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I I I I I I I I I I I I I I I I I I I The following is a brief description of what is known of each of the five major flood events mentioned above: FLOOD OF 1-2 June, 1914 FLOOD OF 21-23 May, 1876 Heavy rains in the mountains that hastened the melting of a deep snowpack estimated at 50 percent above normal produced what newspaper accounts called "the worst flood on Boulder Creek following the 1894 flood". Boulder's water supply system and the Boulder County farm were severely damaged. Numerous roads and bridges in the mountains were also damaged or destroyed. Li ttl e is known about the 1876 flood. The Greeley Tri bune reported "The Boul der, swollen into a great river, in many places fully a mile and a half wide, inundated the land and farms and meadows and swept away fences and bridges." FLOOD OF 29 May -2 June, 1894 Flood of 2-7 June, 1921 Little is known of this flood except that it produced the highest peak discharge ever recorded at the U.S. Geological Survey Orodell gage, located about three miles upstream from Boulder and one mile upstream from Fourmile Creek. The Orodell gage has been continuously operated since 1916. A discharge of 2,500 cfs was recorded on 6 June, 1921. Rainfall totaled 3.36 inches at Boulder through the period of 2-7 June, 1921. Heavy rains fell over the northern Colorado mountains in this period. Rainfall over the Boulder Creek basin was particularly heavy. Mountain rainfall of 4.5 to 6 inches combined with snowmelt runoff from heavy snowfall. The resulting flood came roaring down the valley during the night of 30 May, 1894. In the mountains above Boulder, numerous bridges, several miles of roads and railroads, mountain communities, and mining properties were damaged. Estimates were made of the peak discharge of this flood 18 years after its occurrence. These ranged from 9,000 to 13,000 cfs. FLOOD OF 4-8 May, 1969 In Boulder, floodwaters covered the entire area between Water Street (now called Canyon Boulevard) and University Hill to depths as great as eight feet. Every bridge in Boulder and a number of residences were swept away. Other types of damage included commercial establishments, public utilities, railroad property, roads and streets, and irrigation structures. Many people were trapped in their homes and had to be rescued. Only one life was lost; this was due, in part, to the flood's slow onset. The flood of May 1969 resulted from a long duration storm. Runoff resulted from a combination of rainfall and snowmelt which was reported heaviest in the mountains. In the Boulder and South Boulder Creek basins, the rainfall continued at a moderate rate for nearly four days. Total precipitation for the storm amounted to 7.60 inches at Boulder and 9.34 inches at the Boulder Hydroelectric Plant located about three miles up the canyon from Boulder. Peak flooding at Boulder occurred on 7 May, 1969. Estimates of discharge at the Orodell gage indicate a peak of 1,220 cfs, The discharge near Broadway in Boulder was estimated to be between 2,500 and 3,000 cfs. Instances of erosion damage to bridges and streets, trees, and agricultural lands were recorded. Large areas were flooded downstream from Boulder. . In the valley downstream from Boulder, the floodplain was reported to have been inundated to an average width of approximately one mile for several days. Agricultural damages included loss of livestock, crops, pastures, fences, roads, and deposition of sand and silt on floodplain lands. In addition, considerable crop losses were suffered on lands outside the floodplain which were dependent on irrigation diversions from Boulder Creek. 4