(A) Approval. All construction drawings shall be approved by the Planning Commission acting upon recommendation for approval by the City Engineer.
(B) Construction drawings. Construction drawings shall be complete in detail, and shall include plans, profiles, drainage facilities, sanitary sewers and all utilities and service facilities which are to be installed by the subdivider.
(C) Pavements. Pavements shall be installed with curb and gutter as shown in sheets one through four of the standard drawings. An equivalent concrete section may be considered for industrial and collector streets.
(D) Sidewalks. Sidewalks shall be required on all residential subdivision streets, on both sides of the street. Concrete for sidewalks shall be concrete, and shall meet the specifications set forth in ODOT Item 608, and shall be given a reasonably smooth float finish. Where site features prevent the construction of a sidewalk on both sides of the street, the owner or developer may appeal to the Board of Zoning Appeals for a variance. Subdivisions that abut existing public streets shall provide sidewalks along the full distance of the development beginning and terminating at the project's property lines, unless otherwise approved by the Planning Commission.
(E) Storm drainage.
(1) Pipe for storm water system, when any portion of the run is underneath the pavement, shall be per ODOT Item 706.02(IV) minimum and in all cases shall be placed with good bedding. Pipe for storm sewers and drains, when entirely outside of the pavement, may be per ODOT Item 707.42.
(2) The storm water system shall be designed based on a post-development 25-year storm. The storm water system includes all closed conduits, open channels, inlets, manholes and all features designed to collect storm water from streets and lots, including the necessary piping for the collection of sump pump drains. The Rational Method will normally be used when calculating peak rate of runoff in determining conduit size and grade. If the drainage area is greater than 20 acres, TR55 should be used.
(3) In general, all conduits shall be designed on a 25-year flowing full design using the Manning Formula, with a minimum diameter of 12 inches with a minimum cover of 18 inches. All changes in size, grade, alignment and the intersection of two or more sewers must take place in a manhole or catch basin. If the main route of the storm sewer passes through a catch basin, the catch basin must have a separate access point for cleaning purposes. The roughness coefficient (n) shall equal 0.015 for all pipe materials, unless approved by the City Engineer. The allowable velocity shall not be less than 3.5 feet per second or greater than 18 feet per second based on a 25-year frequency storm. Rock channel protection and/or other means of energy dissipation must be used when the outlet velocity is higher than the permissible erodible velocity for the channel it enters.
(4) Inlets or catch basins shall have a capacity not less than the quantity of flow tributary to the inlet. Inlets at low points or grade pockets should have extra capacity as a safeguard for flooding from flows in excess of design flows. Calculations shall be submitted verifying the capacity of each inlet. Special inlets may be required for streets with steep gradient to provide the extra capacity such situations require. The inlets shall be so located that they shall pick up no more than 5.0 cfs, and this only when street grades do not exceed 6% on either side of the inlet, and when the maximum concentration of water on each side of the inlet does not exceed 2.5 cfs. Inlets shall be located upstream of all sidewalks at street intersections, crosswalks, driveways, and roadways; in all pockets in streets, where a street grade flattens, and at intervals no greater than 350 feet in gutters. Inlets or catch basins shall be spaced and located as the conditions may require, but generally not over 400 feet apart or from a high point. Inlets shall be placed in such a manner that no storm water shall flow through or into any intersection. Not more than 500 linear feet of street shall be permitted to drain into one pair of catch basins when draining from two directions. Gutters shall be depressed 1-1/2 inches at all catch basins or inlets. Manholes shall be placed on conduits 36 inches in diameter or less, at not more than 400 feet. Manhole tops, which otherwise cannot be set outside of the pavement area, shall be set to meet the pavement grades evenly. All manholes and catch basins which are on the main route of the storm sewer system shall be provided with channels to afford a smooth, unobstructed flow. Easements not less than 15 feet in width shall be provided for all sewers or pipe drains not in a dedicated public right-of-way, depending on the depth of the sewer. Inlets or catch basins shall have a capacity not less than the quantity of flow tributary to the inlet. Inlets at low points or grade pockets should have extra capacity as a safeguard for flooding from flows in excess of design flows.
