(a) Outlets. The Planning Commission shall not approve any subdivision unless there is an adequate outlet for storm water as determined by the City Engineer. Generally it will be necessary to pipe stormwater to an adequate watercourse, stream or existing storm system which has the capacity to accommodate the flow, or to utilize acceptable on-site water retention methods adequate to minimize excessive off-site storm water flows.
(b) Preservation of Natural Drainage Courses. No natural drainage course shall be altered and no fill, building or structures shall be located within such drainage course unless provision is made for the flow of surface water, in a manner satisfactory to the City Engineer. An easement shall be provided on both sides of the existing surface drainage course adequate for the purpose of future widening, deepening, enclosing or otherwise improving said drainage course. If such drainage course crosses private property, easements must be obtained by the Owner/Developer for construction and future maintenance. These easements must be shown on the Construction Plans, including the volume and page number of recorded easement.
(c) Surface Routing Paths. Generally, it is not economically feasible to size a storm drainage system to collect and convey more than frequent storm runoff. The complete drainage system of a proposed subdivision shall contain two (2) separate drainage elements. Storm sewers comprise the initial system. Surface routing paths shall be provided to carry the storm water runoff, which exceeds the capacity of the initial system. The system of surface routing paths shall have the capacity to carry runoff from a storm with a return period of not less than one hundred (100) years, without causing significant threat to property or public safety.
(d) Grades. All surface areas not covered by hard surface improvements or stone shall be seeded or sodded and sloped to drain according to the following:
(1) Grass areas shall have a minimum slope or grade of eight tenths of one percent (0.8%)
(2) Grass areas next to buildings shall slope away from the building at not less than five percent (5%) for a minimum of ten (10) feet.
(3) Ditches or swales in grassed areas with a design velocity between three and five feet per second (3-5 fps) shall be sodded. Ditches or swales with a design velocity greater the five feet per second (5 fps) shall have a paved or stone gutter. Under drains shall be required in ditches or swales with bottom grades of less than two percent (2%).
(e) Submittal of Drainage Data. Information and data pertaining to water volumes and velocities for all water sheds entering and on the property, along with calculations to show that proposed drainage improvements will adequately address such flows, shall be submitted to the City Engineer along with required Construction and Grading Plans. A Professional Engineer shall approve such drainage data. Storm drainage systems shall generally be designed so that the peak rate of storm water runoff from the site after development, does not exceed the peak rate of runoff before development; however, the City Engineer may grant administrative exceptions to this requirement when specific conditions warrant such action. The methods and techniques proposed to address surface runoff shall be designed to accommodate the design frequency storm and shall be consistent with storm water design criteria established in the City’s Stormwater Design Manual.
(f) Culverts. All culverts shall be constructed of concrete, and shall have the appropriate headwalls and other structures and improvements to protect the facility, as determined by the City Engineer. The design of the culverts shall be as stipulated in the City’s Stormwater Design Manual.
(Ord. 5-01. Passed 2-26-01.)
(Ord. 5-01. Passed 2-26-01.)