Flash Flood Alley Segements


Boulder's Substantial Flood Risk Around Downtown and Just Downstream

The town of Boulder, Colorado, is subject to intense flash floods. There is one particular section of town (along the creek near the center of the city) that is known to be a particularly hazardous zone with respect to both how quickly and violently a flash flood could impact the area.

  Helpful Links:  

City of Boulder Information on Flood Events

Boulder County Flood Protection Handbook (PDF)

Background on Floods in the Boulder Creek Drainage Basin

Historic Front Range Floods and Heavy Rainfall Events

Facts About the Deadly Big Thompson Flash Flood


central zone

Boulder's Central Flood Hazard Zone

There is little doubt that areas around Boulder Creek (especially those close to the Canyon mouth) will eventually be devastated by a large flood. Perhaps the biggest consideration is that this could happen with little warning.

The area highlighted to the left shows both the "100-year floodplain" (in blue) and the area that is expected to have the deepest and most powerful current (in red). This area includes City of Boulder facilities, University of Colorado married student housing, many residences, businesses and Boulder High School. Since no one can tell just where the flooding channel will move, anyone living in or near this area should be prepared to evacuate very quickly and/or move to a higher floor if their building is strong enough to handle the powerful current. Many other additional precautions for life and property safety can be found throughout this web site.

See the larger City of Boulder Flood Hazard Map

The 1894 flood devastated downtown Boulder with most of the current flowing down what is now Canyon Street. The eventual repeat flood of this magnitude (or higher) could cause hundreds of millions of dollars of damage.

Boulder's Last Big Flood: May 31 - June 2,1894

In late May of 1894, heavy rains fell in the Boulder and South Boulder Creek basins. Rainfall records for a 96-hour period showed that the mountain drainage area received from 4.5 to 6 inches of precipitation. The mountain rainfall combined with the snowmelt runoff to produce the greatest flood known in Boulder, which came roaring down the valley during the night of May 30th. Buildings, bridges, and even long sections of roads and railroads were washed away.

The estimated flow on Boulder Creek at 4th Street was 11,000 to 13,500 cfs (cubic feet per second). This is similar to the flow of a "100-year flood." But much higher flows are indeed possible in any given year and even more than once in the same year.