Coastal areas are important residential, commercial and industrial areas; but coastal hazards can pose significant threats to these areas. Shoreline/coastal protection elements, both built structures such as breakwaters, seawalls and revetments, as well as natural features such as beaches, reefs and wetlands, are regular features of a coastal community and are important for community safety and development. These protection structures provide a range of resilience to coastal communities. During and after disasters, they help to minimize damages and support recovery; during non-disaster times, the values from shoreline elements shift from the narrow focus on protection. Most coastal communities have limited land and resources and few can dedicate scarce resources solely for protection. Values from shore protection can and should expand to include environmental, economic and social/cultural values. This paper discusses the key aspects of shoreline protection that influence effective community resilience and protection from disasters. This paper also presents ways that the economic, environmental and social/cultural values of shore protection can be evaluated and quantified. It presents the Coastal Community Hazard Protection Resilience (CCHPR) Index for evaluating the resilience capacity to coastal communities from various protection schemes and demonstrates the use of this Index for an urban beach in San Francisco, CA, USA.
Coastal areas have attracted people for millennia, developing into major population centres and loci for trade and economic development. In the USA, coastal states, excluding Alaska, have less than 50% of the land area. Yet, as of 2012, almost 80% of the US population lived in coastal states and almost 85% of the national gross domestic product (GDP) came from coastal states. Globally, about 40% of the population lives within 100 km of the coast; almost 75 million people live in low-lying coastal areas at less than 1 m elevation; 328 million people live in coastal areas at less than 5 m elevation; and about 700 million people live in coastal areas at less than 10 m elevation (; data from 2010). Over half of these low-lying coastal populations are also concentrated in urban areas . Approximately $944 trillion (US) of the global GDP—Market Exchange Rate is located in these low areas, between mean high water (MHW) and 1 m MHW; approximately $1800 trillion is between MHW and 5 m MHW . These estimates only cover the direct values of property in low-lying areas and do not include any indirect values such as the businesses supported by coastal wage earners or the inland businesses that depend upon coastal supply chains.
The large concentrations of people and property in low-lying areas along the coast provide an indication of the possible consequences of coastal events, ranging from routine storms to massive tsunamis, hurricanes or tropical cyclones. The populations and assets that are at less than 1 m elevation could routinely be subject now to erosion, wave impacts and flooding and future inundation due to rising sea level; hurricanes and tropical storms also pose wind-related threats. These threats would be realized globally, unless the area has some type of effective shore protection. The people and resources that are at less than 5 m elevation would be vulnerable to wave attack, flooding and erosion due to major storms, hurricanes and tsunamis. Such events would be of global concern, but individual events would be damaging at regional or local scales. The 10 m elevation provides an indication of the people and assets, globally, that could be at risk from extreme storms, hurricanes and tsunamis. As seem from events of the past 10–15 years, extreme coastal events have occurred around much of the globe, and while each has been regional in scale, each resulted in disastrous consequences at a global scale. Table 1 provides a summary of several of the more devastating coastal events of the twenty-first century. Despite knowledge of the coastal risks, warning systems and shore protection structures, coastal events regularly cause enormous losses that can take years, if not decades for full recovery.
Community resilience, at its essence, means changing from a repetitive cycle of damage, rebuilding, damage and rebuilding. Resilience addresses the ability of a community to minimize damages from events such as tsunamis and coastal storms, and to recover from and to return to a state of normalcy after a damaging event. Resilience connotes more than getting through a hazard event. A resilient community can be represented by the following characteristics :
— survival of the people living in the community;
— ability of people to remain in the community during the event or return quickly;
— infrastructure remains functional or becomes functional soon after the event; and
— maintenance or enhancement of community amenities such as ecosystem areas and recreational space.
The traditional role of shore protection has been to provide physical resistance  and has focused on the first three aspects of resilience. Resistance will remain an essential aspect of shore protection. This purpose is abundantly clear from the number of people and value of assets that could be at risk from a damaging event. The next section of this paper discusses general lessons about shore protection that came from several recent field investigations of disaster events. These lessons do not address specific design requirements or the types of protection that are most appropriate for specific locations, but rather, the bigger issues that need to be considered for all coastal protection efforts.
