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1' 1 <br />~ III IIIIIIIIIIIII III ~ <br />999 <br />Spann Engineering, LLC <br />=t801 So Galapago St <br />Englewood CO 80110-6432 <br />Phone: 303-781-2•l30 <br />2S June 2001 <br />Mr. Paul Mol[z <br />ACA Products <br />702 Gregg Dr <br />Buena Vista CO 81211 <br />Dear Mr Moltz. <br />Tim Krocesky requested design information for the Trout Creek flood and channel capacity in <br />order evaluate the protection of the'rock quarry The channel be ow t edam was designed for the 50- <br />year Bood as determined by the "Estimation of Natural Streamflow Characteristics In Western <br />Colorado" Water Resources In•aestigations Repcrt 85-4086, published by the U S. Geo4ogical Survey, <br />Lakewood, Colorado. 1 originally used the referenced regression procedures to determine the reservoir <br />outlet release requirements and the 100-year flootl for the spillway A copy of my calculations is <br />enclosed. You can see I had also determined other flood magnitudes including the 10-year Flood of <br />208 c f.s. The channel design below the spillway stilling basin was based upon the 50-year flood flow <br />of 354 c.f.s. I should be noted the channel can carry the 100-year flood of 421 c.f.s., however with a <br />diminished free oar <br />' Below are listed the parameters used in the calculation of the 10 year and 50 year Flood <br />channel both of which are more than that required by the state. You may want to continue the 50-year <br />de"sigr~ criteria because it was the design for the spillway stilling basin channel. <br />10-YEAR FLOOD 50-YEAR FLOOD <br />Channel Slope 201% 2.D1% <br />CY~annel Base W idtl'~ 7.0 ft 10.0 ft <br />Channe! Side Slopes 2 i 2'.1 <br />help. <br />Manning's n with n.Qrap .030 030 <br />O Discharge X208 c.f.s C54 o f s~ <br />Depth of Flow 2:07- 2.35 <br />Channel Freeboard 1.0 ft 0 65 ft <br />Average Velocity 9 0 fUSec 10.2 tt/sec <br />Riprap Size 14 inches 14 Inches <br />If you have any questions or need additional information, please call me and I'll be glad to <br />Sincerely, <br />Stephen A Spann <br />Professional Engineer <br />Enclosure <br />