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.

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