The crowding of people and assets in close proximity to the shoreline also highlights the importance of coastal land for access to fishing areas, open space, recreational opportunities and as tourist attractions. The challenge in congested coastal areas is to integrate shore protection into these other community amenities. Whatever elements are used for coastal protection, communities and coastal managers are beginning to realize that protection elements can be important for community vitality and resilience, providing economic, environmental and social/cultural values. As such, it is useful to understand the positive and negative community values that shoreline protection systems offer, independent of their protective values. Decisions on additions or changes to shore protection will need to consider how these elements maintain or enhance community amenities for the non-disaster times. The third section of this paper discusses this larger aspect of shore protection elements and introduces the Coastal Community Hazard Protection Resilience (CCHPR) Index that characterizes and quantifies several comparable non-disaster values provided by shore protection elements.
2. Shoreline protection—lessons from recent disasters
Decisions to settle and maintain coastal communities, invest in homes, establish businesses and start new industries are predicated upon the assumption that the community will be relatively safe from coastal hazards. Recent coastal disasters have provided an impetus to better characterize and model these events, and in the case of tsunamis, have resulted in warning centres that can rapidly forecast and model these destructive waves . However, recent disasters also bring into question some assumptions about the safety of coastal communities and highlight the need for effective protection.
The field observations from coastal disasters have had many useful results. Examination of successful designs provides clues for future successful designs, but so too do failures and failure consequences. Shore protection elements are expected, first and foremost, to offer the inland development safety from coastal hazards. Field surveys provide key lessons about the effectiveness of shore protection, ranging from consideration of the system aspects of protection to design details and considerations. These general lessons are more than forensic examinations of past disasters. They provide focus for coastal communities in their examination of overall shore protection and resilience so that future coastal events will not turn into disasters. This section summarizes some of the key findings from field investigations that are relevant to the protection for a broad range of coastal areas—that community protection functions or fails as a system, nature-based protection is part of the system, land-use planning needs to be part of community protection, protection is dynamic, performance conditions change, survival of protection structures is important to recovery, engineering details, elevation and scour are important, and that extreme events need to be considered even if not used as the design condition. As Synolakis & Kanoglu  discuss in this issue, it was the lack of consideration of the appropriate extreme earthquake that doomed the Fukushima Dai-ichi nuclear power plant, and possibly the engineering detail of the location of the emergency diesel generators, which they report as having been at the basement of the plant.
(a) Shore protection works as a system
Coastal communities develop and expand over time, and normally the available coastal protection develops from an amalgam of disparate features constructed at different times, for a range of purposes, and different design levels. Often community development will outpace the available protection, the original purpose for the protection may no longer exist, or the structures may have been modified over time, thus changing the design conditions. These structures are now often expected to work as a coherent system. Some structures may overlap and augment the overall protective function of the system, while others may diminish the protective function of other parts of the system or leave some areas under protected. New Orleans was an example of these many problems with coastal protection that became evident in the aftermath of Hurricane Katrina [13,14]. Failures of small levee sections had a cascading effect, leading to community-scale flooding and damage. A key focus of the post-Katrina reconstruction was to replace the prior protection elements with a more systems-wide approach for protection of the entire community.
(b) Nature-based protection
Natural features such as reefs, wetlands, beaches and enclosed bays provided the initial protection for most early coastal communities. Engineered protection has augmented this natural protection; however, many communities continue to be protected by ‘green infrastructure’. Sand dunes provided protection to inland development on Phuket, where development inland of intact dunes experienced only a gradual rise in water level, yet development was destroyed inland of an area where the dune had been lowered to provide views of the ocean . Overland penetrations of waves in Sri Lanka were observed to be greater inland of areas where coral had been mined from the offshore reef . However, no protection is infallible and many natural barriers were not able to withstand extreme conditions. The high flow levels measured during the Tohoku tsunami underscore the differences in time scales between normal flooding and extreme events .
Figure 1 shows two examples of protection resulting from natural features. The importance of nature-based protection is growing. As noted by the US Army Corps of Engineers , ‘coastal risk reduction can be achieved through a combination of approaches, including natural or nature-based features’. Quantitative monitoring of living shoreline and ecosystem areas will improve the ability to put ranges on their protective capacity . More effort is needed to quantify site-specific risk reductions and to better link green and grey infrastructure options, through better monitoring and analysis . In addition to the risk reduction properties of these natural systems, they also offer the resilience potential of being able to repair some damages and do self-maintenance.
