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<br />..~o F~ <br />~ Q., <br />f frdI ) <br />'5 Tm <br />~ 'I!.J ,f <br />~ ~'Y <br />&l:In . }.t;)\ <br /> <br />~f,C~:~fBLOOD HAZARD NEWS <br /> <br />rt. '0 '/'l,,\et <br />CO\Ol"~~QlI <)OllIc1 <br />cot\5e~ <br /> <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 /> <br />~ <br />I <br /> <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 <br /> <br />~ <br />, <br /> <br />i[ <br /> <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) <br /> <br />-~- -. ~..;.:~' <br />