Survival Analysis of Elevated Homes on the Bolivar Peninsula after Hurricane Ike

Hurricane Ike was the third costliest hurricane to hit the United States, causing almost $30 billion in damage after making landfall on the Bolivar Peninsula, Texas, in September, 2008. Following the disaster, a case study of the peninsula was conducted to evaluate hurricane-generated wave and water level effects on wood framed, pile-elevated coastal residences. This study provided information about the structural characteristics most influential to the survival of these homes and may be used to validate future wave force prediction and fragility models for elevated coastal residences. A total of 1922 homes on the Bolivar Peninsula were sampled, and hindcasts of significant wave heights and water levels during the storm were run to relate environmental factors and structural attributes to a home’s probability of survival. Freeboard, calculated as the difference between the elevation of the lowest horizontal structural member and the combined wave crest and storm surge elevation, was shown to play a critical role in determining survival: survey data indicated that a positive freeboard resulted in a near 100% survival rate for homes subjected to significant wave heights above 3.5 ft (1.07 m). Survival was also strongly influenced by maximum significant wave height itself; below significant wave heights of approximately 3.5 ft, the freeboard requirement for survival dropped sharply. Uncertainty of numerical hindcasts of significant wave heights was considered when evaluating survival as a function of wave height; however, these estimations were considered more accurate than assuming depth-limited breaking waves at each house location. Homes experienced much larger survival rates in areas subject to small significant wave height conditions than in locations affected by larger waves. This analysis was the first step in accurately determining expected damage resulting from specific wave and water level loadings. A more generalized analysis will mitigate possible effects of construction techniques, survey bias, debris impact, and environment-specific wave height estimations on quantitative survival criteria.