The year 1994 marked the 100th anniversary of the 100-year (1%) flood event on Boulder Creek. Many days of rain, water-soaked mountain soils, and rapid spring snowmelt produced widespread flash-flooding in downtown Boulder, May 30 - June 2, 1894. In the May 31, 1894 issue of the Daily Camera, a report described the flood event:
"The Spring of 1894 came late; snow lay deep on the mountain sides and filled the gulches. As May drew to an end the weather turned warm and moisture-laden winds from the east struck the cold heights. It began to rain, and with fearful eyes the mountain people watched the creeks for rising signs of water. They had not long to wait."
"Sixty hours of almost continuous rain had transformed the quiet little stream (Boulder Creek) into a raging river. The creek had swollen into a river in Boulder Canyon, boulders crashed and roared, wagon roads and railroad bridges, washed from their timbers, came crashing down the street."
"At Fourth Street, the long railroad bridge was twisted into a semicircle with the rim and rails of the track remaining, while the timbers blocked the flow of the stream and sent its waters far out upon low-lying land, inundating a wide tract between the south side and Pearl street . . ."Smaller floods have occurred on Boulder Creek and the eleven tributary streams in recent years (1969, 1972, 1985, 1990, and 1992). These less-damaging floods, along with improved watershed flood gauges, warning systems drills, and a designated high-hazard zone may have unwittingly relaxed the public's concern and preparedness for the next catastrophic flash-flood.
Another 100-year flood (12,700 cubic-feet per second) today would probably cost many lives and several billion dollars in property damage and repairs. This event could easily be much worse than the killer Big Thompson flash flood of August 1976 where 139 lives were lost, hardly more than 20 miles north of Boulder.
The opportunity presented here will enable you to discover both exemplary and questionable approaches to urban floodplain management. The City of Boulder has enacted model high-hazard floodplain mapping and building prohibitions. On the other hand, filling to allow development in the 100-year floodplain conveyance zones continues, and stream channelization and beautified flood walls still are done on Boulder Creek's tributaries. Incidentally, these areas tend to be heavily populated but have absolutely no warning systems or evacuation drills. The University of Colorado, which does not need to follow local flood ordinances, locates family housing and other structures in high-risk flood zones, contrary to local municipal guidelines - or even conventional wisdom!
Before you begin the field study, it would be insightful to know why Boulder Creek is subject to catastrophic flooding. The Preview exercise continues with a look at the physical geography of Boulder Creek. Please continue to Page 2 of this exercise.