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Design velocities~r the channel will not exceed fps for bare soil <br />ditches or 5 fps for grass-lined or rip-rapped channels. Channel slope will <br />be primarily dictated by the slope of reclaimed drainage located above the <br />permanent drainageway. Generally, channels will be seeded to promote <br />vegetation growth, and increase stability and reduce erosion potential. The <br />cross-section shape of the channel will typically be trapezoidal, with side <br />'I slopes of 3: 1. The channel bottom will typically be 10-12 feet for <br />calculated peak runoff flows above 7 cfs. Wide flat-bottomed channels are <br />observed to be stable in undisturbed areas and vegetation may become <br />established relatively easily. Channel sides and bottoms will 6e scarified, <br />channel sides and possibly channel bottoms will be broadcast seeded. The <br />seed mixture used for stabilization is the same as the currently approved <br />pastureland seed mix. <br />Additional measures may need to be taken to minimize erosion until <br />vegetation becomes established. During the construction of permanent <br />drainageways, channel bottoms will be scarified when possible to increase <br />roughness: Another method used to increase roughness would be the creation <br />of small check dams and undulations using the rough spoil material in the <br />• drainage bottoms. These would be installed perpendicular to the direction <br />of flow. Additlonal rip-rap may be installed in some steep channels. <br />In some permanent drainageways, Colorado Yampa Coal Company may <br />construct additional check dams to supplement those created with spoil <br />material. For these additional check dams, rip-rap will be used to fill and <br />protect the top and apron of the check dams. A typical design of these <br />check dams is depicted on Figure 28-3, Typical Gully Check Dam <br />Reinforcement. In other instances, rip-rap alone may be installed to <br />provide additional erosion protection. <br />Examples of specific channel design specifications are presented on <br />Table 28-3, page 28-25, of this exhibit. The locations of the drainages are <br />shown on Map 28-3, Existing and Potential Permanent Drainageway Locations. <br />Diversion ditch construction will follow the same guidelines outlined <br />above. However, in some cases, diversion ditches will be V-bottom rather <br />than flat-bottom for ease of snow removal. Past experience of Colorado <br />Yampa Coal Company has shown V-bottom ditches can be more easily cleared of <br />28-14 <br />... _,.,.~...,.: ~4 _. ~. w..... _ . .. sl <br />