SEA LEVEL RISE RESPONSE OF DEVELOPED BARRIER ISLANDS: SEAWALLS ARE DAMS

The impact of sea-level rise on developed barrier islands will, of course, depend entirely on decisions made by humans. It is fair to assume that property owners will attempt to stabilize shorelines and prevent island migration at all costs. It is also fair to assume that response of coastal cities to sea-level rise will prove to be a higher priority than preservation of barrier island development and hence funding of costly efforts to hold the shoreline in place will be lacking. The anticipated 3-foot sea-level rise by the year 2100 will certainly work against shoreline stabilization by beach nourishment making the hard stabilization option (seawalls) the more likely approach. But seawalls, which eventually must completely surround the islands, must be viewed as dams rather than walls to protect communities from storm surges. The efficacy of seawalls as dams, however, depends greatly on the substrate on which the seawall is built. The islands of Southeast Florida, for example, overlie the highly porous Miami Limestone which would completely negate the anti-flooding objective of shoreline structures. Recognition of seawalls as dams raises the costs of shoreline stabilization considerably and makes the retreat option all the more necessary. But how do we retreat from a high-rise lined barrier island? It is an economic impossibility to move the high rises. Long-range planning must involve plans to demolish barrier island buildings. Of immediate importance is the need for prohibition of additional high rise buildings anywhere on barrier islands