*In the best of all worlds, development would be based on providing maximum aesthetic enjoyment to the property owner, minimizing any risk from natural hazards, and providing a reasonable economic return to the developer. Natural processes and natural settings would be evaluated for their hazard potential. Mitigating future property damage would be a routine part of planning for development (fig. 8.1).
Rules and Reality
*Principles and rules often evolve from the trial and error of experience. Realizing that hindsight is a luxury that early developments did not have, some principles still emerge.
*The best time for mitigation is at the beginning of development. The initial stage of development in the coastal zone is one of opportunity to minimize vulnerability to natural hazards. Strict requirements can be set on siting (e.g., elevation requirement, rules minimizing vegetation removal or dune disruption), and the development can be platted to conform with the environments rather than a grid superimposed on the natural topography and habitats (e.g.,roads can curve around or over dunes without cuts, evacuation routes can be sited in the least vulnerable locations, potential overwash passes or inlet locations can be avoided, lot depth can be adequately established for future relocation). The initial development plan, plat restrictions, and community regulations can set the course for minimizing risk. This principle is offset by the fact that the majority of coastal communities have grown haphazardly without long-term planning (development often proceeded from low-risk sites to high-risk sites). In other words, for most coastal communities it's late in the game.
*Planned development has the potential to be less vulnerable (at lower risk) than haphazard development. Planning involves establishing island dynamics, risk evaluation, and mapping, and working to incorporate natural processes and property development in such a way as to reduce both short-term and long-term hazard impacts. For example, distant initial set back can be sold as "low-risk," planned development, but if the erosion rate is high, or the sites' elevations low, then nature will catch up quickly in the form of storm surge and flooding.
*In truth, the real world provides very few good examples of planned developments on barrier islands, primarily because developers/communities do not stick to the plan. Kiawah Island, SC is often cited as an excellent planned development, but, several developers later, some cracks in the "plan" are developing as housing density increases and nature begins to show its influence in beach erosion. The interior of Hilton Head Island, SC also initially provided an example, but development density now exceeds island carrying capacity and the potential for property damage in a future storm is huge. Given the new planned retirement development to add another 8600 units to the island, we would not want our parents or grandparents to be in an evacuation situation there! Bald Head Island, NC looked good (moderate density development, no cars allowed), but here, too, the seaward incursion of development, disruption of dunes and vegetation, and landward incursion of the shoreline does not suggest long-term low risk. Little Cumberland Island, GA may be a good example (low density development, elevation, vegetation cover), but its exclusiveness suggests only a few can enjoy this ideal. Sanibel Island, FL also enjoys a good reputation as a planned development and meets some of the criteria for using initial planning as a mitigation tool.
*Our test for risk mapping is a category 3 hurricane. The above examples have not yet experienced the head-on test of nature, but most have failed the longer-term test of the pressures to expand the development, protect the first threatened shorefront house with a seawall, cut new streets through the interior dunes, or locate the new strip mall in that prime maritime forest. A corollary principle is: Don't expect the original developer to stay with the development, and don't expect the original plan to stay in effect.
*Planned development does not imply low-risk development. This observation grows out of the previous discussion; a good development gone bad. Unfortunately it also applies to many young communities along our coasts. Previously undeveloped islands were platted to maximize lot and housing unit sales. Finger canals destroyed back-island marsh protection (and habitat), placed a greater number of houses in the flood zone, and sometimes raised the potential for new inlet formation; all for the sake of recreational boat access. Marco Island, FL is a typical example of a planned development that put population at risk.
*Communities that were poorly planned, that grew haphazardly, or where risk potential has increased can change this trend through island-wide mitigation strategies that preserve, augment, and repair natural environments. Implementation of this recommendation involves taking active steps to repair damage to the natural setting brought about in the name of development. Such repairs will prepare individual buildings, as well as entire communities, for storms, will reduce property damage during storms, and will speed recovery after storms. Thus, coastal residents will be working with rather than against the natural setting.
When to Mitigate?
*Property damage mitigation techniques can be implemented on a pre-storm, immediate pre-storm, and post-storm basis. In one sense, a "pre-storm" situation always exists. That is, recovery from any storm should be done with the next storm in mind. Storm recovery should involve active steps to repair the island itself and to enhance the protective characteristics and capabilities of the natural setting.
