Wohler Culvert Repair
Summary
SCH Number
2025120075
Public Agency
Sonoma County Regional Parks
(SCRP)
Document Title
Wohler Culvert Repair
Document Type
NOE - Notice of Exemption
Received
Posted
12/2/2025
Document Description
The project is to repair a culvert occurring on Sonoma County Regional Parks' property near Wohler Road. Last winter this culvert backed up substantially causing flooding on Wohler Road and causing water to flow over the road and reroute around a portion of the drainage with riparian vegetation restoration. The purpose of the project is to repair and stabilize the existing culvert so that water can flow to the restoration area, downstream sedimentation is avoided, and Wohler Road does not flood.
In summer of 2025, under guidance of the Northern California Regional Water Quality Control Board, Regional Parks retained Miksis Services to unblock the culvert and stabilize deteriorating culvert ends. Once the work to remove about 20 feet of roots grown into the culvert and resulting trapped sediment had been performed, Miksis determined that the culvert needed to be lined to preserve long-term function. Regional Parks approved the additional scope and work was scheduled to be conducted during the remaining small window of dry weather.
This became impossible because, when Miksis came to begin work on the culvert lining, they discovered that the culvert changes size from 18” to 24” partway through. The intended culvert lining, Dynaliner, can only expand 1 culvert size (for instance, to 21” would be possible, but not all the way to 24”). To maintain functional stability over the long term, the culvert needs to be lined with one continuous liner.
Miksis Services will remove the upstream 17’ of the 18” CMP upstream of the 22-degree bend, digging to the culvert invert in the existing road, and replace it with 24” CMP. A confined space crew will clean the damaged 40’ of 24” CMP with a dry-vacuum industrial loader truck. Once the preparatory work is completed, a 24” Dynaliner seamless thermoformed PVC pipe liner will be installed to achieve a continuous diameter pipe. Both ends of the culvert will be stabilized.
The project will benefit residents of Sonoma County by protecting water quality and winter users of Wohler Road by preventing or limiting flooding.
Contact Information
Name
Laura Saunders
Agency Name
Sonoma County Regional Parks
Job Title
Planning Technician
Contact Types
Lead/Public Agency / Project Applicant / Parties Undertaking Project
Phone
Location
Coordinates
Cities
unincorporated area
Counties
Sonoma
Regions
Northern California
Cross Streets
Wohler Road and Eastside Road
Total Acres
0.028
Parcel #
110-220-009
Schools
Socooro Maldonado
Waterways
Russian River and tributaries
Township
8N
Range
9W
Section
29
Base
Mt Dblo
Notice of Exemption
Exempt Status
Emergency Project
Type, Section or Code
Sec. 21080(b)(4); 15269(b)(c)
Reasons for Exemption
Repair work on the culvert was anticipated and undertaken during the dry season of 2025 to resolve the flooding on Wohler Road that occurred during the winter of 2024-2025. The extent of damage discovered during culvert repair was excessive as sections of the CMP were rusted through and failing, and it was even more unexpected when the culvert turned out to change size partway through its length, extending the time window necessary for project completion. While the culvert could be replaced next summer, the debris and roots that were holding it up have already been removed. Thus, there is a very high chance that substantial rains this winter will cause the culvert to collapse resulting in increased flooding on the road, sediment downstream, and new erosion channels. Therefore, it is urgent to put the culvert into its long-term stable configuration as soon as possible.
Per Condition VI.A.6, “All repairs and construction shall be kept to the minimum necessary to alleviate the immediate emergency and limited to in-kind replacement or refurbishment of on-site features.” In order to use the most environmentally sensitive solution, digging only in the upstream end of the culvert located under a road and in the fill for the road, the project includes a minor upgrade to make the entire culvert 24”, instead of reducing the size of the downstream end of the culvert, resulting in impacts on riparian vegetation and perhaps channel disturbance.
It is exempt because doing the work now is likely to help mitigate flooding this winter, but the circumstances requiring the work to avoid flooding were not known and could not have been known prior to embarking on the routine culvert unclogging and repair last summer.
County Clerk
Sonoma
Attachments
Notice of Exemption
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