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DUTCH CREEK DIVERSION PROJECT (1998) <br />The Dutch Creek Diversion is intended to function as a replacement structure for the Dutch Creek <br />Flume, located to the east of the Project location. The Flume has been in place for a long period <br />of time, and has required a number of repairs in order to ensure its structural integrity. Slope <br />movements to the east and west of the structure are an additional threat to its longevity. <br />The Dutch Creek Diversion Project will create a permanent channel to replace the Flume. The <br />channel will be constructed to pass the expected flows of Dutch Creek in a manner which mimics <br />the channel of Dutch Creek above the Flume location. <br />The Diversion will be constructed as a channel within a channel. The smaller inner channel will <br />consist of a fairly sinuous channel designed to accommodate a channel gradient similar to the <br />undisturbed channel of Dutch Creek. The larger outer channel is designed to accommodate larger <br />flows. The dual channel system has adequate capacity to pass the maximum expected flow. <br />Because the channel is expected to be a permanent diversion, it has been designed as an active <br />system. This means that like a natural stream system, the channel will be dynamic, and therefore <br />aggradation and degradation can be expected to occur within the channel. As with the existing <br />Flume, the Diversion has not been engineered to transport large debris flows. It is not within the <br />scope of available funding to accommodate such events. <br />In order to create the channel, approximately 27,000 cubic yards of material will be cut to create <br />the desired form. Approximately 2,500 cubic yards of rip rap materials will need to be placed <br />within the channel as armor. It is anticipated that this material will be screened from the cut <br />material. The majority of the cut material will be preferentially placed in order to help establish <br />the desired elevations adjacent to the stream channel. <br />Following completion of the channel, areas outside the Diversion which contain cut material will <br />be revegetated using the standard mine site seed mixture. Trees will be planted at a rate of 200 <br />stems per acre. This will be accomplished at the time of planting of the remainder of the facilities <br />area. Within the channel, species adapted to a wetlands environment will be planted. These <br />species will be purchased with funds from the OSM grant. Planting may not occur until the spring <br />following channel construction in order to minimize the loss of immature plants during spring <br />runoff <br />23 <br />