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<br />Amethyst Mine Culvert <br />West Willow Creek passes through a 7- foot diameter corrugated metal culvert just beside the <br />Amethyst Mine tunnel. A photo of the culvert entrance and "grizzly" follows. The area around <br />the culvert was briefly surveyed in order to model the ability of the culvert to convey flood <br />flows. Figure 2.2.35 shows results from HEC-RAS at the upstream end of the culvert. The <br />Amethyst Mine tunnel is located on the right and a small shed is on the left of the cross-section. <br /> <br /> <br /> <br />Station (ft) <br /> <br />Figure 2.2.34. Entrance to Amethyst culvert <br />Figure 2.2.35. (right) Flood elevations at entrance to Amethyst mine culvert <br /> <br />The analysis shows that only the 100-year flood should cause overtopping of the culvert. This <br />flooding should flow through a low area to the east of the culvert and will probably cause <br />damage to the road access to the mine tunnel. Although the culvert has sufficient capacity to <br />pass all but the 100-year flood, debris will probably plug the culvert at a much smaller flow. <br />Currently, large amounts of debris must be removed annually from the iron "grizzly" that <br />protects the culvert entrance. The reach just above the culvert is quite steep and contains a large <br />amount of timber debris. A large volume of cobble has also collected just in front of the culvert. <br /> <br />Culverts between Commodore and Amethyst Mines <br />Four 7-foot diameter corrugated metal culverts are located on <br />West Willow Creek between the Commodore and Amethyst <br />Mines. A photo shows one of these culverts. Although hydraulic <br />analyses were not conducted for these culverts, it is expected that <br />the culverts will be overtopped by large flood events. However, <br />structures will not be damaged by flooding at these culverts, and <br />the risk of localized road damage is probably not as high as the <br />cost of replacing these culverts. On the other hand, the culverts <br />are very susceptible to plugging by timber debris during smaller <br />flood events, and reduction of debris sources would be very <br />worthwhile. <br /> <br />Figure 2.2.36. Culvert above cross-section 40 <br /> <br />2-36 <br /> <br />