The global coastline - Fundamentals of the Physical Environment - page 405

Figure 17.7
Plunging wave form and
associated water and
sediment transfers.
Source: After Carter (1988)

Water movement
Sediment movement

Jet

Surf bore

Sand fountain

Bed shear

Bed shear

Bed scour

Plate 17.3 Coastal chemical weathering; solution pits
(lapies) formed by the solution of Carboniferous limestone on
a wave-cut platform in County Clare, Ireland.
Photo: Ken Addison

us to chart the quantities and transfer routes involved with
varying degrees of accuracy ( Figure 17.8 ). Coastal erosion
contributes a surprisingly small proportion - about 1 per
cent of terrigenous yield - and biogenic sediments make
substantial local contributions. Shell and other calcareous
debris can be important on wave-dominated coasts, with
plant debris more abundant on tide-dominated coasts.
Offshore sources are difficult to assess, and temperate
high latitudes depend heavily on finite Pleistocene
glacigenic supplies. Although the -20 m submarine
contour is the maximum limit within which wave motion
can move sand shoreward, the offshore source was well
stocked as Late Devensian and Flandrian sea levels, rising
some 110-130 m between 15 ka and 5 ka BP ,drove
sediment landward. The mid-Holocene end to this

Plate 17.2 Cliffs and arch, with a wave-cut notch at their
base, in Cretaceous chalk at Bempton, Yorkshire. The soft
chalk could not sustain vertical rock walls without continuous
undercutting at their base.
Photo: Ken Addison

are terrestrial sediments carried seaward by rivers and
glaciers, products of coastal erosion, offshore sediments
carried landward and in situ accumulation of biogenic
debris. The continental slope is the ultimate sink for
transient coastal sediments. Sediment budgets, calculated
with increasing attention to coastline management, allow