14-4-4 DRAINAGE AND STORM SEWERS

1. GENERAL REQUIREMENTS. The Planning and Zoning Commission shall not recommend for approval any plat of subdivision which does not make adequate provision for storm or flood 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 using a storm return period of ten (10) years, or other methods as approved by the Planning Commission, 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 six hundred (600) 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. 2. NATURE OF STORM WATER FACILITIES. a. LOCATION. The applicant may be required by the Planning and Zoning 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. Such drainage facilities shall be located in the road right-of-way where feasible, or in perpetual unobstructed easements of appropriate width, and shall be constructed in accordance with the construction standards and specifications. b. ACCESSIBILITY TO PUBLIC STORM SEWERS. 1. 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 water, subject to the specifications of the City Engineer. However, in subdivisions containing lots less than 15,000 square feet in area and in business and industrial districts, underground storm sewer systems shall be constructed throughout the subdivisions and be conducted to an approved out-fall. Inspection of facilities shall be conducted by the City Engineer. 2. If a connection to a public storm sewer will be provided eventually, as determined by the City Engineer and the Planning and Zoning Commission, the developer shall make arrangements for future storm water disposal by a public utility system at the time the plat receives final approval. Provision for such connection shall be incorporated by inclusion in the performance bond required for the subdivision plat. c. 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. d. 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. City 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 developing of the subdivision will overload an existing downstream drainage facility, the Planning and Zoning Commission may withhold approval of the subdivision until provision has been made for the improvement of said potential condition in such sum as the Planning and Zoning Commission shall determine. No subdivision shall be approved unless adequate drainage will be provided to an adequate drainage watercourse or facility. e. AREAS OF POOR DRAINAGE. Whenever a plat is submitted for an area which is subject to flooding, the Planning and Zoning Commission may approve such subdivision provided that the applicant fills the affected area of such 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 maximum probable flood, as determined by the City Engineer. The plat of such subdivision shall provide for an overflow zone along the back of any stream or watercourse, in a width which 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 therein. The boundaries of the overflow zone shall be subject to approval by the City Engineer. Areas of extremely poor drainage should be discouraged. f. FLOOD PLAIN AREAS. The Planning and Zoning 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 which lies within the flood plain of any stream or drainage course. These flood plain 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 and Zoning Commission. DEDICATION OF DRAINAGE EASEMENTS. a. GENERAL REQUIREMENTS. Where a subdivision is traversed by a watercourse, drainage way, channel, or stream, there shall be provided a storm water easement or drainage rightof-way conforming substantially to the lines of such watercourse, and of such width and construction or both 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. b. DRAINAGE EASEMENTS. 1. Where topography or other conditions are such as to make impractical the inclusion of drainage facilities within road rights-of-way, perpetual unobstructed easements at least fifteen (15) feet in width for such 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 be carried from the road to a natural watercourse or to other drainage facilities. 2. 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. 3. The applicant shall dedicate, either in fee or by drainage or conservation easement of land on both sides of existing watercourses, to a distance to be determined by Planning and Zoning Commission. 4. 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 their natural state as drainage ways. Such land or lands subject to periodic flooding shall not be computed in determining the number of lots to be utilized for average density procedure nor for computing the area requirements of any lot.