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EXHIBIT 7, ITEM 20, PART E
<br />PERMANENT CHANNEL DESIGN
<br />There are eight permanent channels associated with the South Taylor Mine Plan. These are
<br />presented on Map 41 A. Channel profiles for these channels are documented on Map 33B.
<br />Specifically, these channels include the following:
<br />• Section 21 East Tributary Ditch (peak flow of 50 cfs, length of 2,300 feet, average slope
<br />of 21 percent, 3H:1 V sideslopes, 10 year, 24 hour design event)
<br />• Section 21 West Tributary Ditch (peak flow of 50 cfs, length of 2,200 feet, average slope
<br />of 22 percent, 3H:1 V sideslopes, 10 year, 24 hour design event)
<br />• Section 28 East Tributary Ditch (peak flow of 37 cfs, length of 2,200 feet, average slope
<br />of 22 percent, 3H:1 V sideslopes, 10 yeaz, 24 hour design event)
<br />• Section 28 West Tributary Ditch (peak flow of 37 cfs, length of 1,800 feet, average slope
<br />of 19 percent, 3H:1 V sideslopes, 10 year, 24 hour design event)
<br />• East Taylor, East Tributary Ditch (peak flow of 38 cfs, length of 3,000 feet, average slope
<br />of 21 percent, 3H:1 V sideslopes, 10 year, 24 hour design event)
<br />• East Taylor, West Tributary Ditch (peak flow of 38 cfs, length of 2,200 feet, average
<br />slope of 23 percent, 3H:1 V sideslopes, 10 yeaz, 24 hour design event}
<br />• West Taylor, East Tributary Ditch (peak flow of 38 cfs, length of 7,700 feet, average
<br />slope of 21 percent, 3H:1 V sideslopes, 10 year, 24 hour design event)
<br />• • West Taylor, West Tributary Ditch (peak flow of 38 cfs, length of 6,800 feet, average
<br />slope of 19 percent, 3H:1 V sideslopes, 10 year, 24 hour design event)
<br />Note that the peak flows shown above aze for the entire drainage azea at the inlet to the
<br />associated sediment pond, not just for the porkion contributory to the individual ditch. This was
<br />done as a conservative design element. All of the contributory drainage areas are listed on the
<br />individual pond design maps. See the results of the associated SEDCAD runs for verification of
<br />the predicted peak flow. By inspection, the areas contributory to each ditch is less than 1.0
<br />square mile, thus the appropriate design storm is the 10 year, 24 hour event specified in Rule
<br />4.05.3.
<br />Exhibit 7, Item 14 as prepared under permit change TR-63 describes the design methodology .
<br />used at the mine. Further, Exhibit 7, Item 14H provides a generalized ditch design procedure
<br />using a graphical approach based on numerous SEDCAD runs. Using this information, (See
<br />Figure 3 of this Item) all of the above channels have been designed with the following minimum
<br />standazds:
<br />• a trapezoidal channel with a 12 foot bottom width at the channel slopes shown above,
<br />• a total depth of 4.0 feet to insure 1.0 feet of freeboard,
<br />• 3H:1V sideslopes, and
<br />• a minimum D50 riprap diameter of 18 inches.
<br />• It can further be shown that this design is adequate for the 100 year, 24 hour design event for
<br />these ditch segments. Table 1 of this part summarizes the ditch design For these structures.
<br />Exh. 7-20E-1 Revision Date: 3/29/07
<br />Revision No.: PR-02
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