Because Boulder is situated at the base of the mountains, there is an ever-present threat of flood, particularly when spring rains or cloud bursts combine with melting snow from the mountains. (Flooding may occur with or without the addition of melting mountain snow in the creeks and is therefore not limited to the spring runoff.) Creeks can quickly turn into raging rivers, especially if they are already swollen from melting snow. It's important to note that though the plains are considered semi-arid, the Continental Divide receives 40" of moisture per year, mostly in snow. Floods have always been a part of Boulder's history. Floods have been recorded every few years, and a 100-year flood occurred in 1894. (A 100-year flood means that there is a 1% chance of a major flood with a peak discharge of 12,000 cubic feet per second in any given year. Approximately 1/4 to 1/3 of Boulder would be effected by flood waters of this magnitude.) In that year upslope conditions brought rain that lasted 60 hours. The snow pack began to melt. The following is one witness' account of the flood: "The Flood of 1894 was caused by a warm rain that fell on the heavy accumulations of snow at the headwaters of Four Mile, North Boulder, Middle Boulder, and South Boulder Creeks. The flood waters from Sixth Street through the city did immense damage, carrying away bridges, some houses, many out building, besides pouring mud and sand into basements and the first floors of many houses. The waters covered almost the entire territory from Walnut Street to beyond Arapahoe, and from 9th Street to the city limits. The flood waters were several hundred feet wide on level ground between Boulder and Valmont. Boulder and the tributary mountain canyons have never regained their original wonderful beauty since this flood." With the completion of Barker Dam in 1910, many people believed flooding from Boulder Creek was no longer a danger. The dam does regulate some runoff into Middle Boulder Creek but it has no effect on North Boulder Creek and Four Mile Creek which joins Middle Boulder Creek just a few miles up the canyon from Boulder. Most important is the fact that rain storms usually occur at elevations below the dam. During the next 75 years many plans were discussed for flood control, most involving structural changes to Boulder Creek and its tributaries, but little was done. One of the most controversial issues was whether to continue development on the flood plain. A 100-year flood of the magnitude of the 1894 flood would certainly cause greater property damage and threaten more lives simply because of increased development on the flood plain. After the tragic 1976 flood in the Big Thompson Canyon where 139 people were killed, citizens began to take the threat of flood seriously. Rather than institute severe structural changes in Boulder Creek and the other creeks flowing into Boulder, the city decided to work with nature and to respect the ecology of the creeks. Bridges were modified and replaced to accommodate peak flood flows. Areas near the creeks were constructed to contain flood waters and to divert them away from homes and businesses. Stricter building requirements in the flood plain were implemented. Today there are fifty-three stream and rain gauges located in the canyons of the nine drainage areas entering into Boulder. These gauges monitor rainfall and measure water level changes in the creeks. Information is automatically entered into computers operated by the City and County of Boulder. Should a dangerous level occur, sirens will sound throughout the city and at the University of Colorado signaling flood danger. There is no warning system in the canyons. How much warning time would there be? Not much, according to Larry Stern, director of the Office for Emergency Management. In the event of a l00-year flood we would have perhaps a 40-minute warning before a ten-foot wall of water rushed from the canyon into Boulder. What to do in case of a flood? Get to high ground fast. What you should not do is to try to outrun the flood in your car. Many people are killed by floods when trying to reach safety by car. "Climb high or die" is the best advice for flash floods.



Sources

Smith, Phyllis. (1987). History of Floods and Flood Control in Boulder, CO, City of Boulder.

Stern, Larry. Director of Emergency Management, City and County of Boulder BE SURE TO CHECK OUT HISTORY OF FLOODING IN BASIN HISTORY BEYOND BASIN

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