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•) <br />TIPTON AND KALMBACH, INC. <br />ONE PAR%CENTRGI.SUITE 1<OI <br />1515 ARAPAMOE 3TRf ET <br />C LINTON W~ MfHRIN G. PRESIDENT <br />E. R. MIGHELL. E%EC. V ICE PRESTO ENT <br />M. F. BISHOP. V ICE PR ESIOENT <br />A. J~OEUTBOH.TREASURER <br />J. M. TURNER. SECRETARY <br />Mr. Richard Atkinson <br />Colowyo Coal Company <br />5731 State Highway 13 <br />Meeker, Colorado 81641 <br />DENVER,COLORADO 80202 <br />PHONE (3031 ST2-0001 <br />May 14, 1981 <br />Subject: Colowyo Permit Application <br />Colorado Mined Land <br />Reclamation File No. C-019-81 <br />Dear Mr. Atkinson: <br />CABLE <br />ARTIP - DENVER <br />TV: %: <br />910.931-2540 <br />In accordance with your request we have reviewed those portions of the Colc ado Mined <br />Land Reclamation's Adequacy Review, Colowyo Coal Company -Colowyo Strip, P.^ril i0, <br />1981, that relate to our engineering work for Colowyo's Permit Applimtion. Our responses to <br />specific points in the Adequacy Review are as follows: <br />2.05.3 (4) Ponds, Impoundments and Diversions <br /> <br />• <br />1 . Culvert Designs:+ The Adequacy Review stated that in using the McMath <br />formu~or peak flow estimates that incorrect rainfall intensities were used. <br />We have reviewed the peak flow mlculations for the 23 culverts, and in <br />consultation with Mr. Richard A. Domingue, Reclamation Specialist, Colorado <br />Mined Lond 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 Streams in Colorado" is a <br />more applicable method for determining culvert discharges for drainage areas <br />of the size and lomtion of these alverts. The discharges were 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 puss the design 10-year frequency discharges, and the <br />120" diameter Taylor Creek culvert was found to be adequate 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, and recommendation <br />for outlet riprap, Table 2 presents constructed culvert layout details. <br />2, USLE Calculations: The Adequacy Review asked for justification for use of the <br />method out fined in "Hydrology and Sedimentology of Surface Mined Lands" by <br />Haan and Barfield in determining the sediment delivery ratios. In the calculations <br />submitted with the mine permit application we had computed the delivery ratio <br />