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RULE 2 PERMITS <br /> <br />Rule 2 Permits 2.04-39 Revision Date: 11/1/21 <br /> Revision No.: TR-150 <br />and the other on a limiting tractive force concept. Table 2.04.7-24 shows allowable velocities and <br />tractive force values for several kinds of channels. This table is taken from Lane (1955) and is <br />based on the work of Forier and Scobey (1926). <br /> <br />When using the limiting velocity concept, one sizes the channel so that it has adequate capacity <br />and so that the average velocity does not exceed the permissible velocity for any given material. It <br />is estimated this maximum allowable non-erosive velocity in the Colowyo mine area is <br />approximately 6 feet per second. <br /> <br />When using the limiting tractive force concept, a channel with adequate capacity will not erode if <br />its average shear stress (given by the equation, shear stress is equal to the unit weight of the fluid <br />times the hydraulic radius of the channel times the slope of the channel in ft/ft) is equal to or less <br />than the permissible tractive force for any given material. It is estimated this maximum allowable <br />tractive force is approximately 0.7 lbs. per square foot at the Colowyo Mine site. <br /> <br />It can be seen that the allowable velocities and tractive forces for erodible channels are quite small, <br />thus requiring very wide shallow channels for the slopes at the Colowyo Mine. This type of channel <br />would appear unnatural and becomes unacceptable as rill erosion and gullying would develop in <br />the channel bottoms during the low flows associated with precipitation events less than the given <br />design storm. On the other hand, if the channel is protected from erosion, the allowable velocities <br />can be increased resulting in a deeper, narrower and more natural looking channel. An effective <br />and permanent form of protection is rock riprap lining of channels in those sections with excessive <br />velocities or tractive forces. <br /> <br />An examination of the premining and postmining stream profiles show that the stream gradients, <br />while at somewhat different elevations, are very similar (see Map 33). The original stream channels <br />in steep slopes had scatterings of rock, boulders and debris. Frequently these channels were into <br />bedrock, providing a stable channel. It should be kept in mind that the original streams had <br />developed over centuries to reach this state of dynamic equilibrium. The mining operation <br />necessarily removes the bedrock in its natural state, and it is replaced in an unconsolidated <br />condition. While it is impossible for the mining and reclamation operation to reconstruct the <br />stabilizing affects of these drainages in bedrock, it is possible and desirable to recreate the <br />stabilizing affects of the rock protection. This method has been elected to armor and stabilize the <br />permanent stream channels constructed or to be constructed at the Colowyo Mine site. A summary <br />of these channels is presented below, and the location of the areas to receive rock riprap protection <br />are shown on Map 12- Hydrology, South. <br /> <br /> Length of Drainage Channels – Feet <br />Destination Unprotected Rock Protected Total <br /> <br />Southwest Tributary to Streeter 0 3,200 3,200 <br />South East Tributary to <br />Streeter 2,500 4,000 6,500 <br />Streeter Gulch 5,700 13,000 18,700 <br />Section 11 Ditch 0 1,000 1,000