Laserfiche WebLink
• The new design for the Magpie Creek permanent diversion inc]udes riprap <br />placement in the steep channel section, and a series of rock dam drop <br />structures and a grass lined channel in the low gradient upper section. <br />Detailed designs are shown on Magpie Creek Permanent Diversion, (Map <br />25a). Prior to final reclamation of the mine site, the Magpie Creek <br />diversion will be upgraded to permanent diversion specifications to <br />safely pass the peak discharge from a 100-year, 24 -hour event. <br />The reconstructed channel will closely follow the currently existing <br />channel grades, resulting in maximum final channel grades, in two short <br />sections, of ten (10) percent. Channel bottom widths will vary from 10 <br />feet to 15 feet, with•sideslopes of 2H:1V or less, and minimum <br />freeboard of 1 foot. <br />In the upper channel section, from Station G to Station R, rock dams <br />with 2 feet drops will result in intermediate channel grades of one- <br />half (0.5) percent. Since the existing channel bottom and sideslopes <br />are well vegetated, construction of the rock dams will be accomplished <br />in a way to minimize disturbance of the vegetation. All areas disturbed <br />during construction of the rock dams and minor channel regrading will <br />be immediately revegetated utilizing the Drainage Channel seed mixture <br />shown on Table 33a, in Section 2.05.4 of the permit. This grass mixture <br />will provide the equivalent erosion control as the tall fescue grass <br />used in the SEDCAD analysis of peak channel flows shown in this permit <br />section. Any other disturbance that is not covered with riprap, and is <br />above the projected flow depth, will be revegetated with the approved <br />reclamation seed mixture. <br />Design details, including design flows, depth of flow and velocity, <br />riprap size, and channel configurations are summarized on Magpie Creek <br />Permanent Diversion, (Map 25a). The referenced channel sections are <br />shown on the diversion profile drawing included on the Magpie Diversion <br />As-Built Drawing, (Map 25). <br /> <br />139a Revised 11/21/01 <br />Technical Revision No. 32 <br />