Channelization and Channel Modification Activities and Impacts
4.1.2
NAVIGATION
The primary objective of channel modification to support navigation is to establish and maintain
an adequate navigable depth. Rivers that have sufficient natural flows to support commercial navigation
utilize dredging operations and in-channel training structures to remove accumulated sediment within the
channel to maintain a navigable depth. River systems with flows regulated by Dams provide opportunities
for navigation by providing periodic adequate flows by regulated releases through the dam. It is not only
critical to maintain project depth, but also control migration of the channel thalwag, bendways, and channel
sinuosity to insure project dimensions for safe navigation.
4.1.3
SEDIMENT CONTROL
Although sediment transport in an alluvial channel is considered a natural phenomenon, sediment
can be classified as a non-point pollutant, and sediment may be present in excessive quantities that have
damaging effects on the environmental and physical aspects of river systems. Excessive sedimentation can
result from erosion and runoff resulting from man-induced practices such as mining, farming, development,
construction, and channel maintenance activities. Excessive sediment can result from degradation of the
channel bed and streambank erosion or failure resulting from river system instabilities. In navigable
waterways, millions of dollars are expended annually to remove accumulated sediments from the navigation
channel. Deposition of sediments in sensitive biological communities can result in a reduction of substrate
diversity that in turn can affect the population of benthic invertebrates. Conversely, a reduction of sediment
supplied to wetland environments adjacent to river systems can result in land loss. Kesel (1988) reports
that the decrease in suspended sediment loads in the Mississippi River combined with the construction of
artificial levees has resulted in an accelerating decline in Louisiana coastal land area. Excessive
sedimentation reduces the capacity of flood control channels and can impact the infrastructure. Potable
water supply operations can be severely impacted by excessive suspended sediment concentrations.
Sediment control activities include sediment removal (dredging), the implementation of streambank and
channel stability projects, better construction methods, trapping or storing sediments, structures for diverting
flow, construction of sediment retention dams, and increased use of protective vegetation.
4.1.4
INFRASTRUCTURE PROTECTION
Frequently, man-made structures such as buildings, bridges, and control structures are located
adjacent to channels or tributaries. Channelization and channel modification projects can accelerate erosion
processes and lead to damage or complete failure of an adjacent infrastructure. Excessive sediment
transport and sedimentation can impact water supply and diversion operations. Local channel and
streambank stabilization activities are implemented to halt channel and streambank degradation, and
subsequently protect structural foundations. Typical channel and bank protection activities include armoring
techniques such as lining banks and channels with riprap, the use of grade control structures to stabilize
eroding channels, and the use of training structures such as dikes to divert flows that impinge on structural
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