Effects of Highway Construction and Operation
on Water Quality and Quantity in an Ephemeral
Stream in the Austin, Texas Area
By Michael E. Barrett, M.S., Joseph F. Malina, JR., P.E., Randall
J. Charbeneau, P.E., George H. Ward, Ph.D.
Regulatory agencies recently have focused attention on nonpoint
sources of pollution such as urban runoff. The U.S. Environmental
Protection Agency (EPA) National Pollutant Discharge Elimination
System (NPDES) regulations regarding stormwater runoff are evidence
of this effort to protect the water quality of receiving waters.
In Texas, the Barton Springs/Edwards Aquifer Conservation District
(District) and several environmentally oriented organizations became
concerned about the potential for aquifer contamination as a result
of proposed highway construction activities over the Edwards aquifer.
The proposed construction corridor crosses and parallels three creeks
and overlies a portion of the recharge zone of the Barton Springs
segment of the Edwards aquifer. The Edwards is a karstic (cavernous)
aquifer with numerous recharge features and thin soil cover and
is particularly susceptible to degradation from nonpoint sources
In January 1990, a Consent Decree and Judgment was issued requiring
the Texas Department of Transportation (TxDOT) to fund a study to
assess water quantity and quality impacts of highway construction
in the Edwards aquifer recharge zone. One part of the study involved
a field monitoring program of the quantity and quality of the surface
water in the creeks and drainage ways affected by the construction
and operation of highways in the target study areas. Surface water
quality has a direct impact on water quality in the aquifer, because
85% of recharge to the aquifer occurs through beds of the major
creeks (Slade et al., 1986).
The monitoring program was used to assess the impact of new highway
construction on water quantity and quality in creeks flowing across
the recharge zone. A suitable representative drainage area was selected
since it was not economically feasible to monitor highway runoff
at every location. The results can be extrapolated to assess the
impact of the entire project. Results of this study also will add
to the general body of knowledge regarding stormwater runoff, an
issue of increasing importance throughout the United States.
Danz Creek, an intermittent stream that flows in a natural channel
beneath both lanes of State Highway 45 (also known as the Outer
Loop) was selected as a representative receiving water for a number
of reasons: (1) Danz Creek is crossed three times by the TxDOT construction
corridor, (2) The creek was easily accessible to project personnel
for the collection of flow measurements and water samples, and (3)
Portions of the creek were amenable to flow monitoring using established
techniques. The impact of highway runoff on Danz Creek was assessed
by determining the difference in water quality between sections
of the creek upstream and downstream of the highway right-of-way.
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