Surface drainage and all secondary channels within or adjacent to the addition shall meet the following conditions:
A. Secondary drainage channels which have a primary function of collecting surface water from adjacent properties or intercepting and diverting side hill drainage shall be provided with an improved open channel.
B. Secondary drainage channels which have a primary function of transporting water through the block or collecting water from cross channels and which have a drainage area of less than forty (40) acres shall be improved with closed storm sewers; and where the secondary drainage channel has a drainage area of greater than forty (40) acres, an improved open channel or closed storm sewer may be provided. Within greenway developments, when the unit area to be drained is less than four (4) acres, the city engineer may modify the requirements of the first part of this subsection to permit a paved, open channel, designed for use as a sidewalk, having a minimum width of four feet (4') and provided with six inch (6") curbs.
C. A drainage channel shall not be located in a street easement unless it is placed in an enclosed storm sewer, except as provided below:
1. Unless a paved street surface at least two (2) lanes wide is provided on both sides of a paved channel so as to provide access to abutting properties;
2. Except where lots are platted to back up to the street right of way where the drainage channel is located between the rear lot line and the paved street, provided that there is no access to the rear of the lot from the street, and further provided that at no time in the future shall access be allowed or constructed over the open drainage channel to the rear of a lot so platted. For the purpose of these regulations, a lot which sides is not considered to back up to the street right of way;
3. When a condition in either subsection C1 or C2 of this section is present, adequate space shall be dedicated as right of way to provide for maintenance of the paved drainage channel and its unpaved bank.
D. In a single-family residential high density development, site grading shall be carried out in such a manner that surface water from each lot will flow directly to a storm sewer, improved channel, sodded swale, or a paved street without crossing more than four (4) adjacent lots.
E. Surface water collected on streets shall be diverted to storm drains at satisfactory intervals to prevent overflow of six inch (6") high curbs during a 25-year frequency rain for the area and grades involved. Drainage area allowed for surface flow on streets at point of diversion shall not exceed twenty (20) acres, regardless of flow.
F. Drainage easement of satisfactory width to provide working room for construction and maintenance shall be provided for all storm sewers.
G. Open channels shall be improved by providing a paved section that will carry the runoff from a rain of 25-year frequency within the lined section and a sodden section to carry the additional runoff from a rain of 50-year frequency. Whenever an open improved channel is required or authorized for a secondary drainage channel under the provisions of these regulations and the channel crosses residential lots which have been developed under the community unit plan of development, or where the channel improvement is to be designed as an area that will be maintained by a property owners' association, then, upon recommendation of the city engineer, the city council may modify the requirements of the first part of this subsection to permit a channel improvement design in keeping with landscaping architectural plans, providing all hydraulic requirements to support the overflow resulting from a 50-year frequency rainfall are met. (Prior code §7-6)