Geoscience Reference
In-Depth Information
Coastal management in the southern
North Sea
HUMAN IMPACTS
IPCC 2007 forecasts of global sea-level rise by
AD
2100 have been revised downwards again (as in the 2001
assessment), to between 0·18 m and 0·59 m above the 1980-99 level for the period 2090-99 (
Figure 17.19
).
This
could accelerate if the Greenland Ice Cap commences irreversible melting - beyond a forecast threshold temperature
which is close to being met early. Why are we so concerned about such apparently modest sea-level rise? Inundation
of coastal land threatens human lives, economic activity and infrastructure. Impacts extend beyond flooding to
permanent land erosion, seawater intrusion of agricultural and urban land, further encroachment of tidal waters into
estuaries and river systems, and higher storm surges. Inshore and offshore coastal ecosystems and biodiversity are
threatened with loss of habitat, with consequential socio-economic damage to coastline-dependent communities.
Rising sea levels are converging with human populations migrating to the coast. Both processes have dramatically
driven up IPCC estimates of human populations directly threatened by coastal flooding and storm surges (see p.710).
Ninety per cent of those at risk live in coastal areas of developing countries in south-east Asia, the Asian Pacific
Ocean, West Africa and the southern Mediterranean Sea. Tangible evidence of risks and losses are evident from the
fact that 70 per cent of Earth's sandy beaches are retreating, representing 15 per cent of the global coastline, and
the forecast that 22 per cent of global coastal wetlands may be lost by
AD
2080.
Closer to home, countries bordering the southern North Sea basin (the United Kingdom, Belgium, Netherlands,
Germany and Denmark) share an Integrated Coastal Zone Management (ICZM) scheme for coastline protection,
infrastructure development, habitat creation and conservation around the Thames-Scheldt-Meuse-Rhine megadelta
and other low-lying coasts. Over 40,000 km
2
are threatened by storm surges (
Figure 17.20
).
After centuries of Dutch
experience, in particular, in low-lying coastal loss and reclamation, the 1953 storm surge triggered eventual
construction of the Delta Work on the European side of the common delta and the Thames Barrier (1984) on the UK
side. Over 300 Britons lost their lives, mostly on the East Anglian coast, but the same watersnoodrampcaused over
1,800 deaths on the Dutch coast, flooding 200 k ha and requiring the evacuation of 72,000 people. ICZM is
complemented by several other agencies such as the UK's Environment Agency, Thames Estuary Partnership and
International Commission for the Protection of the Rhine, which includes France and Luxembourg. The 1953 once-
in-300-years event occurred as northerly gales drove a storm surge south down the North Sea basin, towards terrestrial
floodwater moving into the megadelta from antecedent and associated heavy rainfall.
What is the risk of future similar events - which almost happened again during the winter of 2007? Six elements of
the combined hazard have worsened, increasing risk substantially, in the past fifty years - five of which are directly
associated with climate change. Global sea level rose by 1.8 ± 0.5 mm yr
-1
from 1960 to 2003 (totalling some 0.8
m), storminess, rainfall intensity/totals and extreme floods are forecast to increase in northern Europe - added to
which, much of the basin continues to subside through glacio-isostasy. On the human side, population and
infrastructure continue to grow along the coastline. The Thames Barrier, with an initial design life to
AD
2030, allowed
for several centuries' regional subsidence in the design - but not sea-level rise! (
Plate 17.7
)
It is the largest UK tidal flood structure forming part of 300 km of lower Thames flood protection, including thirty-six
industrial barriers and 480 lesser structures, floodwalls, floodgates and embankments in the tidal Thames below
Teddington Lock (
Plate 17.8
).
The estuary forms 75 per cent of vulnerable coastline in England and Wales. The barrier
protects 1.30 M Londoners and infrastructure worth £80 G across 125 km
2
of central London. When closed, it could
send a reflective wave down-river, increasing overtopping risk in the lower estuary. It was closed on average
2 yr
-1+
up to 1990, 5-10 yr
-1
on three occasions between 1991 and 1998, then ten times in 2000, fifteen in 2001 and nineteen
in 2003. In 2007 Lionsgate Films made Flood, about a fictional 25 m storm surge. Although of very low probability
(0.05 per cent, compared with 0.35 per cent for the 1953 surge), the Environment Agency co-operated to raise public
awareness of increasing risks (
Plate 17.9
).
Similar concern is shown by the Association of British Insurers, which
forecast UK extreme-year coastal flood losses of £16 G by the 2040-2060s compared with £6 G in 2007.
