Thursday, February 27, 2014

Preliminary Cost Benefit Analysis of Storm Surge Hazard Mitigation in the Tuamotu Islands: an overview Anna Rios Wilks

In order to assess the most efficient method of reducing storm surge damage on the low-lying Pacific Island atoll of Rangiroa, French Polynesia, a cost benefit analysis is conducted which compares the expected costs and benefits produced from 4 types of adaptation option.

Findings suggest that for the specific storm surge considered, the relocation of buildings away from the immediate beach line and the use of a sea wall produce far lower expected infrastructure damage reduction than the general elevation of buildings by 1 m or more. The analysis concludes that in this case the gradual implementation of elevated MTR buildings would be the most efficient method of risk reduction.
Rangiroa is one of the largest atolls in the world, measuring over 75 km in length and 25 km in width it holds 2,473 inhabitants in the two main villages alone (ISPF, 2007). The towns are located on small islets surrounding the lagoon. Critically the maximum width of these islets (between the ocean and the lagoon) is only a few hundred metres and they offer no high ground to which inhabitants could flee in the event of a storm surge (Damlamian et al., 2013). Consequently, cyclones and storm surges can have devastating effects on the community.
Although the government is constructing cyclone shelters which will protect inhabitants during such events, there are still great losses to infrastructure and property to be expected. This CBA seeks to inform policy makers of what might be the optimal method of further adapting to the risk of storm surges in order to reduce this damage. Numerous options exist that the Government could pursue to mitigate damage. Four types of options have been analysed so that a way forward can be identified:
  • the construction of a sea wall,
  • the use of anti-cyclonic MTR buildings (“kit houses”) elevated to 1.5 metres,
  • the elevation of normal buildings to 1 m,
  • the implementation of a setback zone1.

When only the value of the reduction in damage to buildings is quantified in the benefit analysis, the benefit cost ratios for all adaptation options are still slightly below 1, implying that no option generates enough savings in reduced damage to buildings to cover their costs.

On the other hand, both the elevation and MTR options also generate benefits that were not quantified in this analysis such as the reduction in damage to household goods and reduction in post disaster losses to business and services that may otherwise see their stock or machinery inundated. Furthermore, it is likely that for all types of adaptation option, there would also be a reduction in damage from other smaller, more frequent events.

Consequently, it is likely that once these other elements are included, analysis will demonstrate that adaptation options which allow for elevation of buildings will provide an overall gain to society.

by Anna Rios Wilks
SOPAC Geoscience and Technology Division of SPC
The 30th Science, Technology and Resources Network (STAR) Conference, Rarotonga, Cook Islands - October, 2013 and
the 9th Pacific IslandsConference on Nature Conservation and Protected Areas, Suva,Fiji– December, 2013
Pacific Disaster Net

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