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<br />iii iiiiiiiiniiiiii <br />GREG LEWICKI AND ASSOCIATES <br />October 18, 1992 <br />Joe Dudash <br />Colorado Division of Minerals and Geology <br />1313 Sherman Street 2nd Floor <br />Denver, Colorado 80202 <br />1645 Court Place <br />Suite 309 <br />Denver, Colorado 80202 <br />REP~EI V~~9335 <br />OCT 191992 <br />MINERALS ~ ~ ur <br />~EOL'vG'v <br />Re: Violations C-'9"2~0f~ and <br />C-92-014 <br />Dear Joe: <br />Enclosed is additional information which supports the claim that <br />the rainfall event which occurred on June 29, 1992 was larger <br />than the 10 year - 24 hour event. <br />Using the OSM STORM model, it was shown in my submittal on <br />September 10 that the peak flow for a 10 year - 24 hour event in <br />the drainage basin leading to the bridge crossing was 49.4 cfs. <br />It should be noted that many kinds of storms of different <br />intensity, duration, antecedent moisture condition and other <br />factors could produce a peak runoff of 49.4 cfs. Basically, any <br />storm that produces this runoff from the complex set of <br />parameters of the drainage basin and the storm should exempt the <br />operator from compliance. <br />Using pictures taken by Dan Mathews of the Division taken the day <br />of the storm, it is seen that the bridge crossing contains a <br />large flow which is entering the Delagua drainage. It is also <br />seen that upstream from the bridge crossing, the berm channeling <br />the flow to the crossing has also breached and water is also <br />entering the Delagua drainage from this point. <br />Although it is difficult to estimate flow from the pictures, the <br />following calculations are presented to demonstrate that the flow <br />was most likely 50 or more cfs at the peak period. <br />Using Manning's equation for flow in a channel: <br />