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dine No. 4 - Design <br /> The sedimentation and drainage control structures at 1,�ne 1b. 4 portal include <br /> the following: Design details are sl�� on Plates 4-2 and 4-3. Pond design criteria <br /> are strized in calculations - paragraph 5. <br /> a.) Sedimentation Ponds Min. Requlsec_i Storage- <br /> 4-1- Nest Side 0.84 ac/ft <br /> 4-2A East Side <br /> 4-2B Combined <br /> 4-2C capacities of <br /> 4-2D 0.11 ac/ft <br /> b.) Collect-ion and Diversion Ditches <br /> c.-) Diversion Beans <br /> Sedimentation Pond 4-1. is an existing structure t;k3t zest be modified to met <br /> embankment design criteria in accordance with O&M Regulations. Nbdification <br /> include increasing fill slopes (2:1 and 3:1) from existing 1.5:1 slopes instal- <br /> lation of an emergency spi l.lw-ay and a gated outlet works. <br /> • Sedink--nt and runoff from Drainage Nsea 4-1 will be diverted to Pond 4-1 by <br /> ditches and sw-•ales. Sedinent and runoff from mdisturbed areas will be collected <br /> in a Swale formed by the higg 11 and a newly constructed earth berm at the high- <br /> wall toe. (see detail sheet 5-2) This rmoff and sedi�rit then will be allowed <br /> to cross-over the pad sediment collector Glitch via an 18-inch dimeter corrugated <br /> metal pipe. Trris pipe will discharge over and onto to steep sloping s.>oils dumb. <br /> Sediment and runoff from the road above Pond 4-1 also will be conveyed to the 18- <br /> inch crossover pipe. <br /> Drainage area 4-1 will be formed by regrading the road crown at the pad en- <br /> trance area to pew t overland flows to enter Pond 4-1. <br /> Pond 4-1 is located within a potential avalanche path as well as a potential <br /> slope fail,=e area. <br /> . Four Sedimentation Ponds, 4-2A, 4-2B, 4-2C, and 4-2D are proposed to be <br /> const_ucted as shown or. Platers 4-1 and 4--2 in order to met OSM Regulations and <br /> water quality standards. <br /> -7- <br /> 49 <br />