A. General. The following subsections of section 17-15-10 contain the standards of construction for lands to which this chapter applies per subsection 17-15-3 A and are further restricted or supplemented by the requirements that follow. In all cases, impact to adjacent, upstream or downstream properties shall be taken into account.
1. The water surface elevation may not be increased by more than one tenth of one foot at any point located off of the property which is to be occupied by the anticipated development.
2. The velocity of the watercourse may not be increased by ten percent or by more than 1.0 foot per second, whichever is less.
B. Standards of construction in floodprone areas
1. Anchoring
a. All new construction and substantial improvements shall be anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy;
b. All manufactured homes shall meet the anchoring standards of subsection 17-15-10 F. 2. b.
2. Construction materials and methods
a. All new construction and substantial improvements shall be constructed with materials and utility equipment resistant to flood damage;
b. All new construction and substantial improvements shall be constructed using methods and practices that minimize flood damage;
c. All new construction, substantial improvement and other proposed new development shall be constructed with electrical, heating, ventilation, plumbing, air conditioning equipment, and other service facilities that are designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding;
d. Within FEMA zones AH or AO, adequate drainage paths around structures on slopes are required to guide floodwaters around and away from proposed structures;
e. Structures designed or utilized for human habitation, whether full or part time, shall only be permitted where the product of the flow depth d, in feet, times the square of the flow velocity v, in feet per second, of the surrounding floodwaters of the base flood does not exceed the numerical value of 18 (dv2 = 18) for a period greater than 30 minutes in duration as determined by an Arizona registered professional civil engineer and accepted by the floodplain administrator and the surrounding floodwaters of the Base Flood do not exceed three feet in depth; and
f. All structures designed or utilized for human habitation or commercial enterprise, whether full or part time, located within a floodplain or erosion hazard setback area shall provide protection for scour and lateral erosion based upon a scour/erosion analysis sealed by an Arizona registered professional civil engineer and accepted by the floodplain administrator. In all cases scour protection shall be designed to be a minimum of three feet below the lowest point of the adjacent channel or thalweg.
3. Elevation and flood-proofing
a. New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated at or above the regulatory flood elevation.
b. New construction and substantial improvement of any residential structure in zone AO shall have the lowest floor, including basement, elevated at least one foot higher than the depth number shown on the FIRM measured from the highest adjacent natural grade or one foot higher than the BFE from a town approved drainage study, whichever is greater.
c. New construction and substantial improvement of any residential structure in zone A with no base flood elevations shall have the lowest floor, including basement, elevated at least four feet higher than the highest existing adjacent grade unless an engineering analysis is performed by an Arizona registered professional civil engineer to determine the base flood elevations, at which the requirement will then be a minimum of one foot above the base flood elevation.
d. New construction and substantial improvement of any residential structure in zone X-500-alluvial fan shall have the lowest floor, including basement, elevated at least 18 inches higher than the highest existing adjacent grade.
e. Non-residential construction shall either be elevated in conformance with the preceding requirements or shall, together with attendant utility and sanitary facilities:
i. be flood-proofed so that below the regulatory flood level the structure is watertight with walls substantially Impermeable to the passage of water;
ii. have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy; and
iii. be certified by an Arizona registered professional civil engineer or architect that the standards of this subsection are satisfied. Such certifications shall be provided to the floodplain administrator.
f. All new construction and substantial improvements with fully enclosed areas below the lowest floor that are useable solely for parking of vehicles, building access or storage in an area other than a basement and which are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must either be certified by an Arizona registered professional civil engineer or architect to meet or exceed the following minimum criteria:
i. a minimum of two openings on different sides of each enclosed area that have a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided;
ii. the bottom of all openings shall be no higher than one foot above finished grade; and
iii. openings may be equipped with screens, louvers, valves or other coverings or devices provided that they permit the automatic entry and exit of floodwaters.
g. Manufactured homes shall meet the above applicable standards and also the standards in subsection 17-15-10 F.
h. If fill is used to elevate any structure, the fill shall extend at such elevation for a distance of at least fifteen feet beyond the outside limit of the structure unless a study/analysis prepared by an Arizona registered professional civil engineer demonstrates that a lesser distance is acceptable.
i. Upon the completion of the structure and prior to the issuance of a certificate of occupancy the elevation of the lowest floor including basement shall be certified by an Arizona registered professional civil engineer or surveyor and provided to the floodplain administrator.
