Environmental Engineering Reference
In-Depth Information
considered. For example, the installation of in-stream
structures and large wood to improve or increase the
area of fi sh habitat may lead to local improvements in
fi sh numbers but unless other factors, such as lack of
spawning habitat or poor water quality, are addressed
population recovery may still fail to come (Stewart
et al
. 2006 ).
The main purpose of this chapter is to present a
broad understanding of the state of river restoration,
rehabilitation and enhancement with a European
focus. For the purposes of this chapter, these three
terms are all referred to as restoration since the distinc-
tion between each is often diffi cult to specify; the level
of river
intervention
feasible for ecological benefi t
is often determined by local, regional and global factors,
of social, economic, fi nancial and infrastructure
dimensions, along with the historical management
practices of the river and associated fl oodplain as
depicted in Figure 17.1. The chapter discusses the
impact of such factors, including
disturbances
, as
well as the importance of economics, public policy and
scientifi c understanding in terms of best practice to
achieve optimum, holistic river restoration outcomes.
environmental conditions acting upon them. In other
words, fl uctuating climatic and other drivers mean
that rivers and their fl oodplains are always adjusting to
both local changes that affect annual variability of
fl ood frequency and the size of fl ow events, and global
variation that can result in major shifts in river plan-
form pattern (i.e. the characteristic path of the channel)
and transform their natural geomorphological state.
The precise mechanisms of geomorphological change
in rivers cannot be explained within the confi nes of
this chapter, but many textbooks already cover these
issues (see e.g. Callow & Petts 1992; Knighton 1994;
Gregory 1997 ; Thorne
et al
. 1997 ). Nevertheless, the
importance of understanding
geomorphic processes
cannot be over-estimated. It can both hold the key to
explaining the changes that have occurred in a riverine
landscape as a result of anthropogenic intervention
and help to predict how specifi c restoration methods
will enhance degraded rivers.
17.2.1
Natural impacts
Although rivers and fl oodplains have constantly been
shaped by changes in climate over time (see Table
17.1), the riverine topography we have inherited today
owes many of its features to the impacts of the last
major Ice Age that ended some 10 000 years ago. This
formed not only many of the rivers themselves but also
the valleys and entire catchment basins. In northern
17.2 HISTORICAL CONTEXT TO
EUROPEAN RIVERS
Wherever rivers are not confi ned, they continually
change their course in response to the specifi c range of
Global, Regional and Local
Ecosystem
resources &
functions
Catchment
Political
drivers
Land-Water
Connectivity
Habitat & Organism
Cultural
inluences
Future land
use
Water quality &
chemical factors
Hydromorphological
& Physical factors
Ecological factors
Historical land
use & features
Socio-economic
drivers
Figure 17.1
The essential elements of river restoration science. The complex, scale-based, hierarchical dependencies
between elements essential for successful river restoration are shown.
