A long-term influence on coasts is the sea level, which is affected by tectonic activity, climate change, subsidence, and the movement of ice sheets (notably through isostatic rebound following glacial retreat). On shorter time scales the dominant shaping processes are waves and tides: here Davis explains the basics of ocean waves and their refraction and diffraction, longshore and rip currents, tsunamis, seiches, tides and tidal currents, and storm surges.
Four chapters then consider different kinds of coasts. One looks at salt concentrations, circulation, and tidal and river deposition in estuaries, at tidal flats, and at salt marshes and mangroves. Turning to deltas, Davis looks at where they develop, how fast they grow, and their importance for human life; they can be classified according to the relative influence of river, tides, and waves.
Next comes a survey of the structure and dynamics of beaches and dunes and, offshore, of barrier islands and tidal inlets. Rocky coasts are shaped by waves, tides and freeze/thaw cycles, by biological agents, and by chemical weathering; notable geomorphological features include cliffs, platforms and terraces, and sea stacks and other erosional remnants. An epilogue looks at human efforts to control coasts through seawalls, breakwaters, groins and jetties, beach replenishment and dredging, and at the often unintended effects of causeways and urbanisation.
The Evolving Coast is not at all technical, but it had quite a bit in it that was new to me. It's an accessible overview, nicely illustrated — no glossy photographs, but a good range of diagrams and colour halftones — and should be widely read. I just wish it had been longer, though a nice feature is a further reading selection offering a few items for each chapter.
November 2005
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