Let It Flow: Lessons on innovative flood management policies from Napa

By Calvin Meister, Planning Intern at M-Group

Nearly 20 years ago, a group of environmental leaders and ecologically-conscious business owners began meeting in the County of Napa to discuss how to alleviate a natural disaster common in the valley and expected to worsen in the face of climate change: flooding. Since then, Napa residents have reaped the benefits of innovative river management.

Like many areas troubled with untamable rivers, the Napa Valley has had to choose between preserving and sacrificing its river’s natural course in order to protect adjacent development from floods. Tired of previous ineffective mitigation measures, a coalition of local water experts, engineers, environmentalists, business owners, and community leaders produced and passed the “Napa County Flood Protection and Watershed Improvement Expenditure Plan”. The project is an ambitious and innovative strategy that consolidates nature preservation and infrastructure development. It incorporates “living river” principles to create flood control techniques that restore the river’s natural flood-management capacity.

FIGURE 1 | From  http-//bloximages.chicago2.vip.townnews.com/napavall eyregister.com/content/tncms/assets/v3/editorial/b /44/b448d376-d2bc-11e1-9dac-001a4bcf887a/500cbcdc487d8.preview-620

FIGURE 1 | From http-//bloximages.chicago2.vip.townnews.com/napavall eyregister.com/content/tncms/assets/v3/editorial/b /44/b448d376-d2bc-11e1-9dac-001a4bcf887a/500cbcdc487d8.preview-620

County of Napa residents passed the plan in 1998 under Measure A, and have since witnessed massive changes to their downtown infrastructure (Figure 1), already enjoying many of the projects’ benefits. Over 1,200 acres of wetlands and 1,800 linear feet of creek space are now restored. The river bank is teeming with native plant life, and the many new walkways now provide an enjoyable public amenity. Home and business owners can rest assured their properties are more protected than ever before, and other flood-prone municipalities have insight into an efficient flood-management system they may adapt to serve their needs. Many of these communities already adopted or are working on producing similar initiatives.

Humans have been altering the Napa River’s 55-mile course, from just south of Mt. St. Helena to the San Pablo Bay, for many years. Evidence suggests that Native Americans along the river shaped its course for millennia, but it wasn’t until the arrival of European settlers and their livestock that the watershed began to transform into something far from its natural state. Fire suppression, swamp drainage, stream straightening, excessive dredging, and agricultural development gradually eliminated the many side channels and natural floodplains responsible for the Napa Valley’s famously rich soil. This unrelenting channelization created massive flood zones that now shadow significant portions of every city along the Napa River, making each vulnerable to surges of water that have nowhere else to go.

FIGURE 2 | From http-//napavalleyregister.com/app/images/site/article/1 10220flood/110220floodmap

FIGURE 2 | From http-//napavalleyregister.com/app/images/site/article/1 10220flood/110220floodmap

More than twenty-eight major flood events have been recorded along the Napa River since 1862, representing a significant loss of life and economic damages totaling in the hundreds of millions of dollars. Following what is arguably the County of Napa’s most severe flood of 1986 (Figure 2), the Army Corps of Engineers spent nine years devising a permanent solution to the issue that featured the same techniques responsible for damaging the river’s systems in the first place. The plan faced significant community opposition since its application would further reduce recreational opportunities, endanger more species, and hinder economic development potential. 

Instead, county voters approved Measure A with a 68% majority.  Contrasting the recommendations by the Corps of Engineers, the Napa County Flood Protection and Watershed Improvement Authority drafted a tax ordinance to fund an Expenditure Plan that emphasized the need for rivers to maintain their historical flexibility, inherent floodplains, native habitat systems, and other natural processes. The strategy also includes innovative plans for bridge replacement, pump station construction, and bypass channel creation in order to reduce the frequency of flood events. The Napa County Flood Protection and Watershed Improvement Authority sets forth the plan’s intent as follows:

“The ultimate goal of the Plan is to provide flood protection, save lives, protect property, restore the Napa River, Napa Creek, and other tributaries, maintain Napa County’s economic vitality, and enhance riparian environments.”

Funding mechanisms for the Plan include a 20-year 0.5% sales tax ordinance designed to finance the local portion of each project, as well as federal and state grants. As of 2014, the County generated nearly $198 million in sales tax to fund various protection and improvement projects, which is approximately $60 million more than initially estimated. The Army Corps of Engineers already provided over $211 million from federal funds. Project opponents have sparked some controversy against spending taxpayers’ money on ecological rehabilitation projects, but the numerous hydrological, ecological, and economic benefits are increasingly apparent.

The City of Napa’s award winning Oxbow Dry Bypass (Figure 2), considered the heart of the flood plan, is also nearing completion. The Napa River’s oxbow required significant attention since it lacked the capacity to bear large water flows, often resulting in the costly flooding of the Soscol Gateway area. An oxbow is a naturally occurring “U” shaped curve found throughout the course of meandering rivers. Overtime, the river flow accentuates these curves, leaving a very narrow strip of land between bends. During a flood, rising waters cut across the land in between the bends and cause large amounts of water to back up further upstream. Rather than straightening the river and eliminating the oxbow completely, planners and engineers took advantage of the river’s tendency to cut across narrow land gaps and created a bypass capable of conveying around 50% of a flood’s total flow, effectively alleviating the congestion experienced upstream.

