New Zealand: Earthquake aftershocks complicate rebuilding and repair in Christchurch

Last Updated: 12 October 2011
Article by Mark Simister
Despite setbacks from further aftershocks, progress is being made with rebuilding Christchurch, New Zealand, Mark Simister MWH's Asia Pacific Director for Program Management reports.

You would not be mistaken for thinking the residents of Christchurch, New Zealand, are feeling somewhat punch-drunk after 12 months of continuing aftershocks following a 7.1 magnitude earthquake in September 2010. The subsequent aftershocks in 2011 included two earthquakes at magnitudes of 6.3, one of which was particularly devastating. As a result of the initial earthquake and aftershocks, 10 percent of Christchurch's bore water wells were rendered unusable. An additional 44 percent, according to Christchurch City Council, were damaged. Substantial damage was caused to stormwater, drinking water and wastewater network and treatment facilities, and roads. Overall, damage to infrastructure is estimated at US$1.9 billion (NZ$2.5 billion).

Shortly after the first earthquake, the global engineering consultancy MWH and contractor Mainzeal Property and Construction entered into a joint venture, which was appointed to manage and coordinate the repair and rebuilding effort for a significant portion of Vero Insurance New Zealand and AA Insurance claims. In a strange twist of fate, having the MWH-Mainzeal team already in place at the time of the most devastating earthquake on February 22, 2011 enabled a rapid response to undertaking essential make-safe and emergency works. By the end of April, the team had completed more than 1,000 make-safe repairs to homes, most of which were completed within one day of receiving notice. Since then, much of this work has been subject to the effects of the additional June 13, 2011 aftershock, registered at a magnitude of 6.3.

Drinking water is now restored to all suburbs and residences in Christchurch; however some suburbs are still operating without normal household toilet facilities. As of mid-August, 1,600 homes were still using chemical toilets and portaloos due to damage to the sewer network. The setbacks of the aftershocks have created a number of challenges to the urban infrastructure, but basic repairs are being completed wherever possible to restore essential services and to allow time before permanent repairs and renewals can be designed and built. In the face of setbacks and challenges, the spirit and resolve of locals to Christchurch never ceases to both impress and amaze.

The drinking water supply system in Christchurch is decentralized, comprising a series of bores spread across the city. The initial quake and aftershocks damaged the majority of those bores and pipes in some way, resulting in remediation interventions including the introduction of chlorine. Water supplies have been chlorinated to a level that is agreed upon by the Medical Officer of Health and is in line with the best practice used in cities with chlorinated water. The tap water in the city and on Banks Peninsula is regularly tested to the New Zealand Drinking Water Standards and is safe to drink.

Twelve kilometers of pipe damaged in the February quake and 10 kilometers of damaged pipe from the September quake had been replaced by early June when the aftershock hit, setting the counter largely back to zero. Progress is being made, but the time it will take to rebuild the city and suburbs is best estimated at years. Relevant authorities not only need to rebuild the city, but also need to navigate the heightened emotions of whether rebuilding in parts of the city is practical and possible. Already, the tough decision has been made not to repair or rebuild 6,000 homes. Christchurch locals are aware of this dichotomy and officials are working as transparently and speedily as possible to give closure to those still unsure whether they will be able to rebuild, or be required to relocate.

The residential parts of the city have been color-coded to categorize the ground conditions that will determine whether repair or rebuild can occur. Homes in the residential red zones will be demolished. Homes in the green zone are able to be repaired or rebuilt, though work has been delayed until the aftershocks have eased. In other zones – white and orange – the decision to repair and rebuild will depend upon further assessment of ground conditions.

Those involved in the infrastructure rebuild are awaiting clarity around which parts of the city will be repaired and rebuilt, as this has influence as to both where and when they will apply their effort to the full repair and replacement of damaged infrastructure. There is also considerable thought being given to the provision of 'engineered resilience' in the rebuild. Christchurch is now assessed as a seismically active area; therefore ongoing seismic events will occur, which could again damage the city's infrastructure. Because of this, every effort is being made to rebuild a system, which can perform more resiliently in higher magnitude earthquakes. This will involve the use of more robust materials for pipes, jointing systems, pump station design, and consideration of pumped sewer systems as opposed to deep gravity-based systems.

The passing of the Canterbury Earthquake Recovery Act 2011 bestows far-reaching powers on the Canterbury Earthquake Recovery Authority (CERA). The purpose of the legislation includes facilitating, coordinating, and directing the planning, rebuilding, and recovery of affected communities, including the repair and rebuilding of land, infrastructure, and other property. This also includes generally restoring the social, economic, cultural, and environmental well-being of greater Christchurch communities. CERA is responsible for working with stakeholders (in particular the Christchurch City Council) and residents to develop the master plan for Christchurch, which will be delivered within the next six months. It will, as best it can, not only accommodate the need to preserve what can be preserved, but also incorporate protections for vital infrastructure including water, wastewater, stormwater, and roads.

The engineering community is working closely with the necessary authorities to help inform decisions as well as to develop a cost-effective, resilient, socially, and environmentally sympathetic master plan.

Once the master plan has been approved, action plans for individual suburbs will be developed. Due to the nature of natural disasters like earthquakes, some suburbs have fared better than others. Some will require little to no engineering intervention to restore infrastructure and services, whereas others will require intensive intervention and, in the worse cases, abandonment.

A structure may look like it has not sustained too much damage, but what is unseen – such as the foundations and structural connections behind walls, under carpets and above ceilings – can determine its future. Initially, information is gathered, such as spot level recordings and measurements, to determine how out of plumb a structure is. These assessments may indicate foundation distress or the impacts of liquefaction, but often foundations are buried so the damage cannot be easily seen.

While damage to personal homes, commercial premises, infrastructure, and amenity areas are foremost in the minds of residents and government officials, the quakes have also changed ground levels and substantially exposed parts of the city to an increased risk of flooding.

MWH served as program manager for infrastructure projects in New Orleans after hurricanes Katrina and Rita in 2005. With a demonstrated history in working complex responses to natural disasters, MWH is in a regular state of research and information gathering from sources around the globe to help ensure what is recommended will be the best solutions for Christchurch. While there is still community spirit among residents living in the affected suburbs, timely decisions now need to be made. Special legislation was passed in 2011 to create the Canterbury Earthquake Recovery Authority (CERA) to lead and coordinate the recovery effort. CERA is now working with the many stakeholders (local authorities, government agencies, private and public businesses, insurers, banks, realtors, architects, engineers, and builders) to coordinate and, wherever possible, fast-track the recovery.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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