Channelization and Channel Modification Activities and Impacts
4.2.10.1 Hydraulic Effects
Indirect bank stabilization methods act to deflect flows from affected areas or reduce current
velocities adjacent to banks. After eroding banks are stabilized, the sediment discharge is reduced in the
system. If the reduction of sediment discharge is significant, the system may adjust by eroding and
degrading the channel bed. The operation of reservoirs to accomplish bank stability by reducing peak
discharge and lowering the flowlines in the downstream channel may result in tributary instability be lowering
their effective base level. Additionally, the reduction of sediment supply downstream from reservoirs may
induce channel degradation downstream. This can result in increased bank heights and bank instability.
4.2.10.2 Environmental Effects
Direct methods of streambank protection initially involve some bank preparation and removal of
vegetation. This initial adverse impact on the riparian ecology is offset by the benefit of halting the existing
erosion. Bank protection can increase habitat diversity if the bank is re-vegetated with environmentally
beneficial plants as part of the bank protection scheme. Extensive streambank protection works can result
in a reduction of channel migration, which reduces habitat diversity.
4.2.10.3 Remedial Measures
Currently, environmentally compatible methods of stream bank protection are based on extensive
use of vegetation, particularly used in combination with structural applications. Allen (1978) describes the
use of plants to control erosion of streambanks, reservoir shorelines, and other areas. Shields and Palermo
(1982) indicate field studies were conducted on the Missouri, Sacramento, Willamette, and Lower
Mississippi Rivers on the environmental effects of bank protection projects and methodologies to reduce
adverse environmental effects. Demonstration projects were conducted in the Ohio and Yazoo River
Basins for testing various combinations of vegetation and structure. The reduction in habitat due to paved
channels can be alleviated by the use of riprap as a lining, with the voids between the riprap filled with
stream gravel.
4.2.10.4 Operation and Maintenance of Channel and Bank Stabilization Projects
As with all in channel structural improvements, periodic inspections are required to insure that the
project functions as intended. For direct methods of bank protection, inspections should be conducted to
insure that surface armor such as riprap remains in-place and has not been displaced by high discharge
events. The channel should be periodically inspected for signs of instability that could cause future
maintenance problems.
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