Statement as of 10:01 AM PDT on October 22, 2014
... Public information statement...
This is day three of California flood preparedness week.
Be aware... be prepared... and take action.
Todays focus is on alluvial fan... debris flow... flash and
In the United States more people die as a result of flooding than
any other natural disaster. Closer to home... in the past twenty
years every single County in California has been a federally
declared flood disaster area at least once.
California is unusual... not only is the state subject to riverine
and coastal flooding... but also flash... alluvial
fan... tsunami... floodplain... stormwater and debris flow flooding.
Californians need to be aware and be prepared... not only where they
live... but where they work and visit.
Californians are encouraged to assemble a family emergency
kit... family evacuation plan and be aware of flood risks.
Alluvial fan flooding... an alluvial fan is a fan shaped buildup of
sediment found at the base of Steep Mountain canyons. Alluvial fan
flooding is characterized by relatively shallow depths... high
velocities... moving soil and sediment and indefinite
channels... creating uncertainty about where rising water and soil
will travel. Alluvial fan flooding is a concern primarily in
central and Southern California... especially in desert areas.
Debris flow flooding... debris flow floods are made up of
water... mud... rocks and debris. They can form and accelerate
quickly... reaching high velocities. Debris flows are commonly
caused by heavy... localized rainfall on hillsides where vegetation
has been destroyed by fire... or are geologically unstable. Debris
flows can demolish homes and other structures... wash out roads
and bridges and sweep away cars. In debris flow flooding... mud and
debris remain after the flood water has receded... causing
additional expense to remove.
Flash flooding... flash floods are the number one weather related
killer in the United States and cause more than two billion
dollars in property damage each year. They can roll
boulders... tear out trees... and destroy buildings and bridges
quickly. A flash flood is a sudden... rapid flooding of low lying
areas typically caused by intense rainfall. Flash floods can also
be caused by the collapse of a dam or levee. Rapidly rising water
can reach heights of 30 feet or more. Flash floods can occur
throughout the year... anywhere... especially in mountain and desert
areas. California's rainy season lasts from November to April.
This is when the chance of major flooding and flash flooding risk
Localized or stormwater flooding... localized flooding occurs in
both urban and non urban areas during or after a storm. Any
storm... particularly slow moving... steady rain storms... can
overwhelm drainage systems. When the system backs up... pooling
water can flood roads..street... yards... and even the lower floors
of homes and businesses. Less intense storms can cause this type
of flooding when leaves... sediment and debris plug storm drains.
Localized flooding poses most of the same problems caused by
larger floods... but typically impacts fewer people and affects
geographically smaller areas. Flooding of this type tends to recur
year after year at low water crossings... underpasses... and in
areas with poor drainage or blocked storm drains. The aftermath
can mean costly damage to homes and property. In many
cases... stormwater flooding can easily be avoided by keeping
storm drains clear of debris.
If your vehicle stalls... abandon it and seek higher ground
Stay away from rising creeks... stream and rivers. Six inches of
fast moving water can knock an adult off his or her feet. Do not
attempt to cross flowing water that may be more than Knee Deep.
If you have doubts... do not cross.
Turn around... do not drown. Practice safe driving during flood
events. Do not drive through water on the roadway... during
floods... more people are trapped and die in their vehicles than
anywhere else. Do not drive around a barricade. Barricades are
there for your protection. Turn around and go another way.
Related websites for more information:
California dwr flood preparedness website
California dwr flood management website
Fema tsunamis information website
California oes my hazards website
Fema flood insurance program
NWS advanced hydrologic prediction system
NWS California Nevada river forecast center