(A) Drainage structures shall be constructed in such locations and of such size and dimensions to adequately serve the subdivision and the contributing drainage area, and in accordance with the drainage study. The developer shall provide all the necessary easements and rights-of-way required for drainage structures, including storm sewer, open or lined channels, or overland flow discharges. Easement width for open or lined channels shall be at least 15 feet wider than the top of the channel, ten feet of which shall be on one side to serve as an access for maintenance purposes. Design flow of storm drainage water is to be calculated based on the major and minor storms.
(B) Streets shall be designed so that in a minor storm, water will not overtop the curb. Flow may spread to the crown of the street. Streets and adjoining properties shall be designed so that in a major storm, water will not inundate residential dwellings and public, commercial, or industrial buildings at the lowest finished floor elevation. The depth of water at the street crown may not exceed 12 inches. The depth of water over the gutter flowline shall not exceed 24 inches.
(C) The design, size, type, and location of all storm drainage facilities shall be approved by the City Manager or City Engineer. 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, 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 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.
(1) Open or lined drainage ditches. Open or lined drainage ditches, as required by the City Engineer, shall be constructed in the locations defined in drainage study. All open or lined channels shall have a minimum bottom width of four feet, and shall be designed based on the major and minor storms. Side slopes of channels shall not be steeper than one foot vertical rise to four feet horizontal distance unless approved by the Director of Public Works shall determine if the velocity or other factors warrant a lined channel.
(2) Storm sewer. Water in excess of the maximum allowed shall be carried by storm sewers or channels. Location and design of storm sewer shall be approved by the City Engineer.
(3) 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, 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 subdivision improvement agreement required for the subdivision plat.
(4) 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, 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 permitted by the Zoning Ordinance.
(5) 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 City Engineer 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.
(6) Areas of poor drainage. Whenever a plat is submitted for an area that is subject to flooding, the City Engineer 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 12 inches above the elevation of the 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 City Engineer may deny subdivision approval for areas of extremely poor drainage.
(7) Floodplain areas. The City Engineer may, when it deems 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 the City Engineer.
(D) Dedication of drainage easements.
(1) General requirements. When a subdivision is traversed by a watercourse, drainage way, 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 rights-of-way, perpetual, unobstructed easements at least 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 by a drainage easement or conservation easement, land on both sides of existing water-courses to a distance to be determined 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 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 procedures nor for computing the area requirement of any lot.
(3) Intersections.
(a) Streets shall be laid out so as to intersect as nearly as possible at right angles. A proposed intersection of two new streets at an angle of less than 75 degrees shall not be acceptable. An oblique street should be curved approaching an intersection and should be approximately at right angles for at least 100 feet therefrom. Not more than two streets shall intersect at any one point unless specifically approved by the Planning and Zoning Commission.
(b) Proposed new intersections along one side of an existing street shall, wherever practicable, coincide with any existing intersections on the opposite side of such street. Street jogs with centerline offsets of less than 150 feet shall not be permitted, except where the intersected street has separated dual drives without median breaks at either intersection. Where streets intersect major streets, their alignment shall be continuous. Intersection of major streets shall be at least 800 feet apart.
(c) Minimum curb radius at the intersection of two local streets shall be at least 20 feet; and minimum curb radius at an intersection involving a collector street shall be at least 25 feet. Alley intersections and abrupt changes in alignment within a block shall have the corners cut off in accordance with standard engineering practice to permit safe vehicular movement.
(d) Intersections shall be designed with a flat grade wherever practical. In hilly or rolling areas, at the approach to an intersection, a leveling area shall be provided having not greater than a 2% rate at a distance of 60 feet, measured from the nearest right-of-way line of the intersecting street.
(e) Where any street intersection will involve earth banks or existing vegetation inside any lot corner that would create a traffic hazard by limiting visibility, the developer shall cut such ground and/or vegetation (including trees) in connection with the grading of the public right-of-way to the extent deemed necessary to provide an adequate sight distance.
(f) Bridges. Bridges of primary benefit to the applicant, as by the City Council shall be constructed at the full expense of the applicant without reimbursement from the local government. The sharing expense for the construction of bridges not of primary benefit to the applicant as determined by the City Council, will be fixed by special agreement between the governing body and the applicant. The cost of bridges that do not solely benefit the developer shall be charged to the developer pro rata based on the percentage obtained by dividing the service area of the bridge into the area of the land being developed by the subdivider.
(E) Road dedications and reservations.
(1) New perimeter streets. Street systems in new subdivisions shall be laid out so as to eliminate or avoid perimeter half streets.
(2) Widening and realignment of existing roads. Where a subdivision borders an existing narrow road or when the master plan or zoning setback regulations indicate plans for realignment or widening a road that would require use of some of the land in the subdivision, the applicant shall be required to improve and dedicate at its expense those areas for widening or realignment of those roads. Frontage roads and streets as described above shall be improved and dedicated by the applicant at its own expense to the full width as required by these subdivision regulations when the applicant's development activities contribute to the need for the road expansion. Land reserved for any road purposes may not be counted in satisfying yard or area requirements of the Zoning Ordinance whether the land is to be dedicated to the municipality in fee simple or an easement is granted to the local government.
(Ord. 2005-6, § 5.4, passed 9-20-05)