Environmental Engineering Reference
In-Depth Information
clear if this was related solely to climate change or
else exacerbated by the hydrodynamic effects of the
numerous bridges constructed during this period.
Nevertheless, the effects of the Little Ice Age were not
restricted to the United Kingdom and records across
Europe show a similar pattern, with many lakes and
rivers freezing over and evidence of glacier expansion.
Furthermore, records of this period imply that this was
also a time of dry weather and hence intermittent riv-
erine activity (Benito
et al
. 1998 ).
rivers throughout much of Europe were harnessed as
a source of energy to drive mills for a range of activities
from cloth to fl our - making industries. Thus began a
long period of major human constraint to, and control
over, river courses. The impact of these mills cannot be
overestimated. An entry from the Domesday Book of
1086 (Martin 2003), for instance, shows that in south-
ern England alone there were 5624 watermills, which
equates to one mill for every 50-60 head of popula-
tion. Further manipulation of the water courses
occurred during the fourteenth-eighteenth centuries
as water meadows became popular as a way to increase
food crop production by keeping water on the fl ood-
plain over winter, which in turn prevented the ground
from freezing, thereby allowing the grass and crops to
start growing earlier in the spring. These systems sub-
sequently became redundant and fell out of use after
the introduction of fertilizers and intensive farming
methods in the late nineteenth century.
During the 1930s, dredging and straightening
became the primary management activities in many
lowland European Countries with a view to improve
fi eld drainage of agricultural land with little thought
about the impact of this on river
biodiversity
or
hydrology
. The removal of hedgerows, which acted
as buffer strips, increased the amount of soil load
being washed into river systems. Further arterial
drainage schemes were implemented during the
1960s in many countries, partly as a push towards
ensuring self - suffi ciency of food after World War II; in
Austria, for example, 30 000 km of river have been
regulated in the last 50 years. At the same time, an
increase in housing development and associated infra-
structure resulted in further straightening and deep-
ening of rivers, disconnection from their associated
fl oodplain areas and water abstraction to support the
increased development. Many of the rivers of Europe
today have effectively been turned into carriers of
fl oodwaters in an attempt to move water from both
rural agricultural land and from urban areas as
quickly as possible, with little or no consideration of
biodiversity or the natural fl ow dynamics and mor-
phology of river systems (see Brookes 1988; Petts
et al
.
2002). These changes often result in a far more varied
fl ow regime, including more fl ash fl oods, than would
occur otherwise.
Deepening of channels prevented waters from
reaching fl oodplains under high fl ow events. The nega-
tive impacts of these historical activities, as outlined in
Table 17.2, are now beginning to be addressed, both in
17.2.2
Human impacts
Climate and local weather are instrumental in driving
the form of Europe's rivers, but these have gradually
been matched in importance by an increase in the
degree of human intervention. Although distinctive
phases of human activity that ultimately affect our
river systems can be identifi ed since the early Holocene,
circa 10 000 years
BP
, with simple woodland clear-
ance, it remains diffi cult to disentangle anthropogenic
impacts from nonhuman determinants. Take for
instance the impact of human interference through
deforestation compared to natural decline in forest
cover as a result of periods of glacial activity. Immedi-
ately it becomes apparent that trying to distinguish the
relative impacts of each of these is problematic. Fur-
thermore, especially in northern Europe, many river-
ine areas are still recovering from the Little Ice Age,
while others have been widened and deepened to drain
the land for farming or else for purposes of navigation.
It is important to recognize the additional diffi culties
associated with a long period of human intervention
and constraints when evaluating degraded rivers with
a view to restoration. The identifi cation of a pristine
riverine state to start with is diffi cult, if not impossible,
and in many cases, as expressed by Macklin and Lewin
(1997) , today ' s rivers are often ' climatically - controlled
but culturally blurred'. Thus, the identifi cation of a
reference system
is complicated and necessarily
somewhat arbitrary.
Deforestation in particular has had a major impact
on river systems in Europe, and elsewhere, especially
during the last 4000 years. Estimates of forest decline
along the Rhine vary widely, but all literature indicates
a signifi cant decrease resulting in increased sediment
availability and deposits on the river bed, both directly
- by means of
runoff
- and indirectly, via systems of
fi eld and land drains. During the medieval period,
