All necessary facilities, including underground pipe, inlets, catch basins or open drainage ditches, as determined by the Safety-Service Director or the County Engineer, depending upon jurisdiction, shall be installed to provide for the adequate disposal of subsurface and surface water and maintenance of natural drainage courses. All storm drainage facilities within the subdivision shall connect to an adequate drainage course.
(a) Storm Sewers and Storm Water Drainage. A drainage system adequate to serve the needs of the proposed new streets and the entire subdivision will be required in new subdivisions. Where an adequate public storm sewer main is available at the plat boundary, the subdivider shall construct a storm sewer system and connect with such storm sewer main. If such storm sewer systems are not accessible, adequate storm water drainage shall be provided by natural drainage channels with easements of adequate width.
(b) Culverts and Bridges. When natural drainage channels intersect any street right of way, it shall be the responsibility of the subdivider to have satisfactory bridges and culverts designed and constructed. Where culverts are required, the following minimum requirements shall be observed:
(1) All culverts shall extend across the entire right-of-way width of the proposed road. The cover over the culvert and its capacity shall be determined by the Safety-Service Director, the County Engineer or the State Transportation Department, depending upon jurisdiction. The minimum diameter of a culvert pipe shall be twelve inches. Head walls, depending on existing drainage conditions, may be required.
(2) Driveway culvert installations shall be discouraged. Storm sewers, with drop inlets at driveways, shall be installed unless topography conditions do not permit storm sewer installation. Driveway culverts, if installed, shall be a minimum of twenty feet in length and a minimum of twelve inches in diameter, subject to review by the Director.
(c) Standards and Specifications for Drainage Facilities. The Stormwater Design Manual, as published by the Mid-Ohio Regional Planning Commission, Columbus, Ohio, 1977 (or the most recent issue) shall govern all drainage improvements. The following list of criteria is a general guide for the interpretation of the Manual:
(1) In general. A proposed development which will increase rates or volumes of run-off shall be required to control the discharge of run-off prior to release to off-site lands.
(2) Exemptions. A single-family residential land use and subdivisions for single-family residential purposes, not involving the construction of public or private streets, and with a lot size of one-third of an acre or greater and an average maximum of thirty percent impervious, are exempt from the run-off control criteria.
(3) Waiver or reduction of control criteria. Development situations may arise such that site conditions, location, design aspects and/or prior considerations indicate that the project will not have any or will have few of the harmful effects associated with increases in run-off rates and volumes. For such cases, the project engineer shall submit sufficient information for the City Engineer to determine if a waiver or reduction of run-off control criteria is justified (in writing and clearly detailing all aspects of the proposed development). Additional information or calculations requested by the City Engineer shall also be submitted by the applicant. The decision to grant a waiver or reduction of run-off control criteria shall be made by the City Engineer. The City Engineer shall give, in writing, to the Safety-Service Director, reasons for approving or not approving a reduction of run-off control criteria.
(4) Run-off control design frequency.
Increase in Two-year Control Design
Rate of Run-off Frequency
1-2 times 10-year
2-3 times 25-year
3-4 times 50-year
over 4 times 100-year
The maximum allowable release rate shall be based on the two-year storm under predeveloped (not existing) site conditions, for all rainfall events up to and including the twenty-five year storm. Facilities designed for fifty or 100-year frequency multi-stage outlets, which are designed to control the fifty or 100-year storm to pre-development rates, shall be approved. All control facilities shall be designed with overflow provisions to handle the proposed 100-year discharge.
(5) Storm sewers. Storm sewers shall be designed pursuant to Section 1476.15
of the City of London Codified Ordinances.
(Ord. 106-83. Passed 3-3-83; Ord. 239-23. Passed 12-7-23.)