Surface Water - Alabama Department of Environmental Management

Cahaba River (0315-0202)
Number of sub-watersheds with (M)oderate or (H)igh ratings for each point source
category (Appendix D).
Category
Overall
Potential
% Urban Development Septic tank
failure
Moderate 3 2 2 4
High 4 6 5 1
Historical data/studies: The majority of assessments conducted within the Cahaba River
CU were from the 15 projects and programs and listed below. The most recent field
studies by EPA Region IV in 2002 verified that the Cahaba River continues to exhibit
numerous impairments of its aquatic life use (O’Neil 2002, Howard et al. 2002). These
results have been supported by extreme diurnal swings of dissolved oxygen concentrations
in the lower parts of the Cahaba River where nuisance growths of periphyton have been
observed during low flow. Causes have been attributed to siltation (embeddedness and bed
load) from urbanized areas and nutrient/eutrophication from urban runoff and municipal
WWTPs (O’Neil 2002, USEPA 2003). Excessive sedimentation has been a primary factor
in habitat degradation within Cahaba River (Howard et al. 2002, O’Neil 2002, Hartfield
2002). Two methods of siltation loading have been observed in the basin: acute sediment
loadings are discrete, short events occurring during high flows; chronic sediment loadings
describe long-term channel instability caused by magnified stream flows from impervious
surface runoff. The worst siltation impacts were observed at Cahaba River at Bains
Bridge, Little Shades Creek, Patton Creek, and at bridge crossings throughout the basin.
Fecal coliform samples collected 1999 through 2003 by ADEM and Jefferson County
indicated very high pathogen concentrations in certain segments after rain events and
during high flows. Pathogen sources include urban runoff, failing sanitary sewers, and
failing septic systems (ADEM 2003b).
2002 NPS screening assessment: Seven sub-watersheds were targeted for assessment
during the 2002 NPS Screening Assessment because they were recommended as NPS
priority sub-watersheds in 1997, had a moderate potential for impairment from nonpoint
sources, were on ADEM’s 2002 §303(d) list of impaired waters, or recent data were
unavailable. Appendix F lists the 12 stations assessed.
Sub-watershed assessments: Current and historical assessments were combined to provide
a comprehensive assessment. Habitat, chemical/physical, and biological conditions were
assessed in 15 sub-watersheds (Appendix G). Habitat quality was assessed as excellent or
good at 26 stations and fair at 2 stations. Macroinvertebrate assessments were conducted
at 28 stations. Results of these assessments indicated the macroinvertebrate community to
be in excellent or good condition at 17 (61%) stations and fair or poor at 3 stations (39%).
Fish communities were assessed as good at 13 stations, fair or fair/poor at 3 stations, and
poor at 4 stations.
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