C. Standards for storage of materials and equipment
1. The storage or processing of materials that are, in time of flooding, buoyant, flammable, explosive or could be injurious to human, animal or plant life is prohibited.
2. Storage of other material or equipment may be allowed if not subject to major damage by floods and if firmly anchored to prevent flotation, or if readily removable from the area within the time available after flood warning.
3. Storage of materials and equipment is further restricted in the floodway per subsection 17-15-10 J.
D. Standards for water supply, waste disposal, and other utilities
1. All new or replacement water supply and sanitary sewage systems shall be designed to minimize or eliminate infiltration of flood waters into the system and discharge from systems into flood waters.
2. On-site waste disposal systems shall not be located in a floodplain or erosion hazard setback area if a more suitable area exists on the parcel.
3. Waste disposal systems shall not be installed wholly or partially in a regulatory floodway. Crossings are allowed if buried at least two feet below the calculated scour depth as determined in a study/analysis prepared by an Arizona registered professional civil engineer.
4. Utilities shall be buried at least two feet below the calculated scour depth as determined in a study/analysis prepared by an Arizona registered professional civil engineer.
E. Standards for subdivisions and commercial developments
1. Land which is subject to periodic flooding, which cannot be properly drained, or other land which, in the opinion of the town engineer, is unsuitable for any use shall not be subdivided, except that the town may approve subdivision of such land upon receipt of evidence that the construction of specific improvements can be expected to render the land suitable. Necessary flood control improvements must be included in the subdivision assurances as described in section 17-5-4.
2. All preliminary subdivision plats and development plans shall delineate the FEMA SFHA, floodway if applicable, locally regulated floodplain, erosion hazard setback areas, and Base Flood elevations. The pre- and post-development conditions shall be shown.
3. All final subdivision plats shall provide the elevation of each proposed structure and pad affected by or adjacent to flood hazards. If the site is filled above the base flood, the final lowest floor and pad elevation shall be certified by an Arizona registered professional civil engineer or surveyor and provided to the Floodplain Administrator. All final subdivision plats shall delineate the FEMA SFHA, floodway if applicable, locally regulated floodplain and erosion hazard setbacks in a surveyable manner and sealed by an Arizona registered land surveyor.
4. All improvement plans relating to grading, paving, sewer or drainage shall delineate the FEMA SFHA, locally regulated floodplain, erosion hazard setback areas and base flood elevations. The pre- and post-development conditions are to be shown.
5. All subdivision and commercial development proposals shall be consistent with the need to minimize flood damage.
6. All subdivision and commercial development proposals shall have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize flood damage.
7. All subdivisions and commercial developments shall provide adequate drainage to reduce exposure to flood hazards.
8. All subdivisions with a minimum lot size of 16,000 square feet or less shall be platted such that FEMA SFHA, locally regulated floodplains, and erosion hazard setback areas are not located on individual lots. Such areas shall be contained within common areas.
9. All subdivisions with a minimum lot size greater than 16,000 square feet shall show buildable pad areas for each lot in which a FEMA SFHA, locally regulated floodplain or erosion hazard setback appears on individual lots. Pad elevations, encroachments, and/or erosion hazard setback protective measures shall be designed by an Arizona registered professional civil engineer as part of the project.
