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( <br /> t <br /> � STORM AND SURFACE WATER <br /> ( <br /> l Swcmres such as catch basins and manholes for proposed pipe systems, such as catch basins and manholes, <br /> � must provide a minimum of 0.5 feet of freeboard between the head�vater surface (hydraulic grade line) and <br /> the top of the structure for flow from a 25-year srorm. However, structures may overtop for flow resulting <br /> , from a 100-year storm. When overtopping occurs for the 100-year storm, tF.c additional tlow over the <br /> ground surface is analyzed using the methods described in Section 1-6 and is edded to the flow capacity of <br /> � the pipe system. <br /> 4-2.3 PIPE SYST�NIS <br /> Pipe systems are networks of storm drain pipes, catch basins, manholes, inlets, and outfalls designed and <br /> � constructed to convey storm and surface watec The hydraulic analysis of flow in storm drain pipes is <br /> � typical!y limited to "gravity flo�d'. The follo�ving subsections give des�gn criteria for different components <br /> and aspects of pipe systems. <br /> � 4-2.3(1) PIP�NIATERIALS <br /> i 1. Pipe material,joints, and protective treatment shall conform to the requirements set forth in Section 9- <br /> � OS of the WSDOT/APWA Standard Specifications. <br /> , The following pipe materials are allowed for use in pipe systems in the City o( Lverett; other pipe <br /> materials may be approved on a case-by-case basis: <br /> � <br /> � (a) Plain concrete pipe (12 inches in diameter, used only for driveway culvert) <br /> � (b) Reinforced concrete pipe <br /> � (c) Ductile iron pipe <br /> (d) Galvanized corrugatcd iron or steel pipe, treaunent 1 through 6 (not to be used in city <br /> � maintained systems unless approved in advancc by the City Engineer). <br /> � (e) PVC pipe (SDR35, ASTNI D3034 with 3 fee[of cover, minimum) <br /> � (� Corrugated high density polyelhylene pipe, with smooth interior <br /> ( <br /> 2. Coupling bands shall be of the same material as the pipe. <br /> ( <br /> � 3. Materials for concrete, rubber gaskets, metal castings, reinforcing steel, and masonry units shall meet <br /> the requirements of the appropnate secuons of the\VSDOT/APWA 5tandard Specifications. <br /> � <br /> 4-2.3(2) PIP�SIZGS, SLOI'ES,AND V�LOCITIGS <br /> � 1. No storm drain pipe bebveen catch basins or manholes in the public right-of-�vay shall be less than 12 <br /> inches in diameter, with ihe exception that S-inch pipe may be used bet�veen inlets and catch basins in <br /> runs oP 50 feet or Icss. <br /> � 2. The minimum velocity in any pipe or culvert carrying the design stornt flow shnll be 2 feet per second. <br /> i <br /> 3. The maximum allowaUle velocity in concrete pipe shall be 30 feet per second. <br /> , 4. Changes of pipe size are allo�ved only at junctions, and strucmres must be located at all junctions. <br /> 5. Downstream decrease in pipe si-r.e is not a mcommended practice and will only be allo�ved under <br /> spccial conditions. <br /> l <br /> l <br /> � SL\\DA4DS d.? <br /> � Rcr.J/0? <br /> l <br />