Bulletin Date: November 1999
During 1997, the CDMP developed a statistically based approach to estimating the return times for varying levels of storm surge. This approach was first applied to Montego Bay, Jamaica, where wave and surge effects on Montego Bay from all storms in the National Hurricane Center's database (951 storms) were modeled using the TAOS storm hazard model to develop a comprehensive information base for this statistical study. Annual maximum surges were extracted from this statistical database (yearly maxima for the entire 110-year storm history) and a statistical distribution curve was fit to these annual maxima. Using the selected distribution curve and the specific curve parameters derived from the surge dataset, it is possible to estimate the level of storm surge for any given return period (e.g. 25- or 100-year returns), with the associated confidence levels for that estimate. In the Montego Bay study, surge estimates were developed at Doctor's Cove for 10-, 25-, 50- and 100-year surges. These surge levels were then extrapolated along the coast, based on local topography, to develop flood return period maps.
Storm surge estimates produced by the TAOS model have been validated using recorded surge levels for historical storms throughout the Atlantic basin. To further validate the results of the Montego Bay statistical study, the effects of three major historical storms, which affected Montego Bay, were modeled and compared to reported surges. Although the paucity of surge recordings and the unknown quality of existing recordings complicated this comparison, TAOS surge predictions were found by an independent reviewer to be reasonable estimates.
A workshop on the Montego Bay storm hazard assessment, co-sponsored by the Jamaica Institute of Engineers (JIE) and CDMP, was held in Kingston, Jamaica, in October 1997. Results of the historical storm validation runs and the report on the statistical study were presented and discussed. Other topics covered during the workshop included the presentation and distribution of storm surge information and its application within development planning and control in Montego Bay. CDMP and the JIE jointly prepared a report on the Montego Bay coastal hazard assessment. This report was completed in the fall of 1999.
The statistical approach to estimating storm surge return periods, which was developed for the Montego Bay study, was subsequently applied to the State of Florida for the estimation of storm surge return periods. In the fall of 1998, it was applied again to Jamaica as part of the Kingston Multi-hazard Assessment. Further information on the TAOS model is available on the storm hazard modeling section of the CDMP web site.
The recent storm hazard modeling and mapping work for Montego Bay builds upon CDMP hazard assessment work for this area, which began in 1994. In October of that year, storm surge maps prepared for Montego Bay were presented to technical agencies and local engineers. Questions were raised regarding the accuracy of data used in the model and the statistical analysis that went into the determination of the 100-year return period. Rather than produce a single map with the worst case scenario, it was agreed that a series of maps with various category storms along the most likely tracks should be produced and turned over to local technical agencies. These agencies would in turn work with local engineers and the Meteorological Office to select from the array of maps provided, the scenario that was most comfortable to work with. Maps of the types requested were presented to the Mayor of Montego Bay at a workshop held in November 1995. See the document Report on Proceedings of Workshop on the Interpretation, Application and Institutionalization of Storm Surge Maps in the Development Process for a description of the workshop and workshop recommendations.
The 1995 workshop was sponsored by the St. James Parish council, the Office of Disaster Preparedness and Emergency Management, the National Meteorological Office, and the CDMP. Participants included public and private sector organizations involved in the planning, financing, and regulation of development. The workshop focused on the interpretation and utilization of hazard maps and the institutionalization of these maps in the development approval process. In 1996, the draft National Land Policy of Jamaica called for the use of hazard maps and the CDMP-produced storm surge maps in particular in development review.
Subsequent to the 1995 workshop, little use was made of these maps, due to remaining questions by the JIE regarding the accuracy of the TAOS model and the methods for estimating the return period for storm surge events. The statistical return-period approach to surge modeling described above was undertaken in response to the JIE's concerns.
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