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-15- <br /> <br />C LINTON Y/. MEHRING. PR ESIC E.N'T <br />E. R. MiGHELt. ExEC. VICE P4E510 ENT <br />H. F: 9!SHO-.VICE P4E510 ENT <br />A. J.OJJ TSG H.TR EAe URER~' <br />J. H. TUFN ER. SECRETARY <br />TAr. Richard Atkinson <br />Colowyo Coal Company <br />5731 State Highway 13 <br />Aleeker, Colcrcdo 816~T'1 <br />Dear Mr. Atkinson: <br />TIPTON AND KALMBACH, INC. <br />GM1E =aRrt CEVTga L.EUiTE i<Oi <br />IEiE a•.sPaFCE _'FEET <br />DENVER,CO~ORADO 80202 <br />RHOME (3031 EO2-COBI <br />May 14, 1981 <br />Subject: Colowyo Permit Application <br />Colorado Mined Land <br />Reclamaticn File No. C-019-81 <br />cAeLE <br />4FTIP - DENVER <br />rwx: <br />9i0-93P Z5<3 <br />In accordance with your request v;e have reviewed these portions of the Colorado Mined <br />Land P.eclamation's Adequacy Review, Colavryo Cecl Company -Colowyo Strip, Aeril 10, <br />1981, that reiai2 is a_r cnClReerin0 Y;Crk far COIO'~'/y'O'S Pefmli ACpll WTIOn. C1UC rE__=pa n5 e5 Ta <br />specific points in t:`.e Adecuccy Review ere cs follows: <br />""2,05.3 (~') Pcncs, I:Il~ovndments cnd Diversions <br />1 . Culvert D=_siansi; The Adeauecy P,eview stated that in using the McMath <br />formula far peak flo•.v estimates that incorrect rainfall intensities were used. <br />We have reviewed the p~k flow.calculctions for the 23 culverts, and in <br />.consultation with Mr. P.ichard A. Domingue, Reclamation Speciclist, Colorado <br />dined Land Reclamation Division have concluded that the method outlined <br />in Colorado Water Conservation Board Technical Manual No. 1 "Manual for <br />Estimating Flood Characteristics of Natural-Flow Strc-ams in Colorado" is a <br />more applicable method for determining culvert discharges for drainage areas <br />of. the size and lomtion of these culverts. The discharges v; ere then computed <br />for each of the culverts, and all of the 18" to 48" diameter culverts were found to <br />be of adequate size to pass the design 10-year frequency discharges, and the <br />120" diameter Taylor Creek culvert was found to be cdequate to pass its 20-year <br />design frequency discharge, Table 1 presents data on the culverts including <br />drainage area, discharge for 10-year or 20-year design frequency, culvert <br />diameter, inlet head required for the design discharge, cnd recommendation <br />for outlet riprap, Table 2 presents constructed culvert layout details. <br />2. USLE Calculations: The Adequacy P.eview risked for justificction for use of the <br />method out fined in "Hydroloey and Sedimentoloay of Surface Mined Lands" by <br />• Haan and P,arfield in determining the sediment delivery ratios. In the calculations <br />submitted with the mine permit application we hod computed the delivery ratio <br />