Environmental Engineering Reference
In-Depth Information
Going Underground
The land development activities in the Hill Country would affect not
only surface features but also underground water fl ows. The subsurface
of the region is a vast underground storage vessel of permeable limestone
characterized by caves, sinkholes, and other conduits. Due to its porous
character, the Edwards Aquifer is the most environmentally sensitive
subsurface waterbody in Texas, in direct contrast to most aquifers that
fi lter groundwater. The porosity of the aquifer results in direct interac-
tion between activities on the land and conditions of water quality below
ground. Soil erosion in the Hill Country has an impact on not only the
immediate, visible landscape but also the water quality of the aquifer and
receiving waters—notably Barton Springs. It is this sensitive underground
network of water fl ows that connects land development in the upstream
Hill Country to Austin culture downstream.
Formal studies of the aquifer's complex fl ow paths began over a century
ago with geologic mappings and groundwater monitoring. In the 1950s,
University of Texas geologists began large-scale studies of the Edwards
Aquifer; today, they continue to refi ne their understanding of aquifer me-
chanics using increasingly sophisticated fi eld studies and hydrologic fl ow
models. In 1978, the City of Austin initiated a partnership with the U.S.
Geological Survey to conduct comprehensive studies to characterize aqui-
fer fl ow; in subsequent years, they developed large datasets, models, and
theories to delineate how the aquifer functions. A municipal staff member
notes, “When I fi rst started here in the mid 1980s, we were assuming that
it might take twenty years for water to fl ow through the aquifer. Now, we
know that it is a matter of days or even hours. So the leap in knowledge
has been pretty amazing.” 47
Despite the intensive geologic research projects by university, municipal,
and federal entities, the diverse fl ow paths and unexpected behavior of
contaminants in the aquifer continue to confound scientists. For example,
the results of dye tracer studies completed by the City of Austin and the
regional aquifer authority in the late 1990s negated some of the earlier un-
derstandings of the aquifer's fl ow paths. The aquifer acts as a “trickster,”
eluding precise scientifi c prediction and fostering uncertainty and doubt
with its complex behavior. 48 In 1997, a consortium of scientists, engineers,
and planners published a scientifi c consensus document in an attempt to
solidify the commonly understood characteristics of the aquifer, but the
uncertainty of land use development impacts on the aquifer continues to
hamper efforts to balance urban growth with environmental protection. 49
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