Napa River Flood Protection Project (1998-2012)
Landscape Performance Benefits
- Expanded capacity of the river channel through the City of Napa by 13,000 cfs to 43,000 cfs to accommodate the 100-year flood.
- Restored 75% of the historic wetlands north of Butler Bridge (over 700 acres), which has resulted in 71 species of migratory and resident birds observed on-site, including the Peregrine Falcon and Burrowing Owl.
- Engages an estimated 575 volunteers annually in restoration and education projects at the South Wetlands Restoration Area.
- Integrated 2.5 miles of new, paved trail along the east bank of the Napa River into the developing San Francisco Bay Trail network, which will eventually create a continuous, 500-mile recreational corridor around the Bay.
- Galvanized more than 30 governmental and community organizations (ranging from the Chamber of Commerce, Napa Valley Economic Development Corporation, Farm Bureau, and the Conference and Visitors Bureau to the Sierra Club, Friends of the River, and Land Trust, among others) and 400 individuals to articulate their environmental values, creating the “Living River Principles” that guided the development of the flood protection plan.
- Created an estimated 1,373 temporary construction jobs and 1,248 permanent retail and administrative jobs at properties developed in expectation of 100 year flood protection along the Napa River.
At a Glance
Former Land Use
Veterans Memorial Park, Main Street
Napa, California 94559
Since 1862, 22 major floods have struck the Napa Valley, exacting heavy tolls both in terms of lives and property. In the 1990s, an unprecedented coalition of more than 30 governmental and community organizations and 400 individuals worked together to develop a set of “Living River Principles” to guide the development of a regional flood protection plan. Based on these guidelines, the federally authorized Napa River Flood Protection Project implements a strategy that combines ecology and engineering to protect the City of Napa while restoring the ecological health of the Napa River. The project, which is now 70% complete, included plans to breach dikes and levees, widen the river channel in downtown Napa, remove contaminated soils, rebuild bridges to allow for higher floodwaters, buy out residences and businesses in areas that regularly flood, restore tidal action to the southern portion of the river, and construct the Oxbow Bypass, a soon-to-be excavated channel and park area that will allow water to move safely through downtown during high flows. This revolutionary, ecologically-oriented approach has helped the City of Napa reinvent itself and represents the most systematic effort in the country to take a “Living River” approach to flood control.
- The Napa River Flood Control Project restored 1,011 acres of floodplain, wetlands, and riparian habitats through terracing, the breaching of old dikes and levees along 3.5 miles of river, and the installation of over 1,700 feet of floodwalls in the downtown Napa reach. These improvements met flood control needs while adhering to the community’s “Living River Principles.”
- To date, breaching of dikes along the South Wetland Opportunity Area has reconnected the river to a significant portion of its natural floodplain and led to the restoration of 289 acres of brackish marsh, 112 acres of seasonal wetland, 324 acres of mudflat, and 28 acres of tidal channel.
- Restoration of 84 acres of woodland habitat, 165 acres of native and non-native grasslands, and maintenance of 7 acres of riparian forest and 2 acres of shaded riverine habitat have increased habitat diversity along the riparian corridor.
- To increase the capacity of the river channel within the City of Napa to contain a 100-year flood, 1,700 ft of floodwall were constructed along the channel through the downtown and nearly 120 acres of terracing were excavated and hydro-seeded or drill seeded with native grasses and trees.
- Five road bridges (including 3rd Street, 1st Street, Maxwell, Soscol) and two railroad bridges were replaced with spans that allow the passage of 100-year floodwaters underneath. Three pedestrian bridges were installed to provide a continuous trail network along the river.
- Veteran’s Memorial Park, a 0.5-acre, terraced park on the downtown Napa Riverwalk Promenade, was renovated in 2008 and integrated into the Flood Protection Project’s floodwall system. The park is designed to flood during significant rain events and provide space for musical performances and other gatherings throughout the rest of the year.
- Along the western bank of the river, a 1.25-mile paved trail links Napa’s Lincoln Avenue to Trancas Crossing Park. A planned 3-mile trail extending from Lincoln Ave south to 3rd St will connect to 2.5 miles of trail on the southern end of the project, ultimately providing a continuous link from Trancas Crossing Park to Kennedy Park at the city’s southern limits.