(c) Land use is part of community protection
Land-use protection options, such as setbacks, conservation easements and land acquisitions, will remain effective over time, unless the area is experiencing erosion. Erosion will reduce the effectiveness of these options that will reduce with time. Sea-level rise will further reduce the time period over which these options provide utility. But, if these setbacks, easements or acquisitions can continue to move inland with some identified shoreline feature such as bluff edge or dune crest, then the effectiveness of the easements and setbacks can remain . Eventually, these easements will probably meet an inflexible barrier, such as major roadway, utility corridor or high-density development. If the setbacks and easements are used on non-erosive land to provide flood detention or overflow areas, their utility may last for many years and only decrease if flood levels increase due to climate change or hydraulic modifications.
(d) Coastal protection is not static
Protection provided by natural systems can ebb and flow with changes to the natural system. For beaches, this can occur from seasonal changes in beach width, or from long-term erosion or accretion trends. For reefs, mangroves, wetlands and other living systems, protection can change with the health of the ecosystem, or with the seasonal changes in vegetation growth. When sea-level rise is included in the analysis, both the protection and the assets at-risk will be modified with time and changing hazard conditions. The timing for sea-level rise needs to be considered if the structural or ecosystem functions change with time. Over a number of years, the protective value of these systems may also depend upon whether there is space to migrate and adjust to coastal changes. Such adjustments will be critical for these systems to remain effective with rising sea level.
Built structures may appear unchanged and, with regular maintenance, can remain close to their original design conditions for years. However, without maintenance, the effectiveness of the structures can diminish. With rising sea level, the protection level will decrease for both maintained and unmaintained structures. Major structural modification might be necessary for the structures to provide an equivalent level of protection with rising sea level.
(e) Changing performance conditions
Most engineered structures are initially designed to provide a quantifiable level of protection, such as being sufficient to prevent flooding from a 1% annual probability flood event. Despite this quantification for the design level, structures can out-live their design conditions—a situation that will become more common with rising sea level. Some existing structures can be upgraded to address new design conditions, especially those structures with room to provide for an expanded foundation. New structures should be designed to adapt to future conditions.
Engineered protection may fail due to age, poor maintenance, error and changes in hazard intensity, extreme events or some unanticipated event. Risk and vulnerability assessments need to be based upon realistic protective levels. Structures built initially to protect agricultural areas may become protection for residential, commercial or industrial development as land uses change. The performance level of the protection would not change as a result of the land-use changes, but the significance of failure can change greatly. Owing to different design conditions, structures provide differing levels of protection. Even structures with the same initial design conditions may differ in protection effectiveness over time, due to changes or variations in hazards, local geology, maintenance or structural deterioration through environmental conditions.
(f) Survival of protective structures
Coastal structures can provide several levels of protection. The most effective level of protection comes from structures that prevent damage to inland communities and remain functional. A second level of protection comes from structures that are able to provide protection after a disaster. The structure may not provide complete protection from an extreme event, but when the structure survived the event, it can protect recovery efforts from future smaller events and help community rebuild. The structure may not fit with the future plans for the community, but could be repurposed or removed after rebuilding has occurred. A lesser level of long-term protection may come from structures that collapse or fail during the disaster, but that reduce community damages by providing significant protection prior to failure . The Kamaishi breakwater is an example of such a structure. The breakwater collapsed during the Tohoku tsunami; but model results suggest that the breakwater reduced flooding from an unprotected level of 13.8 m to a measured level of 8 m, and delayed the time of wave landfall by several minutes .
(g) Engineering details
General observations from post-disaster field investigations are that well-engineered structures often survive an extreme event . Engineering details that help hold a structure together during flooding or overtopping are a solid foundation that is either deeply founded or anchored into bedrock; strong connections between elements (three-point contact for revetments or armour units, mechanical connections between concrete panels, caissons, wall segments, etc.); and walls that are tied into rock outcrops or a highly erosion-resistant material [23,24].