*Pre-storm mitigation activities include: conscientious location of development, elevation and orientation of new roads, changing road orientation or elevation of existing roads, building and vegetating dunes, and updating and enforcing erosion setbacks. Although relocating structures and roadways out of hazard zones is often considered a post-storm activity, it is also possible to consider such actions as important pre-storm mitigation options. Immediate pre-storm activities include sand-bagging and removing mobile structures and objects, if possible. Post-storm activities other than reconstruction are implementation of property-protection measures such as: relocating structures and roadways out of hazard zones, rebuilding or upgrading structures, restriction of density of new development, enforcement of new setbacks for relocated and replaced structures, and awareness and avoidance of overwash passes and new inlets. The predicted acceleration of the rate of sea-level rise and increase in frequency and intensity of storms should also be considerations in comprehensive shoreline management policies.
Mitigation Options Summary
*Several mitigation options were presented in Chapters 5, 6, and 7, with emphasis on nonstructural methods. Mitigation options were listed and categorized in Tables 5.1 and 6.1.
*Table 8.1 shows causal relationships between storm effects (Table 3.1) and mitigation techniques (Tables 5.1 and 6.1). The table indicates that certain mitigation options and storm effects can be causally related. That is, implementation of a given mitigation option will reduce (+) or increase (-) a given negative storm effect. Some options (marked "Å") may have positive effects in some places and negative effects in others. An example is a sediment-trapping jetty which, by interrupting the natural alongshore sand transport system, will cause building out of the beach on the updrift side (potentially leading to wider beach and dunes and less potential for property damage), and erosion of sand on the downdrift side. No attempt is made to quantify the effect of each mitigation option in the table. Table 8.1 also shows (along the bottom two rows) whether the environmental impact of each option will be positive (+) or negative (-) (i.e., does the activity upgrade or degrade the natural environment) and whether the long term cost will be relatively high (H) or low (L), in general terms. For example, beach replenishment has a high long-term cost because it must be repeated again and again. Replacing interior dunes, however, is low cost because replenishment may be a one time action.
*Mitigation options work to reduce the risk of property damage in different ways. Recall from Chapter 1 that a risk (in this case, of property being damaged by storms) involves both hazards (the physical processes) and vulnerability ("improved" property, that is, buildings, utilities, infrastructure). Storm processes can not be altered, but it is possible to influence or control how intensely the storm physical processes are felt in a given location.
*Take, for example, a seawall. If you could stand in front of a seawall during a storm, you would certainly see that the wall has no effect on reducing the "strength" of the storm. Immediately behind the wall, however, there would be a noticeable decrease in wave energy for that location. Similarly, building interior dunes, thus raising island elevation locally, will do nothing to limit absolute storm surge elevation, but it will limit the storm surge inundation for that location. These types of approaches are essentially reducing the hazard's impact by modifying the physical processes for small areas of the coast.
*Property damage mitigation techniques also may be used to reduce the vulnerability of a building to damage by modifying the building itself. For example, strengthening the building (to resist damage and to limit damage to nearby buildings by wind-borne or water-borne debris), or moving it out of a hazardous zone.
Fantasy Island
*The best of all worlds is represented in an 'ideal' development (fig. 8.2) and outlined in Table 8.2, developed along the lines of the Pandora's Island concept in Figure 8.1. Given that such initially planned developments are the exception, Table 8.2 lists corresponding mitigation actions for existing communities ("Return to Fantasy Island," Table 8.2).
*The mitigation recommendations presented in this book are all working and well illustrated in various locations along the southeastern United States coastline. From the site-specific nature of the study a list of general Principles of Property Damage Mitigation, applicable everywhere, is offered:
*SOFT STABILIZATION involves some method of augmenting the sand volume of a community or island.
-Sand can be added to the beach, to the dunes or to the island itself. Sand added to the island is more permanent than sand added to the beach.
-Observe the "Sand Commandments" and preserve all sand.
-Beach bulldozing may work but the range of its applicability is limited.
-Sand fencing really only works well where there is both an adequate supply of sand moving onshore and where there is space in front of buildings in which the sand dunes can grow.
-All gaps in dunes that were excavated for building location, ocean view, or ocean access, should be plugged.
-Building (or re-building) interior dunes adds sand volume to the island and may reduce the effects of overwash and storm-surge ebb.
*BUILDING RELOCATION is a sure way to avoid damage--move the structure out of a hazardous location.
-Many houses are now threatened and can be relocated relatively cheaply.
-Larger structures can be relocated if the economic situation is advantageous.
