2016-05-03_PERMIT FILE - C1981008A (14)

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program. A listing of the input parameters for obtaining the peak flows for the reclaimed drainage channels are shown in the appropriate channel attachment. The peak flow determination assumed the total watershed of the reclaimed channel and was determined at the downstream end of the channel. Most of the reclaimed channel will not have to handle that large a peak flow rate. This was done to ensure that the drainage channel capacity will be adequate and yet conservatively designed. A limiting permissible velocity of 5.0 feet per second (fps) was used to ensure that the postmining drainage channels would be non -erodible and stable. The permissible velocity was obtained, Table 3.4, from "Red Book" by Barfield et al., 1981 for a grass mixture vegetated channel. The shape of the reclaimed channel was assumed for design purposes to be trapezoidal with l Oh: l v side slopes as a worst case condition. The side slopes will be no steeper than l Oh: l v. The channel bottom was calculated using the SEDCAD+ Version 3.0 computer program. The channel width was increased to insure that the peak velocity was below the limiting velocity. The typical trapezoidal channel section was selected for design purposes only for the entire length of the reclaimed channel. "Reclaimed Drainage Channel Design" on the following pages contains the specific design information of the reclaimed drainage channel in the eastern portion of the New Horizon 2 permit area (San Miguel Draw). The reclaimed drainage channels will be topsoiled and revegetated according to Sections 2.05.4(2)(d) and (e) respectively. Attachments 2.05.4(2)(C)-1 and 2.05.4(2)(C)-3, which immediately follow this section, show the designs for these restored channels. Any other channels which are left after reclamation are road ditches, as described in Section 2.05.3(3) - Mine Facilities. Morgan Property Grading At the request of the landowner, and in the interest in facilitating quality revegetation, the Morgan Property grading plan has been revised (MR 89) to reduce grades and improve the consistency of grades across said property. Map 2.05.4-1-3 shows the new post mine contours (ft. interval) over top the pre mine topography. The chart below shows the overall improvement in grades on the Morgan Property with this revision. Morgan Property Grades Pre -Mine Topography PR 08 Topography MR 89 Topography Average Land Slope 3.5% 3.2% 3.0% Steepest Slope 15.6% 17.1% 14.7% Revised January 2016 (TR -70) 2.05.4(2)(c)-7