The city requires that stormwater runoff for new commercial, industrial, multi-family and residential developments be managed as follows:
(A) Retention. The required retention to be contained is the stormwater runoff per divisions (A)(1) and (2) below. Half pavements of the adjoining streets may be considered part of the development.
(1) For the areas north of Baseline Avenue, the following retention requirement shall apply: 110% of the stormwater which falls within the development from a 10-year storm of 24-hour duration (approximately 2.4 inches) of which the difference between the natural runoff and the developed runoff must be retained within the boundaries of that development (including street areas if within a subdivision) (see Apache Junction City Code Vol. II, § 10-4-10(B)(1) and (2)).
(2) For the areas south of Baseline Avenue, the following retention requirement shall apply: stormwater which falls within the development from a 100-year storm of 2-hour duration (precipitation per NOAA Atlas 14 Documents) must be retained within the boundaries of that development (including street areas if within a subdivision) (see Apache Junction City Code, Vol. II, § 10-4-10(B)(1) and (2)).
(3) Surface and underground retention is allowed in all newly developed areas.
(4) Underground retention is only allowed in commercial and industrial areas.
(B) Streets.
(1) Ten-year stormwater runoff. Streets must be constructed to carry the stormwater runoff from a 10-year storm event as follows:
(a) For local streets, there shall be no curb overtopping with no requirements for dry lane conditions.
(b) For collector, arterial and parkway streets, there shall be at least 1 dry 12-foot driving lane in each direction.
(2) One hundred-year stormwater runoff.
(a) Calculated peak flow shall be considered to be contained within the right-of-way with:
1. Six-inch maximum depth over the curb;
2. One hundred cfs maximum flow; and
3. Ten fps maximum velocity.
(b) See Apache Junction City Code Vol. II, § 10-4-6 for the street drainage design guide.
(3) Runoff in excess of street capacity. When the stormwater runoff in the streets exceeds the 10-year or 100-year conditions stated in divisions (B)(1) and (2) above, the excess flows shall be contained in an approved storm drain and/or channel system. No open channels are allowed in the city’s right-of-way.
(4) Inverted crown streets. No new inverted crown streets are allowed within the city limits.
(5) Street cross drainage. Cross drainage shall be underground with culverts and bridges. Low water crossings shall not be used without the city engineer’s approval.
(C) Off-site flows.
(1) OFF-SITE FLOWS are flows that originate upstream of the proposed land development site and have historically traversed either through the site or have been channelized in some form adjacent to the project.
(a) Land development projects are required to convey the 100-year, time of concentration (Tc) peak flows around or through the project site. These off-site flows shall be interpolated from Apache Junction’s Stormwater Master Plan report.
(b) Off-site flows shall not be mixed with any stormwater flows originating from within the project’s contributing drainage area unless specifically approved by the city engineer.
(c) Off-site flows shall be carried through the development and discharged at a location and in a manner consistent with historical flow patterns without adverse impact to adjacent, upstream or downstream properties.
(d) Storm drains or box culverts shall be required when off-site flows are discharged from a development site into public right-of-way. See Apache Junction City Code Vol. II, § 10-4-7 for additional information.
(2) Note that “off-site flows” do not include the stormwater runoff from adjacent public right-of-way that the project must retain in accordance with division (A) above.
(D) Special flood hazard area (FEMA-designated area). Any development or construction within a special flood hazard area shall conform to FEMA floodplain development requirements and to the requirements of the latest city floodplain management ordinance. See Apache Junction City Code, Vol. II, § 10-4-13 and Apache Junction City Code, Vol. II, Chapter 5.
(E) Conditions for developing property in flood areas.
(1) (a) Existing washes are not to be filled or altered without a city-approved engineering study. Existing washes can be relocated on-site based on a city-approved engineering study showing adequate capacity and slope for the relocated washes. The washes must enter and leave the subject property in the historic locations. This shall apply to the following lands within the corporate limits of the City of Apache Junction, including but not limited to:
1. All special flood hazard areas as defined by FEMA;
2. FEMA zone X-500, also known as Shaded Zone X, as it pertains to alluvial fan or sheet flooding;
3. Local floodplains associated with washes and/or sheet flow having a 100-year peak discharge of 50 cfs or more;
4. Areas within the erosion hazard setback of a watercourse;
5. All floodplains/flood-prone areas and erosion hazard setbacks identified on previously and subsequently recorded subdivision plats; and
6. All floodplains/flood-prone areas and erosion hazard setbacks identified on drainage studies previously and subsequently commissioned by the city engineer.
7. Any ephemeral natural watercourses that convey runoff during rain events.
(b) For the purpose of this section, the following definition shall apply unless the context clearly indicates or requires a different meaning.
