Environmental Engineering Reference
In-Depth Information
Fig. 11.3
A river with little or no
biodiversity, natural flow dynamics
or channel morphology encased in
concrete; example from the River
Frome, Bristol, UK.
constraint of river courses. The impact of these mills
cannot be over-estimated. An entry from the Domesday
Book of 1086, for instance, shows that in southern
England alone there were 5624 watermills, which
equated to one for every 50 - 60 head of population.
Further manipulation of the water courses occurred
during the 14th-18th centuries as water meadows
became fashionable as a way to increase food crop
production by controlling flow on to the floodplains.
These subsequently became redundant and fell into
decline with the introduction of fertilizers and new
intensive farming methods by the late 19th century.
Dredging and straightening became the primary
objective with a major commitment to improving the
drainage of fields during the 1930s. Further arterial
drainage schemes were implemented during the 1960s
in many countries, partly as a push towards ensuring
self-sufficiency of food after the Second World War;
in Austria for example, 30,000 km of rivers have
been regulated in the last 50 years. At the same time
an increase in housing development and associated
infrastructure has resulted in further straightening
and deepening of rivers, with a disconnection from
their associated floodplain areas and water abstrac-
tion to support the increased development. Many of
the rivers of Europe today have effectively been
turned into carriers of floodwaters in an attempt to
move water from both rural agricultural land and urban
areas as quickly as possible with little or no con-
sideration of either biodiversity or the natural flow
dynamics and morphology of river systems (see
Brookes 1988, Petts
et al.
2002 for more details;
Fig. 11.3). These changes often result in a far more
varied (flashier) flow regime than would naturally occur
as water is impounded and prevented from reaching
its floodplain under high-flow events. The negative
impacts of these historical activities as outlined in
Table 11.2 are now beginning to be addressed both in
terms of economic viability and potential ecological
gain. This has created the opportunity for river restora-
tion to be taken more seriously as a viable alterna-
tive to present management practices as there is
increasing acknowledgment that it is not always
possible or acceptable to channelize and/or regulate
rivers (see Petts 1984).
11.3 Characteristics of European rivers
Natural river systems are dynamic bodies that con-
tinuously change as a result of their inherent phys-
ical conditions such as slope, bedrock geology and the
complexity of the drainage network. Yet, as previously
discussed, their characteristics are also influenced by