10. When a modification or removal of a FEMA SFHA is sought for a development, the following requirements apply:
a. A hydraulic analysis and engineering plans for the modifications must be accepted by the floodplain administrator. New delineations of the floodplain conditions shall be prepared in conformance with the requirements of FEMA for LOMRs, the state director of water resources, and the town.
b. A CLOMR must be submitted to and accepted by FEMA prior to the recording of a final plat for subdivisions.
c. A CLOMR must be submitted to and accepted by FEMA prior to construction of physical improvements.
d. A CLOMR must be submitted to and accepted by FEMA prior to issuance of building permits for subdivision lots. Certificates of occupancy shall not be issued on subdivision lots to be affected by a LOMR until the LOMR has become effective..
e. A CLOMR must be submitted to and accepted by FEMA prior to issuance of building permits for commercial/industrial buildings. Certificates of occupancy shall not be issued for commercial/industrial buildings to be affected by a LOMR until the LOMR has become effective.
f. Any flood control infrastructure necessary to achieve a LOMR must also have a flood control and maintenance easement dedicated to the Town that allows for inspection of said infrastructure and at the Town’s sole discretion the right to repair the infrastructure. The development shall be responsible for maintenance of the infrastructure. Failure to maintain flood control infrastructure on the part of the development shall be a violation of this code.
11. All subdivisions and commercial/industrial developments shall provide all weather access in accordance with subsection 17-15-10 M.
F. Standards for manufactured homes and manufactured home parks or subdivisions.
1. Manufactured homes and manufactured home parks or subdivisions must meet other applicable requirements of section 17-15-10 that have not been supplemented or revised by this subsection.
2. All manufactured homes and substantially improved manufactured homes located within lands to which this chapter applies per subsection 17-15-3 A shall be required to comply with the following:
a. Be elevated so that the bottom of the structural frame or the lowest point of any attached appliances, whichever is lower, is at or above the regulatory flood elevation; and
b. Be securely anchored to resist flotation, collapse or lateral movement by one of the following methods:
i. Provision of an anchoring system designed to withstand horizontal forces of 25 pounds per square foot and uplift forces of 15 pounds per square foot; or
ii. Provision of over-the-top and frame ties to ground anchors, specifically:
a) Over-the-top ties shall be provided at each of the four corners of the manufactured home, with two additional ties per side at intermediate locations, except that manufactured homes less than 50 feet long require only one additional tie per side; and
b) Frame ties shall be provided at each corner of the home with five additional ties per side at intermediate points, except that manufactured homes less than 50 feet long require only four additional ties per side; and
c) All components of the anchoring system shall be capable of carrying a force of 4,800 pounds.
3. All manufactured home parks or subdivisions located within lands to which this chapter applies per section 17-15-3 A shall be required to comply with the following:
a. All manufactured homes shall be placed:
i. on pads or lots elevated on compacted fill so that the bottom of the structural frame and any attached electrical appliances is at or above the regulatory flood elevation; or
ii. on stem walls or pilings so that the bottom of the structural frame and any attached electrical appliances is at or above the regulatory flood elevation.
b. Lots shall be large enough to permit steps.
c. Pilings or stem wall shall be placed in stable soil.
d. Pilings shall be no more than ten feet apart.
4. Certification that the installation of a manufactured home meets all of the requirements of this section is required. Such certification shall be provided by the person installing the manufactured home, the owner, the developer of a manufactured home park or subdivision, or an agency regulating manufactured home placement, whichever is deemed appropriate by the floodplain administrator. Certification of finished floor elevation shall be in accordance with section 17-15-10 B. 3. i.
G. Standards for recreational vehicles. All recreational vehicles placed on site shall either:
1. Be on site for fewer than 180 consecutive days, and be fully licensed and ready for highway use. (a recreational vehicle is ready for highway use if it is on its wheels or jacking system, is attached to the site only by quick disconnect type utilities and security devices, and has no permanently attached additions); or
H. Standards for critical facilities. Critical facilities shall be regulated to withstand the 500-year event. Critical facilities shall be required to meet the following requirements:
1. Structures or facilities that produce, use or store more than 100,000 gallons of highly volatile, flammable, explosive, toxic and/or water-reactive materials shall be located outside of the 500-year FEMA floodplain (shaded zone X) and locally regulated floodplain calculated at the 500 year interval.