Water and waves can find small weaknesses in engineered elements, such as connections, joints, corners, tie-ins and contact points, and propagate small weaknesses into progressive losses or larger failures. Many of the failures of protective structures that were destroyed by the Tohoku-Oki tsunami seemed to have developed from small weaknesses where connections between segmented tsunami walls were insufficient to hold segments together once small gaps developed. Some dike failures probably started with the build-up of hydraulic pressure that dislodged one or two inland panels. The loss of one or two panels would reduce the stability of surrounding panels, and overtopping would scour the underlying fill, remove more panels and rapidly reduce resistance to lateral loads. While the actual failure might have been from the lateral forcing, the reduced stability from loss of panels, overtopping and scour contributed to the collapse . Unless sections are isolated by internal cells or walls, the loss of one wall or levee segment can weaken adjacent sections, leading to cascade failure.
When water is the main source of community damage, elevation is one of the key aspects of protection. Elevation can provide protection in different ways. It can be developed through the protection features used to protect land and development inland of the structure, or through elevation of the individual developments and inland buildings. During Hurricane Ike, much of downtown Galveston was protected from erosion and flooding by the Galveston Seawall. Even small shore protection can provide some benefit to inland development if it stays intact. In Thailand, a low seawall was able to dissipate some of the wave energy from the Indian Ocean tsunami. Inland structures suffered from flooding, but were protected from wave forces . On Bolivar Island, there were no seawalls or shore protection during Hurricane Ike, yet homes that were elevated above the flood level survived . Roadways may be the one exception, where at-grade roads tend to experience less damage during flood events that do elevated roads, possibly because the elevation difference sets up a hydraulic jump that can scour the roadbed as floodwaters recede .
Scour, the removal of sand or bed material from the vicinity of a coastal structure, is a well-recognized problem for structures exposed to high-energy water or fast currents. Despite being a well-known coastal concern, scour is the source of many structural failures, focusing often at the corners or edges of structures or at areas of flow convergence. For example, several tsunami walls experienced partial collapse because of the Tohoku tsunami. Examination of the ends of the surviving sections showed significant scour of the inland wall support, suggesting that failure of the collapsed sections resulted from a critical amount of scour of the foundation or back support material. Failure or complete collapse of structures can originate from scour hotspots [21,27]. General beach scour, or the lowering of beach elevation, can also be damaging to buildings. The drop in beach elevation will reduce wave attenuation, and let larger waves propagate farther inland . Scour can be damaging to structure foundations that are not deeply embedded and inexpensive scour aprons and well-embedded piles can help reduce structural damage from scour impacts.
(j) Examining what-if situations
One main lesson from disaster investigations is the importance of considering the consequences of the disaster event exceeding the design conditions of the structure. Structures are often designed with the expectation that they will perform as expected and remain standing during a tsunami or major storm event. The modes of damage or failure during events beyond the design condition are rarely considered. For example, the Tohoku tsunami waves were higher than most of the protection barriers and the ‘what-if’ situation of overtopping had not been considered in the design. When the walls were overtopped, the walls had no protection from inland scour . More walls might have survived if there were scour protection and inland stability, reducing loss of structures after overtopping. In Japan, a new paradigm for tsunami monitoring and warning systems and design of protective elements has been predicated upon the awareness that large protection structures can fail .
The concept of contingency planning or examining ‘what-if’ situations is to reduce unanticipated failure or having one point of failure lead to complete structural collapse. Contingency planning normally starts with scenario-based analysis of risk and vulnerabilities and it attempts to look at possible failure modes and ‘tipping points’ such as breaches, foundation instability or overtopping that might propagate additional failures. Structures cannot be designed for all possible extreme events; however, contingency planning examines the possible consequences that can result from exceedance of the design conditions . Such planning can lead to structural designs that control small failures and prevent them from growing into major collapses.
Adaptation planning, closely related to contingency planning, has been developed for dealing with the uncertainties of climate change and sea-level rise. Similar to contingency planning, adaptation planning often develops from scenario-based analysis, with the scenario analysis developed from possible amounts of future sea-level rise. The design will be based on some assumed sea-level rise amount. If a higher amount of sea-level rise could jeopardize the structure, the idea with adaptation planning is that options will be included to allow structural modifications if sea-level rise is larger than what was used in the design. In other situations, redundant structures might be more effective than adaptive design. For example, if a coastal road used for evacuation could be threatened in the future by erosion, an alternative inland route or a redundant road could allow for managed retreat of the coastal road without loss of function.
