WATER QUALITY - Water Quality Engineering in Natural Systems - page 9

2.2.3 In-Stream Habitat baseflow attenuation. A preserved riparian area is

shown in Figure 2.3.
reduction or elimination of woods and brush vegeta-
tion eliminates wildlife habitat, canopy cover, and shade.
reduction or elimination of shading by stream bank
vegetation reduces water quality by increasing sun
energy input, which increases water temperature. Cooler
streams contain more oxygen, providing better support
for aquatic life. unshaded streams, partly because of an
increase in sunlight and increased stream temperature,
promote undesirable filamentous algae, whereas shaded
streams support the advantageous diatomatious algae.
Excellent conditions exist when over 80% of the
stream bank is covered by vegetation or boulders or
cobble; poor habitat conditions exist when less than
25% of the stream bank is covered with vegetation,
gravel, or larger material. Shrubs provide excellent
stream bank cover. Poor conditions exist when more
than 50% of the stream bank has no vegetation and the
dominant material is soil or rock.
The reduction or elimination of riparian wetlands
reduces habitat for aquatic and terrestrial organisms and
deprives the stream of buffering capacity for diffuse pol-
lutant loads from surrounding lands. This can adversely
affect the diversity and species composition in streams
and other surface waters since riparian wetlands provide
cover and shelter for fish and other organisms.
As streams increase in size, the integrated effects of
adjacent riparian ecosystems should decrease relative
to the overall water quality of the stream. Higher-order
streams are more influenced by land use within a water-
shed than by the riparian buffer conditions. Conversely,
first-order streams, or smaller intermittent streams, have
little upgradient contributing drainage area and short
contributing flow paths; therefore, the condition of the
riparian buffer may have a significant impact on the
water quality of the stream.

The most common channel-alteration activities are
channelization, impounding for navigation and electric
energy production, channel straightening, reduction of
flow by withdrawals, removal of bank vegetation, and
building of vertical embankments and flood walls. The
impact of these alterations range from minor to com-
plete destruction of instream habitat. Channel altera-
tion that causes little or no enlargement of islands or
point bars are best for maintaining habitat; channel
alterations that cause heavy deposits of fine material,
increased bar development, and the filling of most pools
with silt have the greatest (negative) impact on habitat.
Quantitatively, channel modifications that cause less
than 5% of the channel bottom to be affected by scour-
ing and deposition have minimal impact; modifications
that cause more than 50% of the channel bottom to be
affected and where only large rocks or riffles are exposed
have significant impact. Channel alterations that lead to
unstable side slopes (>60%) or increased erosion will
clearly have negative impacts on in-stream habitat. An
example of severe stream-channel erosion is illustrated
in Figure 2.2.

2.2.4 Riparian Habitat

Forest riparian buffers provide shade that keep stream
temperatures low; filter and sorb pollutants; provide an
area for sediment deposition; promote microbial decom-
position of organic matter and nutrients; minimize or
prevent stream bank erosion; provide terrestrial, stream
bank, and aquatic habitat and species biodiversity; open
wildlife corridors; provide infiltration, which replenishes
groundwater and cool stream base flow; and provide

Figure 2.2. Effect of channel erosion on in-stream habitat.
Source : uSEPA (2005a).

Figure 2.3. riparian habitat. Source : State of California
(2005).