Conveyance structures (outfalls, pipes, swales ditches, culverts and the like) shall be designed in accordance to the County Stormwater Design Manual to fulfill the following requirements.
(A) Outfalls. All proposed pipe outfalls shall have an adequate receiving facility identified on the plans. There shall be no increase in erosion and sedimentation on adjoining properties.
(B) Pipe systems. All pipe systems shall accommodate the ten-year storm event with the hydraulic gradeline in the crown of the pipe. In addition, an overflow route to the detention structure shall be provided for the flows resulting from storms with a return period greater than the ten-year. In situations where an overflow route to the detention structure cannot be created, the pipes shall be designed with the 100-year hydraulic gradeline runoff below the top of casting or provide an easement encompassing the 100-year inundated areas.
(C) Inlets. Inlets shall be located to limit gutter spread during the ten-year storm event such that one lane, based on the roadway width, is open. Multi-lane roadways shall maintain one clear driving lane in both directions. Inlets shall have the capacity to accommodate the ten-year storm or the 100-year storm where overflow channels are not provided.
(D) Culverts. Culverts under roadways designated as thoroughfares, arterials or that provide the only means of ingress and egress to developments, shall accommodate the 100-year flow to the culvert without overtopping the roadway.
(1) Culverts under collector roadways (those roadways connected to designated thoroughfares and arterials) shall accommodate the 50-year flow to the culvert without overtopping the roadway.
(2) All other roadway culverts shall accommodate the 25-year flow to the culvert without overtopping the roadway.
(3) Driveway culverts shall accommodate the ten-year flow to the culvert without overtopping the driveway.
(E) Lift stations. Lift stations shall not be designed as part of a stormwater conveyance system. Proposed stormwater lift stations will only be reviewed if complete documentation of no other reasonable option is provided. Stormwater lift stations will be approved on a case-by-case basis.
(F) Swales. Swales shall be designed to accommodate the ten-year storm runoff within the proposed banks.
(G) Ditches. Proposed ditches shall accommodate the 100-year runoff within the banks or a designated easement.
(H) Perimeter drain collection. All residential development regulated by this subchapter shall indicate on their plans an appropriately sized, common collection swale, ditch or subsurface pipe structure that provides a positive discharge, collects and effectively conveys perimeter drain discharge to an appropriate off-site outlet.
(Ord. 1-4-17, passed 11-18-2003)