Debris Flows
Friends of San Lorenzo Valley Water works to promote improved citizen awareness and understanding of all water-related issues affecting our community. As a consequence of the August, 2020 CZU Lightning Complex Wildfire, multiple areas of our valley are at risk for potentially deadly debris flows when intense winter rains pour down on fire-ravaged hillsides. FSLVW wants to ensure that valley residents have an accurate understanding of the risks that they are facing and of the actions that they can take.
FSLVW initiated this activity in late 2020 with a widely attended webinar presentation by Gail Mahood. We subsequently engaged with the County to provide detailed feedback and recommendations. One year later, we re-engaged with the County with updated feedback.
NOTE: The Atkins map, the most recent and most detailed map of debris flow (and flooding) hazards, was produced 8/31/2021 by consulting hydrologists for the County, and is available at: http://www.co.santa-cruz.ca.us/Portals/0/County/OR3/Workmaps_SantaCruz_Optimized.pdf It is a very large file and may take minutes to download completely.
SAN LORENZO VALLEY WINTER DEBRIS FLOW UPDATE: Review and Recommendations (11/8/21)
Gail Mahood (12/1/20) Presentation on Debris Flows:
Gail Mahood is an SLV resident and Professor Emerita, having retired in 2019 from the Department of Geological Sciences at Stanford University after 40 years of service as a faculty member and administrator. She has been extremely active in educating her local community about the risks of debris flows in the wake of the CZU Lightning Complex Fire of August 2020. The recorded video of her 12/1/20 Webinar and her detailed article in the SLV Post (see links below) are highly recommended for all valley residents.
Gail Mahood (12/1/20) Zoom Educational Webinar Announcement
Gail Mahood (12/1/20) Webinar Homework Exercise
Note: People reported problems in attempting to follow the links in the above document to the online version of the WERT report. The report itself is too large to post here, but the following link should be more reliable:
Watershed Emergency Response Team Evaluation for CZU Lightning Complex Fire
Note: Instead of the link at the top of page 5 of the Homework Exercise, please use the following:
California Geological Survey Boulder Creek Post-WERT Study
Recorded Video of 12/1/20 Webinar
Gail Mahood Debris Flow Article in the SLV Post
Links to Evacuation and Hazard Maps:
County “Debris Flow/Mudflow” Evacuation Map
Zonehaven Real-Time Evacuation Map
Potential Debris Flow Hazards Map by County Geologist and Staff
California Geological Survey Boulder Creek Post-WERT Study
Consulting With an Expert:
Residents located in a sufficiently severe hazard zone may want to consider hiring a Professional Geologist to assess the degree of hazard for their specific property and to make suggestions on what can be done, if anything, to mitigate it.
The following link explains the difference between a Professional Geologist and a Professional Engineering Geologist, and how to make sure you have somebody reputable:
Consumer Guide to Geological and Geophysical Services Publications for Consumers
The following link does not include a listing of members, but it may still serve as a useful starting point:
American Institute of Professional Geologists California Section
The Santa Cruz County planning office provides this list of Engineering Geology firms they have used:
Another option could be to call the County Geologist for a recommendation:
Jeff Nolan, C.E.G. (Professional Geologist with an additional certification in Engineering Geology)
County Geologist
jeff.nolan@santacruzcounty.us
(831) 454-3175
Santa Cruz Museum of Natural History (12/8/20) Presentation by Noah Finnegan (UCSC)