Todd Creek Flood Study

In 2015 FEMA produced a flood insurance study for the Todd Creek watershed.  This study was incomplete and only studied half of the watershed.  The County appealed the study.  In 2020 FEMA conducted a second flood study for the second half of the watershed.  Each study was conducted independently, used a different methodology, and was joined together.  The County appealed a second time, but missed the appeal deadline.  FEMA rejected the County’s 2021 appeal and proceeded with the combined flood study, which is in effect today.

Flood studies affect property owners in several ways:  land value, development, and insurance.  While not quantified, two comparable properties one being in a floodplain and one not, the one property outside the floodplain will have greater value.  Regulations exist for properties in the floodplain and floodway that do not apply outside these zones. Flood regulations affect whether one can develop in the floodway and add cost for development in the floodplain.  The National Flood Insurance Program requires flood insurance for those properties that are within a floodplain and which are backed by a federally backed mortgage institution.  For these reasons alone, it is critical that FEMA’s flood maps are accurate and reliable.  Towards this end, the County pursued a local flood study to have flood maps that are as accurate and reliable as possible.

The County has pursued a request (called Letter of Map Revision) to have the FEMA flood study and flood maps revised.  The technical support for this request is a revised flood insurance study produced and funded by the County.  The County hired an engineering consulting firm to review the FEMA 2015 and 2020 flood studies.  The engineering consulting firm found several key anomalies leading County staff to believe that a new flood study conducted on the entire watershed under one methodology will result in a more accurate flood study.  The County then funded the local flood study and went out to bid. 

In early 2023, Permit Sonoma hired a consulting firm, R&F Engineering, to conduct a revised flood study for the Todd Creek watershed.  The study was completed in 2025 after several submittals to FEMA, and a final study was submitted to FEMA as the technical document of the Letter of Map Revision request.  A summary report documenting the methods, models, and conclusions can be found here.

In May 2025, the County will notify over 950 parcel owners of the results of the County’s study.  The notification is the last step for the County in the Letter of Map Revision process.  FEMA will take the application, conduct a final review, and work towards adopting the County’s flood study.  This will take approximately 3-4 months, as there is a 90-day public comment period per federal regulations.

During the FEMA comment period, the public is invited to review and make comments on the revised, County-sponsored flood study.  If you believe there is an error in your parcel's flood designation, the first step is to review this report and determine if there were errors or omissions that need technical corrections.  To challenge the study or individual parcel flood designations, either errors, omissions, or incorrect methodologies need to be shown.  Antidotal or qualitative statements typically do not result in changes in the flood designations.

The 950 or so notifications summarize the flood zone designation by parcel.  There are a range of scenarios.    In 675 cases, there is no change to the existing flood zone designation.  The existing flood zone designation could be no flood, floodplain, or floodway, depending on FEMA’s flood study.

There are 289 parcels that are seeing a change, with over half of the parcels seeing the floodplain designation removed (n = 164), and there is no other flood zone on these parcels.  This table presents the results of the proposed Letter of Map Revision.

Preliminary Federal Emergency Management Agency (FEMA) Digital Flood Insurance Rate Map (DFIRM)

Impact Summary

• • GIS-Based Study Mapping Tool:  The County has produced an Interactive Map so the public can review the changes within the Todd Creek Watershed.  The mapping tool has a slide feature to easily see the differences between the two studies.  Viewers can also type in their parcel number or address to view their parcel, or viewers can zoom in or out to review the flood maps.

  • Informational Townhall Meeting:  Permit Sonoma will host an informational townhall style meeting approximately one month into the 90-day FEMA review period.  If interested in attending, please sign up for project updates below and we will be sure to let you know once we have a date!  An invitation is not required to attend, but please check back here for updates on the meeting and this process.

  • Todd Creek LOMR Summary Report (coming soon)

  • Regulation References: These regulations apply FEMA approved Flood Insurance Rate Maps and Letter of Map Changes, once approved.
    • Floodway (F1):
      Land area added to the floodway is subject to the County’s prohibition on new development within designated floodways.  The County does allow repair and/or rebuilds due to natural catastrophes or other unforeseen events, such as earthquakes, fires, damage from trees, etc. within the floodway.
      
    • Floodplain (F2):
      Land area added to the floodplain is subject to the County’s floodplain regulations, namely all future development will need to be protected to minimize the impact from flooding.  These measures range from elevating the structure above the BFE and/or flood proofing the structure and utilities.