FIGURE 3

FIGURE 3

A prime example of flood control infrastructure and recreational opportunities built as one, the Oxbow Dry Bypass will soon offer public access to a beautiful new open space in the heart of the city. Public walkways and trails will wander through the area (Figure 4) and link the Downtown and Oxbow Districts, allowing visitors access to park facilities, grassy picnic areas, activity centers, an amphitheater and a kayak launch/recovery area.

Many other programs have been successfully completed as part of the Expenditure Plan as well. The Napa Creek Project restored a significant portion of the riparian ecology surrounding the oxbow (Figure 5), and removed invasive plant species that used to block channels. The revegetation portion of the plan reintroduced 70 native trees, over 2,000 endemic understory bushes and shrubs, nearly 17,000 native grasses, and 2.85 acres of marsh habitat. The plan placed ‘large woody debris’, mostly in the form of recycled redwood root systems, along the banks’ edge to simultaneously combat erosion and provide in-stream habitat for migrating steelhead (Figure 5). The end result is an attractive area for residents and tourists alike that brings in more revenue for local businesses in the valley.

Under the Napa County Flood Control and Water Conservation District’s direction, the Napa River and Tributary Maintenance Program installed a countywide early-warning system for flooding, cleared and maintained 13 miles of channels within district easements, remedied “problem areas” within the river and its tributaries, dredged parts of the river to ease navigation, and funded a significant number of bank stabilization and repair opportunities. Additional projects have restored as much as 135 acres of floodplains from lands previously thought to be stagnant or infertile, particularly by reclaiming the salt flats located in the southern tips of the watershed for their original purpose. These projects not only create habitat for multiple endemic species, but also provide Napa Valley residents with unique recreational opportunities. Each one of them includes on-going maintenance funds to ensure long-term success.  

FIGURE 4 | Paths wandering the oxbow. Photo by Calvin Meister.

FIGURE 4 | Paths wandering the oxbow. Photo by Calvin Meister.

FIGURE 5 | Teeming native plant life, woody debris, and in-stream habitat for steelhead. Photo by Calvin Meister.

FIGURE 5 | Teeming native plant life, woody debris, and in-stream habitat for steelhead. Photo by Calvin Meister.

A major goal of the larger Napa Valley flood control project is to protect the City of Napa from the 100-year flood, a devastating event with an occurrence probability of once every 100 years, or 1% each year. Stream volume gauges currently gather data to determine what a flood event with a 1% chance of occurring each year may look like. Engineers often use these models as a benchmark to design flood protection projects. Napa’s Watershed and Flood Control Operations Manager, Rick Thomasser, assures the project has not only met this objective, but also accounts for increased flood risks over the next century due to sea level rise.

Determining the success of local ecosystem restoration projects can be a challenging task. A good way to assess a river’s health, and therefore the effectiveness of restoration projects, is to track certain “indicator species” that inhabit it. Steelhead smolt, or steelhead juveniles mature enough to migrate to the sea for the first time, are such a species for the Napa River. Jonathan Koehler from the Napa Resource Conservation District has monitored this particular fish population for years. In his words, “the more smolt that are produced, the bigger they are, the more healthy the conditions of the watershed where they grew up.”

Improvements stipulated in the flood plan that can spur the increase in steelhead smolt include removing levees blocking migratory spawning paths, monitoring silt from erosion and runoff that bury or destroy eggs, and reintroducing acres of wetlands that contribute to healthy environments for fish. Reproductive rates are still far from what they once were, though this isn’t necessarily indicative of the project’s effects quite yet. In times of severe drought, fish monitoring becomes notoriously difficult due to an overall decrease in the effectiveness of capture techniques. In addition to monitoring difficulties as a result of dwindling funds and the general infancy of these projects, it is currently difficult to properly track fish populations. Mr. Koehler, however, is confident that steelhead communities have a significantly better chance at making a comeback through the progress the county is making.

As healthy ecosystems become more and more rare in densely populated areas, their contributions to urban communities become increasingly evident. Napa community leaders found a sensible and financially feasible way to combine the long term goals for increased recreation opportunities, flood protection, and ecosystem health into one efficient plan. The Flood Protection and Watershed Improvement Expenditure Plan’s success shows ecosystem rehabilitation projects are stabilizing infrastructure investments for Bay Area residents rather than empty economic hurdles. Flood control projects can and need to be much more than just building levees and dredging rivers. Not only do these projects protect business and property owners, they also offer the opportunity to rehabilitate ecosystems and increase the number of recreation opportunities. Napa’s flood plan is saving the city money from future water quality problems, species endangerment, and river system maintenance. Preventative plans are understandably difficult to conceive and find funding for, especially in an uncertain economy, but action now will prove to be much less expensive than reaction in the future. 

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