Cities at Risk: Planning for and Recovering From Natural Disasters by Pierre Filion & Gary Sands

Author:Pierre Filion & Gary Sands [Filion, Pierre & Sands, Gary]
Language: eng
Format: epub
Tags: Public Policy, City Planning & Urban Development, Natural Resources, Political Science, Nature
ISBN: 9781317166023
Google: A16rCwAAQBAJ
Goodreads: 29443615
Publisher: Routledge
Published: 2016-03-03T00:00:00+00:00

Post-Disaster Land Zoning

The city of Christchurch was planned and built on the Canterbury plains, which were formed by alluvial and fluvial deposits from two overlapping glacier-fed river systems. The same processes that made the area mostly flat and relatively fertile and therefore appealing for European settlement in the 1840s, also made Christchurch vulnerable to significant land damage following the 2010/2011 Canterbury earthquake sequence. Many areas of the city were built on historic river channels, low-lying floodplains, and drained swamps, and later protected from regular flooding by stopbanks and river realignment projects. During the earthquakes, areas such as these were especially vulnerable to ground failure caused by liquefaction, settlement, and lateral spreading. Areas in the Port Hills to the south and east of the city, were vulnerable to rock falls and landslips (Allen et al., 2011).

In response to these land failures, ongoing safety concerns, and the threat of future disruption, CERA made three major zoning decisions. These decisions have significantly influenced the way recovery has progressed in Christchurch and throughout Canterbury. First, the decision to cordon and then declare the Christchurch Central Business District (CBD) a “Red Zone” restricted access to Christchurch’s largest commercial centre. Second, CERA decided to pursue comprehensive land zoning and buy out damaged residential properties. Third, in 2014 the Christchurch City Council decided to reassess the flood risk in Canterbury and expand flood management areas on land with increased exposure to flooding as a result of the earthquakes.

Prior to the earthquakes, the regional and local councils were aware of the major hazards that ultimately shaped post-earthquake land zoning decisions: liquefaction, rockfall, and flooding. Reports prepared by The Ministry for the Environment in 1977 and the Christchurch Engineering Lifelines Group in 1997 identified areas that had the potential for extensive liquefaction and acknowledged the dangers of seismically induced rockfalls and rockslides in the Port Hills (CAENZ, 1997; Platt, 2012; St. Clair and McMahon, 2011). Additionally, in 2007, the regional council, ECan, published a liquefaction potential hazard map for Christchurch (ECan, 2007).

As a result of these investigations, more recent building developments required ground improvement activities to mitigate the effects of potential liquefaction. For example, 10 years prior to the 2010 earthquake, renovations to AMI Stadium in the Christchurch CBD included ground improvement work. Stone columns extending 8–9 meters into the ground, reduced the potential for structural damage and improved public safety by maintaining bearing capacity in the stands in the event of earthquake induced liquefaction (Wotherspoon et al., 2014). Compared to liquefaction mitigation, efforts to address rockfall risk had been fairly minimal. In their 1997 reported they noted that, “Some protection measures can be implemented for house sites … but prediction of specific problems or failure sites is not considered generally feasible” (CAENZ, 1997: 271).

The third hazard, flooding, was part of Canterbury’s public consciousness and policy since the early European settlement. However, until the 1980s and 1990s flood mitigation measures consisted almost exclusively of engineered structures, such as stopbanks, to protect property and lives. Beginning in the 1980s, the

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