River Ecology and Restoration - River Dynamics and Integrated River Management - page 704

floor of the box to the opening, type of material used, whether an internal “ladder” is necessary, height of
placement, and habitat type in which to place the box. Other types of nest structures include nest platforms
for waterfowl and raptors; and tire nests for squirrels. Specifications for nest structures for riparian and
wetland nesting species (including numerous Picids, passerines, waterfowl, and raptors) can be found in
many sources including Yoakum et al. (1980), Kalmbach et al. (1969), and various state wildlife agency
and conservation publications.
Food patches —Food patch planting is often expensive and not always predictable, but it can be carried
out in wetlands or riparian systems mostly for the benefit of waterfowl. Environmental requirements of
the food plants native to the area, proper time of year for introduction, management of water levels, and
soil types must all be taken into consideration. Some of the more important food plants in wetlands
include pondweed ( Potamogeton spp. ), smartweed ( Polyhonum spp. ), duckweeds ( Lemna spp .), coontail,
alkali bulrush ( Scirpus paludosus ), and various grasses. Two commonly planted native species include
wild rice ( Zizania ) and wild millet. Details on these species can be found in Yoakum et al. (1980).
10.4.6 Restoration of Impounded and Channelized Streams
Damming of rivers may greatly change the hydrology, morphology and ecological conditions. Reservoir
operation alters the flow of water, sediment, organic matter, and nutrients, resulting in both direct physical
and indirect biological effects in tailwaters and downstream riparian and floodplain areas. Stream
corridors below dams can be partially restored by modifying operation and management approaches. The
modification of operation approaches, where possible, in combination with the application of properly
designed and applied best management practices, can reduce the impacts caused by dams on downstream
riparian and floodplain habitats. Partial restoration of stream corridors below dams can be achieved by
designing operation procedures that mimic the natural hydrograph. Modifications include scheduling
releases, and making seasonal adjustments in pool levels and in the timing and variation of the rates of
drawdowns (USEPA, 1993).
Adequate fish passage around dams, diversions, and other obstructions may be a critically important
component of restoring healthy fish populations to previously degraded rivers and streams. However,
designing installing, and operating a fish passage facility and the flows necessary for operation are
generally site specific. Figure 10.59 shows the fish ladder on the Bonneville Dam on the Columbia River,
U.S. More than 1 million salmon swim through the fish ladder to pass the dam to upstream spawning
grounds every year.
Fig. 10.59 Fish ladder on the Bonneville Dam on the Columbia River. More than 1 million salmon swim through
the fish ladder to pass the dam to upstream spawning grounds every year.