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Off-channel habitats are waterbodies within the
floodplain that are generally protected from the river’s
floodwaters, except during the most extreme of events.
They include marshes, ponds, and river side channels
that receive flow either directly from the river, from
groundwater or other sources. Salmonids make extensive
use of off-channel habitats for both spawning and
rearing (Lister et al. 1980; Lister 1997). Many historically
productive side channels and ponds have been
isolated and made unusable to salmonids due to flood
protection works, drainage structures, land development
and past forest practices. These same developments
have also destroyed fish habitat and significantly altered
the hydrological conditions in the mainstem of rivers,
sometimes to such an extent that instream restoration
projects are not feasible. The resultant instability is
especially pronounced during floods, when larger rivers
may experience higher than historical levels of flows,
causing bank destabilization, channelization (widening,
straightening or simplification of the channel) and
transport of good spawning gravels out of the system.
The waters may also carry massive quantities of bedload
from higher in the watershed, resulting in filling in of
the remaining gravel with larger substrates. In watersheds
where large woody debris (LWD) is still present
in the floodplain, these high flows can result in transport
of LWD out of the system. Therefore the impacts of
flood regimes in these “flashy” systems further affect
habitats necessary for various life stages of anadromous
salmonids.
Soto, Christina (editor). 1997. Streamline; Vol. 2; No. 1; Spring 1997. Ministry of Environment, Watershed Restoration Program. Streamline. Vol. 2. No. 1
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