Section 11 AAC 95.295 - Road drainage(a) This section sets out the drainage standards that apply to a forest road.(b) An operator shall minimize the erosion of a road bed, cut bank, and fill slope through the use of cross drains, ditches, relief culverts, bridges, water bars, diversion ditches, or other structures demonstrated to be effective. These drainage structures shall be installed at all natural drainages and must be spaced at least as frequently as set out in the following table: SPACING OF DRAINAGE STRUCTURES
(in feet)
PERCENT OF GRADEREGION IREGION II AND III 0 TO 2 Meet other standards of this section 2 TO 71,0001,5008 TO 158001,000 OVER 15600800
More frequent drainage structure spacing or other drainage improvements must be used where site-specific conditions of peak flows or soil instability makes additional drainage structures necessary to prevent degradation of standing or surface water quality. Less frequent drainage spacing is permissible if the parent material of the roadway is not erodible, such as rock or gravel; the topography or other local conditions are not conducive to erosion; or the degradation of surface or standing waters is not likely to occur.
(c) During road construction, an operator shall install the appropriate ditches, culverts, cross drains, drainage dips, water bars, and diversion ditches when the natural drainage is crossed with the roadbed material.(d) A road shall be outsloped or ditched on the uphill side.(e) In the event an incomplete road is left over the winter season or other extended period, an operator shall, before suspending operations, provide adequate interim drainage by outsloping or cross draining the road, or by the use of water bars and diversion ditches.(f) An operator shall to the extent feasible direct ditchline water away from unstable soils and surface waters, and onto vegetated areas.(g) To minimize sedimentation of standing and surface waters, marshes, and non-forested muskegs caused by drainage from road surfaces and ditches, an operator shall use measures such as settling basins, cross drains, or vegetated areas.(h) A relief culvert installed on a forest road must be at least 12 inches in diameter or the equivalent capacity, and be installed sloping toward the downslope edge of the road at a minimum gradient of three percent.(i) A cross drain, relief culvert, or diversion ditch may not discharge onto erodible soil or over fill slopes unless adequate outfall protection is provided and slope stability is ensured.(j) A drainage structure must also comply with the directional and placement requirements of 11 AAC 95.305.Eff. 6/10/93, Register 126; am 6/24/2004, Register 170Authority:AS 41.17.010
AS 41.17.055
AS 41.17.080