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• As shown on Map 41A, a system of secondary channels will also be provided. These are also <br />summarized on Table 1. While only the secondary channels on or across the permanent fill <br />would require a 100 year design, all secondary channels assume this basis for conservancy. This <br />results in all of these channels to be riprapped for erosion protection. <br />Under the 10 year event, many of these ditches would not require riprap assuming the entire area <br />has been revegetated for at least 1-2 years and the contributory drainage azea has a representative <br />curve number of 61. Because other SEDCAD runs provided in this submittal represent a <br />particular period in time when only portions of the area have been reclaimed, the 100 year design <br />basis and the need for erosion protection is consistent with those analyses. <br />As shown on Table 1, the WTE-A Trib ditch has the largest drainage area and has been used as a <br />example for design purposes. The following SEDCAD4 run is provided for this long term case <br />where the 100 year, 24 hour design storm is used and the entire drainage area is assumed to be <br />both contributory and reclaimed (Curve Number 61). The resultant peak flow generated was 31 <br />cfs. As such, all of the secondary channels will be constructed as trapezoidal ditches with a 12.0 <br />foot bottom width, 3H:1 V sideslopes, and a minimum D50 riprap diameter of at least 9 inches. <br /> <br />• <br />Exh. 7-20E-2 Revision Date: 3/29/07 <br />Revision No.: PR-02 <br />