(A) Easements. All storm drainage facilities shall be built within the proper easements. Easements shall also be provided to permit access for maintenance of all stormwater facilities.
(B) Bridges and culverts. All flow of water across continuous streets or alleys shall be through culverts or bridges and shall be designed using the requirements described in the previous sections.
(C) Closed storm sewers. The closed storm sewer will be utilized with the minor system and shall be designed to the storm frequency of that which is economically sound for the minor system.
(D) Open channels. Open channels shall only be used in the major system and designed for the 100-year storm event with a six hour duration. All buildings in the proposed subdivision shall be built above the 100-year flood level a distance of one foot. Sod slopes of improved channels shall have a maximum slope of 2.5 horizontal to 1 vertical. All open channels, including streets, shall be designed using the method described in previous sections.
(E) Artificial channels. Artificial channels include pipe flowing partly full, concrete channels, excavated or dredged and grass lined channels. Determine critical depth, critical slopes for initial selection of size and shape. Use Manning’s equation to determine the normal depth for the design flow and check to see if the critical depth is greater, equal to or less than the normal depth. Critical depth must always be less than normal depth. If the critical depth is greater than normal depth, the slope is too steep and must be changed. Critical depth shall not be approached anywhere in the channel.
(F) Obstructions. Obstructions raise the water depth. Obstructions include bridges, culverts, change in channel shape, Manning’s n coefficient, channel alignment and the like. Where these obstructions exist and are expected to have an impact on the drainage in the subdivision, a backwater computation is required in the application.
(G) Fencing. No subdivision fences shall be constructed in, along or across surface drainageways.
(H) Inlets. Inlets shall be provided frequently enough so that the minor system can flow to its design capacity and so water does not exceed one inch above the crown of the street. The recommended distance between inlets should be 600 feet.
(I) Street gutter. STREET GUTTER shall be defined as the distance from the flowline to the crown of the street.
(J) New commercial developments. All new commercial developments shall provide drainage facilities that conform to this chapter.
(K) Lot arrangement. The lot arrangement shall be such that there will be no foreseeable drainage problems. As a general rule, each lot should provide positive drainage to a street or approved drainage channel without crossing more than two consecutive lots.
(Prior Code, § 11-8-7) (Ord. 594, passed 8-5-1997)