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(a) An adequate storm drainage system shall be constructed for each proposed subdivision. Where new streets are to be dedicated, the storm drainage system shall consist of a system of underground conduits which provide adequate inlets for all surface runoff and a separate storm drainage connection for each individual residential, commercial or industrial unit.
(b) The sizes of storm drainage conduits and channels shall be computed by the rational method wherein Q=cia, defined as follows:
Q - flow of water in cubic feet per second
c - coefficient of runoff
i.- intensity of rainfall in inches per hour
a - area drained in acres
All storm drainage computations shall be based on the following assumption:
The maximum allowable time of concentration at initial inlet shall be twenty minutes.
Values of "ci" have been tabulated and are shown by the graph set forth in Appendix A of this Title Two of Part Twelve - the Planning and Zoning Code. All computations to be submitted shall be accomplished on a form similar to that shown in Appendix B of this Title.
(c) All public storm conduits shall be twelve inches in diameter or larger and constructed at such a gradient as to maintain a minimum velocity of flow of two feet per second or greater when flowing at fifty percent capacity.
(d) All service connections to public storm conduits shall be six inches in diameter or larger, and shall extend from the main conduit to the limits of the dedicated right of way.
(e) Unless otherwise specifically authorized, the minimum depth of the invert of the storm service connection at the right-of-way line shall be six feet below the established centerline grade of the pavement.
(f) All storm conduits fifteen inches in diameter or less, including service connections thereto, constructed within the limits of the dedicated right of way, shall be constructed of vitrified clay pipe meeting the Tentative Specifications for Extra Strength Clay Pipe, American Society for Testing Materials Designation C-200-57T with premolded bituminous joints, American Society for Testing Materials Designation C425-60T. Catch basin connections shall be constructed of reinforced concrete pipe.
(g) All storm conduits eighteen inches in diameter or more, constructed within the limits of the dedicated right of way, shall be constructed of reinforced concrete pipe, meeting the Standard Specification therefor, American Society for Testing Materials Designation C76-68, with all pipe joints sealed with an approved field-applied bituminous pipe-joint compound.
(h) In general, storm manholes shall be constructed at all changes in alignment and grade of the conduit, and at intervals of 350 feet maximum. In certain isolated cases or where the size of the storm conduit is forty-two inches in diameter or greater, the interval between manholes may be increased. Standard plant-fabricated radius pipe fortytwo inches in diameter or greater may be used in certain instances.
(i) In general, inlets shall be so spaced that the length of flow of storm water in paved gutters shall not exceed 300 feet. A double grated inlet shall be constructed in instances where necessary.
(j) All areas which contribute or may contribute storm water, either in conduits or by overland flow, to the proposed storm drainage system shall be considered in the determination of the size of the proposed storm conduits or channels.
(k) The design and construction of all storm drainage systems shall be correlated with such storm drainage plans as may be under consideration by the City for the particular area.
Note: (Sections 1226.02 through 1226.04.) If underground electrical utilities are to be installed, the service connections shall be extended fifteen feet beyond the right of way.
(Ord.1418., Passed 5-23-61.)