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<br />Figure 6. Simulated annual discharge (m3fs;I; 10, mean monthly flow) patterns in the Hanford Reach of the Columbia River, USA.
<br />The same volume o[water passed through the reach in each of the three scenarios (derived from US Geological Survey data, RestoD.
<br />Virginia, USA)
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<br />, aggraded rivers and extensive scouring of floodplain surfaces occurs if revetments are breached, Recent
<br />floods (1993-1995) of such magnitude in larg.rivers of western Europe, southern Scandinavia, Bangladesh
<br />and the USA provided evidence of the value of vacating floodplains to reduce the human costs and exploit
<br />natural flood pulsing (Sparks, 1995).
<br />The strong inference for management is to protect uncolonized floodplains by re-establishing periodic
<br />overbank flooding, allowing the river to rebuild habitats, Elsewhere, incentives will be needed to get people
<br />to vacate floodplains so that revetments can be removed allowing reconnection of channels and floodplains.
<br />If that is not practical or desired by stakeholders, development of strategies for reconnecting severed lowland
<br />floodplain wetlands and backwaters by use oflateral flow control structures may be useful (Gore, 1985; Gore
<br />andShields, 1995), In situations where alluvial areas have been inundated, it,may be possible to lower per-
<br />manently the full pool level of the reservoir, allowing riverine cut and fill alluviation to reconfigure and
<br />restore drowned floodplains, As in dam removal, this scenario requires careful evaluation because sediment
<br />transport dynamics may be different from those that occurred prior to regulation.
<br />Whereas peak flows are needed to restore natural habitat heterogeneity, usually stabilization of base-
<br />flow fluctuations will also be needed to revitalize the varia I zone of the channel (Figure I), Establishment
<br />of sustained baseflows restores biodiversity and bioproduction in shallow water habitats, which are cri-
<br />tically important to benthic insects that must emerge from the shorelines of rivers, and small fishes that
<br />must reside on or near substratum in low velocity habitats (Perry and Perry, 1986; Weisberg el ai" 1990;
<br />Travnichek el al., 1995),
<br />Reregulation in most rivers can be accomplished without substantially compromising storage or hydro-
<br />power (Figure 6), Peak flows are built from storage and runoff and released in concert with natural runoff
<br />timing in the catchment (Figure 4). In wet years, peaks can be reregulated to approach floods of record,
<br />depending on the release capability of the dam. Very high flows are not needed every year to maintain \
<br />instream and floodplain habitats nor is the historical duration of floods likely to be required because
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