(5) All subdivisions must include an adequate flood routing system designed to carry runoff from a 100-year frequency storm. Minimum opening elevations are to be set by the owner's engineer along all 100-year flood routes. These elevations are to be a minimum of 1 foot above the 100-year water elevation. All storm water is to be routed into the detention or retention area. When a storm sewer system outfalls into a flood plain of any major watercourse, the outfall must not be subject to frequent floods or backwaters. Standard wingwall with erosion control shall be constructed for all outfalls. Suitable baffles or other energy dissipaters shall be provided if determined to be necessary by the City Engineer. The invert of the first storm sewer appurtenance upstream of the outfall structure shall be above the elevations of the flood plain.
(6) Streets may be used as a routing path. Where a street is designated as the major drainage way, the depth of flow shall not exceed 8 inches at the face of the curb. Where the major drainage way is located outside a street right-of-way, easements shall be provided and a grading plan is to be submitted with detailed elevations showing the flood being contained in this area.
(F) Culvert design.
(1) Technical Release 55 and the Hydraulic Circular No. 5 are the recommended procedures for design. A single-span culvert should always be used in lieu of multiple-span openings. The only time a multiple-opening culvert shall be considered is when no other single-span structure will function. All culverts which are a part of the flood route for the 100-year storm shall be designed for the 50-year storm with head water and a flood route provided to accept a 100-year storm. Maximum allowable head water shall be 18 inches below the top of the curb and 12 inches below the edge of pavement where curb does not exist.
(2) The design of the drainage system should not cause back water onto any adjacent property. If additional back water is caused, an easement from the affected property owner must be obtained. The back water condition should be checked on the 50-year frequency storm.
(3) A structure having a clear opening of ten feet or more shall be classified as a bridge and be subject to special conditions under the direction of the City Engineer.
(G) Open drainage ditches.
(1) All newly designed open channels shall only accommodate a small drainage area (i.e. lot swale). All other design drainage features shall be enclosed with storm sewer, with the exception of large, major channels. All drainage ditches, where provided as a part of the drainage system, shall have rights-of-way or easements provided for the city to access and maintain the ditches. Ditches are to be designed using a full flow 25-year frequency storm unless the channel is part of the flood routing system, in which case it must be designed using a 100-year storm frequency. The longitudinal slope of a channel should be 1% or greater. All side slopes shall be 4:1 or flatter in residential areas and 3:1 or flatter in commercial areas unless otherwise approved by the City Engineer and Planning Commission.
(2) The maximum permissible design velocity shall not be greater than the erodible velocity of the design year storm used to design the ditch. Channel linings will be required as per the ODOT Design Manual. In designing an open ditch, the flow and grade shall be addressed so as to prevent stagnation. All seeding, mulching and sodding shall be installed immediately after construction as per ODOT Item 659 and 660, and kept in ideal growth conditions until established.
(3) Easements or right-of-way widths for open ditches shall be equal to the bottom width, plus six times the design depth of flow and not less than 15 feet.
(H) Retention/detention basins.
(1) An adequate amount of land shall be designated for the sole purpose of detention or retention of storm water runoff. Said area shall be located on a separate non-buildable lot deeded to and maintained by a homeowner's association or similar legal entity. Said homeowner's association or similar legal entity shall execute a perpetual maintenance agreement suitable for recording with the final record plat at the Recording Office of Hamilton County. If the maintenance of the area does not meet the requirements of the city's NPDES permit, the city has the right to maintain said property as applicable under R.C. §§ 715.41 and 715.47. The detention or retention area shall be used as a temporary sedimentation basin during construction. It will be the responsibility of the developer to ensure that the detention or retention area meets all original design characteristics prior to the end of each of the maintenance bond periods for each of the sections of development.
(2) In order to minimize storm runoff damage to downstream properties and overloading of existing drainage courses, the following criteria shall be followed on all development of parcels one acre or larger in size, and on all redevelopment of existing buildings or site usage as determined by the Planning Commission.
