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The SEDCAD modeling for the ditch system is presented on the following pages. The <br />uppermost ditch in the main stem, West Pit Coal Road Ditch, is designed for the 10 year <br />flow as discussed previously. As seen on Exhibit 7 -14F, Figure 3, the West Pit Coal <br />Road Ditch is divided into two drainage basin areas, the upper portion of 33.90 acres, <br />which drains to the ditch from Station 5 +00 to 20 +82 at an average grade of 3.46% and <br />the lower basin area of 20.45 acres, which drains to the ditch from station 0 +00 to Station <br />5 +00 at an average grade of 5.3 %. As shown on Table 1 from Exhibit 7, page 4, the CN <br />for bare topsoiled land in the permit area is 83. Since the basins for this ditch have had 1+ <br />years of seeding and plant growth, it is conservative to use a CN of 82 for these areas. <br />Using an existing CN of 82, the upper portion has a peak flow of 10.53 cfs and the lower <br />portion (which includes the upper portion) has a peak flow of 19.56 cfs. The upper <br />portion is vegetated with smooth brome and is a V -ditch with sideslopes of 2.5H1.OV. <br />The lower portion is not well - vegetated and this V -ditch will be temporarily lined with <br />Rollmax Bionet SC150BN Erosion Control Blanket until vegetation is established. This <br />blanket is a combined coconut and straw fiber held together by a woven biodegradable <br />jute which will last approximately 18 months until vegetation is established through the <br />blanket. The lower portion requires sideslopes of 3.2H:1.OV. The enclosed SEDCAD <br />output shows how the designs for the upper and lower portions comply with the <br />requirements. The primary SEDCAD output shows the long term case when the lower <br />portion is vegetated, which results in the larger cross section. An added page is attached <br />which shows the results for the SC150 BN liner. The acceptable velocity for the liner is <br />8.0 ft/sec and the actual velocity for the 10 year event is 6.5 ft /sec. The cross sections of <br />the ditches are shown on Exhibit 7 -14F, Figure 3. <br />The next segment, which is the main stem of the West Pit Fill Ditch, is designed for the <br />100 year flow as required by Rule 4.09.2 for a ditch in a valley fill. It has a 100 year flow <br />that requires D50 of 12 inches. After being joined by the East Taylor Pond Ditch, the rip - <br />rap sizing increases to 24- inches due to the larger combined flow and the steeper gradient <br />(25 %). Below that point the combined flow is the largest but the gradient has flattened <br />somewhat to 17 %, allowing the rip -rap size to reduce to 21- inches. <br />The East Taylor Pond Ditch has a gradient of about 3.5 percent which allows the use of a <br />vegetative lining, as demonstrated in the attached 100 year storm SEDCAD output. Peak <br />velocity of 6.5 fps in the 100 year event is below the SEDCAD maximum permissible <br />velocity the vegetative lining for this slope gradient. <br />Exh.7 -14F -3 Revision Date: 5/27/14 <br />Revision No.: TR -102 <br />