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<br />
<br />RESTORATION OF REGULATED RIVERS
<br />
<br />403
<br />
<br />the reservoir, the mechanics of water release (surface, bottom or depth selective), the mode of dam
<br />operations and the influence of tributaries entering downstream from the dam. If the tributaries are large
<br />and unregulated, they may substantially mediate the reset (Stanford and Hauer, 1992). In any case,
<br />conditions at some point downstream from the dam will closely approximate conditions elsewhere in the
<br />continuum. Thus, upstream or downstream shifts in biophysical conditions mediated by dams manifest as
<br />predictable discontinuities in the river continuum. For example, biophysical conditions at some
<br />predictable point downstream from a large bottom release (hypolimnial) dam in the montane transition
<br />of a temperate latitude river will be very similar to pristine conditions far upstream, because of the cool,
<br />clear water released from the reservior. In rivers that are free flowing for long distances downstream from
<br />large dams in the montane reaches, the position of the rhithron-potomon transition can be predicted
<br />from the operational mode of the dams relative to the influence of tributaries,
<br />The predictions of the SDC along the longitudinal dimension have been largely substantiated (Stanford et
<br />ai., 1988; Ward and Voelz, 1988; Hauer et ai" 1989; Stanford and Ward, 1989; Ward and Stanford, 1990,
<br />1991; Munn and Brusven, 1991; Sabater et ai" in press), although recent incorporation of responses of large
<br />floodplains (Ward and Stanford, 1995b) require additional resolution, The main point is that the ecological
<br />consequences of specific regulation schemes are largely predictable, and environmental degradation asso-
<br />ciated with regulation can be ameliorated. We recognize that uncertainties derive from interactions with pol-
<br />lution and the introduction of exotic biota. However, pollution can be curtailed or eliminated, and non-
<br />native biota are likely to be substantially less successful as invaders when dams are operated in ways that
<br />maximize resets of environmental heterogeneity,
<br />
<br />RESTORA nON PROTOCOL
<br />
<br />The era of dam building may be over in much of the world because high efficiency and affordable dam sites
<br />are already developed, Loss of biodiversity and bioproduction, especially riverine and anadromous fisheries
<br />(Frissell, 1993; WeIcomme 1995). underscores the need for restoration of regulated rivers and enormously
<br />expensive reconstructions are underway or are being planned (Dahm et ai" 1995; Gore and Shields,
<br />1995), Even removal of large dams on large rivers is included in some restoration plans because the costs
<br />of damage to fisheries and other attributes of riverine integrity in some instances far exceed the commercial
<br />value of the dams. Removal of large dams is obviously problematic in a variety of ways, such as the mobi-
<br />lization of large volumes of fine sediments stored in the reservoir basin, and methods for evaluating removal
<br />strategies have been proposed (Shuman, 1995), A variety of approaches exist for restoring small streams with
<br />substantial emphasis on engineered structures such as weirs, off-channel ponds, rock gardens (Gore and
<br />Shields, 1995) and many other artificial habitat structures (Hunter, 1991). Commercial operations advertise
<br />engineering expertise for bulldozing damaged streams back to pre-regulation channel configurations and
<br />stories of restored fisheries and improved water quality abound in the popular literature, although scientific,
<br />long-term evaluations of such schemes are much less available (Sear, 1994), Structures placed in stream are
<br />often washed out, fail to restore biodiversity or produce unanticipated negative responses, such as increased
<br />bank erosion or accelerated deposition of fine sediments (Frissell and Nawa, 1992) and increased water tem-
<br />peratures (c. Frissell, unpublished data) associated with weirs and rock gardens, Such problems largely
<br />derive from lack of attention to the conceptual foundations of river ecology and the first principles of the
<br />ecology of regulated streams,
<br />
<br />Formalize the probiem at catchmen{ scale
<br />
<br />Restoration of large, regulated rivers begins with recognition of the river continuum and evaluation of
<br />the loss of ecosystem capacity to sustain biodiversity and bioproduction, Biological (e,g, past and present
<br />distribution of native biota) and physical (e.g, channel configuration) indices of ecosystem resilience are
<br />needed (Frissell et al., 1993); measures of biological integrity as defined by Angermeier and Karr (1994)
<br />may be more useful than biodiversity per se because of the difficulty of accurately determining the distri-
<br />bution and abundance of benthos, fish and other river organisms. Habitat requirements for all life history
<br />stages and generation times (turnover rates) of native, keystone species (i,e" top carnivores and other
<br />
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