Environmental Engineering Reference
In-Depth Information
Floodplains, an integral part of the river system, have
often been disconnected from the river channels,
leading to reduced natural fl ood storage function and
linkage to low fl oodplain and wetland areas. As men-
tioned, this linkage is essential for sustaining the
species that make up the ecological communities, some
of which are now under conservation protection. Simi-
larly, in river ecosystems across Europe there have been
dramatic changes in water quality, for example through
excessive nutrient infl ow leading to
eutrophication
.
As mentioned, interventions such as canalization,
dredging, draining and vegetation removal have also
caused damage and
degradation
to river systems in
Europe and elsewhere. Fish and invertebrate habitats,
for example, have been destroyed by these measures,
and the construction of dams and siltation of spawn-
ing grounds means that many native species are now
threatened with decline or localized extinction or
extirpation
(see Halaham 2000).
Urbanization has had multiple impacts beyond
watercourses simply being constrained in concrete
channels or culverted. The input of effl uent from
sewage works and industrial sites and the runoff from
roads has led to serious degradation in water quality.
Habitats of plant and animal species along the river
corridors within Europe have gradually declined in
response to increased urbanization and the decrease in
fl oodplain forest. Many of Europe's rivers now have
little natural fl oodplain habitat with restricted riverine
corridors, and a thin strand of open water is often all
that remains to act as wildlife corridors. As these habi-
tats have shrunk, 'Biodiversity Action Plans' have been
introduced across Europe with the aim of rectifying
habitat loss and other environmental damage. Within
these plans, specifi c species associated with rivers and
streams have been identifi ed (for the United Kingdom,
these are listed at http://www.ukbap.org.uk/Broad59.
htm; similar lists exist for other countries).
Historically, the fl oodplain was a wet area avoided by
industry and homeowners until drained, but with new
improved fl ood protection techniques in urban areas,
some of this reticence has been forgotten. A fl ood pro-
tection scheme is only as good as its design specifi ca-
tions, and even those designed to withstand a 1 in 50,
or even a 1 in 100 year, fl ood scenario are, by defi ni-
tion, not guaranteed to keep every fl ood at bay. These
engineered schemes are therefore unlikely to be sus-
tainable economically in the long term; hence, there is
now widespread recognition that reconnecting the
fl oodplain and working with the river's natural proc-
esses should be considered as part of any fl ood risk
management scheme.
17.4 RIVER AND FLOODPLAIN
RESTORATION
As indicated in Figure 17.1, river restoration is a complex
subject that affects not only the local situation and users
of a particular watercourse, but also the wider
land-
scape
within a river catchment. All but a few rivers and
fl oodplains within Europe have been severely degraded
over a prolonged period, which means that restoration
projects cannot simply aim for a return to some previous
form. There is a growing awareness in the scientifi c and
political worlds that naturally functioning riverine envi-
ronments are vital to biological and ecological diversity
at the landscape scale and also provide ecosystem serv-
ices to human society. Spending on fl ood risk manage-
ment that works with the rivers natural processes and
aims to reconnect rivers to their fl oodplains is seen as
one way to alleviate current often unsustainable fl ood-
ing problems and indeed EU-wide policy recommends
this approach (see Zöckler 2000; Department for the
Environment, Food and Rural Affairs (DEFRA) 2005;
Environment Agency 2010).
Restoration programmes need to focus on (1) the re-
establishment of a
self - sustaining system
exhibiting
dynamic equilibrium that can allow both the hydro-
morphological form and function of the river and its
fl oodplain to develop as naturally as possible under the
present and future climatic regimes, and (2) the inter-
dependent
habitats
and organisms to properly interact
and utilize available habitat and resources provided by
a natural river. This in turn will help to deliver the
eco-
system services
that are essential within society.
However, very few societies are, at present, in a position
to achieve this, and hence individual needs and objec-
tives must be acknowledged. This can considerably
infl uence the outcomes of restoration schemes. Fur-
thermore, although lessons can be learnt from other
counties, such as the United States (FISRWG 1998;
Bernhardt
et al
. 2005) and Australia (Rutherford
et al
.
2000), the techniques applied there may be wholly
inappropriate for European rivers because of differ-
ences in climate, species assemblages or river typology.
At its most basic,
de - culverting
(or ' daylighting ' in the
United States) can equate to a huge increase in the
biodiversity value of a watercourse. For example, in
Switzerland over the last 130 years, approximately
