Napa River Historic Bridge Fish Passage Retrofit

Location: Napa County, California
Clients and Partners: Napa County, Napa Resource Conservation District, Winzler & Kelly

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Michael Love & Associates (MLA) were the fish passage engineers providing design services for retrofit of an historic 1913 stone-masonry bridge across the Napa River. The perched concrete apron installed under the bridge to protect if from the incising river impeded migration of anadromous salmonids to the upper reach of the Napa River.

MLA conducted the preliminary design effort and a geomorphic assessment of the adjoining river reaches to estimate the response of the Napa River to proposed apron modifications. Concurrently, a hydraulic analysis of potential modifications was conducted to determine feasible fish passage solutions that meet agency fish passage criteria as well as conformance to a FEMA Conditional Letter of Map Revision (CLOMR).

MLA developed a range of feasible design options that were presented to the stakeholders. The selected alternative was developed to final design, which included plans, specifications, and an engineer’s opinion of probable cost.

The engineering and environmental design team worked together to design a project that meets fish passage criteria, retains the character of the historic Zinfandel Lane Bridge and protects aquatic resources near the project.

The new structure was completed in 2011. Since then, fish monitoring has observed fish moving freely through the retrofitted crossing without delay. In total, the project improves salmonid access to more than 60 miles of upstream habitat.