Environmental Engineering Reference
In-Depth Information
11
Restoration of rivers and
floodplains
Jenny Mant and Martin Janes
11.1 Introduction
and species form part of the European Union's (EU's)
natural heritage. Threats are often trans-boundary in
nature and various EU directives now in place are
aimed at implementing measures at the EU level that
advocate conservation of sites under pressure from
development and associated pollution; see especially
the EU Habitats Directive 92/43/EEC (EC 1992a)
and the more recent Water Framework Directive
2000/60/EC (EC 2000). One of the objectives of river
restoration is to promote activities that initiate or accel-
erate recovery of degraded ecosystems and hence
help to implement some of these Union Directives.
River restoration is a complex subject that affects
not only the users of a particular watercourse but also
the land and natural ecology within a river catchment.
All but a few rivers and floodplains within Europe have
been severely degraded over a prolonged period. Thus
any restoration cannot simply imply a return to some
previous state, such as making an assumption that re-
meandering of a river, based on historical evidence,
will be sustainable. Instead it should focus on the re-
establishment of a self-sustaining system that can allow
the form and function of the river to develop as
naturally as possible under the present and future
climatic regimes and in doing this it should improve
the ecological conditions. Ideally, restoration should
recognize that floodplains are an integral part of the
natural functioning of riverine systems and as such
there should be at least intermittent hydrological
connectivity between the two. At its most basic,
de-culverting (or daylighting, in the USA) equates to
a huge increase in the biodiversity value of a water-
course (Fig. 11.1). In Switzerland over the last 130 years,
The rivers and floodplains of Europe are of great import-
ance for plants, fish, birds and mammals (including
humans) but the diversity of their habitats has
declined particularly over recent years. Floodplains have
often been disconnected from their rivers, reducing their
flood-storage function and hence the range of low
floodplain and marsh areas required to sustain, for
example, reed bunting (
Emberiza schoeniclus
), wood-
pecker (
Alcedo atthis
), European beaver (
Castor fiber
)
and otter (
Lutra lutra
). Similarly, aquatic plants such
as water plantain (
Luronium natans
) and river-water
crowfoot (
Ranunculus fluitans
) have been affected by
eutrophication, whereas intervention such as canal-
ization, dredging, draining and vegetation removal have
all been instrumental in degrading our river systems.
Similarly, fish habitats have been destroyed by these
measures and the construction of dams and siltation
of spawning grounds has meant that many native
species such as salmon (
Salmo salar
) and sea trout
(
Salmo trutta
) are now threatened with decline or local-
ized extinction. Today very few of Europe's rivers can
be truly defined as natural and this has serious implica-
tions for the associated ecosystems. Furthermore, as
explained by Postel and Richter (2003), natural river
flow is a key element in sustaining a healthy river
system, including absorbing pollutants, decomposing
wastes, producing fresh water and the redistribution
of sediments and habitat replenishment during floods.
There is therefore a huge potential resource that
could be restored to increase and improve diversity
of habitat. It is now accepted that threatened habitats
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