Lessons from Hurricane Ike

Ch5: Predicting Storm Surge

5 Introduction Every hurricane has the potential to inflict damage in one or all of the following ways: wind, rainfall, tornadoes , and surge. Of these, storm surge has been responsible for some of the most devastating hurricane-related damage. Storm surge occurs when sea levels rise in the face of low barometric pressure. the resulting mass of water is pushed onto shore by strong hurricane winds as described in chapter 3 (fig. 5.1). long known for its damaging effects, storm surge is difficult to predict and has been responsible for the loss of thousands of lives and billions of dollars in damages along the texas and louisiana Gulf coasts. Sea walls, levees, bulkheads and the like have all been built in attempts to protect lives and communities from the onslaught of this powerful force. however, as residents move towards coastal areas in greater numbers, the potential for significant loss continues to increase. As in any natural hazard scenario, the safety of a community is directly Predicting Storm Surge Clint Dawson and Jennifer Proft Figure 5.1. As the storm surge from hurricane ike continues to rise, Bill Murphy, second from right, waits with three rescuers for a boat to pull them to safety after Murphy’s wife Barbara and two others were rescued by a Coast Guard helicopter in high island, texas. Photo courtesy Guy Reynolds/dallas Morning news. Dawson and Proft 51 tied to the ability of forecasters to successfully predict the location and timing of storm surge and respond. to do this, it is necessary to understand the causes and physical effects of surge, both on the meso- and the micro-scale. Recently, computer modeling has become an effective tool for studying storm surge mitigation. Modeling lets forecasters predict the location and severity of storm surge prior to hurricane landfall. Prior to the advent of computer-based modeling, one could only make an educated guess based upon historic, empirically observed data (Resio et al. 2008). For example, if a historical Category 2 hurricane resulted in a 5-foot storm surge, a future storm with similar wind speeds would be expected to have roughly the same surge effects. the inaccuracies associated with such observational analyses are evident given the myriad of complex factors involved in the formation of hurricanestormsurge .thesefactorsinclude wind speed, wave-current interaction, tides, atmospheric pressure, riverine flows, rainfall, wetting and drying capacities , and local topography and bathymetry (Bunya et al. 2010). they are best understood through computational methods. Given the complexity of such factors, attempts to understand hurricane storm surge by observation alone invariably fall short. the benefits of storm surge modeling are easily characterized and fall into one or more of the following categories: structural mitigation, land use, long-term land development, and evacuation. The Benefits of Storm Surge Modeling Sea walls, dikes, levees, flood gates and the like have historically played a role in protecting vulnerable communities from the effects of storm surge. however, simply placing a solid structure of an arbitrary height between a community and the sea is a dangerous way to go about protecting both people and property (fig. 5.2). during hurricane Katrina, the levees in new Orleans were not only breached, but the Arpent Canal levee failed completely and approximately 131 billion gallons of water flooded the city. Computer -based simulations allow forecasters to model various storm surge heights against proposed structural mitigation, testing their response and enabling city officials and emergency management to make educated decisions about what type of structure, if any, will protect communities in a particular area. While structural mitigation plays an important role in storm surge management , equally important is the role of land use and non-structural mitigation . Where and what we choose to build may have far reaching effects, Predicting Storm Surge 52 either increasing or decreasing the damage storm surge can inflict. For example, coastal wetlands are able to attenuate the large volumes of water from storm surge, resulting in reduced surge elevations further inland. Ecological preservation and wetland restoration in coastal areas is one way to mitigate the effect of storm surge. these areas have an incredible capacity to slow the forward motion of surge, as well as store the water after the event. Computer-based modeling allows planners and policy makers to better understand which areas function well as natural barriers to the sea and limit development in those areas. land use decisions in areas vulnerable...