London scoping - ukcip

Final Report
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systems below ground level and in the ingress of surface water into sewers from above ground
surface flow. The effects of both will be higher flows in sewers and associated pumping and
treatment costs, and could potentially lead to increased incidents of sewer flooding from
separate and combined systems. Climate change could also affect the capacity of receiving
waters to assimilate discharges from sewer systems. For example, any increase in summer
storms may cause combined sewer overflows to discharge pollutants into rivers which will have
lower summer flows and thus reduced dilution capacity.
Sustainable Urban Drainage Systems (SUDS) are soft engineering facilities to help alleviate
flooding associated with moderate rainfall events, involving the reduction of storm runoff
volume (through ‘peak-lopping’) and increases to travel time of flood peaks to receiving water
courses. For example, the restoration of natural wetlands in headwater catchments can provide
source control of water derived from rainfall events as well as benefits to biodiversity.
However, as with any drainage system SUDS have a capacity that can be exceeded given long
duration events of the type experienced in the autumn of 2000 (see Table 5.6 and Figure 5.5),
SUDS may be relatively cheap to install but can incur high maintenance costs and have limited
operational life spans. There are also issues surrounding the legal ownership, maintenance and
availability of appropriate sites for SUDS development in London given competing pressures to
use brownfield sites for housing. The underlying London clay makes it difficult in some areas
to use significant infiltration techniques.
5.5.4 Tidal Flood Risk
The potential implications of sea-level rise for Great Britain have been comprehensively
reviewed by de la Vega-Leinert and Nicholls (2002). The most significant flood threat to
London arises from tidal surges caused by low pressure systems travelling south or southwest
over the North Sea, and the funnelling of water from the southern North Sea into the Thames
Estuary (see Figure 5.6). The coastal flooding of 1953 resulted in over 300 fatalities in eastern
England, but London was spared (Steers, 1953). Nonetheless, the event highlighted the
potential threat to London, and resulted in a national flood defence strategy culminating with the
completion of the Thames Barrier in 1983.