Where the peak flows exceed the capacity of the public street to convey the peak flows, storm drains shall be installed and sized to carry the excess flows (e.g., when the 10-year peak exceeds the spread criteria or exceeds the curb capacity of the public street or when the right-of-way cannot convey the 100-year peak storm within the constraints of Apache Junction City Code Vol. II, § 10-4-2 of these standards). All storm drains within a development will outlet into on-site retention/detention basins, on-site channels or off-site channels, washes or storm drains.
(A) Storm drain hydraulics.
(1) Hydraulic calculations shall be prepared as indicated in the FCDMC Hydraulic Manual, Section 4, with the following modifications:
(a) Storm drain piping shall be sized to carry the excess runoff to meet the street flow criteria described in Apache Junction City Code Vol. II, § 10-4-2 of these standards.
(b) Where a storm drain is the sole flow path to a retention basin from a development or site, the storm drain shall be sized to carry the 100-year storm peak flow rate.
(c) The hydraulic grade line (“HGL”) may be above the pipe, provided that it remains at least 1 foot below the ground elevation at all manholes, catch basins, inlets and the like.
(2) Calculations for establishing the HGL for storm drainage catch basins, pipes, and structures are to be submitted with the engineering improvement plans. The HGL shall be shown on storm drain piping profile drawings, including catch basin runs.
(B) Storm drain main.
(1) Location.
(a) The alignment of a storm drain is normally within the pavement area of a public street other than principal arterials and parkways unless otherwise approved by the city engineer.
(b) The storm drain should not normally cross the centerline of the public street, nor cross under curb lines, sidewalks, driveways and the like.
(c) Public storm drains located outside of public right-of-way shall be centered within a 20-foot drainage easement.
(2) Pipe size.
(a) The minimum pipe size of the lateral collector shall be 15-inch ID, and the minimum pipe size of the main is 18-inch ID.
(b) At changes in pipe size, the crowns of the pipes shall match.
(3) Depth. Storm drains located within public rights-of-way shall comply with the following:
(a) Consideration shall be given regarding the depth of any manhole to be installed on a public storm drain in establishing the depth of the storm drain pipe. Shallow manholes shall be avoided and require approval by the city.
(b) The crown of storm drain pipes whether public or private shall not encroach or protrude into the pavement section of the public street (ABC base and surface courses of asphalt).
(c) The crown of storm drain culverts shall not normally encroach or protrude into the pavement section of public streets. With city engineer approval, the asphalt courses may be placed directly onto the concrete slabs of box culverts.
(4) Direction changes. When the pipe changes direction more than 30 degrees, there shall be a drop between match points of at least 0.1 feet. In no case shall the deflection angle be greater than 90 degrees. Manholes shall be required at all storm drain pipe direction changes.
(5) Separation of storm drain pipe from water and sewer lines.
(a) Horizontal separation of storm drains and water or sewer lines shall be a minimum of 6 feet, outside of pipe to outside of pipe.
(b) Vertical separation of storm drains and sewers should be 2 feet (sewer below) unless the sewer line is manufactured from ductile iron with mechanical joints or equal.
(c) Vertical separation of storm drain and water line (water line below) shall be 2 feet clear.
(d) Separation is measured from the outside of the two pipes.
(6) Velocity. The velocity of stormwater flowing within public storm drains shall be in the range of 2 feet per second (2 fps) to 10 feet per second (10 fps).
(7) Pipe classification.
(a) The minimum D-load class specification shall be Class 3 or the actual installation requirement, whichever is greater.
(b) Trench loading calculations shall be provided upon request during the plan review process.
(c) The civil engineering improvement plans shall clearly identify the class of the pipe for all storm drains, whether public or private within city right-of-way.
(8) Pipe materials. The following materials are acceptable for constructing conveyance components of publicly maintained storm drains within the city:
(a) RGRCP. Rubber gasket reinforced concrete pipe (“RGRCP”) conforming to Section 618 of the Uniform Standard Specifications as published by MAG.
(b) RCP. Reinforced concrete pipe (“RCP”) is approved for storm drains 36 inches or larger. RCP shall conform to Section 618 of the MAG Uniform Standard Specifications.
(c) CIPP. Cast-in-place pipe (“CIPP”) conforming to Section 620 of the MAG Uniform Standard Specifications is subject to the following.
1. CIPP generally should not be placed under a road bed. The city engineer must grant specific approval for the installation of CIPP. Letters of request shall include a justification statement and shall be submitted to the public works department - engineering division for processing.
2. Minimum size shall be 36 inches.
3. A soils report shall be provided that confirms that soil conditions are adequate for the installation of CIPP.
4. The hydraulic gradient for the design events shall be kept within the pipe.
5. Details of the CIPP shall be prepared for and approved by the city engineer.
(d) Other pipe. Where a lateral conveyance is not subject to pavement loading from public streets (e.g., laterals directly from inlets into a retention basin), the following pipe materials may be used with prior approval from the city engineer.
