(1) Basic Drainage System Required
A drainage system shall be designed and constructed to provide for the proper drainage of the surface water in the subdivision and the drainage area of which it is a part. The following requirements and methods shall be followed:
(a) Storm Drainage Report Required
(i) A subdivision plat shall not be considered for final approval until the subdivider submits a drainage report by a registered engineer as to the ability of existing watercourse channels, storm sewers, culverts, and other public improvements pertaining to drainage or flood control within the subdivision to handle the additional runoff which would be generated by the development of the land within the subdivision.
(ii) Additional information shall be submitted to adequately indicate that provision has been made for disposal of surface water without any damage to the developed or undeveloped land downstream or below the proposed subdivision.
(iii) This report shall also include:
A. Estimates of the quantity of storm water entering the subdivision naturally from areas outside the subdivision;
B. Quantities of flow at each pickup point (inlet); and
C. The location, sizes, and grades of required culverts, storm drainage sewers, and other required appurtenances.
(b) Access to Drainage Facilities
The City of Tipp City shall have the right, but not the responsibility, to enter upon any lot in a subdivision to inspect, monitor, and if necessary make improvements, to drainage facilities in accordance with § 155.04(K).
(c) General Standards and Best Management Practices
(i) The material and construction specifications and the design criteria for storm drainage systems shall be based on standards contained within the Tipp City Subdivision Design and Construction Standards, the Notice of Intent (NOI) for Coverage under Ohio Environmental Protection Agency General Permit, and the SWPPP.
(ii) Nonstructural stormwater management practices shall be used to the maximum extent practicable. Such practices may include, but not be limited to, preserving riparian areas, preserving existing vegetation and vegetative buffer strips, phasing of construction, and designation of tree preservation areas.
(iii) Post-construction best management practices, based on the Ohio EPA's Construction Stormwater General Permit and the Ohio Department of Natural Resource's Rainwater and Land Development Manual are to be provided when applicable.
(d) Grading
No final grading, sidewalk, or pavement construction, or installation of public improvements shall be permitted in any proposed street until the final plat has been approved by City Council. The subdivider shall grade each subdivision in order to establish street, block, and lot grades in proper relation to each other and to topography as follows:
(i) If grading results in the stripping of topsoil, the topsoil shall not be removed from the site or used as spoil, but shall be uniformly spread over the lots as grading is finished.
(ii) As many trees as can be reasonably utilized shall be retained and the grading adjusted to the existing grade of the trees where practicable.
(iii) Final grading must conform to the grading and drainage plan prepared by the engineer. A minimum 2% grade must be established adjacent to all structures to allow for property drainage away from such structures. See Figure 155.04-C.
(e) Street Grading
A grading plan shall be prepared for the streets along with street improvement details. The grading of the street shall extend the full width of the right-of-way. Planting strips shall be graded at a gradient of not less than 2% upward from the curb to the sidewalk or property line.
(f) Block Grading
Block grading shall be accomplished in 1 or more of the following methods:
(i) A ridge constructed along the rear lot lines providing for drainage into the streets;
(ii) Parts of all lots draining to a sidewalk or ditch along the rear lot lines; and/or
(iii) Drainage across rear or side lot lines, provided that drainage onto adjoining properties shall be skillfully controlled.
(g) Lot Grading
Lot grading shall be accomplished as follows:
(i) Lots shall be graded so that water drains away from each building at a minimum grade of 2%. See Figure 155.04-C.
(ii) Surface drainage swales shall have minimum grade of 2%, and shall be designed so that the surface water will drain into a driveway, street gutter, storm sewer, drain inlet, or natural drainage way.
(iii) The minimum grades of driveways shall be 0.4% and the maximum grade shall be 8% for driveway areas within a street right-of-way.
(h) Drainage System Requirements
(i) All storm sewers shall be designed for a minimum 10-year storm frequency. All culverts, under streets, shall be designed for a minimum 25-year storm frequency and a 100-year storm shall not breech the street.
(ii) For curbs and gutters, curb and gutter inlets, and open channels, an intensity of 4 inches per hour shall be used in all computations.
