The global coastline - Fundamentals of the Physical Environment - page 417

Plate 17.7 The Thames Barrier, in a semi-closed position, with central London to the left and a small part of the incoming tide
being let through.
Photo: Environment Agency

THE GLOBAL COASTLINE

Whatever the nature and controlling mechanisms of indi-
vidual coastal landforms and landsystems, four universal
influences are recognized in coastline patterns at the
global scale. The youth and vigour of sea-floor spreading
and continental margin orogenic activity impart mor-
photectonic control. Global tide and atmospheric circu-
lation establish tidal range and wave energy patterns,
complicated by continental coastlines. Tectonic and cli-
matic causes of sea-level change, varying temporally and
spatially, create patterns of emergent and submergent
coastlines.
Tidal cycles refer to the daily number of tides ( Figure
17.22 ). A water-covered Earth with a moon orbiting its
equator would experience equal semidiurnal tides. This
pattern is upset by the continents, and a lunar orbit

Plate 17.8 Flood storage pond, embankment and pump
house at Thamesmead on the river Thames, downstream of
the Thames Barrier. The pond is below the level of the Thames
beyond the embankment.
Photo: Ken Addison