FLOOD ADVISORY DEFINITIONS

FLOOD STAGE:  A site-specific river level at which flood damage may start to occur; usually at or above the top of the riverbank.  Flood heights are often measured relative to the flood stage elevation .  At the Concrete and Mount Vernon gauges, flood stage is 28 feet.

FLOOD WATCH:   The first of two basic advisories issued by the National Weather Service.  A flood watch is issued when conditions are favorable for flooding.  A watch does not mean that flooding will definitely occur, but it does give a community an early notice of potential flooding and allows the community to review flood safety steps.

FLOOD WARNING:  The second basic advisory issued by the National Weather Service.  A flood warning is issued when flooding conditions are expected to develop.  In some cases, the food warning will be river stage or height reading.  The National Weather Service tries to issue flood forecasts with an accuracy of plus or minus one foot.  But there are many variables that can enter into this forecast.  Some of the variables are difficult to predict, yet have great impacts on flood forecasts.

PHASE 1 FLOODING: Phase 1 floods can cause catastrophic damage in the valley. A very large phase 1 flood would be considered a 100-year flood which means the probability of a flood of this magnitude would have approximately a 1% chance of occurring in any given year. The last Phase 1 flood occurred in November 2021 when the Skagit River reached a height of 38.93 feet on the flood gauge in Concrete, well above the Phase 1 criteria of 37 feet.

PHASE 2 FLOODING:    Phase 2 floods inundate a wider area and may cause significant damage. Phase 2 flooding occurred in 2018, 2016, and 2015, when the Skagit River reached heights above 32 feet on the flood gauge in Concrete.

PHASE 3 FLOODING:  Phase 3 floods inundate low areas near the Skagit River, may cover sections of roads, and occur roughly every few years. They generally cause minimal damage in the Skagit River Valley.

100-YEAR FLOOD: A term used to define an extreme flow rate that has a one percent chance of being exceeded in any given year. The 100-year flood is a flood that is equaled or exceeded once every 100 years on average. The term should not be taken literally as there is no guarantee that the 100-year flood will occur within a 100-year period or that it will not recur several times.

cfs: The rate of flow (see Discharge) past a given point, measured in cubic feet per second. One cubic foot of water equals about 7 gallons.

DIKING DISTRICTS: These districts are given responsibility over the approximately 80 miles of dikes and levees in Skagit County. These districts can assess those within the district that are receiving benefits as well as petition the county, state, and federal government for funding and assistance. Funds raised are used to construct and maintain dikes, levees, tide gates, keyways, and bank stabilization. These districts are administered by a board of commissioners which are elected but do not receive a salary. If you would like Dike District information please call Skagit County Surface Water Management at 416-1400.

FLOOD INSURANCE: The insurance coverage provided through the National Flood Insurance Program.

Flood Insurance Rate Map (FIRM): An official map of a community on which the Federal Emergency Management Agency has delineated both the special hazard areas and the risk premium zoned applicable to the community. FIRMs typically identify the elevation of the one percent annual chance flood and the areas that would be inundated by that level of flooding; they are used to determine flood insurance rates and for floodplain management. FIRM maps are available at the Skagit County Planning and Permit Center.

GAGE HEIGHTS AND PHASE

Skagit River Gage near Concrete
This USGS gage is located near the community of Concrete at river mile 54.1 on the Skagit River

Skagit River Gage near Mount Vernon
This USGS gage is located at the Riverside bridge on the main stem at river mile 17.0.

Gage heights are measured in feet.