-Adopt the 10/100-year relocation concept for communities with large structures.
*HARD STABILIZATION is not generally recommended because of its cost and long-term deleterious impacts on the beach.
-Shoreline armoring ultimately results in loss of the recreational (and protective) beach.
-The impacts of shoreline engineering can only be fully understood and evaluated after a several-decades-long observation period.
*VEGETATION, especially maritime forest, is critical for reducing damage from storms.
-Remove as little vegetation as possible, especially forest.
-Encourage marsh or mangrove vegetation growth as a way to slow erosion on the lagoon side of barrier islands.
-Protect and encourage dune vegetation as a way to stabilize sand to offer protection from storm surge and overwash.
*MODIFICATION OF DEVELOPMENT AND INFRASTRUCTURE are ways to change what has already been built to make it less likely to be damaged or to increase damage.
-Many roads were built perpendicular to the shoreline making ideal channels to be exploited by storm overwash and storm-surge ebb flows. These roads should be elevated, curved, humped or resurfaced to impede such flows.
-Many dunes were notched so that roads could go through the dune instead of over it. Here, dunes should be rebuilt and the road rerouted around the rebuilt dune.
-Many homes were built before building codes or when enforcement was poor. These should be retrofitted.
-Breakaway ground level construction in homes elevated on stilts becomes rubble that rams other structures during storms. All such ground level construction should be prohibited.
*ZONING WITH NATURE means identifying hazard areas and avoiding them by proper planning.
-Recognize hazard areas and avoid them.
-Understand inlet dynamics--each inlet is different.
-Reasonable setbacks based on erosion rates and predictions of erosion rates.
A Complex Picture
*Property damage mitigation is at once a simple and a complex task. The principles are simple, but the implementation is complex. Part of the complexity arises because property damage mitigation involves expertise from engineering, the physical sciences and the social sciences. Engineering, and to a large degree the physical sciences, are relatively straightforward, or at least can be dealt with independently. Engineering involves such things as design of shoreline stabilization structures, beach replenishment, building codes, infrastructure design and relocation. The applied physical sciences provide information about coastal geology, ecology, biology and environmental science, to meteorology and climatology--predicting hurricanes and other storms. The social sciences have the truly onerous tasks involved in property damage mitigation. They must address complex issues such as land use planning, emergency preparedness and emergency response, coastal zone management, and politics. Thus, the social aspects constitute the area of much needed focus. Coastal geologists can point out inlet hazard areas and likely overwash zones, calculate erosion rates and so forth. However, it takes a more integrated effort in order for people to understand and accept that we must live with nature, not try to fight it.
*The following case studies illustrate that each island/community is unique, and, historically, the approaches to mitigating natural hazard impacts are as diverse as community social structure and politics.
*Table 8.2. Fantasy Island. Characteristics of the ideal developed barrier island and methods to return to Fantasy Island for already developed islands.
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"FANTASY ISLAND" "RETURN TO FANTASY ISLAND"
(undeveloped) (already developed)
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1. Perpendicular access of utilities; buried.
2. Large craft marina on mainland.
3. No finger canals.
4. Backside erosion control by encouraging vegetation.
5. Fixed span bridge.
6. Do not disturb salt marsh
7. No utilities across inlets.
8. No development on spits.
9. Minimum disruption of topography and vegetation.
10. No shoreline stabilization except by replenishment.
11. No development in inlet hazard areas. Each inlet area studied for historical trends.
12. High rise development on lagoon side of island only.
13. Development density based on islands natural carrying capacity.
14. All buildings exceed codes and regulations (e.g., extra elevation, extra connectors, design to minimize wind impact).
1. Existing utilities made as safe as possible. Consider burying.
2. No new large-craft marinas.
3. No new finger canals. (consider filling some?)
4. No additional bulkheading of lagoonside.
5. Upgrade bridges for evacuation--no drawbridges.
6. No dredge and fill. Monitor pollution.
7. Relocate utilities.
8. Relocate development off of spits.
9. Strict planning. Restore frontal, interior dunes, re-vegetate dunes and forest.
10. To protect beaches, adopt long-term plan to remove seawalls, as South Carolina has done.
11. Rezoning and relocation of development out of inlet hazard areas, including historic, present and potential inlets.
12. New high rises on lagoon side only.
13. Slow or stop development.
14. Building construction upgraded to reduce hazard impact (e.g., addition of connectors, opening ground-level obstructions to flow, flood proofing).
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