PERMFILE62629

• Permit No: C1981010
• IBM Index Class Name: Permit File
• Doc Date: 3/20/1989
• Doc Name: DRAINAGEWAY RECONSTRUCTION IMPROVEMENTS AND REPAIRS
• Section_Exhibit Name: Appendix W 1988 Report Section 3.0
• Media Type: D
• Archive: No

•
SECTION 3.0 Drainageway Reconstruction, Improvement
and Repairs at Trapper Mine in 1988
3.1 Drainage reconstruction in 1987-88
Portions of four major drainageways and their tributaries were regraded and appropriately treated to reduce
the erosion rate and assist in permanent gully stabilization in 1987 and 1988 (see attached "Drainage
Reconstruction' map). Erosion control techniques were applied In Coyote, East No-Name, West No-Name,
and Johnson Gulch drainages and included 28,750 feet (5.4 miles) of permanent drainageway treatment. In
1988, approximately 8,600 feet of permanent drainageway reconstruction was completed in lower Coyote
Drainage, Coyote tributary, Johnson Gulch and Johnson Gulch tributary in E pit. (Coyote tributary was
treated with straw bales in 1987 and was a temporary erosion control measure rather than a permanent
measure as reported in the 1987 Drainage Reconstruction Report).
A wide variety of erosion control materials, methods and sediment reducing measures were used in
reconstructed drainageways and on adjacent reclaim sideslopes.
3.2 Drainage measures and materials
The following measures were implemented on reclaimed sideslopes, drainageways and/or on regraded
spoils to reduce the amount of water and sediment load into drainageways.
Dozer basins (sediment basin) were constructed to trap and store sediment on newly stripped topsoil areas
and on regraded spoils to reduce or abate the sediment load. Basins are used to prevent the siltation of
• diversions, waterways, livestock ponds, and streams; to trap sediment originating from the active mine site
and to prevent undesirable deposition on undisturbed bottomlands and reclaimed areas. The dozer basins
primary use is to trap sediment, reduce on-site erosion, reduce peak Flows at downstream locations, and
reduce gully erosion.
Livestock watering tanks (ponds) are used to trap water on reclaimed sideslopes, in drainageways, and to
reduce peak flows at downstream locations making available reliable water for wildlife use. The location of
livestock ponds is such that a minimal amount of sediment will be deposited. This was accomplished by
installation of ponds at headwater locations or on relatively gentle grades often within water harvesting
diversions on reclaim sideslopes.
Water harvesting diversions are channels constructed across slopes with a supporting ridge on the lower
side that Is used to transport excess water from areas that need protection to sites where water can be used
or disposed of safely. A diversion's effectiveness as a sediment reducing measure is in diverting the runoff
which would otherwise flow across erosion susceptible areas, thus detaching and transporting soil particles.
Contour Farming and live haul topsoil transport are used on all reclaimed sideslopes and drainage areas
when possible. Topsoil replacement, seedbed preparation, and planting are done on the contour.
Contouring can reduce erosion by 40 to 50 percent. When contour farming is combined with live material
topsoil transport the erosion loss potential can be further reduced. Contouring provides excellent erosion
control by reducing transport from moderate rainfall events. Contouring in combination with diversion
establishment can be very effective in reducing erosion potential.
Rock check structures are used to dissipate the energy of flowing water within the drainageway channel.
Debris and sediment tend to be deposited and trapped upstream of structures. This in turn permits
• establishment of vegetation behind structures which further stabilize the channel. In addition, filter fabric is
installed and used to line rock check structure core trenches, thus providing additional structural support
and reduces the potential for advancement of downstream headcutting to move upstream.