CHAPTER 4
CHANNELIZATION AND CHANNEL
MODIFICATION ACTIVITIES AND IMPACTS
This chapter introduces general categories of channelization and channel modification projects along
with activities implemented to achieve project goals and to offset adverse impacts.
Channel modification activities have a variety of impacts on riverine processes and the associated
riparian ecology and terrestrial environment. These activities can impact river morphology and related
ecology for many years after construction. Projects undertaken to straighten, enlarge, or relocate the
channel in alluvial river systems can initiate channel instability that ultimately leads to stream bank instability.
The resulting bed and bank erosion produces changes in the rates and paths of sediment erosion, transport,
and deposition within the river system. Accelerated erosion and sedimentation processes resulting from
channel modification activities can be detrimental to the infrastructure such as bridges or roadways. Bank
erosion and bank failure results in a loss of riparian habitats as well as commercially valued real estate
adjacent to the stream. Degradation of the bed results in a loss of native substrate and a reduction in the
diversity of aquatic habitats. The downstream migration and subsequent deposition of sediments resulting
from channel and streambank erosion can adversely impact the in-stream habitat of flora and fauna. Shields
and Palermo (1982) present the following six areas of adverse environmental effects of channelization:
1)
Loss of aquatic habitat or reduction in aquatic habitat diversity;
2)
Loss of terrestrial habitat or reduction in terrestrial habitat diversity;
3)
Increased sediment concentrations and turbidity due to bed and bank instability;
4)
Reduction of aesthetic value of streams and riparian habitat;
5)
Water quality degradation, principally due to increasing water temperature and suspended
sediment concentration; and
6) Changes in the stream related hydrology such as fluctuating water levels, draining of wetlands,
and increasing uniformity of flow conditions.
Channel modification activities have deprived wetland and estuarine shorelines of enriching
sediments, changed the ability of natural systems to both absorb hydraulic energy and filter pollutants from
the surface waters, and caused interruptions in the different life stages of aquatic organisms (Sherwood et
al., 1990). A frequent result of channelization and channel modification activities is a diminished suitability
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