All minor tributaries and surface drainage located within or immediately adjacent to and serving the subdivision shall be improved by the developer, as follows:
A. Standards:
1. All minor tributary channels shall be improved in accordance with standards set forth in figures 4, 5, and 6 as shown in section 12-5-9 of this chapter or other equivalent standards, as determined by the city's consulting engineer. Specifications as shown on figure 7 in section 12-5-9 of this chapter shall be used only for channels or minor tributaries which drain less than eighty (80) acres and which are designed as an integral part of the landscape of the area so that maintenance of sodded slopes will be the responsibility of the property owners abutting the channel.
2. All channels shall be designed for self-cleaning and ease of maintenance, shall have sufficient hard surface along the flow line to prevent ponding of water, and shall have design characteristics of alignment, materials of construction and cross sectioned elements that will be hydraulically efficient and visually harmonious with the adjacent landscape.
B. Enclosed Storm Sewers: Enclosed storm sewers may be required by the city's consulting engineer where special or unusual conditions make open channels hazardous or otherwise unfeasible.
C. Drainage Channels: A drainage channel shall not be located in a street easement unless it is placed in a closed storm sewer, or unless a paved street surface is located on both sides of a paved drainage channel to give access to abutting properties.
D. Site Grading: Site grading shall be carried out in such a manner that surface water from each lot shall flow directly to a storm sewer, improved channel or paved street without crossing more than two (2) adjacent lines.
E. Surface Water: 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 fifty (50) year frequency rain for the area and grades involved; provided however, that in no case shall the drainage area served by one street exceed twenty (20) acres, regardless of the amount of flow.
F. Drainage Easements: Drainage easements of satisfactory width to provide working room for construction and maintenance shall be provided for all storm sewers. In no case shall the total easement be less than twenty feet (20').
G. Bridges And Culverts:
1. Bridges or culverts shall be provided where watercourses cross continuous streets or alleys.
2. Bridges and culverts shall be sized to accommodate a 100-year frequency rain, based on the drainage area involved.
3. Design of bridges and culverts shall conform to city construction specifications.
H. Closed Storm Sewers: Closed storm sewers shall be constructed of precast or prefabricated pipe or built in place of closed box design to conform with city construction specifications to serve a 100-year frequency rain for the drainage area involved.
I. Open Paved Storm Drainage:
1. Open paved storm drainage channels shall be constructed in accordance with city specifications.
2. Side slopes above the paved section shall be shaped and sodded on a slope of four (4) horizontal to one vertical or flatter.
3. Fences shall be outside of the 100-year frequency flooding line, shall not be erected below the shoulder of the sodded section, and in no case shall fences be closer than six feet (6') (measured horizontally) to the edge of the paved section, except on figure 4 sections in section 12-5-9 of this chapter.
4. Hand laid riprap may be substituted for sodded shoulders where desired for landscape purposes. (Ord. 1978-10, 10-3-1978)