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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />5 <br /> <br />miles of highly developed area. From the headwaters to the <br /> <br />confluence with Sand Creek, the total fall in the watershed <br /> <br />HISTORICAL FLOODS <br /> <br />is 425 feet, or an average slope of 0.9 percent. Thus the <br /> <br />From 1942 to the present, there have been 14 years with <br /> <br />watershed tends to have a rapid response to storm events in <br /> <br />flooding events on Westerly Creek of more than a nuisance <br /> <br /> <br />level; that is, flooding of premises and impedance of <br /> <br />both individual local subareas and in the basin as a whole. <br /> <br />The basin at the present time contains approximately 900 <br /> <br />traffic occurred. This incidence of flooding represents an <br /> <br />acre-feet of detention storage, 80 percent of which is in <br /> <br />occurrence of about once every 2.2 years. <br /> <br />man-made storm detention facilities of varying adequacies to <br /> <br />We have extracted and tabulated the most severe rainfall <br /> <br />control flooding. <br /> <br />depths for selected storm durations from the above flood <br /> <br />As shown on Drawing No.3, the basin above Lowry Air Force <br /> <br />events, as shown below. <br /> <br />Base is bisected by the Highline Canal, a man-made leveed <br /> <br />Table 1 <br /> <br />channel constructed in the late 1800's to carry irrigation <br /> <br />water for municipal, industrial, and agricultural use in the <br /> <br />Historical Floods <br /> <br />,.---'- .."-- <br /> <br />Denver area. Formerly, the canal acted as a drainage divide <br /> <br />stream to the downstream portions of the watershed. This is <br /> <br /> Estimated <br />Duration Depth Storm Date Return Period <br />(hours) (inch) (years) <br />1 2 August 8, 1945 60- <br />3 2.05 July 18, 19, 1945 40+ <br />6 2.25 June 16, 1950 20+ <br />12 3.40* May 6, 1973 65 <br />18 3.42 August 3, 1951 50 <br />24** 4.33* May 6, 1973 90+ <br /> <br />effectively shutting off contributions of flow from the up- <br /> <br />no longer true because of the increased and increasing urbani- <br /> <br />zation of the upper watershed and the extremely limited <br /> <br />capacity of the canal under storm flow conditions to intercept <br /> <br /> <br />and carry off overland flows into adjacent drainage areas. <br /> <br />*Rainfall at Toll Gate, Aurora gage. <br /> <br />**3-hour-duration depth from this storm was 1.16-inch (Estimat- <br />ed return period, 2 years) <br /> <br />Flood-causing rainfall in these years caused overland inundation <br /> <br />of homes and streets to depths of as much as 4 to 4.5 feet, <br />