Redwood Coast Severe Watches & Warnings NOAA Weather Radio

Public Information Statement
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 stormwater flooding.

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 is greatest.

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.

Safety messages...

If your vehicle stalls...abandon it and seek higher ground immediately.

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 http://www.Water.CA.Gov/floodsafe/CA-floodpreparedness/fpw_home.Cfm

California dwr flood management website http://www.Water.CA.Gov/floodmgmt/

Fema tsunamis information website http://www.Ready.Gov/tsunamis

California oes my hazards website http://myhazards.Calema.CA.Gov/

Fema flood insurance program www.Fema.Gov/National-flood-insurance-program

NWS advanced hydrologic prediction system http://water.Weather.Gov/ahps

NWS California Nevada river forecast center http://www.Wrh.NOAA.Gov/cnrfc