2. Public and private utility facilities that are vital to maintaining or restoring normal services to flooded areas before, during and after a flood shall be located outside of the FEMA special flood hazard area and the locally regulated floodplain. Such facilities shall be designed to avoid the 500-year floodplain or certify the safety of the development per subsection 17-15-10 H. 4.
3. Police stations, fire stations, hospitals, nursing homes, assisted living homes, public vehicle and equipment storage facilities, emergency operations centers and schools designated to be used as temporary shelters shall be located outside the FEMA special flood hazard area and the locally regulated floodplain. Such facilities shall be designed to avoid the 500-year floodplain or certify the safety of the development per subsection 17-15-10 H. 4.
4. The developers of critical facilities referenced in subsections 2 and 3 above shall certify the safety of the development by providing the following information to the satisfaction of the floodplain administrator:
5. Freeboard requirements shall be such that the finished floor elevation shall be elevated one foot above the 500-year water surface elevation.
6. Developer shall delineate any 500-year floodplains and the respective erosion hazard setback areas within 200 feet of the parcel or development.
7. The 500-year water surface elevations shall be delineated by the developer on the preliminary/final plats, development plans and improvement plans.
8. Toe downs and bank protection shall be designed to withstand the 500-year flood.
I. Standards for excavations, including sand and gravel operations.
1. Excavations, including sand and gravel operations may be permitted provided the following minimum conditions are met in addition to any other requirements per the town code. Additional conditions apply for operations occurring within a regulatory floodway as required in subsection 17-15-10 J.
2. Extraction of sand, gravel and other materials is allowed provided that excavations are not so located or of such depth, or width, or length or combination of depth-width-length as to present a hazard to structures (including but not limited to roads, bridges, culverts, and utilities), to the banks of watercourses, to other property, or which adversely affects groundwater recharge.
3. No stockpiling is permitted within special flood hazard areas of materials or tailings that may obstruct, divert, or retard the flow of floodwaters except as reviewed and accepted by the floodplain administrator on an individual floodplain use permit basis.
4. Due to the rapidly changing hydraulic characteristics of watercourses in the town, and the effects excavations have on these characteristics, floodplain use permits for excavations shall only be issued for a limited time period not to exceed one year, subject to annual renewal and review by the floodplain administrator. Renewals will only be granted after receipt and acceptance of a report by the operator showing that the sand and gravel excavations remain in compliance with the conditions of the previous floodplain use permit, current floodplain conditions and all current related floodplain management regulations.
5. In addition to those conditions provided for elsewhere, floodplain use permits for excavations may impose site specific conditions based upon hydraulics and sediment transport regarding the area and location in which excavations are allowed, the maximum amount of material to be excavated, and other reasonable restraints on the methods of operating in relationship to the floodplain conditions.
6. The floodplain administrator may require hydrologic, hydraulic and geomorphic analyses addressing the existing conditions as well as the impacts under the proposed method of operation.
J. Floodway requirements
1. Located within special flood hazard areas established in subsection 17-15-3 B are areas designated as floodways. The floodway is an extremely hazardous area due to the velocity of floodwaters which carry debris, potential projectiles and erosion potential. Encroachments are prohibited in the floodway, including fill, new construction, substantial improvements and other development. The following subsections clarify how the floodway may be developed.
2. The following open space uses are permitted within the floodway to the extent that they are not prohibited by any provision of this Title or any other ordinance, law or regulation, and provided they do not require fill, excavation, or the storage of materials or equipment:
a. Agricultural uses, including general farming, pasture, grazing, outdoor plant nurseries, horticulture, viticulture, truck farming, sod farming, and wild crop harvesting.
b. Industrial-commercial uses such as loading areas, airport landing strips, and parking areas.
c. Private and public recreational uses, including golf courses, tennis courts, driving ranges, archery ranges, picnic grounds, boat launch ramps, swimming areas, parks, wildlife and nature preserves, game farms, fish hatcheries, shooting preserves, target ranges, trap and skeet ranges, hunting and fishing areas, hiking and horseback riding trails.
