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• established vegetative lining. The steep lower section was armored with <br />24 inch riprap. <br />Design results for the existing Magpie Creek temporary diversion are <br />summarized on Figure 7, Magpie Creek As-Built Diversion-Design Detail, <br />in this section. Channel characteristics are summarized for each <br />channel section. The channel sections are shown on the diversion <br />profile drawing included on the Magpie Creek Diversion As-Built <br />Drawing, (Map 25). <br />In August 1992, the mine received significant precipitation from a <br />series of high intensity thunder storms. Monitoring of flow during the <br />storm events was not possible due to associated safety hazards. <br />Subsequent to the storm events, f]ow in the Magpie Creek diversion was <br />estimated by measuring the high water mark in the 8.8 foot culvert at <br />the lower end of the diversion. Flow depth was measured at 5.5 feet <br />which, using a standard culvert monograph, equates to an estimated flow <br />of 240 cfs. This flow exceeds the calculated flow from a 10-year, 24- <br />hour event (172 cfs). <br />During the storm events, the upper grass lined section of the <br />diversion, (Station G to Station Q) was undamaged and remained stable. <br />This verifies that the design for the upper section of the diversion, <br />as a temporary structure, is more than adequate. <br />The lower section of the diversion was, however, damaged by the high <br />flows with displacement of riprap and some channel erosion. This <br />section of channel had been constructed with insufficient cross <br />sectional area to carry the high flow. Following this event, EFCI <br />elected to redesign the entire diversion to meet permanent diversion <br />specifications. The new design, submitted to and approved by the <br />Division, included installation of a series of gabion drop structures <br />in the steep channel section and installation of ENKAMAT fabric in the <br />upper reach of the diversion. However, due to site conditions and other <br />factors, EFCI has proposed a new design for the Magpie Creek permanent <br />diversion. <br /> <br />139 Revised 7/24/01 <br />Technical Revision No. 32 <br />