A new Post "Bridge Culvert Removal Project at Pacifica" was written on the October 26, 2009 at 2:31 am on "Precasted Concrete".
The City of Pacifica intends to eliminate the existing box culvert at
the Adobe Bridge and replace it with a free standing bridge. The
Project, which is located along the mainstem of San Pedro Creek, will
improve access to historic steelhead spawning and rearing habitat;
improve conditions for movement by juveniles; and address local
flooding issues. The project consists of 1] removal of fish passage
obstacle at the Adobe Bridge, 2] placement of rock weirs to facilitate
fish passage, and 3] qualitative effectiveness monitoring for the
project.
*Purpose:*
The need for the project was determined during a study of fish passage
conducted by Hagar and Associates (2001). They conducted a Level IV
habitat classification (Flosi et al. 1998) of approximately 10% of the
stream, made visual streamside observations of fish, and evaluated
potential obstacles to passage. This report was funded by a grant from
the Department of Fish and Game to the San Pedro Creek Watershed
Coalition and City of Pacifica, in order to obtain an up to date
assessment of the creek. Hagar found that the mainstem and the Middle
Fork contained the greatest amount of suitable habitat for steelhead.
Hagar thought that four migration obstacles in the main-stem and one
in the Middle Fork had the potential to limit movement of adults and
juveniles, to varying degrees. The most significant problem was at
Capistrano Drive where the box culvert had created a fish migration
barrier, and down-cutting by San Pedro Creek created a 12-foot jump
from a downstream pool into a dysfunctional fish ladder. In fall 2005,
the City restored a 1300 linear foot section immediately below the
Capistrano Bridge. The bridge at Linda Mar Boulevard is a long, wide
culvert with a flat bottom, which slopes at greater than 3%. This may
provide an obstacle at high flows and at low flows. The bridge at
Adobe Road may also pose obstacles to migration of at least some life
stages. A small, perched culvert on the Middle Fork of the stream,
just upstream of its confluence with the South Fork in San Pedro
Valley County Park, may provide an obstacle for migration of
juveniles.
In additon to fish passage, the project also addresses the need for
flood control. The Adobe Box Culvert is 8 foot wide by 8 foot high.
When creek flows exceed 500 CFS, the culvert is subjected to immense
pressure. Back flooding occurs when the CFS reaches approximately 700
to 1200 CFS. When the flows exceed culvert capacity, the creek over
tops it banks and floods approximately 15 to 20 acres of surrounding
neighborhood in the north south direction, before making its way back
to the creek. In 1982, a 13-year flood washed out the entire Adobe
Bridge structure leaving the culvert in the stream channel. Repairs
were subsequently made to the bridge structure however, the existing
culvert was left in place. The area downstream of the Adobe Bridge can
handle a 100-year flood.
Read more from the original sourcehere:
source
Nice Info
http://www.precastedconcrete.com/box-culvert/bridge-culvert-removal-project-at-pacifica
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