3. Resilient protection systems for coastal communities
Each coastal community will have its own mix of protection. Offshore protection, such as reefs or breakwaters, can reduce incoming wave energy and provide the first line of protection from hazards. However, it is important to identify gaps in these features because wave energy and currents can intensify in the gaps. Closer to shore, protection can result from marshes, sea grasses or a beach that can reduce and dissipate wave energy, as well as accommodate changing water levels and shifts in sediment erosion and accretion. Dunes or coastal bluffs, immediately inland of the beach, either resist wave energy that exceeded the beach capacity, or augment and supplement the beach volume and beach area through erosion. Engineered structures may replace or augment the protection from bluffs and dunes, and development close to the coast may have been designed with their own protection, through setbacks, elevation, flood-proofing, storm shutters and such. Protection and risk reduction comes from the combined interactions of all these elements together.
An inventory of protective features—man-made and natural—and an assessment of their individual and combined effectiveness in protecting from coastal hazards provide a start to understanding community resilience. Protective efforts provide protection in different ways. Some, like walls and barriers, block wave forces and high water levels and halt erosion; others, like breakwaters and marshes, attenuate wave energy, reduce water levels and slow erosion. However, these protective features also need to be evaluated relative to overall community values and benefits under both day-to-day and episodic event conditions. Overall resilience of coastal protection has four components or phases: the pre-event actions that can provide temporary or event-based improvements, the protection and value during and immediately after the event, the immediate recovery, and then the on-going use until the next event . The values and benefits of various protection efforts change from phase to phase. For example, a surge barrier may provide some peace of mind on a day-to-day basis, but its highest value is for life safety during a disaster event. A breakwater can provide protection during storms, but under normal conditions, its main value may be to navigational safety.
It is important that communities have a good understanding of their protection systems and the adequacy of the system to protect important community assets from the routine and extreme events that can attack the community. Such an evaluation of disaster resilience is, by necessity, specific to the community, configuration of community assets and the hazard events that are possible for the area. An examination of resilience for disasters is essential for the community. However, an examination of resilience only in terms of disasters and risk reduction overlooks many of the features and values of the coast, such as fisheries, recreation, tourism, habitats and water quality that are important for community during the non-disaster periods of recovery and on-going normalcy. Shoreline protection elements can either support or be detrimental to many of these aspects of coastal communities and the multi-purpose benefits from coastal protection elements cannot be overlooked. These non-disaster benefits come from the economic, environmental and social/cultural contributions that are provided by the protection. There can be :
— economic value, such as fisheries, changes to tax base or increased revenues;
— environmental value, such as improved air or water quality, and ecosystem enhancement; and
— social/cultural values, such as recreation, open space, quality of life and cultural heritage.
Shore protection can provide both direct benefits and secondary benefits to a community. Direct benefits have an immediate connection to the protection, as for example the environmental values that marshes might provide by improving water quality. Secondary benefits derive from what is being protected, rather than from the protection directly. For example, a seawall would provide a secondary environmental benefit, if it were to prevent toxic or hazardous material in a land fill from getting into the marine environment. The direct characteristics do not depend upon the use of the protection, whereas the secondary values are use- or location-specific. The direct benefits from a breakwater will be the same if the inland development is a nuclear power plant or a flower garden, even though the secondary values will differ. Table 2 summarizes some of the direct benefits, or costs, associated with each value.
(a) Coastal Community Hazard Protection Resilience Index
Community resilience from coastal hazards needs to combine multiple attributes of protection. The evaluation of coastal hazard protection will occur at a number of different scales, from the micro, asset-specific scale to determine when to implement maintenance, to the detailed, community-wide scale to determine the benefits and costs of a billion dollar investment in a new engineered protection structure. Techniques exist to evaluate and compare shore protection designs for protective benefits. Comparing responses to various storm return frequencies or a particular water level may provide insight into the available protection level. Risk analysis can provide a community with an understanding of the degree of protection that is available from different protection options; a cost–benefit analysis can allow the financial comparison of different protection options. However, these approaches do not address the economic, environmental or social/cultural values of the protective feature through all the disaster phases experienced by a community.
