Section Env-Wq 1508.21 - Stormwater Control and Conveyance Practices: Earthen Terraced Slope or Benching(a) For purposes of this section, "bench" means a terrace having a reverse grade to the grade of the slope.(b) If diversion swales are incorporated to keep upstream drainage off a constructed slope, benches shall be provided wherever the vertical height between the top of the slope and the bottom of the slope exceeds 40 feet.(c) If diversion swales are not incorporated to keep upstream drainage off the constructed slope, benches shall be provided wherever the vertical height of: (1) Any 2:1 slope exceeds 20 feet;(2) Any 3:1 slope exceeds 30 feet; or (3) Any 4:1 slope exceeds 40 feet.(d) Benches shall be located to divide the slope face into equal parts.(e) Each bench shall: (1) Convey the stormwater to a stable outlet;(2) Be a minimum of 6 feet wide; and(3) Be designed with a reverse slope of 6:1 or flatter from the top of the lower slope to the toe of the upper slope and with a minimum of one foot in depth.(f) The channel gradient from the bench to the outlet shall be between 2 and 3 percent.(g) The flow length within a bench shall not exceed 800 feet.N.H. Admin. Code § Env-Wq 1508.21
Derived from Number 41, Filed October 12, 2023, Proposed by #13758, Effective 9/28/2023, Expires 9/28/2033 (formerly Env-Wq 1508.20) (see Revision Note #4 at chapter heading for Env-Wq 1500).