(iii) Where an adequate public storm drain is available, the subdivider shall construct a storm sewer system and connect with such storm sewer line. If such a storm sewer system is not accessible, natural drainage channels with easements of adequate width shall be provided, as determined by the City Engineer.
(i) Street Drainage System
(i) All streets shall be provided with an adequate storm drainage system.
(ii) The street storm sewer system shall serve as the primary drainage system and shall be designed to carry street, adjacent land, and building storm water drainage. No storm water shall be permitted to run into the sanitary sewer system within the proposed subdivision.
(iii) Curb drainage inlets shall be provided at intervals along streets. While these inlets connect to storm sewers, a catch basin shall be installed with the inlet. Storm drain inlets will be placed so that crosswalks will not be flooded during the design storm intensity of 4 inches per hour.
(j) Off-Street Drainage System
The design of the off-street drainage system shall include the watershed affecting the subdivision, and shall be extended to a watercourse or ditch adequate to receive the storm drainage:
(i) When the drainage system is outside of the street right-of-way, the subdivider shall make provisions for dedication of an easement to the city to provide for the future maintenance of said system.
(ii) The size and location of all off-street watercourses or ditches running through the subdivision shall be enclosed or left open subject to the approval of the City Engineer. If a watercourse or ditch is left open, it may be required to be protected by a fence, as determined by the city. The watercourse or ditch easement shall be wide enough to contain said ditch slope with ample clearance for the operation of maintenance equipment.
(k) Drainage Easements
See 0.
(l) Culverts and Bridges
(i) Where natural drainage channels intersect any street right-of-way, it shall be the responsibility of the subdivider to have satisfactory bridges or culverts constructed. Where culverts are required, they shall extend across the entire right-of-way width of the proposed street.
(ii) The cover over the culvert and its capacity shall be reviewed by the City Engineer based on the submission of the subdivider.
(iii) The minimum diameter of a culvert pipe shall be 18 inches. Head walls shall be required.
(m) Protection of Drainage Systems
(i) The subdivider shall adequately protect all ditches to the satisfaction of the City Engineer and the approved SWPPP. Ditches and open channels shall be seeded, sodded, or paved depending on grades (slopes) and types of soil.
(ii) As a general rule, ditches and channels with grades up to 1% shall be seeded; with grades from 1 to 4% shall be sodded; and with grades over 4% shall be paved. Seeding, sodding, and paving operations shall be in compliance with the State of Ohio, Department of Transportation.
(2) Flood Hazards
(a) General Prohibition
(i) Land subject to flooding or otherwise uninhabitable shall not be platted for residential use or for any other use which may increase the danger of health, life, or property, or aggravate erosion or flood hazards. Such land within the subdivision shall be set aside on the plat for such uses as will not be endangered by periodic or occasional inundation, or will not result in conditions contrary to the public welfare (e.g., use as open space, extensive recreation use, conservation purposes).
(ii) To ensure that lots will be located on land where they will provide flood-free sites, the city may require the subdivider to provide elevation and flood profiles sufficient to demonstrate that the sites will be free from the danger of flooding.
(iii) Fill may be used in flood-danger areas to render lots habitable if such fill does not inhibit the flow of the waters and thereby unduly increase flood heights in other areas, and such fill meets with the approval of the Floodplain Administrator, or its duly authorized representative. Such information shall be prepared by a registered civil engineer.
(b) Stream Easements
If a stream flows through or adjacent to the proposed subdivision, the plat shall provide for a storm water easement or drainage right-of-way along the stream for a floodway of at least 10 feet. For the smaller streams, the plat shall provide for channel improvement to enable them to carry all reasonable floods within banks. The floodway easement shall be wide enough to provide for future enlargement of the stream channels as adjacent areas become more highly developed and runoff rates are increased.
(c) Streets
Approval shall not be given for streets within a subdivision which would be subject to inundation or flooding. All streets must be located at elevations which will make them flood-free in order that no portion of the subdivision would become isolated by floods.
(Ord. 5-14, passed 3-17-2014)