(a) Definitions. Certain terms as used herein are defined as follows:
(1) "Flood hazards" means overflow water having sufficient velocity to transport debris to scour the surface soil, or to dislodge or damage buildings. It also means erosion of the backwater courses.
(2) "Inundations" means standing water or water in motion, of sufficient depth to damage property due to mere presence of water or of the deposition of silt.
(3) "Average recurrence intervals” means the average intervals in years between storm water flow of a given magnitude, or greater, over a long period of time, such as 50 or 100 years.
(4) "Waterways".
A. "Major" means those with tributary area in excess of four square miles.
B. "Minor" means those with a tributary area of one or less square miles.
C. "Secondary" means those with a tributary area of between one and four square miles.
(b) General Requirements. Subdivisions shall be protected from flood hazards and inundation by storm water, springs and other surface waters. The design and construction of the drainage facilities shall be such that water courses traversing the subdivision and water emanating from within the subdivision shall be carried through and off the subdivision without any injury to improvements, residential sites or residences to be installed within the tract. Drainage water entering the subdivision shall be received and discharged from the subdivision at the location, and as nearly as possible in the same manner, as existed prior to the construction of the drainage facilities. Design of these facilities shall be such that they shall conform to the ultimate drainage plan for the watershed area in which the subdivision is located.
(c) Design of Drainage Facilities.
(1) Basic information and data shall include:
A. A contour map of the site and adjacent areas including all natural topographical features, possible outfalls and ditches and any adjoining terrain sloping toward the site. The contour interval shall not be more than two feet.
B. A drainage working drawing, as an additional map, shall be submitted. This drainage shall show the layout of the paved areas and building areas, as well as all future master plan developments. It shall show tentative finished grade contours, all existing and proposed pipelines, manholes, inlets, outfalls, individual drainage areas in the subdivision, slopes and like streams.
C. Boring plans and soil profiles prepared on the basis of soil tests, indicating data on ground water elevation. This data shall include infiltration properties of the soil.
(2) Hydrologic design. Those waterways set forth in an adapted plan for Columbiana County in sections related to drainage shall be designed and constructed for the quantities of water indicated in accordance with the following frequencies:
A. Major waterways; an average recurrence interval of 100 years.
B. Secondary waterways; an average recurrence interval of 50 years.
C. Minor waterways; an average recurrence interval of 10 years. Design quantities of flow for major waterways shall be provided. Design flow for secondary and minor drainage facilities shall be computed by the subdivision's engineer by use of the rational formula: Q = C i A.
Where Q = Cubic feet per second
C = Runoff coefficient
i = Intensity of rainfall in inches per hour
A = Tributary area in acres
(3) Hydraulic design. The hydraulic design of the area shall be such that, after accumulating all energy losses through the various drainage transmission systems within the subdivision depths of flow shall not exceed curb height for a ten year average recurrence interval. For more remote events depth of flow or ponding shall not exceed a level of which would cause inundations of foundations or basements in residential structures within the subdivision. Further, unless approved by the Director, no design energy grade line of any closed or open waterways, or any bridges, culverts or other appurtenances thereto, excepting curb gutter or road side ditches sections, shall at any point be less than three feet below ground level. Within the subdivision, catch basins shall be so placed along the streets that the width of the flow in the gutter shall not exceed two feet for a one year average recurrence interval and will not exceed the top of the curb for a ten year average recurrence interval. Site grading within the subdivision shall be such that all lots and service areas will drain readily. Bridges and box culverts spanning open waterways shall have a minimum freeboard above water surface of one and one-half feet. French drains may be used as a temporary flow correction, but only after approval by the Director.
(4) Structural design. Catch basins, manholes, inlet structures, temporary drains and sumps placed within the subdivision shall conform to standard drawings as adopted by the latest Ohio Department of Transportation Construction Design Manual.
A. Channels. Centerline radius, minimum top and bottom widths, side slope ratios, factor of roughness and other channel flow data shall conform to the County Engineer's requirements. Earth channels constructed within the subdivision shall have side slopes of one foot vertical to two feet horizontal or flatter. Revetment, bank stabilization and stream bed stabilization along constructed or natural channels, shall be required if the channel velocities are sufficient to cause bank or invert erosion. The top of the bank shall be so graded that side drainage shall enter channels only at points where structural inlets are provided to prevent bank erosion. Side drainage tributaries shall enter the main channels as nearly parallel with stream flow as possible. Earth channels constructed in those areas not reveted, shall be secured from erosion, siltation and increased flow concentration by planting of vegetation and by mulching as specified by the Planning Commission.
