Glossary of Terms

100-yr Flood

Has a 1% chance of being equaled or exceeded in any given year.


A natural or manmade linear depression or large "ditch" that carries flood waters.

Cubic feet per second

The rate of discharge representing a volume of 1 cubic foot passing a given point during 1 second and equivalent to 7.48 gallons per second or 448.8 gallons per minute.


A closed conduit for the passage of surface drainage water under a roadway, railroad, or other impediment.

Detention Basin

A flood control facility consisting of a basin and dam that reduces the amount of storm water that can get past a point. These basins range in size from 15 acres to 300 acres.


The volume of water that passes a given point within a given period of time.

Flash Flood Watch

A flood is possible in the area. It is only issued by the National Weather Service.

Flash Flood Warning

A flood is already occurring or will occur very soon. It is only issued by the National Weather Service.

Flood Control Facility

A channel, stormdrain, or detention basin that is built to control storm water flows to reduce property damage and loss of life.

Flood Hazard Area

The area subject to flooding as defined on maps by the Federal Emergency Administration of the Federal Emergency Management Agency (FEMA) and/or the applicable map accepted by the local entity.

Floodplain Management

Provides the guidance, conditions, and restrictions for development in floodplain areas while protecting the public's health, safety, welfare, and property from danger and damage.

Local Drainage

Smaller drainage facilities in neighborhoods that collect flows and route them to the regional system.

Master Planning

Performing the analysis and design of 100-year flood control facilities and reconfiguring facilities that were constructed to a lesser standard, to provide an increased level of flood protection to residents, businesses and tourists from the hazards of flooding in the valley.


Rainwater that is not absorbed into the ground.

Storm drain

A large underground pipe or box that conveys stormwater through developed urban areas to.

Stormwater Pollution

Water from rain and excess irrigation that pick up pollutants (cigarette butts, trash, automotive fluids, used oil, paint, fertilizers and pesticides, lawn and garden clippings and pet waste) from streets, parking lots, driveways and yards and convey them through the storm drain system untreated.


A natural stream channel common in the western United States.


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