(A) Recommendations and calculations.
(1) The Plan Commission shall not recommend for approval any sub-division plat which does not make adequate provision for storm water runoff channels or basins. The storm water drainage system shall be separate and independent of any sanitary sewer system. Storm sewers, where required, shall be designed by the Rational Method, or other methods as approved by the Plan Commission, and a copy of the design computations shall be submitted along with the plans. Inlets shall be provided so that surface water is not carried across or around any intersection, nor for a distance of more than 600 feet in the gutter or when the encroachment of storm water into the street disrupts traffic.
(2) When calculations indicated that curb capacities are exceeded at a point, no further allowance shall be made for flow beyond that point and catch basins or inlets shall be used to intercept flow at the point. Surface water drainage patterns shall be shown for each and every lot and block.
(B) Nature of storm water facilities.
(1) Location. The subdivider may be required by the Plan Commission to carry away by pipe or open ditch any spring or surface water that may exist, either previously to, or as a result of the subdivision. The drainage facilities shall be located in the street right-of-way where feasible, or in perpetual, unobstructed easements of appropriate width.
(2) Accessibility to public storm sewer.
(a) Where a public storm sewer is accessible, the subdivider shall install storm sewer facilities, or if no outlets are within a reasonable distance adequate provision shall be made for disposal of storm water. However, in subdivisions containing lots less than 15,000 square feet in area, and in commercial and industrial districts, underground storm sewers systems shall be constructed throughout the subdivision and be conducted to an approved outfall. Inspection of facilities shall be conducted by the Street Commissioner.
(b) If a connection to a public storm sewer will be provided eventually, as determined by the Street Commissioner, the subdivider shall make arrangements for future storm water disposal by the public utility system at the time the plat receives final approval.
(3) Accommodation of upstream drainage areas. A culvert or other drainage facility shall in each case be large enough to accommodate potential runoff from its entire upstream drainage area, whether inside or outside the subdivision. The subdivider's engineer shall determine the necessary size of the facility, based on the provisions of the required construction standards and specifications assuming conditions of maximum potential watershed development is permitted by the Zoning Ordinance.
(4) Effects on downstream drainage areas. The subdivider's engineer shall determine the effect of the proposed subdivision on existing drainage facilities outside the area of the subdivision. Where it is anticipated that additional runoff incident to the development of the subdivision will overload an existing downstream drainage facility, storage basin retention facilities must be constructed by the subdivider to control the appropriate runoff rate.
(C) Dedication of drainage easements.
(1) Where a subdivision is traversed by a drainage course, drainage-way, channel, or stream, a storm water easement or drainage right-of-way shall be provided, granted or dedicated to the city or county conforming substantially to the lines of the watercourse, and of the width and construction as will be adequate for the purpose of both drainage and maintenance of right-of-way. Wherever possible, it is desirable that the drainage be maintained by an open channel with landscaped banks and adequate width for maximum potential volume of flow.
(2) Where topography or other conditions are such as to make impractical the inclusion of drainage facilities within street right-of-way, perpetual unobstructed easements at least 20 feet in width for the drainage facilities shall be provided across property outside the right-of-way lines and with satisfactory access to the street. Easements shall be indicated on the plat. Drainage easements shall be carried from the street to a natural watercourse or to other drainage facilities.
(Prior Code, § 155.43)