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The term is used to describe an event that has a 1-in-100 chance of happening in any given year. When you do the math, there is a 65% chance that there will be a “100-year flood” in 100 years. Likewise, a “50-year flood” has a 2% chance of happening in any given year, and there’s a 4% chance of a “25-year flood” every year. Keep in mind that calculations are based on less than a hundred years of flood records. The reason you often hear the “100-year flood” mentioned is that it’s a yardstick to measure inundation by flooding. Our Project is being constructed to protect the community from this 100-year event, which would be a larger flood than the 2005 event, larger than 1995, even larger than 1986.
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Fortunately, this Project provides both. The primary purpose of the Project is to protect the community from flooding, but there are also substantial quality of life benefits to come, like Oxbow Commons Park, the six-mile river trail and improved access to the River. Project funds are spent as outlined by the Community Coalition that guided the Project in the late 1990s and by the legal requirements of Measure A that was passed by two-thirds of local voters in 1998.
There are number of specific sites within the Napa project area that will not be afforded protection. For example, areas south of Imola Avenue; most of the east side of the River north of Lincoln Avenue; Compadres Restaurant and Napa Small Animal Hospital just south of Lincoln on the west bank; and the Napa Sea Scout building and Napa Yacht Club building. In order to provide protection for these sites, in some cases it would have been necessary to remove the structures in question, and in other cases the impacts on environmentally sensitive areas was deemed unacceptable in the design phase.
It is difficult to provide a reliable measurement, but most people with some local flood experience believe the damage from this flood was less that it would have been if the wetlands, flood terraces and bridge replacements had not been completed.
No. For emergency information on availability and proper use of sandbags, go to the City of Napa Emergency Information page.
Find information about this on our How the Flood Project Protects the Community from Flooding page.
The money comes from a variety of sources. The local share is generated by the Measure A half-cent sales tax that was passed by Napa County voters in March 1998. The Federal share comes by way of allocations to the U.S. Army Corps of Engineers. These allocations are made annually in the Federal budget process. Additional revenue for the Project has taken the form of grants from the Federal Emergency Management Agency (FEMA) and the Coastal Conservancy, and from the California Flood Control Subventions fund.
No, it’s not true. The money spent so far has gone to acquire property, build four bridges, relocate utilities, restore 600 acres of wetlands, construct about 2 miles of flood plain and marsh plain terrace, and build the Hatt to First Floodwall and Promenade. Unfortunately, the Project cannot function fully until it is all complete.
Money drives construction forward, and there are many reasons why the Project has not received as much money from the federal government as needed to maintain the intended pace of work. The original plan was to have the work done as early as 2005 or 2006. While the local share of funding that comes from the half-cent sales tax has outperformed revenue projections, the Project has not received all the needed funding from the state and federal governments. When the money is delayed, the work is delayed. One of the primary reasons for lower than expected levels of funding is the terrorist attacks of 9/11/01 and the resulting increases in domestic security and military spending. In addition, the Napa Project competes each year with other Corps of Engineers projects, many of which are much larger in scope.
No, there has not been a 100-year flood recorded since people began keeping these statistics (although the 1986 flood was larger than FEMA’s 1979 estimate of a “100-year flood. Later study of flood records from 1940 to 1988 led FEMA to estimate that the 1986 flood was a “50-year flood.”) That means no one living today has seen a real 100-year flood on the Napa River.
No. The Napa River-Napa Creek Flood Protection Project is designed to alleviate flooding up to the level of the “100-year event” in specific areas along the River from Trancas Street to Imola Avenue. Parts of the Project have been constructed downstream of Imola Avenue but “100-year event” protection is not provided in those locations, such as Napa Valley College and Kennedy Park. The Project will also alleviate flooding on Napa Creek east of Jefferson. Flooding problems on other tributaries, such as Dry Creek, Milliken Creek, Tulocay Creek and others will not be affected by the Project. Flooding caused by overwhelmed storm drains will not be solved by the Project. These creek flood zones and interior drainage problem areas are localized and require separate solutions.
All flood protection projects are constructed starting at the downstream end and working upstream. If you change water flows upstream first, flooding will be made worse for people downstream. However, after the 12-31-05 flood, the Corps of Engineers has said they believe the improvements on the Napa River that have been built downstream of Third Street make it feasible for improvements on Napa Creek to proceed at any time. Due to the federal Stimulus funding in 2009, the work on Napa Creek is expected to being in 2010.
No, early estimates say this was a “25 to 50-year flood” event. It appears to have been a bigger flood than 1995 and 1997 but not as big as 1986.
These communities have their own share of Measure A funds to use for their own projects. Yountville has already built a flood wall that protected their mobile home parks in the recent flood. St. Helena has a plan in the design stage, and the other communities are using their funds as they see fit.
In the City of Napa where the Napa river-Napa Creek Flood Project is being built. the most flood-prone areas are shown on the map that can be seen on the City of Napa website in the Emergency Information section.
Tides do not have any impact on the water level in the City of Napa when the river is flooding. A chart of river levels when there is no flood shows the river rising and falling with the tidal cycle. Charts during a flood show no rise and fall, regardless of the height of the tide. During a flood it’s rainfall and runoff that determines the river level, not the tide. The force of floodwaters is greater than the force of the tide. It is true that high tides can cause flooding in certain areas closer to the Bay. That type of flooding sometimes occurs when there is no rainfall and has no connection to the creek and river flooding we see in most of Napa County.
Extensive trails are planned for both sides of the River. To find more information about these trails visit our Future Public Access to the River page.
Current schedules show final completion in 2015 if all needed funding is received on schedule.
Get details at the Napa County Emergency Operations Center page.
The Napa River-Napa Creek Flood Protection Project was only about 40% complete at the time of the 12-31-05 event. Flood protection will be achieved using an integrated system that includes wetlands, terraces, bridge replacements, a bypass channel, floodwalls and levees. All of the components must be constructed before the Project will work as designed.