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• The assumed hydrologic condition is the post- mining condition wherein the entire <br />watershed is reporting to the lowest portion of the ditch, and for which the density of <br />vegetation will vary depending on the time since the particular area has been mined. <br />There is a small fraction of the watershed that will be undisturbed. As shown on the <br />attached SEDCAD printout for the 100 year, 24 hour storm used to design the lowermost <br />segment, below the confluence of the main stem of Taylor Tributary Ditch and East <br />Taylor Ditch, the peak flow is 397.4 cfs. <br />These flows are based on a Curve Numbers of 74 for the lower (northern) portions of the <br />watershed that will have 3 or more years of revegetation growth, and 77 for the upper <br />most portions of the watershed which are assumed to have only 1 to 2 years of revegation <br />growth, as adopted pursuant to TR -73. There are also 48.9 acres of undisturbed lands <br />along the western edge of the permit boundary which were assigned a Curve Number of <br />63, representing native sage brush in fair condition for infiltration, as specified in the <br />above described TR -73. This undisturbed land amounts to only 3.6 percent of the total <br />watershed. <br />For ease of construction, a trapezoidal channel cross - section 12 feet in width will be <br />employed for the rip -rap lined portions of the ditch. Channel side slopes will be 3H:1 V <br />slopes and a minimum depth of 4.0 feet will be used for all sections. Riprap size has <br />been selected based on the SEDCAD modeling as described in the Introductory Text in <br />this Exibit 7 Item 14, pages Exh. 7 -14 -1 through 4. For design consistency and <br />• simplicity, a minimum riprap size of 18- inches has been selected which exceeds the <br />minimum size of 15- inches calculated in SEDCAD for the all reaches except the <br />lowermost reach below the confluence with East Taylor Ditch. There a minimum rip -rap <br />size of 24 inches is required. There are also relatively flat sections in the system where a <br />vegetative liner is adequate, as presented in the attached SEDCAD printout. <br />I� <br />U <br />The following pages present the SEDCAD analysis for the entire Taylro Tributary Ditch <br />for the 100 year event. The SEDCAD runs for the East Taylor Ditch and the Taylor <br />Ditch are included respectively in Sections I and L of this Exhibit 7, Item 14. The ditch <br />design parameters resulting form this analysis are also described in Table 1 in Exhibit 7, <br />Item 14. <br />Exh.7 -14C -3 Revision Date: 12/31/10 <br />Revision No.: TR -81 <br />