Some protection elements, such a breakwaters, wetland restoration or large-scale beach nourishment, are major economic investments and the monetary costs and benefits are important for project analysis. In recent years, attempts have been made to expand traditional benefit–cost analyses to monetize the non-market values, such as environmental and social/cultural values from natural coastal areas and ecosystems (e.g. [29,30]). These quantifications can greatly enhance the decision-making process. Planning and examination of resilience options could begin long before any detailed analysis of individual additions or changes to overall coastal hazard protection for a community.
Not every type of protection can be used in every location, or for every level of protection. Some protection options, such as insurance and warning systems, have been found to be extremely effective and should be considered as useful elements for many hazard situations [28,31]. In particular, the tsunami warning system has been largely effective at saving lives from far-field events . Once protection options are developed to provide the appropriate or needed protection that are appropriate for the location, the CCHPR Index can help communities with their overall examination of resilience and help highlight the main weaknesses or limitations in the current resilience efforts.
The CCHPR Index facilitates a general examination of a community's existing protection, allows a determination of the major values that can be attributed to this protection and allows a comparison of this existing situation to changes to the available protection, or to the community assets that are most at risk. Options for the future could range from maintenance of existing elements, or addition of new protective elements, to removal or replacement of certain community assets that cannot be fully protected by either natural or engineered protection elements.
With the CCHPR Index the direct economic, environmental and social/cultural values are evaluated as having either a positive or negative value that is high, medium, low or no value. These qualitative values are assigned quantitative values ranging from 3 to −3, with 3 for high, 2 for medium, 1 for low and 0 for no positive or negative value . Table 3 summarizes the economic, environmental and social/cultural values of many of the more commonly used natural and engineered shoreline protective elements. The values summarized in table 3 are direct values that can be attributed to the type of protection and they are not location-specific or design-specific. The direct values in the CCHPR Index are the combined values for each protection element derived from both recovery and ongoing activity phases and the values have been weighted by the average times for recovery (25%) and non-disaster times (75%). These weightings are based on professional judgement and examination of disaster stages; these weights can be revised for communities that seem more or less disaster-resilient than these assumed distributions.
Beaches are one of the primary types of protection for many communities and are used as an example of the values provided in table 3 . Beaches generally have slight to moderate economic value during recovery as tourism is not a strong community element during recovery. But, beaches would have a moderate environmental value and provide a high social/cultural value to the community members as they participate in recovery. Thus for the recovery phase, beaches are given values of 0–2 for economic value (average value of 1), 2 for environmental value and 3 for social/cultural value. For the ongoing activities phase, beaches would foster some tourism and the economic value would increase to 3; the environmental and social/cultural values would remain the same as for recovery conditions. Combining the recovery and ongoing normalcy condition values by the 25% and 75% weighting, respectively, the index values for beaches are 2.6 for economic value, 2 for environmental value and 3 for social/cultural value.
Revetments provide a second example of the Index . During recovery, revetments would have a low economic value of 1 as they might encourage more rapid recovery. These structures can capture debris and trash so their environmental value would be neutral to slightly negative (0 to −1) and they would have no social/cultural value. During routine or ongoing conditions, revetments would provide no economic value to the community; their environmental value would be slightly to moderately negative (−1 to −2) as they would displace beach habitat; and their social/cultural value moderately to highly negative (−2 to −3) because they would interfere with along-shore beach access, recreation and the overall beach experience. Based on these values and the same 25% and 75% weightings, the Index values for revetments are 0.3 for economic, −1.3 for environmental and −1.9 for social/cultural. In contrast to revetments, breakwaters provide shelter to boats and protection for navigation and have a high economic value for recovery and ongoing conditions.
The CCHRP Index also includes secondary values. The secondary values are community-specific and derive from the types of development that are being protected. Like the direct values, these secondary values are assigned positive or negative values of 3 for high, 2 for medium, 1 for low and 0 for no economic, environmental or social/cultural value. Table 4 provides the CCHRP worksheet that a community can populate with the specific protection elements and back shore development that will provide the direct and secondary economic, environmental and social–cultural values from shore protection. For many sections of the shoreline, there are multiple protective features. When that is the case, the values from each protective element would be included in the worksheet. The value assigned to the shoreline where the protection occurs is calculated by multiplying the protection value by the shore length. Similarly, the secondary values for what is being protected are developed by multiplying the secondary values by the shoreline length. The total value for the beach area is summed for the individual sections and weighted by the total shoreline length.
