Elevation Certificates in Sonoma, CA

Sonoma Creek is one of the three streams Sonoma County's hazard mitigation plan names as causing the most frequent damaging floods in the county, along with the Russian River and the Petaluma River. The plan describes Sonoma Creek as overtopping its banks even in relatively small winter storms, with short floods that can still last several days and hit the low land along the creek hardest. During the 2005 to 2006 New Year's storms, the plan records significant flooding on Sonoma Creek as well as the Petaluma River. Sonoma Water's flood protection Zone 3A covers the Valley of the Moon watershed, the upper Sonoma Creek drainage, which funds channel maintenance and drainage planning.

Inside the city, Nathanson Creek is the waterway the City is watching most closely. In October 2026 the City of Sonoma, Sonoma Water, and the Sonoma Ecology Center asked owners with Nathanson Creek on their property to report downed trees and debris that could restrict flow in heavy rain. The City's Planning documents include a Flood Hazard Elevation Certificate, so expect a certificate to come up if you build or substantially improve in a mapped flood zone. Buyers of older homes near the creeks often meet the same question from their lender. The flood elevation certificate gives a measured answer instead of a guess from a map line.

For a Sonoma elevation certificate we tie to a benchmark in NAVD88, the datum of the county's current Flood Insurance Study. We measure lowest and highest adjacent grades, lowest floor, garage and crawlspace levels, flood openings, and the heights of mechanical equipment, then photograph the building and sign the FEMA form. If your house or barn sits on ground at or above the Base Flood Elevation but the map shows it inside the zone, we can prepare letter of map amendment data and file through eLOMA when eligible. Sonoma is a scheduled trip from our Lotus base. See our elevation certificate service, the Petaluma and Santa Rosa pages, or surveying in Sonoma.