Risk assessment underpins all preparation and planning for marine oil spill response in New Zealand. It includes the assessment of both the likelihood of a spill occurring and the consequences or effects of the spill.
In 1992 a national risk assessment was completed for New Zealand. This established the basis for the first New Zealand Marine Oil Spill Response Strategy. In 1998 the Maritime Safety Authority completed its second national marine oil spill risk assessment. The purpose of these risk assessments was to provide further information on:
The first assessment did not address the possibility of an unpredictable catastrophic spill, however, the 1998 assessment did.
The 1998 risk assessment measured and presented marine oil spill risk in a manner similar to that used for other forms of emergency response. The probability that a spill event of a particular size occurring in any given year (Probability of Exceedance Level or PEL) was estimated and assigned a value.
The 2004 risk assessment demonstrated that while there had been some changes of the risk profile at the national and regional level, overall the risk profile had been predicted. There was a small increase in the volume of crude oil imported to Marsden point, but overall there were a smaller number of ship visits as the overall size of the tankers had increased. There was also a shift in shipping patterns with the change occurring in the type of vessels for container traffic.
These early risk assessments concentrated upon the chance of oil spills occurring and although mapping environmental sensitivity did not combine the calculated probability with the potential impact of oil on the coastline. The 2010 risk assessment did use environmental sensitivity, and when combined with the greater level of environmental mapping gave an output that represents environmental risk.
The Maritime Transport Act (MTA) (1994) requires the Director to develop and maintain the NZ Marine Oil Spill Response Strategy (The Strategy). This describes how New Zealand will efficiently and effectively minimise the impact on the marine environment of oil pollution from ships and transfer sites. The Strategy recognises the need for the national spill response capability to reflect the current risk profile with the risk assessment underpinning this need.
The purpose of the Strategy as laid out in s284 of the MTA is to:
The 2004 risk assessment base data-set has been improved through better data fidelity and data depiction undertaken for the oil pollution levy work by Russell Plume. Much of this data has been deduced from the 2004 risk assessment and improved to produce accurate depiction of the movement of oil in vessels around the NZ coast. This data has been incorporated into this current risk assessment.