B. Closed Conduits. Except for adequate natural waterways and allowable gutter flows, all storm drainage within the subdivision which is capable of being transmitted in a reinforced concrete pipe forty-two inches or less in diameter or equivalent material with the same flow capacities shall be carried R.C. P. or equivalent, and the minimum clearance between top of pipe and ground shall be two feet. The alignment of closed conduit shall be as nearly straight as practicable without undue bends and angle points; manholes shall be provided at all angle points and at intervals not to exceed 400 feet along the conduit. Inverted siphons shall not be permitted except for temporary structures. Nonreinforced concrete pipe, or the equivalent, may be used outside of road right-of-way provided the strength of such pipe is sufficient to withstand loads imposed upon them. In the event of possible erosion conditions in closed conduits, additional paving shall be provided as necessary to assure a project life of fifty years.
(d) Headwalls.
(1) Headwalls (cut-off) shall be required on all surface drainage pipes. Where we have cross pipes, at least the main streets shall have headwalls.
(2) Headwalls or rip rap or both shall be required on all pipe structures. These are pipe structures that are large enough to take the place of a bridge. All headwall structures shall be designed to State Highway Standards.
(e) Right of Way for Drainage Purposes.
(1) Right of way for closed conduits and appurtenances. An easement not less than eight feet in width and sufficient to contain the closed conduit and appurtenances plus two feet on either side thereof shall be dedicated on the final map of the subdivision as follows: "Drainage Easement to Township". Drainage easements for closed conduit 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) Right-of-way for natural waterways. Where natural waterways traverse the subdivision requiring sufficient waterway area to contain design discharge within design limits as hereinafter stated, and where such natural waterways are endowed with sufficient natural beauty and have proved themselves reasonably stable, the subdivider may leave such channels in their natural state. Such scenic waterways as dedicated under this section need not be fenced, but shall have permanent marker posts extending three feet above ground set at all intersecting property lines along the right-of-way line and at angle points. When natural waterways contain sufficient waterway area or where such waterways have proved themselves unstable only at frequent locations, and where minor construction could provide an adequate channel and still preserve, in the main, the natural channel beauty, the subdivider may make such minor improvements as is required to provide a channel which would otherwise meet the conditions of this section.
(3) Right of way for constructed channels and appurtenances. Earth channels constructed within the subdivision shall have sufficient right-of-way dedicated to contain the top width of the channel plus an eight foot horizontal continuous maintenance way on one side, and two feet horizontal on the other side for channels less than fifty feet in top width. A ten foot horizontal maintenance way shall be provided on both sides of channels having a top width greater than fifty feet.
A. Right-of-way concrete lined channels shall extend to edge of concrete only, with ten feet access provided at intervals of not less than 1000 feet. Such access shall extend to channel invert by means of access ramps having a maximum slope not to exceed fifteen percent (15%).
B. All constructed channels shall have either a five foot high chain link fence or a four foot chain link fence with a two-strand barb wire placed along the right-of-way line. Chain link drive gates shall be provided at road intersections and all other points of access.
C. The right-of-way width for earth channels shall be increased over that given above as necessary to provide an eight foot access around any structure of bridge and in the event that the right-of-way does not intersect a road, ten feet access shall be provided for a road.
D. Right-of-way for constructed channels shall be dedicated as a separate parcel, or parcels, on the final subdivision map and designated as follows: "Right-of-way to "
(f) Tentative Drainage Plans. The Planning Commission may require where it deems necessary that a tentative subdivision map with sufficient data for the Commission's staff 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)
A. Tributary drainage area delineated on the map
B. Times of concentration
C. Intensity of rainfall
D. Runoff coefficient
E. Design flow.
(2) Hydraulic calculations.
A. The plan and profiles of all drainage ways shall be provided, imposed upon which shall be the design energy and hydraulic grade lines.
B. Sizes and types of drainage improvements, including special structure, typical sections, right-of-way width and fencing.
C. Supporting calculations for upstream and downstream channel capacities as they affect overflow or backwater within the subdivision. Such calculations shall substantiate such additional survey information as is required to determine profile and cross section of the upstream and downstream channel portion under consideration.
D. Sufficient contours and grading details to indicate proposed street grades and elevations and site grades and elevations throughout the subdivision.
(g) Construction Plans. The final construction plans for drainage within the subdivision shall conform to the provision of these Subdivision Regulations and to any special conditions as required by the Planning Commission in approving the tentative map. Such construction plans for drainage shall be approved by the staff of the Commission prior to construction of any drainage facilities within the subdivision.
(Ord. 1164. Passed 8-16-82.)