FLOODPLAIN or FLOOD- PRONE AREA. Any land area susceptible to being inundated by water from any source. For regulatory purposes, this involves either a FEMA special flood hazard area, an area platted on accepted city plans as
being flood-prone, or an area near washes that, in the opinion of the Floodplain Administrator, may be impacted by water during a base flood.
(2) It is unlawful to divert, obstruct or retard a watercourse. Affected agencies or persons may seek legal action.
(3) Construction in designated flood zones.
(a) Construction in an AH designated flood zone, as shown on the FIRM, requires an existing site topography prepared by a State of Arizona registered land surveyor and a city-approved engineered grading plan. The lowest floor, garage and equipment is to be designed to be at least 1 foot above the base flood elevation (“BFE”) (State of Arizona regulatory flood elevation (“RFE”)). Certification by a State of Arizona registered civil engineer stating that the development will not raise the base flood elevation more than 1 foot is required.
(b) A subdivision of 5 or more acres or 50 or more lots located all or partially in an A designated flood zone shall have the base flood elevations determined for the A Zone. The base flood elevations may extend outside the A Zone and the limits of the base flood elevations shall be shown on the grading and drainage plan of the subdivision. The lowest floor, garage and equipment are to be designed to the RFE.
(c) When constructing in an A designated flood zone, without designated floodway and base flood elevations determined, the lowest floor of a structure shall be a minimum of 2 feet above the highest adjacent grade (“HAG”) at the pad location of the structure.
(d) Construction in an AE designated flood zone where the floodway and base flood elevation is determined, the lowest floor of a structure to be constructed outside the floodway shall be a minimum of 1 foot RFE above the base flood elevation shown on the FIRM.
(e) Construction in Flood Zones A and AE will allow fill dirt to be imported to the site with a city-approved engineered grading plan. A city excavation and grading permit shall be required.
(e) Construction in Flood Zones A and AE will allow fill dirt to be imported to the site with a city-approved engineered grading plan. A city excavation and grading permit shall be required.
(f) After construction of the building and after all machinery and/or equipment, such as water heaters, air conditioners and other associated equipment, have been installed and the grading around the building is completed, a State of Arizona registered land surveyor or a registered engineer shall file a finished construction FEMA elevation certificate for city files.
(4) Any grading resulting in alteration of floodwater capacity or re-alignment of a flood area in an A Zone area may require an Army Corps of Engineer’s 404 Permit and/or FEMA approval.
(5) Manufactured homes shall be elevated so that the bottom of the structural frame or the lowest point of any attached appliances (e.g., a ground-mounted AC unit), whichever is lower, is at or above the regulatory flood elevation, and is securely anchored to an adequately anchored foundation system to resist flotation, collapse or lateral movement.
(6) Nonresidential buildings constructed in any A Flood Zone are to be elevated or floodproofed to 1 foot above the base flood elevation or higher. A certification by a State of Arizona registered civil engineer is required, stating that the development grading and building will not raise the base flood elevation more than 1 foot. An as-built FEMA elevation certificate prepared by a State of Arizona registered land surveyor or registered engineer is also required.
(7) Constructing buildings on posts or pilings does not remove the building from the special flood hazard area for flood insurance purposes. The posts or pilings are to be designed to resist lateral movement due to forces of the floodwaters.
(8) Construction is prohibited in floodways unless it has been determined by a State of Arizona registered civil engineer that construction will not increase flood levels during the occurrence of the base flood discharge by any amount. Construction in the FEMA floodways as indicated on the area FIRM map requires that there be no rise in the 100-year flood elevation and a certification letter by a State of Arizona registered civil engineer to this effect. The work may require an Army Corps of Engineers 404 Permit and/or approval of FEMA.
(9) Waste disposal systems cannot be installed wholly or partially in a floodway.
(10) Removing a property from a FEMA flood zone requires a State of Arizona registered civil engineer to process a request in accordance with FEMA procedures.
(11) The city’s floodplain management ordinance set forth in Apache Junction City Code Vol. II, Chapter 5 should be consulted for further information.
(F) Stormwater collection and retention plan. A conceptual stormwater collection and retention plan and a preliminary drainage report shall be submitted to the city with a preliminary plat or site development plan, and shall be approved prior to the approval of the plat or plan. Drawings, plats, plans and the like shall comply with the city standards, set forth in Apache Junction City Code Vol. II, § 10-4-4(A).
(G) Drainage report. A drainage report shall be submitted to the city wherever development and/or grading is proposed within the city limits. DEVELOPMENT shall mean any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation or drilling. See Apache Junction City Code, Vol. II, § 10-4-4(B).
(Ord. passed - - ; Ord. 1511, passed 10-5-2021)