(a) General Requirements.
(1) Subdivisions shall be protected from flood hazard and inundation by storm water, springs and other surface waters. The design and construction of drainage facilities shall be such that all watercourses traversing the subdivision and water emanating from outside and/or within the subdivision will be carried through and off the subdivision without any injury to roadway, residential sites or residences to be installed within the tract.
(2) Existing watercourses entering the subdivision shall be received and discharged from the subdivision as nearly as possible in the manner as existed prior to construction of the drainage facilities within the subdivision. Design of drainage facilities within the subdivision watershed. Run-off water originating in a subdivision shall be drained to an adequate outlet. All acts of pollution as defined in Ohio R.C. 6111.01(A) shall be prohibited. Also no "sewage," "industrial wastes," or "other wastes," as defined in Ohio R.C. 6111.01, may be discharged into any watercourse from the subdivision.
(3) A drainage plan shall be submitted simultaneously with the plat of any subdivision, showing the proposed scheme of surface drainage. All necessary facilities including underground pipe, inlets, catch basins or open drainage ditches shall be installed to provide for the adequate disposal of subsurfaces and surface water and maintenance of natural drainage courses. The types and sizes of all drainage facilities used to carry water through and off the subdivision must be approved by the City Engineer. Open drainage ditches, should they be included on any plat, require the special approval of the Planning Commission.
(4) Where an adequate public storm sewer main is available at the plat boundary the subdivider shall construct a storm sewer system to connect with the storm sewer main. If such storm sewer systems are not accessible, adequate storm drainage shall be provided by storm sewers with easements of adequate width as approved by the City Engineer.
(5) As a safety measure for the protection of the health and welfare of the people of the City, the Planning Commission shall reserve the right to disapprove any subdivision which is subject to periodic flooding, contains extremely poor drainage facilities or has other physical impairment. However, if the subdivider agrees to make such improvements, as will make the area completely safe for residential occupancy, provided that in lieu of the improvements the subdivider shall furnish a surety bond or a certified check covering the cost of the required improvements, the subdivision may be approved subject, however, to the approval of the Board of Health and the City Engineer.
(b) Design of Drainage Facilities.
(1) Hydrologic design. Drainageways for those waterways set forth in an adopted master plan for drainage for the County shall be designed and constructed for the quantities of water indicated in such master plan. All other drainageways shall be designed in accordance with the following frequencies:
A. Major waterways. Major waterways are defined as those with a tributary area in excess of six square miles. Such major waterways shall be designed for an average recurrence interval of fifty years.
B. Secondary waterways. Secondary waterways are defined as those with a tributary area of between one-half and six square miles. Such secondary waterways shall be designed for an average recurrence interval of ten to twenty-five years.
C. Minor waterways. Minor waterways are defined as those with 320 acres or less of tributary area. Such minor waterways shall be designed for an average recurrence interval of five to ten years.
Design quantities of flow for major waterways and waterways included in an adopted master plan for drainage will be provided the subdivider by the City. Design flows for secondary waterways shall follow the procedures outlined in Circular No. 4 of the Hydraulics Branch of the Bureau of Public Roads. Design flows for minor drainage facilities shall be computed by the use of the National formula:
(Q = CiA) | WHEREIN: Q = Cubic feet per second |
C = Run-off coefficient | |
i = Intensity of rainfall, inches per hour | |
A = Tributary area |
Basic data prerequisite to the determination of "Q" and "i" will be made available to the subdivider of the City.
(2) Hydraulic design. The hydraulic designs of the subdivision shall be such that, after accumulating all energy losses through the various drainage transmission systems within the subdivision, depth of flow in the streets shall not exceed curb heights for five year average recurrence intervals and for more remote events depth of foundations or easements in residences constructed within the subdivision for twenty-five years average recurrence intervals. Site grading within the subdivision shall be such that all lots will readily drain in areas where topography is less than two percent (2%) or greater than ten percent (10%). A lot drainage plan shall be submitted.
(3) Structural design. All bridges, culverts, catch basins, manholes, inlet structures, etc., placed within the subdivision shall conform to standard plans on file with the City. Structural design of all drainage facilities shall be subject to the approval of the City Engineer.
A. Open channels. Minimum centerline radius of constructed channels shall be a minimum of five times the top width of the channel. Minimum bottom width of constructed channels shall be six feet.
1. Earth channels constructed within the subdivision shall have side slopes of 3:1 or flatter. Revetment, bank stabilization and stream bed stabilization, along constructed or natural channels, will be required if the channel velocities are sufficient to cause bank or invert erosion.
