This paper describes the New Zealand (NZ) approach used to define the likelihood and consequences of oil spills through the Maritime Safety Authority (MSA) Marine Oil Spill Risk Assessment process.

A new methodology for consequence analysis was developed using 20 kilometre coastal cells established across the country for ranking and mapping sensitivity. For each cell, the resources present were evaluated under “environmental” categories (shoreline character, plants and animals, protected sites) and “human” categories (economic, cultural, and social, amenity & recreation). Factors within each category were allocated scores reflecting the sensitivity, vulnerability and reversibility of impacts at local, regional and national levels on a semi-quantitative 5-point score (very low / low / moderate / high or unknown / extreme). Qualitative descriptions (e.g. “no vulnerable plants or animals” ranging to “a number of vulnerable plants or animals of national importance, or at least one that is irreplaceable”) were used to ensure national consistency in scoring.

Determining the presence or absence of environmental and human factors within each cell enabled individual scores to be summed for each category and graphically presented using diagonally split colour-coded squares on a map. This was overlain with the results of the regional oil spill likelihood analysis (e.g. how much, how often, where, what oil, and where from) providing an overall risk profile for NZ. The methodology was refined through national level multi-stakeholder meetings, and tested at two regional workshops to produce a data collection template for use by regional response agencies.

The unique contribution of this work has been to incorporate consequence analysis into the assessment of regional and national risk profiles. Further quantifying the relative contribution of different activities and factors to the risk profile of each region, and nationally, will guide preventive and preparedness measures to lower the likelihood and impact of a spill. This in turn will determine the relative contribution each risk activity makes to the total risk profile which forms the basis for setting Oil Pollution Fund levies used to fund spill preparation in NZ.

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