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<br />Vol. 27, No.1
<br />
<br />December, 1997
<br />
<br />The 1997 Floods in the District
<br />by
<br />Kevin Stewart, P.E., Project Engineer, Floodplain Management Program
<br />
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<br />The summer of 1997 willbe long
<br />remembered for the devastating July 28
<br />flash flood in Fort Collins which killed
<br />5 people and caused millions of dollars
<br />in damage along Spring Creek and at
<br />Colorado State University. The
<br />following evening, storms on the
<br />eastern plains continued to threaten
<br />lives and destroy properties, inundating
<br />large areas sunounding the
<br />communities of Sterling, Atwood and
<br />Weldona. On August 1 President
<br />Clinton declared three Colorado
<br />counties (Larimer, Logan and Morgan)
<br />federal flood disaster areas. Ten
<br />additional counties were subsequently
<br />included.
<br />This federal declaration was the first
<br />for Colorado since the 1984 western
<br />slope floods. While the extent of
<br />flooding and storm magnitudes varied
<br />among the 13 disaster counties, the
<br />Colorado Water Conservation Board
<br />reported that six counties (Larimer,
<br />Logan, Morgan, Elbert, EI Paso,
<br />Lincoln) experienced storms with
<br />rainfall amounts exceeding 10-inches.
<br />Upon first glance it might appear
<br />that the District "dodged-the-bullet,"
<br />but a closer look reveals that the Denver
<br />area, while escaping "flood disaster
<br />status," did experience its worst
<br />flooding of the past decade. The
<br />remainder of this article is devoted to
<br />the more notable floods of 1997
<br />occurring within the District.
<br />
<br />Saturday, July 19:
<br />At approximately 4:00 p.m., a
<br />severe thunderstorm in NE Denver and
<br />NW Aurora produced 3.83" of rain in
<br />less than an hour, exceeding the official
<br />Denver one-hour record of 2.2" set on
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<br />August 13, 1921. This storm was
<br />accompanied by copious amounts of
<br />bail with stone diameters reaching 1.25
<br />inches. It is interesting to note that
<br />although these observations were made
<br />by the National Weather Service (NWS)
<br />at their forecast office near Smith Road
<br />and Havana, the 1921 event retains its
<br />status in the record books because the
<br />"official" Denver rain gage, now
<br />located at DrA, only measured 0.59
<br />inches.
<br />Westerly Creek, a tnbutmy to Sand
<br />Creek which enters the old Stapleton
<br />International Airport property from the
<br />south, flowed out of its banks and
<br />nearly overtopped Montview Blvd. The
<br />Montview culverts are designed to
<br />safely pass a 10-year flood, a project
<br />completed by Denver, Aurora and the
<br />District in 1980.
<br />The Sand Creek ALERT gage at
<br />Brighton Road in Commerce City
<br />peaked at 3350 cfs exceeding its prior
<br />gage record of 2760 cfs (7/9190). The
<br />new gage record set on July 19 was
<br />exceeded again on two separate
<br />occasions before the month's end by
<br />discharges of 4200 cfs of July 29 and
<br />3690 cfs on July 30. The historic flood
<br />of record for Sand Creek (25,000 cfs)
<br />occurred on May 8, 1957, from a 4"
<br />plus rainfall covering much of the .
<br />upper basin. The infamous 1965 flood
<br />resulted in a peak of 18,900 cfs.
<br />The July 19 storm caused a roof
<br />cave.in at the Leather Factory
<br />Warehouse near 51st Ave. and Havana
<br />while another storm dropped 4" of rain
<br />near the Interlocken Office Park in
<br />Broomfield, causing the closure of US
<br />Highway 36 where floodwaters
<br />overtopped the concrete median barrier.
<br />
<br />In hindsight, July 19 was a
<br />precursor of things to come and a
<br />landmark day denoting the start of the
<br />Denver monsoon season, as it was
<br />preceded by 23 days of relatively dry
<br />weather where no heavy rainfall was
<br />predicted and followed by an 18-day
<br />period of significant flood potential.
<br />Henz Meteorological Services issued
<br />messages to local authorities on all but
<br />two of these days. Flash flood watches
<br />affecting the District were issued by the
<br />NWS for eight days in this period, and
<br />three flash flood warnings were also
<br />issued
<br />
<br />Sunday, Jnly 27:
<br />Between 3:00 and 4:00 p.m.,
<br />Goldsmith Gulch in Denver was hit by
<br />heavy rains with 1.66" falling at the
<br />Denver Tech Center (DTC).
<br />Downstream floodwaters approached
<br />l()"year levels causing the recently
<br />completed side-channel detention
<br />facility near Iliff Avenue to function.
<br />This flood control facility, constructed
<br />by Denver and the District in 1996 was
<br />credited with preventing damages
<br />downstream. Local residents were
<br />pleased with its performance. A minor
<br />glitch did occur, however, when the
<br />pump which drains the facility failed to
<br />start. Denver Wastewater Management
<br />Division officials corrected the problem
<br />the next day. This event received
<br />extensive media coverage and good
<br />photo documentation was obtained.
<br />The Eastman Avenue ALERT gage
<br />peaked at 4 p.rn. at a depth of7.4' with
<br />an estimated discharge of 1670 cfs,
<br />exceeding its prior record of 1470 cfs
<br />(812191). The Temple Pond gage at the
<br />(Continued on page 18)
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