(a) Stage 1 shall allow the discharge of the ten-year pre-developed storm flow and provide for the detention of a volume equal to the ten-year storm flow, post-development less the ten-year pre-developed discharge.
(b) Stage 2 shall allow the discharge of the 25-year pre-developed storm flow and provide for the detention of a volume equal to the 25-year storm flow, post development less the 25-year pre-developed discharge.
(c) Stage 3 shall allow the discharge of the 25-year pre-developed storm flow and provide for the detention of a volume equal to the 100-year storm flow, post development less the 25-year pre-developed discharge. The detention volume shall be determined by multiplying the above difference by 25 minutes. The method of retention is subject to approval by the City Engineer.
(d) Outlet flow control devices shall be multistage.
(e) Other requirements may be imposed for specific cases.
(f) All detention systems shall include an emergency overflow to control the storm water flow when maximum storage capacity is surpassed.
(g) No on-site storm drainage shall outlet downstream of the main retention facility without providing supplemental retention as per the above criteria.
(3) The bottom of the detention area should be constructed with a minimum slope of 0.5%. Side slopes for detention facilities shall be no steeper than 4:1, unless existing natural conditions do not make this possible. Anti-seep collars shall be used on all pipe outlets of retention basins or ponds. There shall be a minimum of six inches of freeboard between the top of the dike and the water surface in the reservoir with the emergency spillway flowing at the 100-year design flow. The emergency spillway shall safely pass the peak flow for a 100-year frequency storm with a safe velocity of not more then 8.0 fps. The spillway is to be cut on existing ground, or other protection on the fill slope is to be provided. A minimum of 20 feet access easement shall be provided for easy ingress and egress to and from the basin. The access shall have a maximum slope of 25%. Trash guards should be installed when clogging of the outlet structure is probable. Anti-vortex devices should be used at the top of all riser pipes in retention ponds.
(I) Sanitary sewers.
(1) Sanitary sewers shall be constructed in accordance with the standard plans and specifications for sanitary sewers as prepared and adopted by the Metropolitan Sewer District.
(2) In general, sewerage works and facilities shall be designed in accordance with State Health Department requirements, and all rules and regulations of the Metropolitan Sewer District, and will be subject to State EPA approval.
(J) Water mains. Water mains, service connections and appurtenances shall meet the requirements set forth in Operation and Regulations of the City of Cincinnati Waterworks or subsequent amendments.
(K) Records. The owner or his engineer shall file with the City Clerk copies of the as-built drawings, corrected to show exact location, grades and necessary elevations and other pertinent data, for all structures or facilities installed under the surface of the ground, including all water and sewer mains and service connections.
(L) General. All sewer and utility pipelines shall preferably be placed outside the limits of the pavement. All excavations for public utilities made under paved areas shall be properly backfilled with approved granular materials thoroughly compacted in place.
(1) The streets shall be graded, surfaced, and improved to the dimensions as required by these Subdivision Regulations. All streets shall be graded the full width of the right-of-way. Grading for street improvements shall not create soil slopes exceeding a vertical rise of one foot for each three feet of horizontal distance unless otherwise recommended by the City Engineer and the Planning Commission.
(2) The surface of all streets shall be of Portland cement concrete or asphaltic cement. All streets shall be constructed in accordance with design characteristics at least equal to the minimum requirements of the city. The Planning Commission may require the use of heavy-duty asphalt pavement and/or special consideration of sub-grade construction in locations where large volumes of vehicles or heavyweight vehicles and truck traffic are anticipated.
(3) Prior to the construction of street pavements, adequate surface and any necessary subsurface facilities shall be installed by the subdivider.
(4) Provisions for storm drainage shall meet the requirements of § 153.336.
(5) All construction shall be completed in accordance with the approved specifications, and in a manner acceptable to the city authorities having jurisdiction. When changes from the accepted plans and specifications become necessary during construction, written approval from the Zoning Enforcement Officer shall be secured prior to the execution of such changes.
(Ord. 09-3306, passed 10-15-09)