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<br />PAST FLOOOS <br /> <br />ra i nfal I ~mounts to produca an I ntermooiate R&J iona I Flood. The <br />Intensity of the 1912 and 1965 events in an hour or less dlstin- <br />gulshes them frornthe dally maximums shown In table 4. <br />Table 6 shows the rainfall records which were r&corded <br />at Castle Rock during the 16 June 1965 storm. The rain gage at <br />Castle Rock Is an ~utom<ltlc recordIng gage that """I functioned durlng <br />the storm losing the Intermediate rates of rainfall but recordIng <br />the total precIpitation. Interviews with locdl resIdents Indicate <br />that most of the precipitation occurrAd before 5,00 p.m. M.$.T. <br />From these interviews it was disclOSed that an area northeast of <br />Castle Rock received as much as 10 Inches of rain, and an area west <br />of Larkspur received 12 Inches. A second storm occurred the follow- <br />Ing day on 17 June 1965 further southeast that was even more Intense. <br />Five areas received over 12 inches of rainfall durIng the storm. <br />The Intanslty of rainfall for these two storms equaled or excee<led <br />thaf whIch would produceeStandard ProJect Flood If a sImilar storm <br />occurred over the drainage basIns of any of the streams covered In <br />this report. The 16 and 17 June 1965 precipitation also far exceed <br />the ri:ll nfall at the three gagi ng stations sho...n I n table ~ or the <br />short duration records of table 5. Although the streams covered In <br />this report have not recently experienced storms like those expe- <br />rienCed only 30 miles away in 1965 SUCh a storm Is posslbla. <br /> <br />This section explains the flood hIstories and storm <br />characteristics typical of the Denver area. <br /> <br />Flood Records <br />Discharge measurements, high water marks, and Other flood <br />data have not been officIally recorded for any of the five streams <br />studied In this report. <br /> <br />Rainfall Records <br />Rainfall records ...ere studied for an Indication of periods <br />of past flooding and for a comparison with the 1965 flood ...hlch <br />demonstrated the potential for this area. <br />Table 4 shows the maximum dally precipitatIons which <br />occurred each year at threa gage locations for the 21 year period, <br />19~9 through 1969. The Lakewood and Edgewater gages are the closest <br />to the streams studied In this report. These gagos and the Denver <br />c;ltygagerepresent high plains precipTtatlon...hlle the IdanoSp rings <br />gage shows typical mountaIn precipItation. A comparIson of the ~ages <br />shows no apparent dlfterence bet...een mountain and plains raInfall. <br />It Is notad that table 40nly shows tne rnaxTmumdally precIpitation <br />that occurred during tho yoar while In fact there "ore some years <br />when several dally rainfalls ...ere almOST as large. For example, In <br />1957 the Edgewater gage recorded the maxImum rainfall of 2.82 Inches <br />on 2 April, 2.35 inches en 8 May, and 2.05 Inches On 21 August. <br />Table 5 shows the maximum short d~rat!on precipitation <br />amounts at the Denver city gage from 1876 to 1935andi:lttneDenver <br />airport gage affer 1935. ne2.2 Inches of raInfall produced In I <br />hour an 14 July 1912 and the 1.99 Inches praduca In 30 mInutes on <br />2S July 1965 approximate the Intensltv of the Intermediate Regional <br />Flood ralnfal I at one location. However, the enflre area of any ono <br />€If the drainag" basins tinder consideratTon must receIve similar <br /> <br />22 <br /> <br /> Table 4 <br /> MAXIMUM DAILY PRECIPITATION ,; <br /> Gage Location <br /> Lakewood Denver City Idaho Springs <br /> aY b~ "Y bll aY bll <br />1969 2.70 5n 2.37 5n ~.IO 5n <br />1968 .72 ~/17 . ,81 4117 1.06 612~ <br /> 5/10 <br />1967 2.33 ~/I} 1.85 4/13 1.30 4/13 <br />1966 1.19 6;' ,66 .;, ,8< 'I' <br /> " <br />