Geoscience Reference
In-Depth Information
active intervention and physical changes to the
channel.
The next most effective restoration strategy
would be restoration of processes (Beechie
et al
.,
2010). Examples include high flows released
from reservoirs, gravel added to sediment-starved
channels downstream of reservoirs, and removing
dykes that block flood waters from inundating
floodplains. In these cases, by restoring the
processes the river can be expected to create
complex forms (and thereby diverse habitats).
The approaches that are least sustainable and
least likely to succeed are those that attempt to
create directly, through mechanical action, the
complex habitats of the natural river (especially
if the restoration goals are based on outdated
notions of stability as the desired state of the
ecosystem).
If the
espace de liberte
is the most sustainable
approach, how can it be implemented universally?
There are urban environments in which buildings
and infrastructure have so encroached to the river
banks that there is insufficient room for an active
corridor. There are low-energy, low-sediment-
load streams whose spontaneous recovery from
channelization or other such impacts might take
centuries, if indeed it were to occur at all. We
can envisage the effects of these two factors
on the potential for effective implementation of
the
espace de liberte
approach (Figure 18.2). The
Figure 18.2
The suitability of the
espace de liberte
vs other, more intrusive river management approaches, as a function
of degree of urban encroachment (x-axis) and available stream power and sediment (y-axis). See text for explanation.
From Kondolf (2011).
