Biological impacts can be broadly categorized into either terrestrial or aquatic. The major
terrestrial impact involves alteration or elimination of riparian zone vegetation due to
construction or project features. The riparian zone provides and supports a wide variety of
plant and animal life and often provides critical habitat for certain species. Riparian vegetation
also supports aquatic species by providing habitat for these species and input to the food
chain. Channel stabilization can affect succession of riparian vegetation and decrease
diversity. Aquatic organisms, including benthos and fish, may also be affected due to changes
or reductions in required habitats as a result of project features.
Other impacts that may occur due to streambank protection projects include loss of wetlands
and historic sites, changes in land use, increased recreational pressure, and economic or
social impacts.
6.9.2 Effects of Channelization
Patrick (1973) assessed that the stream and its floodplain constitutes an integrated system that
is well designed for moderating the effects of flooding waters and for maintaining high
productivity in the stream. Disturbing the system inevitably results in a reduction in diversity of
species and productivity. Because the functioning of the aquatic ecosystems is impaired, the
ability of the stream to cleanse itself and to assimilate wastes is lessened, and the
improvement of water quality is slower. The stream, instead of being one that is aesthetically
pleasing and highly productive, becomes degraded and its recreational use is minimized. The
chief effects of channelization are as follows:
Removes the natural diverse substrate materials that allow the development of many types
of habitats for aquatic organisms
Increases sediment load that decreases light penetration and primary production
Creates a shifting bed load that is inimical to bottom-dwelling organisms
Simplifies the current pattern and eliminates habitats of diverse currents
Lowers the stream channel and often drains adjacent swamp areas and aquifers that help
to maintain stream flow during time of low precipitation
Destroys floodplain ponds that are the breeding ground for aquatic life and that act as a
reservoir for species of the river proper
Reduces the stability of the banks and causes cave-in of trees and other overhanging
vegetation that are an important food source for stream life and whose shade reduces high
stream temperatures during the summer months
Kellerhals et al. (1985) concluded that most existing engineering design criteria for river training
works are in direct conflict with general concepts of fish habitat maintenance since their aims
are well aligned, uniform and stable channels, with minimum local scour and no opportunity for
debris jamming. The objectives of fisheries mitigation works are often quite the opposite; a
degree of instability, rough and irregular banks, deep local scour holes, debris jams and
overhanging vegetation. Well founded guidelines for designing such diverse and irregular
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