Flood Information

Font Size

Useful links
Advanced Hydrolgic Prediction Services - River levels

Flood Safety Tips and Resources
Idaho Water Science Center
National Weather Service Forecast Office
NOAA All Hazard Radio Frequencies
Payette River levels

 

For questions regarding the current flood status or evacuation notifications please contact the Payette County Dispatch Center at 208-642-6006 ext 1175 

 


River Channel:  A river channel is a natural or artificial watercourse that has a definite bed and banks to confine and conduct the flowing water.

Floodplain:  The floodplain is a normally dry area of low land adjacent to a river, or other watercourse that is susceptible to inundation during the high water events.

Bank Full Stage:  Flood stage is designed to indicate an elevation where appreciable damage begins to occur to urban or agricultural properties.  

Left Bank:  When you are facing downstream, the bank on your left is the left bank.

Right Bank:  When you are facing downstream, the bank on your right is the right bank.

CFS:  Cubic feet per second

River Gages:  River gages on the river that have measuring devices; they either measure in feet (how high the river is) or in CFS (cubic feet per second) how fast the river is flowing.

(Note):  The river might be out of its banks and still not be a flood stage.  In normal river flow, it takes 12 hours for water at Black Canyon Dam to reach the Payette Bridge.  Twin Bridges-Payette is always 2000 CFS higher than Black Canyon due to Willow Creek and other drainages.  There is a gage below the Black Canyon Dam on the Payette River, it is measured in CFS.  There is also a gage on the Payette River, near Letha, also measured in CFS.  There is a gage at the Twin Bridges-Payette that is measured in both CFS and feet.


18,000 to 22,000 cubic feet per second or 12.0 feet to 14.0 feet


The first response phase for planning to fight floodwater is to look at the strong indicators of a future flood threat.

Some of these indicators are:

  1. Deep Snow Pack
  2. Seasonal Flood Threats
  3. Changes in Weather Patterns (warming)

Flood Watch:  The National Weather Service issues Flood Watch/ Flood Warnings.  Flood Watch is issued when the conditions are favorable for flooding.  The watch does not mean flooding will definitely occur, but it is to alert the community of a potential flood threat.

Flood Warning:  This is issued when flooding conditions are expected.  (The flood warning will usually be accompanied by a predicted flood height expressed as river stage or height above flood stage.  They might refer to this as the river crest.)

The Payette County Sheriffs Office and the Emergency Disaster Services Director monitor the rivers closely.  This is done by checking river gages, monitoring the Black Canyon Dam and keeping in contact with the National Weather Service.  The public is encouraged to listen to local radio and television stations.

What about Sand Bags, how many do I need to protect our home?  It takes approximately 800 sandbags to build a one foot barrier that would cover a 100 linear foot area.  It would take approximately 5000 sandbags to cover a three-foot high barrier that is 100 feet long.  Realistically, the practical amount of sandbags that a residence needs would be less than 50 sandbags.  Most homes have an average of three exterior doors and one garage door.  The amount of sandbags that it will take to cover the bottom of these doors is the amount needed.  The average sandbag measures 14’X25’ and is filled approximately half full.  This allows for proper stacking and placement.  A properly filled sandbag should weigh approximately 40 pounds.  Sandbags should be neatly stacked rather than dumped into place.  The sandbags should be lapped to improve strength and reduce seepage.  If available, sheets of plastic should be used on the waterside of the sandbag line to reduce the problems of seepage and a need for a pump.

In the event of a declared disaster (flooding), Payette County will provide citizens with a very limited amount of sand bags.  This will be on a first come-first serve basis as Payette County has a limited supply and we must keep enough sand bags for maintaining the county infrastructure.  There will be sand available and will be provided at specific locations upon request.  Our stockpile of sand bags and sand is located at the Weed and Gopher building at 640 S. Main Street in Payette.  We strongly encourage citizens to purchase their own sandbags and be prepared.  Sandbags can be purchased at some hardware stores or on-line.  By using a search engine, type in “sandbags” and there are numerous websites that provide bulk savings on sandbags.   

Sandbag Storage:  Do not store sandbags already filled, the bags will harden like concrete.


When the National Weather Service gives the flood warning, they will forecast the amount of time before expected river crest, height of the expected river crest and the duration of the crest.

We know that residences near the Black Bridge area will receive the heavy water first, then the trailer park by the Twin Bridges, Park Street, homes near Kiwanis Park, Killebrew area and areas near the Freemont/ Falk’s Bridge area.

It is difficult to set a time for people to be out of their homes.  The weather service may tell us the water crest will hit a certain area around (example:  10:00 a.m.) and we may have a couple of hours to make notifications.

Payette County Sheriffs Office will assist in making notifications and emergency rescues.  In the event evacuees do not have a place for shelter, please contact the Payette County Sheriffs Office.  We will have shelters available in the neighboring churches and other safe zones.


Water enters a river system from a variety of sources.  When large water runoffs enter the water network too fast or in excessive quantities, flood develops.  Heavy rains on water saturated or impermeable lands in urban areas are major sources of water runoff.  Water entering the river system has two noticeable effects on the river.  These are the increased flow in the river and the level of water in the channel.  As the river rises, the velocity of the water flow will also increase.

The combination of the increasing water levels and higher velocities can greatly multiply the hydrodynamic loads placed on water and flood control structures.

Levees are placed in the river to direct water.  If a levee were to break, the flood depth on the breach side is likely to be higher than if the water had been allowed to naturally inundate the entire floodplain.

In addition, the violence of a levee breach can cause more damage than would the slowly rising waters of the natural inundation process.  

A levee breach will also provide little time for evacuation and public protection.  So part of the pre-flood watch is to check all waterways and drainage channels for excess debris and other materials that may restrict and block the water flow.

Particular attention should be paid to junk cars, fallen trees, and accumulation of dead brush that can obstruct the water flow at bridges or work as a battering ram against control structures.