(A) Natural channels. Whenever possible and appropriate existing natural drainage channels must be preserved in their natural state. When this is the case, a drainage easement or right-of-way shall be dedicated over the 100-year floodplain of the natural drainage way.
(B) Man-made channels. When man-made channels are required, the emphasis would be placed on a “natural” appearance. Side slopes 6:1 or flatter is preferred with “natural” vegetation planted per the city’s parks and recreation department requirements and approval.
(1) Design criteria.
(a) Open channels. Open channels are not allowed in the city right-of-way. Open channels shall be designed to convey at least the 100-year peak discharge within the main channel.
(b) Channel details. Channel lining, freeboard, toe protection, under drains, design velocity, drop structures and the like shall be as shown in the FCDMC Drainage Design Manual, Volume II, Hydraulics.
(c) Hydraulic capacity. The capacity of the drainage channel shall not be impeded or diminished by the lining or landscaping materials. The conveyance of the historical flows (“Q” values) shall be substantially maintained.
(d) Maximum velocities/erosion protection. In general, the maximum velocity shall not exceed the scouring velocity of the soil (with natural cover). When the scour velocity is exceeded, additional erosion protection shall be provided. The protection may consist of one or more of the following:
1. Concrete/shotcrete lining reinforced with 12 gauge, 4-inch by 4-inch welded wire fabric reinforcement;
2. Natural stone grouted rip-rap 4-inch to 12-inch diameter stones - leave a minimum 1/4 diameter exposed, maximum ½ diameter exposed;
3. Check dams at 3-foot elevation intervals; or
4. Dumped rip-rap of sufficient size and depth with calculations showing size and depth.
(e) Side slopes. Channels shall have side slopes that are approved by the city engineer.
(f) Channel safety. Channels adjacent to pedestrian walkways (which is not limited to concrete sidewalks), whether located within public right-of-way or on private property shall have safety hand railings per MAG Standard Detail 145 or an equivalent design.
(2) Channel types. The following types of channels are acceptable for use, and can be applied individually or in combinations.
(a) Concrete lined. Where used, these types of channels shall have a 4-inch shotcrete or concrete lining reinforced with 12 gauge, 4-inch by 4-inch welded wire fabric reinforcement.
1. A natural coloring or additive may be allowed or required in some areas.
2. Landscaping adjacent to the channel on both sides is required.
(b) Desert landscaped. Where desired or applicable, landscaped channels can be constructed subject to the following:
1. Maintenance of the channel is considered (e.g., 8-foot bottom provided where necessary).
2. Side slopes can be landscaped with appropriate trees, shrubs and rock features which do not impede with the function of or the maintenance of the channel.
3. Appropriate roughness coefficients (“n” values) shall be used in sizing the channel.
4. Appropriate materials as approved by the city shall be used as a channel liner. The engineer shall take into consideration the potential for erosion and maintenance.
(c) Soil cement lining. The use of soil cement requires special approval by the city, and where approved, this type of channel shall utilize native soils to achieve an integral character with the surrounding area.
(3) Dip sections.
(a) The design of public streets to create a dip section in which to channelize the stormwater flows of the design storm across public streets is prohibited except where specifically approved by the city engineer and in the specially designated Rural Area (see Apache Junction City Code Vol. II, Appendix 10-B).
(b) Existing dip sections on public streets that are subject to widening requirements associated with the development of adjacent properties are to be removed or modified.
1. Where the contributing stormwater flows to the existing dip section have been eliminated or reduced to discharges associated with Apache Junction’s design storms and topography permits, the dip section shall be completely removed and the public street reconstructed.
2. Where topography or existing conditions do not permit the removal, the dip section shall be modified so that flows associated with Apache Junction’s design storms and lesser events are conveyed via storm drain facilities and discharges associated with larger storm events would be allowed to flow across the modified dip section in the historic fashion.
(4) Valley gutters.
(a) Valley gutters shall be used to transport runoff across local streets when a storm drain system is not required. However, valley gutters are generally not acceptable for collector or arterial streets and may do so only with the approval of the city engineer.
(b) In unusual cases, valley gutters may be required to cross collector streets in which case a wider 8-foot design width shall be used and must be approved by the city engineer. Mid-block valley gutters should be avoided.
(5) Maintenance.
(a) Access. Open channels to be properly maintained should provide reasonable access for maintenance. Minimum width of access should be 8 feet. Spacing between vehicular access points should be a maximum of ½ mile. A minimum of 1 access point per subdivision is required. Non-vehicular access points shall be provided every 660 feet maximum. If the facility is to be city-maintained, the above minimum requirements are mandatory.
(b) Responsible party. Maintenance of drainage facilities within the city is usually the responsibility of the property owner or the subdivision’s homeowners’ association. Specific maintenance responsibilities should be called out on the recorded plat and the grading and drainage plan.
(Ord. passed - - )