Time, Process Southern England’s Landscapes - Southern England - page 23

FIG 21. Two episodes (17,000 and 12,000 years ago) in the rise of sea level around the
North Sea area. (Redrawn and simplified from Current Archaeology 207 , 2006, Gaffney)
Drowned valleys (Figs 22 and 23) are present on the coastlines of Southern Eng-
land as a result of recent sea-level rise. Formerly, the rivers draining the majority of
these valleys would have transported mud and sand to the sea, where it would have
been deposited on the sea bed. However, with the rise in sea level mud and sand are
now often deposited in the flooded valleys or estuaries instead, and some have deve-
loped carpets of sediment, transported down-valley by rivers or brought up-valley by
the sea where tides and storms have been effective.
Coastlines with low seaward slopes and a soft surface blanket and/or bedrock may
develop beach barriers when flooded by rising sea level. These barriers are ridges of
sand or gravel parallel to the general trend of the coastline (Fig. 24). They are created
by the impact of storm waves on the gently sloping and soft landscape. They tend to
develop a cap of wind-blown sand which is very vulnerable to storm wave erosion, but
may eventually become stabilised by vegetation. Behind the barrier a low-lying area
of more sheltered conditions develops and regular flooding at high tide may bring in
muddy sediment from the sea that can settle and build up salt marshes.