The
dense riparian vegetation and cattail thicket that has sprouted
in Pasadena’s Lower Arroyo in the last five years has
attracted a lot of interest from walkers and Arroyo aficionados.
Now two graduate students in the landscape architecture
program of the University of California at Berkeley have
completed an analysis that describes the Browning Ferris
Industries (BFI) low-flow stream project as “a missed
opportunity.”
The
analysis is very timely because the Arroyo Seco Master Plan,
recently released by the City of Pasadena, recommends extending
the BFI approach into the next cove of the Lower Arroyo, the
AIDS Memorial Grove at the foot of California Boulevard.
Tanya
Patsaouras and Derek K. Schubert, the landscape architecture
students, undertook their review for a class last Fall.
They reviewed the planning documents for the BFI project,
interviewed the project designers, and undertook field
observations to examine the results of the restoration project
four years after completion.
Their report, “Post-Project
Appraisal of Low-Flow Channel and Revegetation, Arroyo Seco,
Pasadena, California”, now available online, summarizes their
findings: “This project represents a missed opportunity
to restore the geomorphic and hydrologic processes that make
stream restoration sustainable in the long term. The steep
canyon walls already provide a contained area where floods could
occur without damage to houses. Removing the concrete channel
altogether would be the best way to restore the Arroyo Seco and
it is still feasible, but the project could have taken other
measures to improve the reach.”
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The
BFI project was planned in the early 90s and completed in 1997,
as an environmental mitigation project to compensate for the
expansion of Sunshine Canyon Landfill in the San Fernando
Valley.
The project has dramatically increased the amount of
vegetation in the area, but requires considerable maintenance to
sustain. Because of the impermeable liner that lies beneath the
low-flow streams and the lack of variable flows characteristic
of a natural stream, Patsaouras and Schubert state the
restoration program does not sustain the full range of processes
of a stream ecosystem. “The
Lower Arroyo Park project may be a good start toward a goal of
connecting habitat along the entire Arroyo Seco,” the
landscape architecture students conclude, “but so far it is
an artificial island in a sea of urbanism.”
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