- Future construction of the Oxbow Bypass will give floodwaters an alternate flow path at one of the most vulnerable locations in the city, while providing recreational opportunities in the form of a park and canoe launch. The bypass will be an excavated dry flood bed designed to carry 50% of 100-year floodwaters under the newly renovated Soscol Avenue Bridge to the mouth of Napa Creek, thereby removing stress from the oxbow itself. The bypass will also connect the Trancas portion of Napa River trail to the Napa Riverwalk Promenade on the west bank and the Kennedy Park trail (via the 3rd Street Bridge) on the east bank.
- Construction of final project phases will result in 100-year flood protection for the majority of the city. These include construction of the Oxbow Bypass, additional floodwalls from Tulocay Creek to 3rd Street and north of the Oxbow, two pump stations, two detention basins, and connecting trails. Pending receipt of funding the Napa River Flood Protection Project is scheduled for completion in 2015.
Such a large-scale, multi-year, multi-stakeholder project presents a wide variety of challenges for those involved, from known issues at the planning level to unforeseen complications at the site scale. Two examples of site-specific challenges the project team faced are extensive soil contamination along the Napa River at Oil Company Road and implementing plans on private property at the historic Napa Mill. At the Oil Company Road industrial site, petroleum had leached through the soil over many years and threatened to pollute the river. Furthermore, terracing of the area was needed to expand the channel’s flood capacity. Using phytoremediation to treat the contamination would take 25 years, which far exceeded the project timeline. Sheet-piling the area, on the other hand, would isolate rather than address the issue. At the historic Napa Mill, project plans called for the acquisition of 20 feet of private property to increase flood capacity of the channel and extend the river trail through the mill-turned-hotel’s parking lot. The landowner wanted project planners to seek an alternative solution.
To govern treatment of the soils at the Oil Company Road industrial site, project planners relied on the “Living River Principles” developed by the community coalition. These principles dictated that the contaminated soil be cleaned up to prevent further pollution of the river. Excavation and removal was deemed the most efficient method of cleanup since terracing of the area was needed to expand the channel’s flood capacity. This solution ensured that the project stayed on schedule and met regulatory mandates for cleanup. At the historic Napa Mill site, project planners worked closely with the Napa River Inn owner and an engineer to create a cantilevered trail with a widened river channel underneath. This increased the river’s capacity and allowed the trail to continue along the river while preserving the Napa River Inn property line.
- Removal of 236,000 cubic yards of contaminated soil from the Oil Company Road area cost approximately $20 million while using sheet piling to isolate the contaminated area would have cost approximately $10 million. While the cost of soil removal was higher in terms of dollars, the decision to remove the contaminants was based on a desire to remain true to the “Living River Principles” and the ecological benefits that would stem from such a removal.
- The Napa County Flood Control and Water Conservation District estimates that after completion of all project phases within the City of Napa, the total project cost will reach $550 million. Prior to the start of the project, floods resulted in $26 million in property damage annually throughout Napa County. Upon completion, this project will significantly reduce, if not eliminate, flood damage in city and downstream communities. Based on these figures, the project will likely pay for itself in just over 21 years.
- Community rejection of previous attempts by the U.S. Army Corps of Engineers to develop a flood control plan for the Napa River put pressure on the Corps to come up with a creative solution. With the help and guidance of MIG and the Napa County Flood Control and Water Conservation District, over 30 community and governmental organizations, along with 400 individuals came together at the start of the Napa River Flood Control Project in the 1990s to develop a vision for the Napa River. The landscape architect facilitated nearly two dozen meetings with these groups over two years, with the entities eventually uniting to become the Community Coalition for a Napa River Flood Management Plan, or the Community Coalition. Their vision coalesced into the “Living River Principles,” which have been used to guide project design and implementation. This process resulted in broad community support, including the 1998 passage of a countywide, 20-year, 1/2-cent sales tax that will provide over $250 million for implementation of the flood control plan over its 20 year duration.
