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The
San Antonio River Oversight Committee had invested a
great deal of time and effort in developing a long-term
improvement program for Mission Reach, a nine-mile stretch
of the river that includes a trail system connecting
many of the area's historic missions. The original
plan called for undoing many of the flood control measures
built in the twentieth century, such as straightened
channels, dams, and concrete structures. Though effective
in reducing the risk of flooding to homes and businesses
over the years, the changes had robbed the Reach of
much of its beauty and environmental quality.
By restoring
the natural meanders of the San Antonio River and incorporating
a system of less-obtrusive flood prevention measures,
the committee hoped to restore the lost balance between
the Reach's developed and natural environments. The
program, which would also create new opportunities for
visitors to explore the area's rich history and environmental
diversity, enjoyed strong citizen support and - perhaps
most importantly - a solid funding strategy through
partnerships with the City of San Antonio, Bexar County,
and the US Army Corps of Engineers.
A master
plan commissioned by the committee pulled together many
divergent stakeholder groups and developed a strong
consensus for returning the neglected portions of the
river to assets for San Antonio. Moving the master plan
forward to implementation, however, became an immense
task. As more data were gathered and an accurate hydraulic
model was constructed of the river, it became apparent
that some strong refinement was needed to move the project
forward.
"The original
master plan for Mission Reach was based on incomplete
data about the area's fluvial geomorphology - the science
of how the grade and shape of a river channel affects
its flow," explains Kevin Conner, a landscape architect
with Carter & Burgess who is leading the firm's
preliminary design services for the Mission Reach improvements
program. "That data indicated a river course with many
tight meanders. The more we studied and modeled the
river flows, it became clear that was not the case."
Indeed, expert studies
commissioned by Carter & Burgess revealed a Mission
Reach with fewer, more gradual meanders. Left unaddressed,
those discrepancies would have had major implications
on the river and adjacent flood-prone areas.
"The flow of a hundred-year
flood carries 80,000 cubic feet of water per second,"
Conner says. "That's enough to fill 900
average-size swimming pools in an hour, and certainly
enough to overwhelm anything in the floodplain."
This
revelation was certainly not the news the committee
wanted to hear. Not only would the revised fluvial geomorphology
force a fundamental change to the design of Mission
Reach, but it would also make the project more expensive.
"No doubt,
we were at a crossroads," agrees Jim Boenig, director
of engineering for the San Antonio River Authority.
"This issue could have easily cost the project much
of the support needed to carry
it through."
But just as rivers ultimately
find a way to the sea, the project team simply altered
the course of the Mission Reach River Improvements Program.
"Obviously, changing the river's fluvial
geomorphology characteristics was out of the question,"
Conner says. "So instead of adapting the entire
vision, we looked for ways to adapt the design and still
fulfill as much of the vision as possible."
For example, the revised
design calls for the addition of land to designated
areas to achieve more meanders combined with a different
riffle structure. "Instead of building several
weirs in the main channel, we specified changes in the
grade that would reduce the speed of the flow,"
Conner explains. "We also designed wider spots
in the river that give the appearance of more meanders."
Boenig agrees that although
the revised design is not what the oversight committee
originally conceived, it may very well be the next best
thing. "From the air, the river will be far less
sinuous than many people imagined," he says. "But
from ground level or a bridge, it will have all the
appearances of the classic meandering river."
Conner notes that although
the Mission Reach project still faces funding and technical
hurdles, the experience has provided valuable lessons.
"There's no such thing as 'overcommunicating'
when multiple agencies are involved," he says.
"Many of the issues that forced redesign affected
the funding structure and responsibilities. You cannot
assume that every agency will see these issues the same
way. The biggest lesson is the importance of sticking
to the vision. When you do that, the community will
support you as you work out the details."
That's
a lesson Boenig heartily endorses. "We learned
that there was no 'right answer,' but rather
a range of options that we had to consider individually
and as part of the overall strategy."
EC
- July/August 2004
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