(a) Stormwater Design Manual. The Stormwater Design Manual, as adopted by the Mid-Ohio Regional Planning Commission, is hereby adopted by the village and the policies, standards, specifications and provisions contained therein shall apply to the development of all subdivisions in the village.
(b) Hydrologic and Hydraulic Studies.
(1) A hydrologic and hydraulic study of any subdivision shall be submitted prior to final plat approval and as part of the construction drawings for such subdivision. These studies shall be used to establish:
A. The adequacy of the drainage system of the development site. As part of these studies, the adequacy of the storm drainage facilities necessary to carry the runoff from the initial storm design shall be shown. The flow routes and drainageways necessary to convey the 100-year storm (the emergency flow way) through the development shall also be shown, as shall any necessary easements;
B. The adequacy of the drainage system of the proposed development to receive and convey the initial and major storms from dominant (upstream) property; and
C. The adequacy of the drainage system of the proposed development so as not to create or worsen drainage problems downstream.
(2) As part of these studies, storage facilities, when used, shall be located and identified by type.
(c) Stormwater Runoff Limitations.
(1) If the hydrologic and hydraulic studies reveal that the proposed development or subdivision would not increase the total volume of stormwater runoff, the peak rate of runoff after development shall not be greater than the peak rate of runoff before development for all return periods of storms, up to 100 years.
(2) If the hydrologic and hydraulic studies reveal that the total volume of stormwater runoff is increased, the peak rate of runoff after development, from the critical storm, shall not exceed the predevelopment peak rate of runoff from a one-year frequency storm. The peak rate of runoff for each storm of greater or lesser frequency shall be determined in accordance with the Stormwater Design Manual; provided, however, that the peak rate of runoff after development may not exceed the peak rate of runoff before development.
(d) Subdivision Drainage Systems.
(1) Storm drainage facilities for the subdivision or development shall be designed to accommodate runoff from the five-year storm frequency. Site design and grading plans shall provide emergency drainageways, in order to avoid both damage to the structure and endangerment of the public safety, which emergency drainageways shall be designed to accommodate runoff from storms exceeding the five-year storm frequency, but not exceeding the 100-year storm frequency.
(2) The initial drainage system shall be located within the street rights-of-way whenever practicable. If the collector facilities cannot be located in the street rights-of-way, then they shall be located adjacent to side or rear lot lines where easements shall be provided to and along the facilities.
(3) All stormwater flow from the proposed subdivision, including flows from upstream areas passing through and further including increased flows attributable to changes in time of concentration or a change in the former runoff factor (imperviousness), shall be conveyed to the proper outlet for the entire tributary area via a natural channel or an artificial channel, either or both of which shall be improved so as to be of an adequate capacity determined in accordance with the Stormwater Design Manual.
(e) Easements and Access. Access to flood control or storm drainage facilities for emergency, inspection, maintenance and improvement purposes shall be provided as follows.
(1) Access to flood control or storm drainage ditches, channels and storage facilities shall be by means of easements. Such easements shall be not less than 15 feet in width, exclusive of the width of the ditch, channel or other facility it is to serve, and an easement of this type shall be provided on one side of a flood control or storm drainage ditch, channel or similar facility.
(2) Access along flood control or storm drainage ditches and channels shall be by means of easements. Such easements shall be not less than 15 feet in width, exclusive of the width of the ditch, channel or other facility it is to serve, and an easement of this type shall be provided on both sides of a flood control or storm drainage ditch, channel or similar facility.
(3) Access along the initial drainage system shall be by means of easements. Such easements shall be not less than 15 feet in width, with a minimum of five feet in width on each side of the centerline.
(4) Access around storage facilities shall be by a ten-foot easement in the case of detention (dry) basins, and a 25-foot easement in the case of retention (wet) basins, measured from the line of the design high water level, and shall include the storage facility itself.
(5) Easements for emergency flow ways shall be a minimum of 15 feet in width.
(6) Flood control or storm drainage easements containing underground facilities shall have a minimum width of ten feet.
(f) Exemptions. An exemption to any of the requirements of this section may be granted if Council and the Village Engineer determine that no downstream flood liability will be incurred. Exemptions to the requirement of access to easements may be granted by Council if the applicant shows adequate access by other means.
(Ord. 5-89, passed 5-8-1989)