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Can We Really Restore Rivers?
<br />by Ellen Wohl, Brian Bledsoe, David Merritt, and LeRoy Poff
<br />Colorado State University and Colorado River Water Conservation District
<br />(Editor's note: This article is adapted from River restoration by Ellen Wohl, Paul L. Angermeier, Brian Bledsoe, G. Mathias
<br />Kondolf, Larry MacDonnell, David M. Merritt, Margaret A. Palmer, N. LeRoy Poff, and David Tarboton, Water Resources
<br />Research, v. 41.)
<br />What is river restoration?
<br />People have manipulated rivers for thousands of
<br />years. Egyptians dammed rivers as early as 2800 B.C.
<br />The Japanese diverted the Tone River more than 60
<br />miles eastward to avoid the city of Tokyo in 1590 AD,
<br />and the Spaniards channelized the Rio Guadalquivir,
<br />reducing its length by 40 %, in 1750 AD. Increasing
<br />population densities worldwide have been associated
<br />with increasing alteration of rivers throughout history.
<br />At any point in time and space, these alterations re-
<br />flect societal expectations of river processes and form.
<br />Viewed in this context, contemporary river restoration
<br />and rehabilitation activities reflect the latest trend in
<br />societal expectations for natural, ecologically healthy
<br />rivers.
<br />Various perceptions of what is meant by `restoration'
<br />reflect the wide disparities in stakeholder interests,
<br />scientific knowledge, scales of interest, and system
<br />constraints encountered in practice. In the parlance
<br />of river management, `restoration' describes activities
<br />ranging from "quick fixes" involving bank stabiliza-
<br />tion, fencing, or engineering fish habitat at the reach
<br />scale, to river - basin -scale manipulations of ecosys-
<br />tem processes and biota over decades. Because both
<br />technical and social constraints often preclude `full'
<br />restoration of river ecosystem structure and func-
<br />tion, `rehabilitation' is sometimes distinguished from
<br />restoration.
<br />A key distinction between river restoration and other
<br />management actions is the intent to reestablish "natu-
<br />ral" rates of certain ecological, chemical, and physical
<br />processes and/or to replace damaged or missing biotic
<br />elements. That is, restoration is often fundamentally
<br />about enhancing ecological integrity [Angermeier,
<br />1997; Baron et al., 2002]. We define ecological in-
<br />tegrity as the ability to self - sustain desirable ecologi-
<br />cal entities (population, community, ecosystem) and
<br />processes (e.g. nutrient dynamics, sediment transport).
<br />Goals of individual restoration projects typically
<br />reflect this general theme but details vary widely be-
<br />cause the particular ecological entities and processes
<br />of interest differ greatly among projects and environ-
<br />mental settings. In many urban rivers, for example,
<br />the potential for ecological improvement is limited,
<br />and the principal benefits from a restoration project
<br />are social, such as building a sense of community by
<br />involving citizens as well as scientists and managers.
<br />River restoration in the United States
<br />Continuing degradation of river ecosystems and loss
<br />of aquatic biodiversity are widespread. River resto-
<br />ration is now accepted by government agencies and
<br />various stakeholders as an essential complement to
<br />conservation and natural resource management. The
<br />number of river restoration projects in the U.S. has
<br />increased exponentially in the last decade, and ex-
<br />penditures on small and mid -size projects alone (e.g.,
<br />excluding projects like the Kissimmee or the Colo-
<br />rado) average > $1 billion a year [Bernhardt et al.,
<br />2005]. From a study of> 38,000 restoration projects,
<br />Bernhardt et al. [2005] found that the most com-
<br />monly stated goals for river restoration in the U.S. are
<br />to i) enhance water quality, ii) manage riparian zones,
<br />iii) improve in- stream habitat, iv) fish passage, and v)
<br />bank stabilization. However, despite legal mandates,
<br />massive expenditures, and the burgeoning industry
<br />of aquatic and riparian restoration, river ecosystems
<br />continue to deteriorate as a result of human influences
<br />[Karr and Chu, 1999]. Furthermore, many restoration
<br />activities have failed [Williams et al., 1997]. Recent
<br />reviews of river restoration projects across the coun-
<br />try suggest some reasons for these failures [Bernhardt
<br />et al., 2005; Wohl et al., 2005].
<br />First, many projects designed to restore rivers are
<br />currently being conducted with minimal scientific
<br />context. Specifically, many projects lack (i) the inclu-
<br />sion of a solid conceptual model of river ecosystems;
<br />(ii) a clearly articulated understanding of ecosystem
<br />processes; (iii) recognition of the multiple, interacting
<br />temporal and spatial scales of river response; and (iv)
<br />long -term monitoring of success or failure in meeting
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