Geoscience Reference
In-Depth Information
1. During global warming the magnitude and
frequency of streamflow can be significantly
changed, resulting in increased frequency of
high-flow events (Macklin 1996). This can result
in increased flooding, especially flash flooding,
hazards such as debris flows and landslides, and
channel change. Rumsby & Macklin (1994) have
shown that in northern England since AD 1700,
channel incision is related to clustering of large
floods, and lateral reworking and sediment
transfer occurs during episodes of low flood fre-
quency. They suggested that increased flooding
in the future (associated with global warming)
could therefore result in increased channel ero-
sion. Longfield & Macklin (1999) attributed
high-magnitude, high-frequency floods in the
Yorkshire Ouse Basin, UK, during the 1980s and
1990s, to increases in the frequency and vigour
of cyclonic atmospheric circulations; these also
have been related to significant remobilization
of mining-contaminated sediment (Dennis et al.
2003). Increases in flooding are also related
to 'priming' of land surfaces by agricultural
practices, which leads to increases in runoff
and accelerated sediment delivery to floodplain
environments (Knox 2001). Global warming
could also lead to increases in the magnitude,
intensity and frequency of forest fires, which may
also exacerbate bank erosion, sediment trans-
port and widespread alluviation.
Cellular computer models are increasingly
being used to study the development of river
basins, and the effects of climate, base level and
other environmental changes on erosion and
sedimentation processes (Veldkamp & Van
Dijke 1998; Coulthard et al. 2000; Coulthard &
Macklin 2001). These models are most effec-
tive when combined with field-based studies
(e.g. Coulthard & Macklin 2001). Models such
as these will, in the future, prove invaluable in
assessing possible future geomorphological and
sedimentological changes in river systems, and
linking these to past, analogous changes. An
example is the FLUVER model, constructed by
Veldkamp & Van Dijke (1998) and applied to
the Allier-Loire basin in France. The model takes
into account tectonic uplift, changes in river
longitudinal profiles and changes in effective
precipitation and sea (base) level. It showed that,
although changes in erosion and sedimentation
were related to climatic changes in some instances,
the role of tectonic uplift and changing base
level had previously been underestimated.
3.6.2 Impacts of increased anthropogenic
disturbance
As requirements for natural resources and land
increase, river systems are, and will continue
to be, put under pressure. Demand for new
housing on almost all the world's continents
means that floodplains are increasingly targeted
as desirable building sites. This has had drastic
consequences in many areas, especially with
recent increases in large-scale floods associated
with climate change. In the UK in the winter of
2000-2001, for example, severe winter storms
resulted in the flooding of 10,000 properties
in over 700 locations and £1 billion worth of
damage. In terms of floodplain sediments, floods
such as these cause deposition of potentially
contaminated sediment in living areas, causing
a potential risk to human health. The increas-
ing urbanization of floodplains has also led to
a loss of accommodation space for sediment
deposition, resulting in silting of channels and
reservoirs. Government organizations such as
the UK Environment Agency have recommended
more stringent restrictions on building on flood-
plains (Environment Agency 2004), in addition
to more efficient land management.
Increased river regulation to provide power
and surface water storage will continue to have
an impact on sediment supply (as well as river
and estuary ecology) both upstream and down-
stream of dams and reservoirs. Dam construc-
tion increased dramatically from the 1950s to
the 1970s, when two to three new large dams
were being commissioned per day (World Com-
mission on Dams 2000). Even though dam
building has declined since the 1970s, major
large dam projects are still ongoing, particularly
in China (which accounts for 46% of dams
built), the USA and India (World Commission
on Dams 2000). Knighton (1998) has pointed
out that the long-term effects of the explosion
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