(A) Minor system.
(1) (a) A minor system is a convenience system and should be designed as dictated by the local economics.
(b) A minor system shall consist of closed conduit, street gutters, flow regulators, ponds and the like.
(c) The minimum design storm frequency shall be a two-year storm with a one hour duration.
(d) The exceptions to this are major business districts where the design of the minor system is based on the ten-year frequency storm with a one hour duration.
(e) Once the stormwater is transported beyond the limits of the subdivision, the water shall then be discharged into the receiving stream which may be an open or closed channel.
(2) Velocities shall be determined using Manning’s equation. Velocities inside conduit shall be safe so as not to expedite the deterioration on the pipe. Outlet velocities shall not exceed the permissible velocity for the receiving channel unless a transition structure is designed to reduce the velocity to an acceptable range.
(3) The hydraulic grade elevations shall be determined and noted at all catch basins for the minor system at the design flow.
(4) The minor system shall remove all water from the surface without overflow or surface backup or localized flooding at the design flow.
(B) Major system.
(1) The major system will be designed with the objective to protect all property in and around the development from a 100-year rainfall event for a six hour duration.
(2) Streets, open channels, detention structures, flow regulators and the like shall be utilized to provide the best engineered and the most economical design for the proposed subdivision.
(3) The design and layout of the major system shall be based on the predevelopment hydrograph. Thus, the hydrograph flow from a proposed subdivision shall not exceed the predevelopment hydrograph for any given storm frequency. In the supporting material, the applicant must show this for two storm frequencies, the minor system’s design storm and a 100-year design. A public easement or right-of-way shall be provided to accommodate the size of the channel needed to control the 100-year storm. Detention ponds used in conjunction with recreational facilities are acceptable and will be encouraged.
(Prior Code, § 11-8-3) (Ord. 594, passed 8-5-1997)