The merits of this quasi-quantitative index are that it allows flexibility in the evaluation and development of a resilience index, while keeping economic, environmental and social/cultural values on an equal basis. Communities could use more elaborate values if they choose, assign different numerical values to the high, medium and low, or even add other ratings such as very high or of irreplaceable value. The CCHPR Index does not assign different levels of importance or weights to economic, environmental or social/cultural values, although communities could also assign different weightings to these if they were so inclined. An example for San Francisco, CA is provided to demonstrate how this CCHPR Index would be applied.
(b) Coastal Community Hazard Protection Resilience Index application to San Francisco, CA, USA
Ocean Beach is San Francisco's western border and the city's open ocean coast. It is approximately 5.8 km (3.6 miles) long, from Point Lobos in the north to bluffs in Fort Funston in the south. Ocean Beach was once part of a vast beach and dune system; however today, as seen in figure 2, many of the dunes have been covered by houses, roads and parking; some dunes have been vegetated to form part of the Golden Gate National Recreation Area. Today, the dominant features along Ocean Beach are the Great Highway, pedestrian paths, parking areas and several large seawalls. Utility corridors for electrical power, sewer and storm water run under the Great Highway. Immediately inland of the Great Highway are restaurants, the San Francisco Zoo and other visitor serving facilities, homes and a wastewater treatment plant.
The Great Highway was built on top of the dunes, on land set aside by the city for a public highway. But, this location placed the highway at risk from wave damage, and soon after the City of San Francisco started building the roadway, the city also began building a large seawall to protect it. The first and northernmost seawall, the O'shaughnessy Seawall, is almost 1310 m (4300 ft) long . This seawall provides for steps down to the beach, and it includes a series of six platforms or bleachers that can be used for seating. South of the O'shaughnessy Seawall is the 200 m long (660 ft long) Taravel Seawall and the 885 m long (2900 ft long) Great Highway Seawall. These three walls together armour much of the Great Highway and demarcate the inland boundary of the northern and central sections of Ocean Beach. No massive seawall has been built along the southern section of Ocean Beach; however, several temporary revetments and beach nourishment projects have been installed in this area (known as South of Sloat) to protect the road and parking areas from erosion .
The CCHPR Index used Ocean Beach as a test case because Ocean Beach has a mixture of protection features and inland development. Furthermore, the City of San Francisco has spent several years studying this coastal section and developing several options for addressing erosion while maintaining many of the important economic, environmental and social/cultural features of this area. Table 5 summarizes the values developed from the main worksheet. At Ocean Beach the shore protection features provide a mix of direct values that have high economic and social/cultural value and slightly lower environmental value, assuming these are weighted equally. The secondary assets have high economic and environmental value, but low social/cultural value.
Overall, the economic values to the community from the beach and protection options are somewhat higher than the features being protected (the direct economic value is 3.6 and secondary economic value is 2.7). Much of the direct economic values derive from the beaches and dunes, suggesting that the city would benefit economically from greater focus on these natural protective assets. The difference between the direct to secondary values is even more the case for the social/cultural values of the existing coastal features. The beach and dune values far outweigh the social/cultural values of the inland assets.
The environmental values present a different situation than the economic and social/cultural values. The environmental values from protecting a sewer line and a wastewater treatment plant are greater than the values from the shore protection features. The environmental value of these secondary assets derives from their water quality benefits and they would be more significant environmentally than damage or loss of the protection features. Efforts to improve protection of these assets would need to consider how the protection steps might change the direct economic and social/cultural values that are provided now by the beach and dunes. Options to reduce the environmental value of the secondary assets, through relocation or replacement with a more inland facility, could improve the relative importance of the direct environmental values, without detrimental impacts to the direct economic and social cultural values from current protection elements .
The CCHPR Index can be used to explore aspects of community resilience, and also to evaluate the significance of future changes to the coast. As demonstrated by the Ocean Beach example, changes to inland uses can lead to changes to protective elements. Options to reduce the secondary values that depend upon protection would reduce the overall importance of the protection whereas options to increase the secondary values would put greater emphasis on protection, or focus more attention on protection that provides partial protection in the failure mode.
