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restoring processes or that are hampered by continuing limitations on flooding
associated with flow regulation (Kristensen et al. 2014). In some projects, the smallscale effects of appropriate restoration do not significantly ameliorate the continued,
watershed-scale effects of stressors such as introduced species or excess nutrients
and other contaminants entering the river corridor (Bernhardt and Palmer 2011).
This does not mean, however, that river restoration is not necessary and vitally
important. It means that we must learn how to more effectively restore river corridors and how to measure the effectiveness of restoration.
Palmer et al. (2005) propose five criteria for assessing the ecological success of
river restoration: (1) Restoration should be designed around a specific guiding
image of a dynamic, healthy river that could exist at the site targeted for restoration.
‘Could exist’ is a critical phrase in this context. Although a meandering channel
may be considered desirable, temporal fluctuations in water and sediment inputs
may be more characteristic of a braided channel planform, for example. The key
point is to understand the context of the river or river segment targeted for restoration and its trajectories of change through time (Campana et al. 2014; Petkovska
et al. 2015; Brierley and Fryirs 2016). (2) The river corridor’s ecological condition
must be measurably improved, as assessed by movement toward the guiding image
in terms of parameters such as water quality, improved bioabundance or biodiversity. This criterion is designed to counteract the tendency to evaluate river restoration solely on visual appeal or physical characteristics. This criterion also
incorporates interactions between process and form. Restoration of substrate heterogeneity in headwater streams of Finland, for example, did not result in full restoration of retention efficiency because the aquatic mosses critical to retention were
removed during restoration activities (Muotka and Laasonen 2002). (3) The river
ecosystem must be more self-sustaining and resilient to disturbances. A river restoration project that requires continual maintenance after restoration indicates that the
restored channel is not effectively adjusted to temporal fluctuations in water and
sediment inputs. (4) No lasting harm should be done to the river corridor during the
construction phase of restoration. (5) Pre- and post-assessment must be completed
and data made publicly available (Palmer et al. 2007).
Because water and sediment inputs are among the primary drivers of river process and form, river management and restoration over the past few decades have
emphasized flow regime. The most recent expression of this emphasis is the concept
of environmental flows.
4.2 Environmental Flows
Initial efforts to protect flows in river ecosystems focused on minimum flows. In
drylands such as the western United States, consumptive flow uses can create river
segments that are completely dewatered continuously or for discrete periods of
time. Fish biologists developed the concept of instream flows as a mechanism for
4.2 Environmental Flows
restoring processes or that are hampered by continuing limitations on flooding
associated with flow regulation (Kristensen et al. 2014). In some projects, the smallscale effects of appropriate restoration do not significantly ameliorate the continued,
watershed-scale effects of stressors such as introduced species or excess nutrients
and other contaminants entering the river corridor (Bernhardt and Palmer 2011).
This does not mean, however, that river restoration is not necessary and vitally
important. It means that we must learn how to more effectively restore river corridors and how to measure the effectiveness of restoration.
Palmer et al. (2005) propose five criteria for assessing the ecological success of
river restoration: (1) Restoration should be designed around a specific guiding
image of a dynamic, healthy river that could exist at the site targeted for restoration.
‘Could exist’ is a critical phrase in this context. Although a meandering channel
may be considered desirable, temporal fluctuations in water and sediment inputs
may be more characteristic of a braided channel planform, for example. The key
point is to understand the context of the river or river segment targeted for restoration and its trajectories of change through time (Campana et al. 2014; Petkovska
et al. 2015; Brierley and Fryirs 2016). (2) The river corridor’s ecological condition
must be measurably improved, as assessed by movement toward the guiding image
in terms of parameters such as water quality, improved bioabundance or biodiversity. This criterion is designed to counteract the tendency to evaluate river restoration solely on visual appeal or physical characteristics. This criterion also
incorporates interactions between process and form. Restoration of substrate heterogeneity in headwater streams of Finland, for example, did not result in full restoration of retention efficiency because the aquatic mosses critical to retention were
removed during restoration activities (Muotka and Laasonen 2002). (3) The river
ecosystem must be more self-sustaining and resilient to disturbances. A river restoration project that requires continual maintenance after restoration indicates that the
restored channel is not effectively adjusted to temporal fluctuations in water and
sediment inputs. (4) No lasting harm should be done to the river corridor during the
construction phase of restoration. (5) Pre- and post-assessment must be completed
and data made publicly available (Palmer et al. 2007).
Because water and sediment inputs are among the primary drivers of river process and form, river management and restoration over the past few decades have
emphasized flow regime. The most recent expression of this emphasis is the concept
of environmental flows.
4.2 Environmental Flows
Initial efforts to protect flows in river ecosystems focused on minimum flows. In
drylands such as the western United States, consumptive flow uses can create river
segments that are completely dewatered continuously or for discrete periods of
time. Fish biologists developed the concept of instream flows as a mechanism for
4.2 Environmental Flows