1. Polyvinyl chloride (“PVC”) SDR 35 or greater conforming to Section 745 of the MAG Uniform Standard Specifications.
2. High density polyethylene (“HDPE”) conforming to Section 738 of the MAG Uniform Standard Specifications.
(e) Restricted material usage. The following materials are not approved for use in constructing storm drains located within City of Apache Junction right-of-way, but are approved for culvert crossings with the approval of the city engineer:
1. Corrugated metal pipe (“CMP”); and
2. Corrugated metal pipe arch (“CMPA”).
(f) Alternative materials. Other materials for public stormwater conveyance may be considered on a case-by-case basis subject to the following:
1. A written request to the city engineer detailing the justification for the use of alternative materials; and
2. The request shall be made through the public works department - engineering division.
(9) Pipe compaction methods. Mechanical compaction methods are required. No jetting or flooding shall be allowed within the city right-of-way without mechanical compaction.
(C) Storm drain inlets. Inlets are those drainage structures that are placed and sized to intercept stormwater flows and direct those flows into a conveyance.
(1) Inlets that have been approved for use within public right-of-way or publicly maintained areas are:
(a) Inlets constructed in accordance with MAG Standard Details 533 (Type “D”), 534 (Type “E”), 535 (Type “F”), all modified with an 18-inch sump area below the invert of the pipe as shown in Apache Junction Standard Detail AJ-533-1M.
(b) Scuppers constructed in accordance with MAG Standard Detail 206-1. No metal tops are allowed.
(c) Projects that are being developed adjacent to existing public streets in which a scupper type inlet exists to direct street runoff onto the project site are required to remove and replace the existing scupper with an approved inlet unless otherwise approved by the city engineer.
(d) Inlets that provide an “access” opening into the box are prohibited. All access openings shall be through the grate.
(e) Slotted drains are not allowed within the city right-of-way unless prior approval is given by the city engineer.
(f) Other inlet types with the appropriate justification may be approved on a project-by-project basis.
(g) MAG Standard Detail 535 (Type “F”) cannot be constructed fully or partially in sidewalk areas.
(2) Inlet capacities on public streets shall be calculated in accordance with:
(a) The Drainage Design Manual for Maricopa County, Volume II, Hydraulics; or
(b) The Federal Highway Administration’s (“FHWA”) Hydraulic Engineering Circular Number Twelve (“HEC” 12), “Drainage of Highway Pavements.”
(c) The engineer shall make allowances for clogging of the inlet structure.
(3) Inlets within public right-of-way shall not be placed or connected in series unless approved by the city engineer.
(4) The minimum horizontal distance between inlets within public right-of-way is 30 feet.
(D) Storm drain laterals. The portion of the conveyance that connects the inlet structure to the storm drain mains or to an outlet structure is considered a lateral pipe. Laterals within the public right-of-way shall conform to the following:
(1) Minimum diameter is 15 inches when the lateral is subject to traffic loading forces or may be 12 inches when not subject to traffic loading forces and approved by the city engineer (e.g., equalization pipes and the like).
(2) The crown of the lateral pipe shall not encroach or protrude into the public street pavement section (ABC, base or surface asphalt courses).
(3) See division (B)(8) above regarding acceptable materials for lateral pipes that are located within public right-of-way.
(4) The connection of the lateral pipe to the main pipe(s) of the storm drain shall be per MAG Standard Detail 524 or via a prefabricated tee component.
(5) The minimum D-load classification for lateral pipes shall be Class 3 or the actual installation requirements, whichever is greater.
(E) Manholes and structures. Manholes or junction structures shall be provided on public storm drains to facilitate maintenance in accordance with the following:
(1) Locations. Manholes and/or junction boxes are required at all of the following:
(a) Junctions of 2 or more pipes;
(b) Changes in grade;
(c) Changes in alignment; and
(d) Changes in pipe sizes (pipe crowns to match).
(2) Spacing. The maximum spacing for manholes shall be:
(a) Four hundred feet on lines 18 inches to 36 inches inside diameter; and
(b) Six hundred sixty feet on lines greater than 36 inches inside diameter.
(3) Manhole construction standards on public storm drains shall comply with the following table:
Table 10-4.1
Manhole Construction Standards
Manhole | Pipe Size | |
≤ 48 in. | ≥ 51 in. | |
MAG Standard Detail | ||
Base | 520 | 521 |
Shaft | 522 | 522 |
Frame and cover | 424 (30 in.) | 424 (30 in.) |
(F) Storm drain outlets. Structures that are located at the downstream terminus of storm drain laterals or mains are classified as outlets. Storm drain outlets that are located within public right-of-way or areas that are subject to maintenance by the city shall comply with the following:
(1) Concrete headwalls shall be installed on 12-inch and larger pipes per MAG Standard Detail 501-4 or an equivalent.
(2) Access barriers shall be installed on the outlets of 12-inch or larger pipes.
(3) Erosion protection shall be provided as necessary.
(4) Safety railing shall be installed on headwalls that, from the top of the headwall to the floor, are 18 inches and greater in height and are 24 inches horizontally, or less, to a public sidewalk per MAG Standard Detail 145.
(Ord. passed - - )