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Awareness of coastal damage from earthquakes essential

Awareness of coastal damage from earthquakes essential in planning responses

August 19, 2013

The 2010 and 2011 earthquakes in Christchurch graphically illustrate why local awareness of the potential for coastal interactions is essential for planning responses to a range of types of hazards, a University of Canterbury (UC) expert will tell an international conference in Paris next week.

Geography researcher Dr Deirdre Hart graphically says preparation and planning for future major events avoids exacerbating existing and future coastal hazards. She will be addressing the 8th International Association of Geomorphologists’ International Conference in Paris starting next Tuesday.

Dr Hart says coastal geomorphic dynamism, combined with the current global population rush to live by the sea, makes coastal hazard management a challenging problem.

``I mentioned the earthquakes as an example in an urban coastal setting to show how one type of geomorphic trigger can induce a cascade of changes that alter numerous coastal hazards risks."

``The events of 2010 and 2011 triggered extreme liquefaction, flooding, sub-aerial and submarine ground deformation, riverbank rafting and channel shrinkage, fine sediment pulses in tributaries, streams, estuaries and beaches, pollutant leakage into waterways and widespread failures of coastal and riverside lifelines networks."

``Instant coastal consequences included relative sea level and horizontal shoreline changes of up to one metre, marine cliff collapses, loss of tidal prism capacity and estuary surface area, isolation of harbour and bay suburbs and prolonged closure or total loss of many coastal and river recreation amenities."

``Ongoing responses include unprecedented fining of beach deposits, low recruitment of marine and estuary biota, shoreline shifts, changes to sediment budgets, mudflat profiles, and storm, tsunami and sea level rise risks.’’

Dr Hart says lessons from Christchurch can make New Zealand’s coastal cities like Auckland, Wellington and Dunedin more disaster-resilient.

In the aftermath of significant earthquakes, coastal risk assessments need to be revisited. This need occurs at the same time as planners are pressured into making swift decisions about the recovery of damaged areas.

Research on the vulnerability of coastal cities to earthquakes is important as around 75 percent of New Zealanders live less than 10km from the coast, including 96 percent of Aucklanders, 76 percent of Wellingtonians and 36 percent of pre-quake Cantabrians, who live less than five kilometres from the coast.

Evidence indicates that, in reality, capacity to incorporate into recovery plans the lessons that could make coastal cities more disaster resilient is limited if the hazard links are not understood before a disaster event such as a major earthquake occurs.

``For places like Dunedin, Christchurch and Wellington it’s not hard to find the links. This means identifying the liquefaction, rockfall, cliff collapse, sewerage, water and transport system risks associated with coastal plains and thinking about what regional forecasts of sea level rise, coastal erosion and pollution rates mean in a tectonic setting,’’ says Dr Hart, who is chair of the New Zealand Coastal Society.


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