Channelization and Channel Modification Activities and Impacts
foundations, Channel realignment activities may be required to isolate the structure from degradational
areas.
4.1.5
MINING
Mining operations typically associated with river systems include sand, gravel, phosphate, metals
and other materials. Mining operations can affect in-channel, riparian, and terrestrial processes. Removal
of large quantities of sand, gravel, or ore from the channel can lower the bed, thus initiate a bed
degradational process that proceeds upstream. The increased sediment load is transported and deposited
downstream. Additionally, mining operations can significantly increase suspended sediment loads through
the mining process, and through the destruction of protective stream side and terrestrial vegetation. Waste
products of mining operations may be deposited adjacent to the streams, and may be re-deposited in the
channel during high water or storm events. Generally, both hydraulic and mechanical dredging activities
are associated with riverine mining activities.
4.1.6
CHANNEL AND BANK INSTABILITY
Unstable riverine systems result in accelerated loss of stream side habitats due to bed and bank
erosion, adverse impacts on aquatic habitats from increased sedimentation and turbidity, and a general
decreases in the recreational value of the system. Channel modification activities are implemented to halt
or slow down processes associated with instability such as bank erosion and channel degradation. Grade
control structures are constructed in channels to stop the degradational process from proceeding upstream.
Grade control structures include simple bed control structures, concrete drop structures, channel linings
or drop pipes (Watson et al., 1998). Stream banks are stabilized to halt erosion and bank failures resulting
from localized effects or overall system instability. Typical channel and bank stability techniques include
the use of surface armor for erosion protection, indirect methods such as dikes, weirs, and retards for
redirecting flows away from affected areas, and the use of vegetation for either direct or indirect erosion
protection.
4.1.7
HABITAT IMPROVEMENT AND ENHANCEMENT
Associated with channel modification projects are activities to improve an in-stream and riparian
habitat. Existing channels that have been modified for purposes such as flood control and drainage
frequently experience a loss of stream side and terrestrial vegetation, bed substrate, and in-stream habitat
diversity. Loss of stream side vegetation can result in an increase in water temperature due to a reduction
of shade, which impacts aquatic species that can only tolerate a narrow range of temperatures.
Additionally, loss of protective vegetation increases stream bank erosion and transport of sediment into the
stream. Increased sedimentation or erosion rates resulting from channel instability can replace the existing
substrate with a more uniform substrate that is not conducive to a diverse colonization of aquatic
invertebrates. Habitat improvement activities include re-introducing vegetation along the stream bank to
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