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Flood Summary for the Denver-Metro Area detention pond in the upper Westerly Creek basin overflowed into nearby streets. Public works employees were able to channel floodwaters back to Westerly Creek without significant impacts. Flood levels at this location were estimated at near the lOG-year threshold. Figure 3.0-2 shows the 10- minute rainfall amounts for this area. In addition, the Granby Ditch detention basin at East 6th Avenue, which is designed to accommodate 100- year runoff, ponded floodwaters 11 feet deep and came within 2 feet of overtopping the street. . Figure 3.0-2 10-minute Rainfall Amounts at Aurora 'Fire Station No.7 on July 30, 1997 Heavy rains fell again on July 31 causing new records for depth at the gages at Holly Dam on Little Dry Creek and at the Grant Street detention basin on Slaughterhouse Gulch. August In Adams CountY on August 4, Little Dry Creek flooded, damaging public facilities and homes in its lower reaches below Lowell Boulevard. To illustrate the force of the flow of water and debris on Little Dry Creek, Figure 3.0-3 shows pedestrian bridges that were shifted along their foundations by as much as 3 feet. Figure 3.0-4 captures how closely nearby railroad features came to being affected by flood waters. August 4 also brought other severe weather events, including up to 2 feet of hail, driving rains, and high winds that caused an estimated $lSG-mi11ion in damage in Lakewood and Denver. A Cherry Creek gage in downtown Denver measured 1 inch of rain in a 10-minute period. With the additional runoff from melted hail, that total exceeded 2 inches. Lower Cherry Creek flowed wall-te-wall at a depth of approximately 5 feet and a peak discharge of 2,640 cfs. September On September 4, Lower Cherry Creek through Denver flowed wall-te-wall again because of heavy precipitation. In fact, five rain gages sounded alarms upon receiving 1 inch of rain in less than 1 hour along Cherry Creek. d479/chap3.doc 08/12/98 3-3