Surface Water - Alabama Department of Environmental Management

Methodology
SITE SELECTION
Alabama’s 2002 §303(d) list and the NPS impairment potential estimates were used to
rank the sub-watersheds within the BWC Basin Group. Additional review of municipal,
industrial, and mining permit tracking databases were used to identify those subwatersheds
with the most potential for impairment from point sources. Existing water
quality reports were used to identify sub-watersheds where recent data were unavailable. A
total of 44 sub-watersheds were targeted to select candidate assessment sites and conduct
field reconnaissance. Two hundred three sites were visited to determine the best sampling
locations for the NPS screening assessment. Where possible, assessment sites were located
in relatively small drainages to relate water quality to specific nonpoint sources and to
compare results to ADEM’s network of least-impacted reference sites. Appendix F lists
the target sub-watersheds and the sites chosen for assessment.
HABITAT ASSESSMENT
In the absence of water quality impairment, biological condition of the fish and aquatic
macroinvertebrate communities is generally correlated with the quality of available habitat.
The presence of stable and diverse habitat generally supports a diverse and healthy aquatic
fauna (Barbour and Stribling 1991, Barbour and Stribling 1994). Therefore, habitat quality
was assessed at each site to evaluate stream condition and to assist in the interpretation of
biological data. Primary, secondary, and tertiary habitat parameters were evaluated.
Primary habitat parameters evaluate the availability and quality of substrate and instream
cover. They include those characteristics that directly support aquatic communities, such
as substrate type and stability. Secondary habitat parameters evaluate channel morphology,
which is determined by flow regime, local geology, land surface form, soil, and human
activities. Channel morphology indirectly affects the biological communities by affecting
sediment movement through a stream (Barbour and Stribling 1991). Secondary habitat
parameters include an evaluation of flow regime, sinuosity/ instream geomorphology, and
sediment deposition and scouring. Tertiary habitat characteristics evaluate bank structure
and riparian vegetation. Bank and riparian vegetation prevent bank erosion and protect the
stream from stormwater runoff from impervious surfaces. The presence of overhanging
riparian vegetation also determines the primary energy source for aquatic
macroinvertebrate communities—the base of the fish food chain (Vannote et al. 1980).
Tertiary parameters include bank condition, bank vegetative protection, and riparian zone
width.
The EPA has published 2 versions of stream habitat assessment forms to evaluate
primary, secondary, and tertiary habitat parameters (Barbour et al. 1999). ADEM used the
original habitat assessment form from 1989 through 1996. The EPA published revised
habitat assessment forms that evaluated riffle/run and glide/pool streams separately (EPA
1997b). The primary habitat parameters of the glide/pool habitat assessment emphasize
characteristics important to this stream-type, primarily pool structure and variability. The
ADEM began using the revised forms in 1996 because they assess habitat quality and
degradation to the glide/pool streams of south Alabama more accurately (ADEM 1999b).
In addition, because they measure impairment to habitat quality, the scores (converted into
percent of maximum score) were comparable between stream types and can be used to
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