Ibe (1990) has found that large-scale protective engineering measures are impractical in Africa because of the high costs to countries in the region. Instead, low-cost, low-technology, but effective measures-such as permeable, nonconcrete, floating breakwaters; artificial raising of beach elevations; and installation of rip-rap, timber groins, and so forth-are considered more sensible.
In Egypt, protection of beaches and associated infrastructure must depend upon continuous and periodic nourishment. The total cost of protection is estimated to be only US$21 million and $42 million for the 0.5-m and 1-m scenarios, respectively (El-Raey et al., 1995). The city of Alexandria is built on three intermittent calcareous ridges, parts of which are leveled and thus constitute a potential pathway for rising water to reach the lowland south of the city. El-Raey et al. (1995) have suggested that maintaining the beaches in front of these pathways, using beach nourishment, will help to prevent surface water from reaching the lowland south of the city through these paths, particularly during storm surges. Construction of small dikes also may be necessary.
According to French et al. (1995), the potential cost of protection against a 1-m rise in sea level in Nigeria ranges from US$558-668 million if densely developed areas are protected (important areas protection) to US$1.4-1.8 billion if all shores are protected from erosion, inundation, and flooding (total protection). Under the "important areas protection" option, the 1-m sea-level rise scenario would require a total of 430 km of seawall and associated fill, costing nearly US$200 million. An additional 474 km of sheltered seawall and 180 km of open-coast seawall is required when total protection is considered. More than 600,000 villagers could be displaced by a 1-m rise in sea level, based on existing population (French et al., 1995). It is impractical to protect these villages and populations at risk in Nigeria from a 1-m rise in sea level. Relocation probably is the most practical solution to the problem of inundation of the villages.
If the option considered in Senegal is "important areas protection," Dennis et al. (1995) suggest that about 70 km-or about 14.5%-of the open coastline would require protection. Total protection would require protection of 2,063 km, including 310 km of open-coast seawall and 1,680 km of sheltered-coast seawall. The cost of total protection is about 2.5-4 times higher than the costs of important areas protection.
With regard to The Gambia, Jallow et al. (1996) argue that if sea-level rise were to occur as envisaged, the most appropriate response (considering The Gambia's economic situation) would be to protect important areas. The projected cost includes US$3.1 million for construction of a 7-km low-cost seawall and US$3.9 million for construction of a revetment. About 16 km of dikes is required to protect villages bordering wetlands and swamplands from seasonal flooding. Four types of actions could fulfill required protection needs:
In Cote d'Ivoire, the most essential response to a potential sea-level rise of 1 m in the next century would be to protect important areas-such as the two ports at Abidjan and San Pedro; the airport; tourism facilities; residential areas; and other areas of high economic importance, particularly in Grand Bassam, Abidjan, Grand Lahou, Sassandra, San Pedro, and Tabou (ICST, 1996). No cost estimates are attached to this protection.
Within an integrated approach, there is a great opportunity to anticipate problems associated with sea-level rise rather than simply react to change as, or after, it occurs (Nicholls and Leatherman, 1994). Furthermore, a well-planned response that seeks to anticipate the physical impacts of sea-level rise in a timely fashion will minimize unwise decisions and result in lower costs for reactive responses such as protection (Nicholls and Leatherman, 1995). Anticipatory responses include urban growth planning, building setbacks, wetland preservation and mitigation, public awareness, and integrated coastal zone management.
Policies and regulations concerning the use of the coastal zone for any form of human activity should include consideration of sea-level rise. Physical planning and building-control measures and regulations should be instituted and implemented. Allocation of land for any economically useful purpose in areas likely to be flooded or inundated should be avoided. The public should be informed of the risk of living in coastal and lowland areas that are threatened by sea-level rise. Timely public education about erosion, sea-level rise, and flooding risks could be a cost-effective means of reducing future expenditures. Where coastal infrastructures such as roads, fish land, and curing plants are approved and must be constructed, the authorities and owners of these infrastructures should make sure that marginal increases in the height of the structures are included to offset sea-level rise (Smith and Lenhart, 1996) and other related phenomena. People located in high-risk areas should be offered incentives to relocate out of these areas. Setbacks could be used as buffer zones to allow sea level to rise without threatening coastal development. French et al. (1995) recommended incorporating buffer zones between the shore and new coastal development in Nigeria.
Adaptation to climate change and concomitant adverse effects will involve an understanding of climate change parameters and dynamics, including monitoring and data analysis of climate change parameters. This strategy should lead to an African Climate Change Scenario (ACCS), upon which countries can base their adaptation options. Existing scenarios and adaptation measures for climate change and sea-level rise are built around Western experiences.
All of the adaptation strategies, options, and policies discussed above will reduce the risks from current climate variability and protect against potential climate change and sea-level rise. These measures should be combined in a coastal zone management plan (CZMP). The CZMP brings together all actors in the coastal area to address coastal-zone problems. The program should consist of a set of principles and plans to guide the use of coastal land for conservation, recreation, and development.
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