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<br />(HEC-RAS encroachment method 4) and a maximum allowable rise of I.0 feet, as defined by <br />FEMA for determination of the floodway, was used to determine the lateral limits of the <br />floodway. Aeral adjustments and flow inputs were used based on the location of appropriate <br />USGS gauging stations, per the USGS web site. The engineering analysis verifies that all pit <br />excavations will be outside the limits of the floodways for Trout Creek and the Yampa River. <br />Trout Creek is extremely stable. Evidence of streambank erosion, indicative of a stream's <br />tendency to migrate laterally, is virtually non-existant. The engineering flood analysis performed <br />on Trout Creek for the proposed operation showed that the 100-year flood flows are contained <br />within the banks of Trout Creek. The proposed 50' setback from the streambank of Trout Creek <br />should be more than sufficient to keep Trout Creek from entering the pit. The Yampa River will <br />be 200-250' or more away from the northernmost edge of the proposed excavation. While some <br />lateral migration of the Yampa River at this location can occur, a buffer of 200-250' or more is <br />very large and should be more than adequate to minimize the potential for the river entering the <br />pit. Near bank velocities in the river at this location during a 100-year flood event are relatively <br />slow, ie: typically 3-5 fps with a maximum velocity of 6-8 fps. The combination of channel <br />shape along with the presence of gravels in the stream banks and moderate velocities indicate the <br />streambank is at a low risk of rapid lateral migration. Therefore, bank erosion of only a few feet <br />during a high water event can be expected. <br />