Debris Flows Santa Cruz Mountains and San Lorenzo Valley

DEBRIS FLOW in the Santa Cruz Mountains – Winter 2020 – 2021

This is a summary of an on-line TOWN HALL meeting hosted by SUPERVISOR RYAN COONERTY  – Notes taken don’t account for every point made in this one hour plus presentation.   

Here’s a link to another Town Hall hosted in November by Supervisor Ryan Coonerty on Debris Flows

12/4/20 DEBRIS FLOW Latest video – from Gail Mahood San Lorenzo Vally Water District

Here are my notes:

Loose soil & rock can move quickly when oversaturated by rains, and even bring down trees.

Speed of a debris flow can reach 30 mph and will destroy everything in its path.

Fire makes drainage worse, leaving a waxy residue on soils so water doesn’t percolate.   Burned slopes lost organic matter that normally stabilizes soils.

Short/Intense rains can send debris flow down quickly.

Cal Fire Watershed Emergency Response Team surveyed and mapped probability of flows with on site and computer modeling.    Local geological staff contributed.

County map plug in your Address!

Dark Blue is highest risk and most likely – Here’s a snapshot of the map as of December 7th 2020

Cannot be stopped, unlike fires, debris fans out quickly: wide and long

Debris flows can move at the speed of an avalanche

Debris flows move much faster than our recent CZU fire moved

Montecito Santa Barbara 1/9/18 Debris Flow incident

  • People were given 24 hours warning
  • 4 AM it started
  • 21 fatalities / 2 missing; never found
  • 425 structures destroyed.   
  • Debris flows can extend for miles
  • This Debris Flow went all the way out to, and buried, Highway 1
  • Residents on flat land can definitively be affected
  • People didn’t heed the evacuation orders – only 28% evacuated
  • County Maps do not include new trailers/tents/yurts– only existing residences
  • Stay in communication with people: neighbors, Facebook groups, etc.
  • know your zone
  • Sign up for emergency alerts:
  • – type in your address, brings you to your zone
  • Code Red app –allows you to sign up to receive notifications once you’ve registered your device/phone, text SCR911 to 99411 or at
  • You can also sign up for Reverse 911 for land lines, watch social media
  • Keep a battery operated weather radio (and fresh batteries) in case power & internet & cellular go out
  • Sheriffs will go door to door & lead the evacuation starting 48 hours in advance of storms
  • You’ll need to evacuate If there’s more than a 60% chance of rain measuring 0.7” in an hour or 0.3” in 15 minutes
  • If you wait for heavy rain, it’ll be too late to get out.

Pre-pack & Plan: go thru evacuation readiness with household

Pre-plan where you will go to shelter

Pre-plan alternative evacuation routes

Zones change to yellow and then red for evacuations

Hotel bills are not reimbursable by insurance unless a disaster is declared

If you evacuate to stay with family or friends, do so in a COVID safe manner

There will be County sponsored evacuation centers

They said there won’t be any road closures by police or sheriffs, but roads could be blocked by slides. Secure your home before leaving; remove valuables.

Don’t move back into a hazard area without clearance from licensed professional geologist

In loss of power situation, cell service and internet can fail, so have a battery operated weather radio.

Debris flows can block roads so emergency services may be unable to reach people who’ve stayed.

Let family/ friends know where you’ve evacuated to.

Red Cross has “safe and well” registration so people can check on your status.

Debris Flow Warning Testing will start next week.    

Their goal is to issue warnings 48 hours in advance of a major rainfall

24 hours evacuation ORDER – gives law enforcement time to go door to door

Insurance typically pays only once an area is declared a disaster

Some of the maps include risks to roads, so even if an area itself doesn’t have debris flow risk, they could get evacuated.

Zonehaven questions: Chief Ian Larkin –

If you’re in a drainage area, or below a steep slope, be highly aware.

Sheriff staff will be greatly increased.    43 deputies in the SLV.    Property security is a key focus.

During PG&E power shut-offs – communications systems can fail.    What is county doing?   Some of communication will be door to door.   That’s why they’re doing advance notifications.  County & PGE do communicate plans with each other.    Battery operated radios are ideal back up info system.

CERT will be handing out info English & Spanish (Community Emergency Response Teams –

Boulder Creek typically gets the most rain in the SLV – 40” is average annual rainfall

A lot of SLV Water District water lines were burned.   Although they’ve mostly been replaced, they are in areas of debris flows so loss of water supply is quite possible.   Store 2 gallons of water per day per person  (for a week?)

11/18/20:    I got this e-mail from <>

This is a message from the Santa Cruz County Office of Emergency services.
Starting on Thursday, November 19th, Community Emergency Response Team members will be going door to door providing educational and preparedness information in regards to debris flow. In addition, they will be conducting a survey to understand the needs of the community and to help them prepare in case of evacuation. We appreciate your cooperation as they work through the neighborhoods that are Risk of debris flow. For more information about debris flow, go to links to maps addressing debris flow hazards – links to geology professionals who can be consulted regarding issues facing individual residents and properties

Last but not least, If your home was lost in the CZU August Lightning Complex Fire:

The DEADLINE to apply for FEMA assistance – for fire losses not covered by insurance – is


The DEADLINE for Debris Removal required Right of Entry forms is


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