d. Accessory residential uses, including lawn gardens, parking areas and play areas.
e. Excavations, including sand and gravel operations may occur in the floodway under the following conditions in addition to those required in subsection 17-15-10 I:
f. There shall be no stockpiling of materials or tailings within the floodway.
g. Excavations may be allowed only in those reaches of watercourses which have, at a minimum, a balanced sediment system; that is, the sediment coming into the reach is equal to or greater than the sediment leaving the reach and the long term sediment balance for the entire river system indicates that the stream channel will aggrade.
h. Flood control structures designed to protect life or property from the dangers or hazards of floodwaters are permitted provided all other provisions of this chapter are met.
i. No use shall be allowed which:
i. Acting alone or in combination with existing or future uses creates danger or hazard to life or property. In determining whether a use creates a danger or hazard to property, the floodplain administrator may require a certification by an Arizona registered professional civil engineer that the proposed use will not result in any increase in the floodway elevations during the occurrence of the base flood nor will the proposed use divert, retard or obstruct the flow of flood waters.
ii. Increases the regulatory floodway elevation.
iii. Adversely effects groundwater recharge.
iv. Increases erosion potential upstream and/or downstream.
v. Places a waste disposal system wholly or partially in a floodway.
K. Erosion hazard setback requirements
1. Close proximity to watercourses poses a hazard to development due to lateral erosion. Per subsection 17-15-3 A, the erosion hazard setback area of a watercourse is a land covered by this chapter.
2. Along natural watercourses where unusual geology, sinuosity or similar physical conditions exist, the erosion hazard setback shall be established on a case-by-case basis by the floodplain administrator, unless an engineering study is done to establish the limits by an Arizona registered professional civil engineer and accepted by the floodplain administrator.
3. Along incised natural watercourses where no unusual geology, sinuosity or similar conditions exist, a standard setback measured from the top of the primary channel bank shall be provided at the time of development. The setback may be reduced by an engineering analysis performed by an Arizona registered professional civil engineer and accepted by the floodplain administrator in accordance with subsection 17-15-10 K. 4.
4. Along non-incised natural watercourses (i.e. sheet flow areas) where no unusual geology, sinuosity or similar conditions exist, a standard setback measured from the base flood limits shall be provided at the time of development. The setback may be reduced by an engineering analysis performed by an Arizona registered professional civil engineer and accepted by the floodplain administrator in accordance with subsection 17-15-10 K. 4.
5. Standard erosion hazard setbacks may be reduced by an engineering study performed by an Arizona registered professional civil engineer and accepted by the floodplain administrator. The reduced setbacks shall not fall below minimum allowable erosion hazard setbacks unless the study also includes an analysis performed by an Arizona registered professional geological engineer. The following table shows the standard and minimum allowable setbacks when no physical construction is made to prevent erosion hazard:
Base flood flow rate (cfs) | Standard erosion hazard setback (feet) | Minimum allowable erosion hazard setback (feet) |
<500 | 25 | 15 |
500 to 1,999 | 50 | 25 |
2,000 to 4,999 | 75 | 45 |
5,000 to 9,999 | 100 | 70 |
10,000 and greater | 250 | 175 |
Santa Cruz River | 500 | 350 |
L. Detention and retention requirements
1. Any development with a net residential density of three or more units per acre after subtracting out common areas, or any residential development larger than one acre that has a density of six units per developed acre, as well as all proposed commercial and industrial developments shall provide some method of peak and/or volumetric runoff reduction. The amount of reduction required shall be as set forth in the latest edition of the Pima county regional flood control district design standards for stormwater detention and retention. The peak runoff reduction shall be provided through detention of storm water and storm water harvesting for irrigation where possible.
