Environmental Engineering Reference
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different permeability of sand and gravel also interact with wave style to create local
variations in wave dissipation and morphology. On a larger scale, the swash from spilling
breakers constructs a steep-faced berm near the high-water mark which survives all but
the most destructive storm waves. Winter beach erosion alternates with summer
reconstruction on many mid-latitude beaches in response to seasonal storminess, although
winter storms may also move large sediment volumes inshore beyond the reach of lesser
waves (see box, p. 375).
Plate 17.3 Large-scale sand bed forms at low tide near the
constricted mouth of the Mawddach estuary, mid-Wales, with
a seagull for scale.
Photo: Ken Addison.
Plate 17.4 Salt-marsh zonation, Mawddach estuary, mid-
Wales. The lower marsh commences behind sand banks (top
left) and is traversed by creeks which flood and drain the
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