Selection and Design of Channel Rehabilitation Methods
It also follows that for a given volume of a flood event, if the peak is of greater magnitude, the
recession must be of shorter duration and of lower magnitude. At some low discharge, critical conditions
exist for fish and other aquatic species. Many channelized streams do not have sufficient depth of flow for
fish survival in summer baseflow. Karr et al. (1986) lists major flow regime factors that affect aquatic
biota, which include: alteration of magnitude of high and low flows, increased maximum flow velocity, and
a decrease in protected sites. These factors which are detrimental to aquatic biota are associated with
increased skewness of the discharge. Therefore, reducing the skewness through flow control can offset
some of the detrimental effects of channelization and channel incision.
In summary, increased storage in the watershed through flow control can be used to adjust
hydrologic response to enhance aquatic and terrestrial habitat, improve channel stability, and to decrease
sediment yield that can severely impair downstream flood control channels, reservoirs, and wetlands.
However, the negative impacts associated with flow control such as decreased terrestrial habitat, reduced
flushing flows for fish, decreased water temperatures, scour downstream of the dam, and blockage of fish
passage must also be considered.