2. Balanced and critical drainage basins are watersheds that have been identified by the chief engineer of the Pima county flood control district on a 1987 map as unsuitable for increased development because of the high probability of increased flooding with development and the potential for flooding of existing improvements or property. The floodplain administrator shall maintain this map of critical and balanced basins within the jurisdictional limits of the town. Drainage basins that have not previously been identified as unsuitable for additional urban development shall be considered balanced basins, but upon study by the floodplain administrator, may be classified as critical basins. Critical and balanced basins may be developed further only upon the incorporation of adequate detention systems or flood control facilities, as reviewed and accepted by the floodplain administrator. These detention systems or flood control facilities shall be incorporated into any and all future basin-development proposals, regardless of size or land-use density.
3. Structural flood control measures may be proposed in conjunction with, or in place of detention/retention systems if it can be clearly demonstrated that such measures will not alter the water and sediment equilibrium of the affected watercourse, and will mitigate environmental impacts. Structural flood control measures, such as channelization to a logical conclusion downstream of the proposed development and/or improvements to existing offsite flood control systems within the applicable drainage or stream reach, shall be completed in accordance with plans reviewed and accepted by the floodplain administrator.
4. Localized areas lacking sufficient improved or natural receiving waters into which runoff may be discharged may be required to follow alternative drainage solutions including complete retention practices as directed by the town engineer.
5. A fee may be collected by the town in lieu of detention/retention system when it can be clearly demonstrated that the detention at the site does not provide offsite flood relief due to the parcel size, location within the drainage basin, or other factors. The fees collected will be used to construct public flood control improvements that will mitigate the potential damage of flood waters originating from the property contributing the fees. In balanced and critical drainage basins, and where development is less than three units per acre, use of a fee system will be encouraged in lieu of a detention system to preserve the natural drainage patterns. The fee shall be equivalent to the cost of a detention system that would otherwise be constructed for the development to mitigate increased storm water runoff created by the proposed development.
M. Access requirements
1. Development shall provide all-weather access in accordance with the following requirements:
a. Developments that fall under the requirements of subdivisions of ten or fewer lots shall provide all-weather access from each lot to the subdivision entrance. All-weather access shall be constructed from the subdivision entrance to the nearest paved public roadway. This requirement may be waived if the following criteria is met:
i. Subdivision is characterized as a residential subdivision
ii. Subdivision is of a rural character, with minimum lot sizes of 36,000 square feet
iii. If, in the determination of the floodplain administrator, it is not reasonably feasible to construct such access to the subdivision entrance
iv. Subsection 17-15-10 M. 2 provisions are utilized.
b. All subdivisions that do not fall under the preceding requirements shall provide all-weather access from each lot to a paved public right of way. A subdivision with more than one access to a paved public roadway need only have one all-weather access.
c. All commercial developments shall provide all-weather access from a paved public roadway to all public portions of their site. Nonpublic portions of a commercial development that are not all-weather access shall be gated and signs posted in accordance with subsection 17-15-10 M. 2.
d. Private residential construction not part of a recorded subdivision shall construct an all-weather access from the property boundary to a paved public roadway. If in the determination of the floodplain administrator it is not reasonably feasible to construct such access to the property, then subsection 17-15-10 M. 2 provisions may be utilized.
2. The floodplain administrator may allow certain exemptions to all-weather access as stated in the preceding section. A condition of allowing this exemption is that the owner shall execute and record a covenant running with the land enforceable by the town which contains the following:
a. An acknowledgement that the vehicular access may be impassable to conventional motor vehicles and emergency vehicles in times of flooding,
b. A hold harmless provision, holding the town, its agents, the floodplain management board harmless from and against all injuries and damages resulting from the traversing or attempting to traverse the vehicle access during times of flooding, and
c. The covenant, successors and assigns shall erect and maintain a sign(s) in a location(s) and size(s) acceptable to the town stating “DO NOT ENTER WHEN FLOODED”
Ordinance 2021-010 amended paragraphs E and L
Ordinance 2022.006 amended Section 17-15-10 B., D.
Ordinance 2022.017 amended Section 17-15-10 E.