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COAL CREEK RE.SOURCE • <br />Page 4 <br />n <br />LJ <br />,join the main cnannel. Figure E-5 depicts armoring for the <br />outlet area of a minor tributary. I have Little confidence <br />in this technique. I foresee only scouring-slope <br />failure--especially when dealing with sandy soils. <br />E=stabl_ishment of a sodforming grass on t_he rundown may <br />suffice in some situations. Application of a geotextile <br />fabric after grass seeding will help control erosion and <br />speed grass establishment. In places too difficult to <br />revegetate, I would explore the use of small drop <br />structures. These need not be very sophisticated or <br />~axpensive to construct. They need only to convey runoff <br />nonerosively to the main channel. <br />Figure E-6 portrays the outlet stabilization of a mayor <br />tributary. This design may work if design flows are not too <br />g~-a~. Considering the nature of the concrete rubble, and <br />without a well-graded sand and gravel blanket beneath the <br />rubble, I fear that the structure would be short-lived. A <br />concrete wall properly designed and constructed at the toe <br />of the slope would help stabilize the rundown. The plunge <br />pool should be beefed up, as well. Structures which must <br />handle large storm flows should probably receive greater <br />design scrutiny. <br />~~ <br />Page E-5, first paragraph, discusses the lowland area <br />reclamation sequence. There is no mention of water for ~ -"J <br />newly-planted trees. ~~- {~ <br />Page E-6, Item Number 3 under "Water": Apparently this <br />conclusion was incorrect as an application has been made to <br />the Corps of Engineers. <br />Page E-7, third paragraph, contains a faux pas. We do not <br />want grass seed to germinate in the fall. As the preceding <br />paragragh of the text points out, the appropriate seeding <br />dates are November 1 to April 1. Seedings made in November <br />are dormant see dings--seed lies dormant until spring. (This <br />is the most reliable way of establishing grass in <br />northeastern Colorado where irrigation is unavailable.) <br />This paragraph goes on to prescribe "hand watering of trees <br />during the first and second years of growth." More recent <br />discussion about this subject seems to have established a <br />commitment to a more reliable irrigation method. <br />Page E-7, fourth paragraph: Weed control will likely be <br />required for several years to ensure a vigorous stand of <br />grass. <br />Page E-7, last paragraph: I have already commented on the <br />tree planting scheme. <br />Page E-8: Additional seeding recommendations may be / ~ <br />required for special situations, such as waterways, sodded ~/ <br />rundowns and around erosion/grade control structures. In <br />