(a) General Requirements. The Planning Commission shall not recommend for approval any plat of subdivision that does not make adequate provision for storm and flood water runoff channels or basins. The storm water drainage system shall be separate and independent of any sanitary sewer system. Storm sewers shall be designed by methods as approved by the City Engineer, and a copy of design computations shall be submitted along with plans. Inlets shall be provided so that surface water is not carried across or around any intersection, nor for a distance of more than 300 feet in the gutter. When calculations indicate that curb capacities are exceeded at a point, no further allowance shall be made for flow beyond that point, and basins shall be used to intercept flow at that point. Surface water drainage patterns shall be shown for each and every lot and block.
(b) Nature of Storm Water Facilities.
(1) Location. The applicant may be required by the Planning 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.
(2) Accessibility to Public Storm Sewers.
A. Where a public storm sewer is accessible, the applicant shall install storm sewer facilities, or if no outlets are within a reasonable distance, adequate provision shall be made for the disposal of storm waters, subject to the specifications of the City Engineer.
B. If a connection to a public storm sewer will be provided eventually, as determined by the City Engineer and the Planning Commission, the developer shall make arrangements for future storm water disposal by a 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 City Engineer shall determine the necessary size of the facility, based on the provisions of the construction standards and specifications assuming conditions of maximum potential watershed development permitted by the Zoning Ordinance.
(4) Effect on Downstream Drainage Areas. The City Engineer shall also study the effect of each subdivision on existing downstream drainage facilities outside the area of the subdivision. Local government drainage studies together with such other studies as shall be appropriate, shall serve as a guide to needed improvements. Where it is anticipated that the additional runoff incident to the development of the subdivision will overload an existing downstream drainage facility, the Planning Commission may withhold approval of the subdivision until provision has been made for the expansion of the existing downstream drainage facility. No subdivision shall be approved unless adequate drainage will be provided to an adequate drainage watercourse or facility.
(5) Areas of Poor Drainage. Wherever a plat is submitted for an area that is subject to flooding, the Planning Commission may approve such subdivision provided that the applicant fills the affected area of the subdivision to an elevation sufficient to place the elevation of streets and lots at a minimum of twelve (12) inches above the elevation of the one hundred (100) year floodplain, as determined by the City Engineer. The plat of the subdivision shall provide for an overflow zone along the bank of any stream or watercourse, in a width that shall be sufficient in times of high water to contain or move the water, and no fill shall be placed in the overflow zone nor shall any structure be erected or placed in the overflow zone. The boundaries of the overflow zone shall be subject to approval by the City Engineer. The Planning Commission may deny subdivision approval for areas of extremely poor drainage.
(6) Floodplain Areas. The Planning Commission may, when it deems it necessary for the health, safety, or welfare of the present and future population of the area and necessary to the conservation of water, drainage, and sanitary facilities, prohibit the subdivision of any portion of the property that lies within the floodplain of any stream or drainage course. These floodplain areas shall be preserved from any and all destruction or damage resulting from clearing, grading, or dumping of earth, waste material, or stumps, except at the discretion of the Planning Commission.
(c) Dedication of Drainage Easements.
(1) General Requirements. When a subdivision is traversed by a watercourse, channel, or stream, there shall be provided a storm water easement or drainage right-of-way conforming substantially to the lines of such watercourse, and of such width and construction as will be adequate for the purpose. 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) Drainage Easements.
A. Where topography or other conditions are such as to make impractical the inclusion of drainage facilities within road right-of- way, perpetual, unobstructed easements at least fifteen (15) feet in width for drainage facilities shall be provided across property outside the road lines and with satisfactory access to the road. Easements shall be indicated on the plat. Drainage easements shall extend from the road to a natural watercourse or to other drainage facilities.
B. When a proposed drainage system will carry water across private land outside the subdivision, appropriate drainage rights must be secured and indicated on the plat.
C. The applicant shall dedicate, either in fee or by a drainage or conservation easement, land on both sides of existing watercourses to a distance recommended by the City Engineer.
D. Low-lying lands along watercourses subject to flooding or overflowing during storm periods, whether or not included in areas for dedication, shall be preserved and retained in the natural state as drainage ways. Such land subject to periodic flooding shall not be computed in determining the number of lots to be utilized for average density procedures nor for computing the area requirement of any lot.
(Ord. 2004-40. Passed 5-24-04.)