Memorandum submitted by British Waterways
CLIMATE CHANGE AND WATER SECURITY
1. WHETHER EXISTING
WATER SUPPLIES
ARE ADEQUATE
AND WHAT
ADDITIONAL SOURCES
OF WATER
MAY BE
NEEDED
1.1 The UK Climate Impact Programme 2002
(UKCIP02) high emission scenario indicates summer precipitation
may decrease by 50% or more by 2080. Canals are predominantly
fed from reservoirs and the dominant demand is during the summer.
Reduced flows into the reservoirs in the summer and also from
natural stream course, that feed direct to the canals, will lead
to shortfalls.
1.2 BW have not modelled the 2080 scenario
but modelling of the high emission scenario up to 2030 indicates
that annually 6,000ml of additional resource would be required
to meet existing demands on the system. The modelling has taken
account of 30% increased precipitation during the winter months
and has assumed reservoir draw-down starts with a full reservoir.
1.3 River navigations and canals that are
predominantly river fed, will also be directly impacted by reduced
summer rainfall leading to reduced flows and reduced water levels.
Navigation will be restricted, but we have no data to predicate
how frequent or severe these restrictions may be.
1.4 The need for additional resources can
be reduced in some locations by re-circulation of existing resources
to minimise water lost from the canal system. The fuel needed
to drive the pumps and associated emissions is, however, likely
to have a detrimental environmental impact.
1.5 The general reduction of resources in
the South East compared with the North West may strengthen the
case for utilisation of the canal system as a means of transferring
water across catchments in an environmentally friendly manner.
2. WHAT WILL
BE THE
IMPACT ON
RESOURCE MANAGEMENT
2.1 Summer soil moisture may reduce by 40%
by 2080 (UKCIP02 high emission scenario).
2.2 Losses from canals will increase due
to higher evaporation and also due to high soil moisture deficit
and lower ground water tables with resultant increase in seepage
rates.
2.3 Top water losses from canals will increase
due to clay shrinkage of embankment surfaces and increased desiccation.
2.4 The increased demand for water as a
result of these additional losses will require additional water
resources to be found. Losses from these sources could be as high
as 10,000ml. Alternatively, capital works could be put in hand
to reduce the losses although the costs of these works are anticipated
to be of the same order as the provision of additional water resources.
2.5 More "Mediterranean" summers
may encourage more boating on the canals—whilst this is
regarded as a positive scenario by BW, the increased use of locks
and, hence, water consumption will exacerbate water resource problems.
2.6 Another area of resource management
that needs to be considered is agriculture. Historically, agriculture
has used canal water as a source of irrigation in the summer months
(900ml). Drier summers will potentially increase demand, but we
see the long-term solution as small winterage storage reservoirs
taking advantage of the predicted 30% increase in winter rainfall.
3. THE IMPLICATIONS
FOR FLOOD
MANAGEMENT, INVESTMENT
IN MITIGATION
MEASURES, AND
FOR WIDER
POLICY SUCH
AS PLANNING
3.1 Winter rainfall may increase by up to
30% and intensity may increase by 20% by 2080 (UKCIP02 high emission
scenario).
3.2 The increased runoff from saturated
catchments will reduce the ability of the canal system to accommodate
flood flows without overtopping of canal embankments (with consequent
risk of a canal breach). The short duration, high intensity storms
tend to be more critical in this respect.
3.3 On the canal system, mitigation measures
to reduce the risk of overtopping can be introduced including
the raising of embankments, the provision of additional flood
weirs or automation of flood sluices. All of these will require
increased capital investment and revenue costs.
3.4 The canal system will also suffer from
the impact of more intense storms generating flows in adjoining
rivers and streams that exceed the capacity of the culverts carrying
these flows under the canal. Embankments will become surcharged
leading potentially to uncontrolled breaches.
3.5 Canals, in some instances, could also
provide innovative solutions to enhanced local flood risk by being
used for flood attenuation or flood routing. The inclusion of
the canals in the EA flood Management Flood Plans would identify
such opportunities.
3.6 The incidence of flooding on river navigations
tends to be more influenced by the prolonged rainfall, forecast
to increase by 30%, rather than the short duration, intense floods.
During such periods, when flow in the rivers makes navigation
unsafe (either due to flow velocity or reduced headroom), flood
gates are operated by British Waterways to control water levels
and ensure a safe haven for craft. Clearly, the incidence of these
events and, hence, the cost of dealing with them will increase
due to climate change.
3.7 Where lock gates provide part of flood
defence system they may need to be raised to sustain the higher
river levels that climate change will bring.
3.8 On both canals and river navigations
the increased intensity and volume of run-off from floods will
cause additional erosion within the catchment and a need for more
frequent dredging of the water channel- both for maintaining navigable
depth and to provide adequate channel cross section to convey
flood flows.
3.9 There is limited understanding of the
impact of climate change on embankment stability. Desiccation
at the ground surface and cracking of clay fill in hotter, drier
summers will make embankments more susceptible to infiltration
of rainwater and the potential for slope failure as a consequence
of loss of soil suction. The overall impact will be increase risk
of flooding from canal embankment breaches. BW are co-sponsoring
a research project led by Newcastle University which will monitor
the behaviour of a trial embankment subject to accelerated, artificial
weather patterns.
4. WAYS IN
WHICH THE
IMPACT OF
CHANGES IN
WATER AVAILABILITY
ON BIO-DIVERSITY
CAN BE
MINIMISED.
4.1 The increased use of existing reservoir
storage in drier summers and pressure to alter traditional draw-down
regimes could have adverse ecological impacts , particularly on
reservoirs that are SSSIs. Protecting these would increase pressure
on other sources of water supply and create demand for additional
new sources.
4.2 Solutions need to be found to the prospect
that some non-native, invasive plants will flourish in the changing
climate and also the increased incidence of algal blooms and weed
growth that the warmer summers will bring.
British Waterways
April 2004
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