Sea Level Rise and Flooding Maps
Project Summary
The City of Petaluma is currently updating its General Plan, a plan that will guide the future development and management of the City for the next 20 years. As part of this work, the City is looking at new data and technology to prepare for future flood risks in the community.
To gain the best possible understanding of flooding in Petaluma over the next 20 years and out to the end of the century, the City engaged experts to develop state-of-the-art computer models that closely examine flood hazards. The models examine several factors including terrain, anticipated storm and rainfall patterns, and water coming up the Petaluma River due to sea levels, tides, and storm surges.
Another major consideration when thinking about flooding over time is climate change will impact flooding. Climate change will bring higher seas, extreme weather events, and higher San Francisco Bay waters, along with potential changes in rain intensity and frequency. Because the Petaluma River is tidal, river levels are also influenced by sea level rise (SLR). There is guidance from the State and general agreement in the scientific community on probability ranges of sea level rise we can anticipate over time. The modeling team used these ranges to help predict potential future flooding.
These projections have varying levels of likelihood. While the flood model shows that the mid-century condition will be similar to the current 100-year floodplain, it’s important to consider scenarios for long term planning.
Maps
The new flood model shows that the mid-century (around 2050) flood hazard condition will be similar to existing conditions. To inform its General Plan Update, the City has developed four scenarios that reflect low and very low probability scenarios that show a potentially significant amount of sea level rise. These scenarios include maps that show Petaluma’s flooding and inundation hazards in the middle of the century (around 2050) and towards the end of the century (around 2100). There are two maps for each time period, including a projected 100-year flooding hazard map that also includes storm surge hazards, and a map of projected King Tide flood hazards. The scenarios also take into account climate change, which will increase the average sea level. The scenarios developed are:
Mid-Century Flood Model for Rain and Storm Surge
This model shows a projected rain with sea level rise of 1.9 feet, including storm surge hazards . This sea level rise has a 0.5% chance of happening and is not expected to occur.
Mid-Century Flood Model for King Tides
King Tides are exceptionally high tides that typically occur several times per year during a new or full moon and when the earth is closest to the moon. This model shows king tides with sea level rise of 1.9 feet.
End-of-Century Flood Model for Rain and Storm Surge
Projected Rain with Sea Level Rise of 3.4 feet, including rainfall flooding and storm surge. There is a low probability that this amount of sea level rise will occur.
End-of-Century Flood Model for King Tides
This model shows the flooding impacts from king tides at the end of the century at 3.4 feet of sea level rise. There is a low probability that this amount of sea level rise will occur.
End-of-Century Flood Model for Rain and Storm Surge
Projected Rain with Sea Level Rise of 6.9 feet, including rainfall flooding and storm surge. There is a very low probability that this amount of sea level rise will occur and will be used only for planning for critical infrastructure projects.
End-of-Century Flood Model for King Tides
This model shows the flooding impacts from king tides at the end of the century at 6.9 feet of sea level rise. There is a very low probability that this amount of sea level rise will occur and will be used only for planning for critical infrastructure projects.
100-YEAR (1%) FLOOD MAP
A one-hundred-year flood is a flood event that has a 1% probability of occurring or being exceeded in any given year. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%.
500-YEAR (0.2%) FLOOD MAP
A five-hundred-year flood is a flood event that have a 0.2% probability of occurring in any given year. A 500-year flood event happening one year does not change the likelihood of it happening the next year, or the next.