Although billions of dollars are spent on river restoration projects worldwide, little agreement exists on how their success is measured. According to lead author Dr Margaret Palmer of the University of Maryland: "Given the rapid rate of global degradation of fresh waters, and the fact that river and stream restoration has become a booming enterprise, it is time to agree on what constitutes successful river and stream restoration." Palmer and her colleagues say that the success of river restoration should be judged according to five criteria: a guiding image; improving ecosystems; increasing resilience; doing no lasting harm; and completing an ecological assessment.
The first step should be articulating a "guiding image" describing the ecologically healthy river that could exist at a given site. The second step should be to demonstrate that there have been measurable changes towards the guiding image, such as larger fish populations and clearer water. Palmer et al stress that restoration success should not be viewed as an all-or-nothing, single endpoint, but as an adaptive process where small improvements build up and lessons are learned from any failures.
The third criteria for successful river restoration is to create hydrological, geomorphological and ecological conditions that allow the river to be a resilient, self-sustaining system. The fourth criteria is to do no lasting harm. "For exampl e, a channel modification project should minimise loss of native vegetation during river reconstruction, and should avoid the fish spawning season for construction work," Palmer explains. The final criteria is ecological assessment. According to Palmer: "It is critical that the broad restoration community, including funding agencies, practitioners and citizen restoration groups, adopt criteria for defining and assessing ecological success in restoration. Standards are needed because progress in the science and practice of river restoration has been hampered by the lack of agreed upon criteria for judging ecological success."
The debate is timely given the many waterfront regeneration projects under way worldwide. But, Palmer argues, many such schemes lack an ecological dimension. "Riverfront revitalisation projects many be successful in increasing economic and social activity near a river, but can constrain natural processes of the river and floodplain. Projects labelled restoration successes should not be assumed to be ecological successes," Palmer says.