|Working Group II: Impacts, Adaptation and Vulnerability|
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17.2.3. Beach and Coastal Changes
The morphology, characteristics, and classification of beaches are influenced by a variety of factors, including island origin, geologic structure and composition (e.g., volcanic, coral atoll, raised atoll, reef island, or emergent limestone), age, elevation, and size (Gillie, 1997; Solomon and Forbes, 1999). Thus, given their varied origins, a wide range of beach types and characteristics is represented in the small island states of the Caribbean and Mediterranean Seas and the Atlantic, Pacific, and Indian Oceans.
Coastal erosionpartly the result of anthropogenic factors such as sand mining (Gillie, 1997; Ragoonaden, 1997) already is a problem on many islands and evidently may be exacerbated by sea-level rise (Mimura and Nunn, 1998). On many atolls (as in the Pacific) and low reef islands (as in the Caribbean), carbonate beaches are maintained by sand produced from productive reefs whose degradation already is causing accelerated beach erosion. Similarly, in the Mediterranean Sea, where the islands are periodically susceptible to flooding and scour from storm surges, an increase in storminess would further stress natural and human systems located at the coast (Nicholls and Hoozemans, 1996). The impact of the equivalent of a 1-m rise in sea level for a cumulative few hours on the coast was observed in Singapore on 7-14 February 1974. The event indicates clearly the vulnerability of the island's low-lying area to flooding and coastal erosion if sea-level rise takes place (Wong, 1992).
Beach erosion rates of approximately 2-4 m yr-1, on average, have been reported for several beaches in Trinidad and Tobago, where mean relative sea-level rise of 8-10 mm yr-1 has been recorded by two gauges during the past 15 years. Although beach erosion results from multiple forces, sea-level rise is considered a contributory factor (Singh, 1997a,b). Ragoonaden (1997) measured shoreline retreat of 2.7 m yr-1 at Flic-en-Flac (Mauritius), and Nunn and Mimura (1997) report that the coasts of some islands in Fiji have retreated by more than 30 m in the past 70 years. In the specific case of Viti Levu and Taveuni, Fiji, beach erosion has been attributed to a combination of human-induced causes (including loss of the mangrove fringe and other natural protection) and elevated sea level, which has been rising at a rate of approximately 1-1.5 mm yr-1 since 1960 (Forbes and Solomon, 1997; Nunn and Mimura, 1997).
It is now widely accepted that strategies for adaptation to sea-level rise tend to fall into three main categories: retreat, accommodate, and protect (Bijlsma, 1996; IPCC, 1996, 1998). Hard engineeringinvolving the construction of groynes, seawalls, breakwaters, and bulkheadshas long been the traditional response to coastal erosion and flooding in many small island states. Unfortunately, this approach has not always been efficiently implemented and has even helped to increase coastal vulnerability in some cases (Mimura and Nunn, 1998; Solomon and Forbes, 1999). In these specific circumstances, the term "maladaptation" (which refers to a response that does not succeed in reducing vulnerability but increases it instead; see Chapter 18) may be applied. Realistically, however, for some islands the application of hard solutions may be the only practical option along well-developed coasts, where vital infrastructure is at immediate risk.
There are other potential options available to small island states, including enhancement and preservation of natural protection (e.g., replanting of mangroves and protection of coral reefs), use of softer options such as artificial nourishment, and raising the height of the ground of coastal villages (Nunn and Mimura, 1997). Raising the height of the ground requires additional aggregate such as sand and stone and a lot of pumping, in which many small islands are seriously deficient. Removal of materials from "unimportant" islands to build up important islands via sand transfer by pipes and barges has been suggested by the IPCC (1990). Some island states may be faced with few practical options. Thus, it might be necessary for them to lose some islands so that the entire nation is not completely inundated (Nicholls and Mimura, 1998).
Similarly, beach nourishment may not be a practical or economical option for many island nations because sand often is a scarce resource (Leatherman, 1997; IPCC, 1998). Moreover, beach nourishment requires maintenance in the form of periodic sand replenishment, sometimes every 5-10 years or less (Amadore et al., 1996). Such a requirement could prove to be unsustainable in small economies. In contrast, on some islands such as Singapore, where the technology and resources are more readily available, beach fill projects (used in combination with offshore breakwaters to form artificial headlands) is a feasible option (Wong, 1985). As a general strategy to respond to sea-level rise, it is likely that Singapore will focus on three main types of responses: coastal protection for developed or heavily populated areas and reclaimed land, anti-salt-intrusion measures for coastal reservoirs, and flood prevention measures (such as tidal gates) for major canals (Wong 1992).
In some islands, such as those in the Caribbean, more emphasis is being placed on the application of "precautionary" approaches, such as enforcement of building set-backs, land-use regulations, building codes, and insurance coverage. In addition, application of traditional, appropriate responses (e.g., building on stilts and use of expendable, readily available indigenous building materials), which have proven to be effective responses in many islands in the past, ought to be more widely considered (Forbes and Solomon, 1997; Mimura and Nunn, 1998).
Given the vulnerability of many small island states to various aspects of global change, integrated coastal management (ICM) is rapidly becoming an attractive paradigm for planning adaptation (Bijlsma, 1996; Cicin-Sain, 1998; Nicholls and Mimura, 1998). Furthermore, ICM can be regarded as both an anticipatory and a predictive tool, with the capability to plan for and respond to medium- and long-term concerns such as sea-level rise as well as short-term, present-day needs (Nurse, 1999; Solomon and Forbes, 1999). In addition, ICM can provide an effective framework for resolving potential conflict among competing stakeholder interests, in a manner that is equitable to all groups. In this context, it is noteworthy that all of the small island states that recently participated in the U.S. Country Studies Program (i.e., Federated States of Micronesia, Samoa, Fiji, Kiribati, Marshall Islands, Sri Lanka, and Mauritius) concluded that ICM was the most appropriate adaptation strategy and should form an essential part of their climate change national action plans (Huang, 1997).
Enhancing the resilience of coastal systems has been suggested (e.g., Bijlsma, 1996) as an appropriate proactive adaptive response to reduce vulnerability. Klein and Nicholls (1998) agree that this could be a more cost-effective way to prepare for uncertain changes such as sea-level rise, rather than relying entirely on building traditional, more costly coastal defenses. Helmer et al. (1996) strongly support the notion of enhancement of coastal resilience whereby dynamic systems (e.g., dunes, lagoons, and estuaries) should be allowed to utilize their natural capacity to grow in response to rising sea levels. This philosophy could be applied through pilot studies in small islands. One of the ways in which a dynamic and resilient coast can be created is by managed retreat, based on an enforced building set-back that allows the coastline to recede to a new line of defense, thus restoring natural coastal processes and systems. An orderly plan to retreat could be a feasible option on larger islands that cannot commit the resources necessary to prevent coastal land loss in the face of rising sea levels (Leatherman, 1997).
One recommended approach to planning adaptation to sea-level rise and coastal change involves an estimation of the costs of protecting or abandoning developed properties. For developed coasts, West and Dowlatabadi (1999) propose that the real economic evaluation of sea-level rise should be regarded as the difference in utility (not just damages) with and without a sea-level rise scenario, in which it is assumed that physical conditions (e.g., erosion and storms) and human behavior remain constant. This is an improvement on past approaches, which provided the estimated costs of sea-level rise on the basis of market value of inundated land and property or the cost of structural protection.
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