Coastal areas are exposed to a number of hazards, such as erosion, flooding and wave attack, that can make coastal communities especially vulnerable to disasters. Despite this, coastal areas have been centres of population growth and economic development for thousands of years. Currently, coastal hazards are expected to worsen with climate change and rising sea level and threats to coastal communities will continue or worsen. Hazard events such as storms, hurricanes or tsunamis cannot be prevented, and communities are not likely to abandon all use of the coast. Therefore, ways to increase community resilience are needed.
Community resilience is important for all phases of a disaster, from the pre-disaster preparations and the disaster through to the recovery and ongoing activities. Coastal protection features are important for community resilience during disasters. As such, this paper has covered many of the lessons for effective community protection. Field investigations following a disaster can provide useful information on how various structures perform under extreme or high load conditions, the characteristics of an event that are most damaging, and the engineering aspects of protective features that are most probably to remain functional or most probably to be damaged. Past disasters, however, cannot identify fully the risks and vulnerabilities of individual communities. Such analysis, often undertaken as part of a study of community vulnerability, requires detailed characteristics of local hazards, bathymetry and topography and careful evaluation of the protective functions of all existing or proposed natural and constructed protective features, and has not been the focus of this research. Nevertheless, the disaster responses of protective features can provide guidance and insight for community-scale vulnerability and risk analyses and many of the lessons learned can be of benefit to all coastal communities.
Disasters tend to dominate much of the discussion of resilience; however, coastal land is often scarce and communities value their shorelines for more than protection from hazard events. As communities assess their existing protection and possible options for changes to protection, more values than simply protection can, and perhaps should, be considered. Over years or even decades, communities spend the majority of time under non-disaster conditions. The CCHPR Index provides a means to compare a broad array of coastal protection elements across several important community aspects that rarely have intercomparable metrics—economical, environmental and social/cultural aspects. The CCHPR Index does not depend upon scale, nor does it require a detailed assessment of community vulnerability or evaluation of the condition of existing shore protection. The assignment of high, medium and low ratings to the economic, environmental and social/cultural benefits (or costs) of each type of protection provides a non-monetary comparison of options and a means to assess the current protective options that are already in use by a community.
The CCHPR Index separates the values that derive from the protective features themselves, from the secondary values of the community assets that are being protected. While a community may decide that certain assets require different levels of protection than other assets, due to their cost, environmental importance or social value, the features provide protection and exhibit economic, environmental and social/cultural values without regard for the inland assets.
The CCHRP Index enables communities to develop a first cut evaluation of the resilience and values of their existing protective features. It will also enable communities to evaluate how the addition or deletion of various protective features will change the various community values. The Ocean Beach shoreline of San Francisco, CA, was used as a test case to provide an example of how the CCHRP Index can be applied by a coastal community. The existing conditions are evaluated, identifying the economic, environmental and social/cultural values for the shoreline protective features and the inland assets that are being protected.
The application of the CCHRP Index to Ocean Beach shows that the different economic, environmental, and social/cultural values capture different aspect of both the shore protective features and the inland assets. It also shows the differences in direct values from the protective feature and the secondary values from the inland assets. At this time, Ocean Beach is the only community that has been evaluated with the CCHRP Index. As more communities are evaluated, or as scenarios for the future of Ocean Beach are evaluated, there will be opportunities to develop a range of economic, environmental and social/cultural values for multiple communities, compare communities with each other and evaluate the significance of the different values. As the CCHRP Index is applied to more areas and as more values are developed, additional utility of the Index will become apparent.
I declare I have no competing interests.
Some of the field observations included in this paper were based upon field surveys to Galveston, TX, American Samoa, Samoa and Japan and were supported, in part, by the American Society of Civil Engineers.
The opinions herein are those of the author and they do not reflect a formal position of the California Coastal Commission.
Drs Costas Synolakis, Patrick Lynett, Reinhard Flick and Daniel Mazmanian provided detailed review and critique of much of the material presented in this paper. The anonymous reviewers provided many valuable suggestions and comments that helped focus this paper and improve the content and readability.
One contribution of 14 to a theme issue ‘Tsunamis: bridging science, engineering and society’.
- Accepted June 27, 2015.
- © 2015 The Author(s)
Published by the Royal Society. All rights reserved.