Reducing flooding and enhancing groundwater in Petaluma Valley
In an effort to mitigate flood hazards within the Petaluma River watershed, Sonoma Water launched the Upper Petaluma River Watershed Flood Control Project to investigate the feasibility of implementing a variety of flood control and groundwater recharge efforts within the watershed.
Recent floods in 2021 and 2023 underscored the vulnerability of the watershed to flooding. Previous droughts and the need to ensure groundwater sustainability in the Petaluma groundwater basin have increased interest in a multi-benefit project where urban areas meet working agricultural lands.
Petaluma aerial: January 2005 flood
Studies find that detention basins are potential solutions
To date, the project has included stakeholder engagement and scoping to determine project priorities, updating hydrologic and hydraulic models, and concept screening of the potential project areas. These project phases helped identify objectives and approaches to flood reduction and groundwater recharge and also evaluated floodplain and detention storage throughout the Upper Petaluma River watershed.
An analysis of potential project locations has identified where detention basins would be most beneficial. The feasibility analysis quantified how each concept basin could individually reduce local and downstream flooding. Tentative locations were identified through a desktop analysis that considered the required size of a detention basin to functionally reduce flooding and a suite of geographic metrics.
The results of the analysis show that detention basins have the potential to reduce flood levels by 0.8 feet at some areas of the lower watershed, with more significant flood reductions (1 to 3 feet) immediately below some detention basins.
At the current stage of the project, Sonoma Water has achieved as much as it can through modeling and is now reaching out to various landowners in areas where the analysis suggests that detention basins could provide the greatest benefit for flood hazard reduction and groundwater recharge.
Discussions with landowners in specified areas within the Upper Petaluma River Watershed will help Sonoma Water project managers determine if there is interest in participating in this voluntary project, and whether the project would be compatible with the site and the landowner’s future plans for the parcel.
After meeting with all potential stakeholders, Sonoma Water will distill the information gathered and determine if there are any sites that may make sense to proceed with further consideration and evaluation. From there, Sonoma Water staff would formulate a list of project actions that can achieve the stated objectives of reducing flood-related damages while supporting ongoing uses.
The remaining phases of the project, which include concept refinement, final design, and implementation, may take between 3 and 5 years depending on the availability of matching grant funds and are contingent on collaboration with landowners.
Petaluma , 1955 flood
Aaron Fulton – Sonoma Water Project Manager: Aaron.Fulton@scwa.ca.gov