Environmental Engineering Reference
In-Depth Information
fatalist attitude to water fl ows and the inevitable decline of the environ-
ment over time. A Watershed Department staff member notes, “Part of
it is throwing up your hands and realizing that it ain't gonna look like a
natural system. Sometimes you just have to go to a highly armored solu-
tion because it's just too much impervious surface to handle the fl ows in
these creeks. So in some cases it's a giving up and realizing that we're not
going back to nature.” 43
The Limits to Improving Urban Water Quality
One might assume that given the municipality's international reputation
among water quality professionals and its newly integrated department
for stormwater management, there would be a plethora of groundbreak-
ing projects to visit throughout the city. However, beyond the scattered
network of sand fi lters and the subtle but signifi cant changes in bank
stabilization approaches as noted earlier, examples of the municipal-
ity's commitment to water quality are few and far between. One of the
most visible examples of the Watershed Department's integrated mission
and most effective means of retrofi tting the central core is its wet pond
program.
A wet pond sounds like a redundant label for a naturally occurring
waterbody, but in this context, it is a highly engineered structure that looks
and acts like a natural water fi lter. Unlike detention basins, wet ponds
have a permanent pool of water as well as wetland plants that remove
nutrients and dissolved contaminants from urban runoff. The ponds serve
as fl ood control devices, water quality fi lters, and aesthetic amenities to
neighboring residents. The most widely known example in Austin is the
highly successful Central Park wet pond in the Waller Creek watershed in
the central core (see fi gure 4.5). This public/private partnership between
the City of Austin, the State of Texas, and a private developer consists of
a ten-acre park and a series of constructed ponds to manage runoff from
172 acres of landscape with typical impervious cover of 54 percent. 44 One
Watershed Department staff member states:
Our group is pretty high on wet ponds because they are an aesthetic benefi t,
there is a reasonable chance at getting some nutrient control, as opposed to sand
fi lters that don't do a good job with dissolved constituents. It's the use of natural
systems but it's still end-of-pipe. In a way, it's kind of like bioretention or natural
systems because you're taking advantage of nature's ability to process all of these
pollutants. You're not just saying, “Let's create a miniature wastewater treatment
plant with a sand fi lter.” 45
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