South Platte Basin:

Denver and Frederick

May 9-15, 1957

April 1957 was an exceptionally wet month along the Colorado Front Range. April precipitation in the Arkansas Valley was more than 200 percent of normal. In the South Platte Basin, even into the upper reaches, there also was above normal moisture. Idaho Springs and Allenspark each had precipitation close to 300 percent above normal at 294 and 284 respectively.

In the beginning of May, an unseasonably cold, giant Canadian air mass stalled over Georgia and a clockwise wind pattern formed around it bringing brisk, dry west winds to New England. Winds coming around the southern edge of the air mass swept across the Gulf picking up moisture and carrying it northwestward into Colorado. For three days the moist air piled into Colorado. Then on May 8, the edge of another Canadian air mass collided with a low-pressure system moving into the state from the Pacific. The low pressure made the air unstable, and the advancing edge of cool air from the north shoved the warm moist air from the Gulf aloft. On May 9, 3.27 inches of rain fell in the Denver area. At the time, this was the third heaviest rainfall in a 24-hour period in the 85 years weather records had been kept. This storm was large: rainfall was reported from Cheyenne to Trinidad and much of the Front Range received significant rainfall. The rain continued throughout the weekend and flooding problems persisted for several days. On May 12, a four-hour rainstorm hit the town of Frederick.

Most of the damage was a result of river flooding. The South Platte went out of its banks between Welby and Adams City (northwest of the I-76 and I-270 interchange). West Toll Gate Creek north of Colfax Avenue in Aurora also overflowed. Subdivision developers had closed the old course of Toll Gate Creek and had been digging a new channel. Witnesses told of a wall of water three feet high roaring down the creek bed. Hundreds of basements were flooded and streets and underpasses were blocked by high water in the Denver area. The Valley Highway was closed for a week at Downing Street due to water several feet deep underneath the underpass. At Stapleton airfield, parking lots flooded with 15-20 feet of water were reported.

Near Fitzsimons Army Hospital, a mother and her two small children drowned in their basement apartment when West Toll Gate Creek jumped its banks. Scores of homes in the area had flooded basements. Raging water also washed out 150 yards of government railroad track east of Lowry air force base. In Denver, the most costly damage was to city streets. Three homes, just north of Stapleton airport in Adams County, fell into Sand Creek on May 10. The creek is usually only a few feet wide, but according to reports it was more than a block and a half wide on that day. East of the airport, floodwaters from the creek cut a 200-foot section of permanent water and sewer lines to the county jail.

Outside the Denver area, crop damage and livestock losses were extensive along the South Platte northeast of Denver and along West Toll Gate Creek east of Aurora. Several rockslides on roads west of Denver hampered travel. Numerous bridges were washed out in Adams, Boulder and Weld counties.

In Lyons, flooding from the North Saint Vrain washed away a 70-foot section of the town's water line. Below Lyons on Colorado 66 more than 100 feet of the Longmont-Lyons spur of the Burlington railroad was ripped out as the Saint Vrain River cut beneath it and into the highway bed.

Rainfall Data:

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