Introduction

Modification of the coast by humans has occurred over countless centuries (Walker, 1984, 1988), but direct alteration of exposed ocean coasts on a massive scale is a relatively recent phenomenon. Large-scale alterations began in the nineteenth century, when there was a need to accommodate vessels of large burden and deep water drafts and there was steam power to enable large modifications (Marsh, 1885 De Moor & Bloome, 1988 Terwindt, Kohsiek & Visser, 1988). Development of the coastlines of the world has accelerated in the last few decades (Wong, 1985, 1988 Koike, 1988 Moutzouris & Marouikian 1988 Cencini & Varani, 1988). Marco Island, on the west coast of Florida, progressed from a wilderness to a fully developed shoreline in fewer than 20 years (Reynolds, 1987). Many coastal communities in the USA experienced dramatic growth in this period, with construction of high-rise condominiums (Carter, 1982 Leatherman, 1987 Schmahl & Conklin, 1991). By the mid-1970s 1687 km (or 37%) of the ocean frontage of the coastal barriers on the US Atlantic and Gulf coasts were occupied by buildings, roads and related features (Lins, 1980). Strip development near the ocean shoreline has historically dominated the land conversion process in coastal communities (Mitchell, 1987), placing the location of much of the development where it is readily affected by wave and wind processes. Shore protection structures are emplaced seaward of these developments where they can have the greatest impact on shoreline processes and the most dynamic coastal landforms.