Environmental Engineering Reference
In-Depth Information
together with the nature of the catchment, and the
land management. This not only affects flow patterns
on a local scale but also is instrumental in affecting
them at the Europe-wide scale. Precipitation, for
example, is highest in the west of Europe and lowest
in those countries to the east of the continent,
whereas there is an increase in evaporation in the south-
ern and eastern extremes. Furthermore, the range of
variation in runoff is considerable and whereas it may
exceed 3000 mm in the Alps, in parts of Spain it can
be as low as 25 mm per annum. Localized seasonal
differences are also critical to the development of rivers
and, while in some areas snowmelt is the driving force
(e.g. 25% of the annual discharge of the Torn Alva
in Sweden occurs during 1 month during summer),
conversely in southern Europe where rivers are fed by
rainfall the main flow regime often equates to the
cyclonic weather patterns in the autumn and spring
with low or no flow occurring in the summer.
the eutrophication and heavy modification of river
systems.
11.3.3 Ecological value of rivers and
floodplains
Rivers and floodplains naturally support a wide
variety of flora and fauna and are an essential com-
ponent in creating pathways or corridors between other
habitats such as woodlands, and like any ecosystem
they contain characteristic communities and functions.
While many species rely on specific hydrological
and sedimentological conditions, for others it is the
connectivity between the floodplain and the river
that is crucial to their survival. For example, fish
show highest diversity within the main channel, yet
dragonfly and aquatic-plant species richness increases
in stagnant backwaters. White bream (
Abramis
bjoerkna
) need both the main flowing river channel
and backwaters to complete their life cycle, whereas
amphibians may migrate to the floodplain areas in
spring to deposit eggs. Others play an integral part in
ensuring the sustainability of the various habitats.
Beavers (
C. fiber
) for one, although in decline through-
out much of Europe, can greatly enhance the habitat
where they live. Water accumulates behind their
dams, creating beaver ponds, which provide extra food
and refuge pools for fish and create additional habitat
for other aquatic wildlife and plants. Equally, their
foraging and feeding behaviour protects valuable
wetlands by keeping them free of scrub and provides
additional deadwood for many species of invertebrates.
Clearly many species rely on this range of river and
floodplain environments which consist of vastly dif-
ferent habitats and therefore can be occupied by very
different species assemblages. Upland bolder-strewn
streams, for example, can provide spawning grounds
for salmon (
S. salar
) and sea trout (
S. trutta
), which
in turn are dependent on the food supply provided
by aquatic and bankside invertebrates. In the siltier
slow-flowing reaches spined loach (
Cobitis taenia
)
and lamprey (
Lampetra fluviatilis
) bury into the sub-
strate. In addition to the river, many backwaters, cut-
off channels (natural and man-made) and pools can
provide permanent and semi-permanent wet habitat
for a range of wetland and sheltering riverine species,
for example marsh warbler (
Acrocephalus palustris
),
11.3.2 Inter-connectivity of rivers with
wetlands and floodplains
No river system should be considered in isolation from
its floodplain and yet throughout Europe there have,
historically, been demands on these areas and as a result
many are now left with a legacy of insensitive land
management and flood-defence strategies often based
on unnecessarily over-engineered solutions. The result
of this is disconnected floodplains which, in a nat-
ural riverine environment, would not only have been
of much higher ecological value but would also have
increased the storage capacity of the rivers in times
of high flow, thus reducing the need to mitigate
against flood impacts downstream. A recent EU-
funded trans-national partnership project entitled
The
Wise Use of Floodplains
(Zöckler 2000) looked at how
sensitive management could contribute to sustainable
solutions to water resources at the scale of river
basins and catchments. The project was primarily a
response to the problems associated with the historic
unwise use of floodplains which has resulted in cata-
strophic flood damage of property, danger to inhabit-
ants and the loss of floodplain wetlands. In addition,
these problems have been exacerbated by agricultural
subsidies which have not encouraged best-practice
(environmentally friendly) farming methods, but rather
