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iii iiiiuiiniii iii <br />999 <br />Development Consultants, Inc. <br />September 20, 1991) <br />Mr. Stuart Francone <br />Wyoming Fuel Company <br />10250 Highway 112 <br />Weston. CO 811191 <br />RE: Refuse Disposal Area • 4 R. Cuhert Cupudty and Requirements. <br />Dear Stuart: <br />Greystone Development Consultants, Inc. (Greys[one) has completed an evaluation of the capacity <br />and [law requircmenu of the 4 f[. diameter culvert shown on the attaached sketch. <br />As shoam, the culvert will carry undisturbed runoff from a 31•acre drainage ttrca. Assuming a 100- <br />year, 24-hour precipitation event (4.2 inches), CN=80, and an average runoff slope of 5~ perce.nt, the P„b._, <br />peak design [low [or the culvert is 108 cis. The peak flow calculation is based ou Urban Hvdroloev [or Small <br />Watersheds - SCS Technical Release No, 55, AppendLx D -Peak Rates o[ Discharge for Small Watersheds. <br />According to Figure B•9, Headwater Depth (or Corrugated - hfe[al Fipe Culverts with Entrance <br />Control (attached), HrD for 110 cfs equals approximately 1.44. Therefore. the total headwater depth equals <br />1.44 times 4 ft. equalling 5.76 ft. if this culvert has a headwall of 2 ft. over the tnp of the pipe (headwater <br />depth = 6 ft.), i[ can camp approximately 116 cis and is adeyuate to carry the P,~,,; even[. Since this culven <br />dues not have discharge restrictions, entrance capacity should he the controlling factor in its design. <br />Should you have questions or need additional information regafding this information, please do nut <br />hesitate to ca1L <br />Since <br />. ~~ <br />K.M. Kohn <br />Senior Engineer <br />MK/ca <br />SOO~i i 5rc.:namnr7 010,., R1~..1 C..: ~., i M ~.. ,.1.........d i'~l Cn, , i <br />