with the largest on 4 April 2002, peaking at 1.2 m high from crest to trough. The jury is still out on their cause, but most long-wave activity seems to turn up when a low-pressure depression occurs well offshore to the east, in the Chatham Islands region.
Guidance note on climate-change effects on coastal hazards
The Climate Change Office (Ministry for the Environment) has commissioned a consortium of NIWA, Beca Carter Hollings & Ferner, and DTec Consulting to prepare a national guidance note to help local authorities plan for coastal hazards. Global warming will have a pronounced effect on the coast, not only through rising sea levels, but also through its effect on the intensity of storms, by altering wave-climate patterns, and possibly by exacerbating coastal erosion through changes to sediment supply.
The guidance note is based on a high-level or “scoping” risk-assessment process to help prioritise those coastal communities most at risk. The coastal hazard guidance note, along with a parallel overview guidance note for generic climate-change planning, will be trialled through case studies with some territorial authorities during April and May.
GPS deployments with LINZ
Installing a GPS instrument in a New Zealand-wide network. (Photo: GNS)
In partnership with Land Information New Zealand, GNS is part-way through a programme to install 30 permanent GPS instruments throughout New Zealand. The instruments, most of which are solar-powered, are spaced about 100 km apart and continuously measure land movement to sub-centimetre accuracy.
The network will enable LINZ to adjust New Zealand’s mapping and cadastral system to take account of land deformation caused by tectonic forces. GNS will also use the data to pinpoint areas of New Zealand that are deforming rapidly, and monitor these areas more closely.
The new network is state-of-the-art and will bring New Zealand into line with other technologically-advanced countries that experience earthquakes and volcanic eruptions. In late 2002 the network picked up sudden and unprecedented movement of land at Gisborne. A large part of Poverty Bay moved to the east by 3 cm over a week.
The network makes it possible to detect this sort of phenomenon. It will also improve the understanding of how earthquake stresses build up in the earth’s crust.
Using radar to measure deformation
GNS is using radar images taken from aircraft and satellites to enhance the detection of land deformation and to improve the understanding of other geological processes in New Zealand.
This innovative technique, which is in its infancy worldwide, works alongside more conventional studies in seismology, geophysics, and ground-based GPS measurements. It helps scientists understand the big picture when it comes to active faults, volcanoes, and other parts of New Zealand that are geologically active. As well as providing a broad perspective over a large area, remote sensing also allows monitoring at times when it may be unsafe to be on the ground, such as during eruptions.
To date, GNS has used this technique successfully in the central North Island, Dunedin, and Auckland. Ultimately, using currently orbiting satellites, as well as those to be launched in 2004 and beyond, GNS will have a routine monitoring technique that will complement other observations in the early detection of potentially hazardous events, such as volcanic unrest, landslides, and coastal instability.