1111 CRAFTSMAN WAY 2016-01-01 MF Import

( ( � DESIGN AND CONSTRUCTION STANDARDS � AND � SPECIFICATIONS SECTION 4 STORVI AND SURFACE WATER 4-1 G�NERt1L � This section o[ the Standards provides ctiteria for the design of storm and surface �vater drainage systems, � including storni pipes, culverts, and catch basins. Each of the sections in this chapter contains the design critena and references standard details for the various systems or facilities. i Drainage control and stormwater treatment shaIl be provided for all property improvements within the City � of Everett per these Standards, thc City's Stormwater Manual, the C�ty's Drama�e Ordinance (#670-30 and subsequent revisions), the City's Surface Water Ordinance (#1750-90 and subsequent revisions), the City's Comprehensive Drainage Plan, and thc City's Zoning Code. ProJ'ects �vhich will disturb one acre or more of land, or create 5,000 square feet or more of impervious swfiace, paved or othenvisc, must refer to the City of Everett's Stormwater Manual for drainage plan and runoff control requirements. 4-2 S'I'ORA'I DRAINAG� CONVTYANCC SYST��I D�SIGN CRITGRIA 4-2.1 OV�RVI�W i For the pumoses of this scction, the convevance system includes all portions of the surface water system that � transport storm and surface �vater runoff, either natural or man-made, except those features protected as � environmeutally sensitive areas under lhe City's zoning code. Environmentally sensitive areas may only be modified as allowed under Qie City of Evcrett Zouing Code. Stormwater must generally be treated and ( detaincd prior ro discharge to an environmentally �ensitive area, including those features created for � mitigaUon. � This section covers the follo�ving components of die comeyance system: ( Pipe systems � Culverts Outfalls i Open channels � �F-2.2 DGSIGN rL0\V r1ND ROUT� R�QUIRGNI�NTS Desi�n Flo�v i All existing and proposed conveyancc systems shall be desi�ned to convcy nmoff from the 2�-ycar stonn. � The method used to determine the design flow will depend on the cha;acteristics of the drainage area and tlic i typc of conveyancc. Tigh[-lined conveyance systems receivin� runoCf from relatively small andlor h�ehly unpervious drainagc arcas shall be sized using flo�vs deterniuied usin� the rational method. Flows for ' culverts or channels receiving runoff from lar�e and/or relatively pervious drainage areas shall be sized � using Flows deterniined usin� hydrograph mediods. These methods of determining desi�n tlows are explained in detail in Scction 1-6 of[he C�ty oF�verett Stormwater D4anagement bianual � A backwater analysis (sec Section I-6 of the Storm��ater Management blanual) may be required for a . � �roposcd or existing pipe system if the ability of the pipe system to convey the pcak rate of runoff from the 5-year dcsign stomi evcnt may be affected by tail�vater conditions (outlet control) any�vhere in the pipe systcm. � � s�.�un,��eus a�i � k�.�.aio