2. The top of the bank shall be so graded that side drainage will enter channels only at points where structures are provided to prevent bank erosion. The design of open channels shall be in accordance with the Bureau of Public Roads publication,"Design of Roadside Drainage Channels," Hydraulic Design Series No. 4. Earth channels constructed within the subdivision in those areas not revetted, shall be seeded over the prepared area (fertilized and limed) with a mixture of 55 lbs. of Kentucky Blue Grass (Poa Pratensis) and 75 lbs. of Creeping Red Fescue (Festuca rubra) per acre to establish a vegetative cover.
B. Closed conduits. Excepting for adequate natural waterways as hereinafter defined and except for allowable gutter flows, all storm drainage within the subdivision which is capable of being transmitted in a reinforced concrete pipe sixty inches or less in diameter, shall be carried in a closed conduit. Minimal conduit size shall be twelve inches diameter PCP or fifteen inches diameter OMP. Minimum clearance between top of pipe and ground shall be fifteen inches.
1. The alignment of closed conduits shall be as nearly straight as practicable without undue bends and angle points. Manholes or catch basins shall be provided at all angle points and at intervals not to exceed 300 feet along the conduit. Inverted siphons shall not be permitted except for temporary structures.
2. Plain concrete pipe or equivalent may be used outside of road right of way provided the strength of such pipe is sufficient to withstand loads imposed on it. In areas having runoff water with acid content or other corrosive effects, all pipes shall be provided with additional lining to assure a project life of fifty years. The above-stated pipe policy and the pipe policy used by the Ohio State Highway Department shall be used in designing storm sewer systems.
C. Bridges. All drainage structures having a span of ten feet or greater and all pipes having a diameter or span of ten feet or greater shall be defined as bridges. All calculations and plans pertaining to bridges shall require both preliminary and final approval from the City Engineer.
D. Culvert.
1. Minor culvert. All culverts having a diameter of thirty-six inches or less shall be designated as minor culverts and shall be subject to the same requirements as "Closed Conduits." Minor culverts should extend from row to row.
2. Major culvert. All culverts having a diameter greater than thirty-six inches shall be designated as major culverts. All major culverts shall be designed in accordance with the requirements of Circular No. 4 of the Hydraulics Branch of the Bureau of Public Roads and shall be subject to the approval of the County Bridge Engineer. Major culverts should extend from row to row.
(c) Easements for Drainage Purposes.
(1) Easements for closed conduits and appurtenances thereof. An easement of not less than twenty feet in width and sufficient to contain the closed conduits shall be dedicated on the final map of the subdivision as "Public Drainage Easement."
Drainage easements for closed conduits shall not traverse a building site and shall, insofar as possible, be placed along or adjacent to lot boundary lines in a straight alignment without angle points.
(2) Easements along streams. Whenever any stream or important surface drainage course is located within the area being subdivided, the subdivider shall provide a permanent easement of sufficient width dedicated to the proper authority for the purpose of widening, deepening, relocating, improving or protecting the stream for drainage or public use.
(d) Drainage Plans. The preliminary subdivision map shall include and shall have appended to it sufficient data for the City Engineer to check the feasibility of the drainage system as proposed by the subdivider. The following data shall be provided:
(1) Hydrologic calculations. At all critical points within the subdivision the following information shall be shown.
A. Tributary drainage areas delineated on the map.
B. Times of concentration.
C. Intensity.
D. Runoff coefficient.
E. Design flow.
(2) Hydraulic calculation.
A. The plan and profile of all drainageways shall be provided including a cross section of open channels showing the maximum depth of flow.
B. Sizes and types of drainage improvement shall include all special structures, typical sections and easement widths.
C. Supporting calculations for upstream and downstream channel capacities as they affect overflow or backwater within the subdivision. Such calculations shall be substantiated by such additional survey information as is required to determine profile and cross-section of the upstream and downstream channel reaches under consideration.
D. Sufficient contours and grading details to indicate proposed street grades and elevations and site grades and elevations throughout the subdivision.
(e) Construction Plans. The final construction plans for drainage within the subdivision shall conform to the provisions of this chapter and to any special conditions as required by the Planning Commission in approving the preliminary map. All construction plans shall be stamped with the seal of a professional engineer registered in the State as required by Ohio R.C. Ch. 4733. Such construction plans for drainage shall be approved by the City Engineer prior to the construction of any drainage facilities within the subdivision. (Ord. 1978-4. Passed 3-6-78.)