(A) Easements for open ditches or watercourses. Where a subdivision is traversed by a watercourse, drainageway, natural channel or stream, there shall be provided an easement or right-of-way conforming substantially to the limit of such a watercourse, plus an additional width to accommodate future needs. Easements for open ditches or watercourses shall have a 15-foot working space provided adjacent to one bank. In no case shall an open ditch or watercourse be located in an easement of less than 30 feet in width.
(B) Off-site drainage.
(1) Easements and drainage facilities shall be provided by the subdivider. The owner or developer of property to be developed shall be responsible for all storm drainage discharge flowing on such subdivider’s property. This responsibility includes the drainage directed to that property by prior development as well as drainage naturally flowing through the property by reason of topography.
(2) Adequate consideration shall be given by the owner in the development of property to determine how the discharge leaving the proposed development will affect downstream property.
(C) Design standards for drainage facilities. Drainage facilities shall conform to the technical specifications of the City Engineer and Director of Public Works in accordance herewith and with the following requirements.
(1) Runoff criteria. Storm sewers, ditches and other drainage structures shall be designed for one cubic foot per second per acre runoff for residential land use and two cubic feet per second per acre for commercial land use.
(2) Ditch slope. Minimum ditch slope shall be one-tenth foot fall per 100 feet. Ditch banks shall have a maximum slope of one vertical on two horizontal.
(3) Ditch depth. Minimum ditch depth shall be four inches from the flow line of the ditch to the edge of the road shoulder. The maximum in any street right-of-way for ditches adjacent and parallel to any street shall be two feet from the flow line of the ditch to the edge of the road shoulder. Ditches of greater depth than two feet shall be enclosed in those cases.
(4) Curb and gutter streets.
(a) The maximum distance storm water shall run in gutters before entering an inlet is 1,000 feet.
(b) Minimum slope on gutters for asphaltic surfaced, flexible base streets shall be 0.25% (0.25 foot fall per 100 feet). Minimum slope on gutters for concrete streets shall be 0.2%. Minimum fall around a curb return shall be one-tenth foot.
(5) Minimum inlet size. There shall be no less than one and one-half square feet of throat opening in any inlet. No more than 800 feet of gutter shall drain into an inlet of this minimum size. Laterals discharging from such minimum size inlets shall be not less than 18 inches.
(6) Valley gutters. Valley gutters shall not be permitted without the approval of the City Engineer and the Director of Public Works. When permitted, they shall be of concrete of not less than two-foot width on each side of the flow line (four-foot overall width).
(Ord. 08-29, passed 10-21-2009)