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COAL CREEK RESOURCE • <br />Page 3 <br />• <br />Page E-2, last paragraph, describes the use of "rubble-lined <br />channels/chutes." I would refrain_from usiny__Log_structures <br />except in minor tributary drainages. Their useful life is <br />not as long as rock or concrete structures; and where heavy <br />flows are encountered, it will be difficult to design and <br />construct them so they will not fail. I also ~estion the <br />use of concrete rubble in structures of any significant <br />size. I think it would be difficult to construct an <br />enduring structure with this material. I'd be interested in <br />seeing the comments from Arapahoe County and the Urban <br />Drainage & Flood Control District. <br />Page E-3, first paragraph, discusses "straw bale sediment <br />:heck dams." I recommend that these be used sparingly; in <br />most situations a properly installed "silt fence" is much <br />more effective and durable. <br />Page E-3, last paragraph, indicates that 120,000-150,000 <br />plants per acre are needed for the warm season cover crop. <br />I erred in my original recommendation to you. I gave you a <br />plant population for forage sorghums; for grain sorghums, a <br />plant population of 80,000-100,000 is sufficient. <br />Page E-4, first paragraph, lists steps involved in the ~~ n L <br />reclamation sequence. Weed control, by mowing or ~ <br />;application of appropria~rbicides, needs to be included. ~ <br />(It should be a component of items 3 through 6.) <br />Page E-4, second paragraph, indicates that creek bottom side <br />:slopes will be reshaped to 3:1 or less. In sandy soils, <br />this is likely to be too unstable to allow successful <br />revegetation. 4:1 slopes would be better; 6:1 slopes are <br />preferred. <br />Page E-4, fourth paragraph, discusses placement of new trees <br />in the creek bottom. (Figure E-4 conveys information, too.) <br />[t is my feeling that these trees will actually accelerate <br />;treambamk erosion. In general, the post-mining creek <br />channel is confined to a smaller cross-sectional area; storm <br />flows may possess higher velocities which will erode the <br />bank areas. ~hc~wo_tions in the channel, such as trees, <br />will create turbulence in the storm flows and result in <br />scouring. A very unstable channel will result, with active <br />erosion in some areas and sedimentation in others. <br />Increased amounts of sediment may be delivered to downstream <br />locations, as well. Cottonwoods don't normally survive in <br />the dynamic creek bottom, anyway. They occupy the slightly <br />higher, more stable positions in the floodplain where they <br />obtain water from larger flood events and avoid, the <br />incessant scouring and inundation typical of the main <br />channel. <br /> <br />{'age E-4, last paragraph, contains information about the <br />:stabilization of areas where minor and maJOr tributaries <br />