The City of Napa is at risk of both slow-rise and flash floods. Typical floods on the Napa River are slow-rise floods. This type of flood is preceded by a warning time lasting from hours to days. There is a sequence of events—rainfall producing heavy runoff, flood watches and river advisories issued— that can be tracked over time.
Creeks and streams may produce slow-rise or flash floods. Flash floods may occur after an extremely short warning time, or with no warning time at all in some situations.
Areas at risk of flooding in Napa are generally from Trancas Street in the north to Imola Avenue in the south, Coombs Street to the west and Silverado Trail to the east. However, it’s important to understand that flooding can and does occur outside these general boundaries. Any creek, stream, or drainage system can be overwhelmed during heavy rains.
The map shown here is a rough guide to areas of flood risk. For detailed information to assist your emergency preparedness, flood maps and flood protection references are available at the Napa City-County Library at 580 Coombs Street; or visit the City of Napa Public Works Department at 1600 First Street to see if you are in a mapped floodplain. If so, Public Works staff can provide more information on past flood problems in the area. If requested, Public Works staff will visit property to review its flood problem and explain ways to stop flooding or prevent flood damage. These services are free.
The map below shows the City’s four defined areas of greatest flood risk. These are labeled as phases 1, 2, 3 and 4. (The phase 1 area, which is primarily at risk from Napa Creek flooding, is known to be inundated independent of flooding from the River, or as a precursor to a larger River flood, or both.) Experience has shown that a major slow rise flood on the Napa River will follow a fairly predictable pattern. Understanding this pattern helps the City anticipate where flooding will develop.