- Community involvement has remained a key aspect of the project even after the visioning process was complete. Today, the Army Corps of Engineers manages the implementation process, with guidance from the Napa County Flood and Water Conservation District. In many regards, the District acts as the project champion, negotiating land ownership challenges and seeking out project funding, all while continuing to follow the guidelines developed by the Community Coalition. The success of the coalition also led to the development of a Technical Advisory Panel, which reviews project phases to ensure consistency with the “Living River Principles” and the Community Coalition’s goals.
- In the first years of the project, separate contracts for the grading of terraces and the re-vegetation of those terraces resulted erosion from from delays in the planting of trees and grasses. Future phases integrated planting into terracing contracts to ensure immediate vegetation of banks and a reduction in bank erosion.
- The project was initially divided into four phases to be completed by the Army Corps of Engineers under four contracts based on location. Changing federal funding and rules accompanying federal allocations, as well as a pressing need to handle contamination issues before beginning downstream improvements, resulted in the need to develop flexibility in the phases and the timing of implementation. Project phases were divided up into smaller components in order to better utilize funds as they were made available and address contamination concerns in a timely fashion.
- As a result of the Napa River Flood Protection Project, the City of Napa was inspired to take underutilized remnant lands along the waterfront – lands that had little real estate value because of their size and their location within the floodplain – and convert them into engaging public open spaces. Through the Community Redevelopment Agency, the city funded the revitalization of the Coombs Street Plaza, the Opera House Plaza, Dwight Murray Plaza, and the 5th Sreet Plaza.
Client: Napa County Flood Control and Water Conservation District
Architect and Engineer: US Army Corps of Engineers
Landscape Architect, Planning Coordinator, and Community Coalition Facilitator: MIG
River Experts: Phil Whilliams & Associates; Woodey Trihey (hydrologist); Dr. Luna Leopold and Professor G. Mathias Kondolf, U.C. Berkeley; Coalition to Restore Urban Rivers
Community Coalition: United Napa Valley Associates; American Center for Wine, Food and Arts; Friends of the Napa River; Homeowners: GSMOL and 1st Street Neighbors; Napa County Landmarks; Napa Valley Vintners Association; Sierra Club; Flood Plain Business Coalition; Up Valley Chambers of Commerce; Napa County Land Trust; Napa Chamber of Commerce; Napa-Solano Building Trades Council; Napa Valley Fisherman’s Associations; Napa Valley Conference and Visitors Bureau; Napa Downtown Merchants; Napa Valley Expo; Napa County Farm Bureau; Napa Valley Grape Growers Association; Napa County Resource Conservation District; Suscol Council; California Department of Fish and Game; Napa Valley Economic Development Corp.; Agricultural Commission; Bay Area Water Quality Control Board; California Coastal Conservancy; Environmental Protection Agency
Design Review and Feasibility Committee: Bill Byland (architect); Liesel Eisele (landscape architect); Juliana Inman (architect); Farnum Kerr (AICP); Mike McKaig (project manager); Chuck Shinnamon (engineer); Barbara Stafford (LA); Phil Vandertoolen (LA); John Whitridge (AICP); Friends of the Napa River; Napa Valley Economic Development Corp.
Role of the Landscape Architect
The landscape architect worked with the Army Corps of Engineers, Napa County and the affected city governments to develop consensus about how to restore the ecological health of the Napa River and protect the interests of the Napa Valley. MIG developed the strategy and process for the Community Coalition, which consisted of a range of public and private stakeholders. MIG and the Napa County Board of Supervisors also led the consensus-building and community outreach process that proposed removing dikes and levees to restore the river’s natural meandering path.
Case Study Prepared By
Research Fellow: G Mathias Kondolf, Professor and Chair of Landscape Architecture & Environmental Planning, University of California, Berkeley
Research Assistant: Shanna Leigh Atherton, MLA-EP Candidate, UC Berkeley
Firm Liaison: Daniel Iacofano, MIG
Kondolf, G. Mathias, and Shanna Leigh Atherton. “Napa River Flood Protection Project (1998-2012).” Landscape Performance Series. Landscape Architecture Foundation, 2013. https://doi.org/10.31353/cs0520