Chapter 17.12 — PROVISIONS FOR FLOOD HAZARD REDUCTION

In all areas of special flood hazard the following standards are required:

• A. Anchoring.

  1. 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.

  2. All manufactured homes shall meet the anchoring standards of Section 17.12.040.

• B. Construction Materials and Methods.

  1. All new construction and substantial improvements, to include manufactured homes, shall be constructed with materials and utility equipment resistant to flood damage.

  2. All new construction and substantial improvements, to include manufactured homes, shall be constructed using methods and practices that minimize flood damage.

  3. All new construction and substantial improvements, to include manufactured homes, shall be constructed with electrical, heating, ventilation, plumbing and 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.

  4. Require within Zones AH or AO adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures.

• C.

• Elevation and Floodproofing.

1. New construction and substantial improvement of any residential structure within A1-30, AE and AH zones shall have the lowest floor, including basement, elevated to one foot above the base flood elevation. Nonresidential structures may meet the standards in subsection (C)(3) of this section. Upon the completion of the structure, the elevation of the lowest floor including basement shall be certified by a registered professional engineer or surveyor, or verified by the community building inspector to be properly elevated. Such certification or verification shall be provided to the floodplain administrator.

2. New construction and substantial improvement of any structure in Zone AO shall have the lowest floor, including basement, elevated above the highest adjacent grade at least as high as the depth number specified in feet on the FIRM plus one foot, or at least three feet if no depth number is specified.

Nonresidential structures may meet the standards in subsection (C)(3) of this section. Upon the completion of the structure the elevation of the lowest floor including basement shall be certified by a registered professional engineer or surveyor and verified by the community building inspector to be properly elevated. Such certification or verification shall be provided to the floodplain administrator.

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City of Patterson, CA

PATTERSON CODE

§ 17.12.010

§ 17.12.010

3. Nonresidential construction shall either be elevated in conformance with subsection (C)(1) or (2) of this section or, together with attendant utility and sanitary facilities:

   • a. Be floodproofed so that below the base flood level the structure is watertight with walls substantially impermeable to the passage of water;

• b. Have structural components capable of resisting hydrostatic and hydrodynamic loads and effects of buoyancy; and

  • c. Be certified by a registered professional engineer or architect that the design and methods of construction of this subsection are satisfied. Such certifications shall be provided to the floodplain administrator.

4. Require, for all new construction and substantial improvements, that fully enclosed areas below the lowest floor that are usable 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 a registered professional engineer or architect or meet or exceed the following minimum criteria:

   • a. Have a minimum of two openings on different sides of the structure having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding;

   • b. The bottom of all openings shall be no higher than one foot above grade. Openings may be equipped with screens, louvers, valves or other coverings or devices; provided, that they permit the automatic entry and exit of floodwaters; and

   • c. Buildings with more than one enclosed area must have openings on exterior walls for each area to allow floodwater to directly enter.

5. Detached garages and accessory structures should be used solely for parking or storage and may be constructed such that its floor is below the base flood elevation (BFE), provided the structure is designed and constructed in accordance with the following requirements:

   • a. Use of the accessory structure must be limited to parking and limited storage;

   • b. Are one story and not larger than six hundred square feet in area when located in special flood hazard areas;

   • c. The portions of the accessory structure located below the BFE must be built using flood-resistant materials;

   • d. The accessory structure must be adequately anchored to prevent flotation, collapse, and lateral movement;

   • e. Any mechanical and utility equipment in the accessory structure must be elevated at least one foot above the BFE;

   • f. The accessory structure must comply with floodplain encroachment provisions in Section 17.12.060; and

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City of Patterson, CA

FLOOD HAZARD AREAS

§ 17.12.010

§ 17.12.040

• g. The accessory structure must be designed to allow for the automatic entry of floodwaters in accordance to the floodproofing requirements stated in this section.

6. Detached garages and accessory structures not meeting the above standards must be constructed in accordance with all applicable standards in this section.

7. Manufactured Homes. See Section 17.12.040.

• (Ord. 419 § 5.1, 1987; Ord. 715 (part), 2010; Ord. 853, 2021)

• A. All new and replacement water supply and sanitary sewer systems shall be designed to minimize or eliminate infiltration of floodwaters into the system and discharge from systems into floodwaters.

• B. On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding.

• (Ord. 419 § 5.2, 1987; Ord. 715 (part), 2010; Ord. 853, 2021)

• A. All new subdivisions and other proposed development, including proposals for manufactured home parks and subdivisions, greater than fifty lots or five acres, whichever is the lesser, shall:

  1. Identify the special flood hazard areas (SFHA) and base flood elevations (BFE).

  2. Identify the elevations of lowest floors of all proposed structures and pads on the final plans.

  3. If the site is filled above the base flood elevation, the following as-built information for each structure shall be certified by a registered civil engineer or licensed land surveyor and provided as part of an application for a letter of map revision based on fill (LOMR-F) to the floodplain administrator:

     • a. Lowest floor elevation.

     • b. Pad elevation.

     • c. Lowest adjacent grade.

• B. All subdivision proposals shall be consistent with the need to minimize flood damage.

• C. All subdivision proposals shall have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize flood damage.

• D. All subdivisions shall provide adequate drainage to reduce exposure to flood hazards. In Zones AH and AO, adequate drainage paths shall be provided to guide floodwater around and away from proposed structures.

• (Ord. 419 § 5.3, 1987; Ord. 715 (part), 2010; Ord. 853, 2021)

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City of Patterson, CA

PATTERSON CODE

§ 17.12.040

§ 17.12.060

All new and replacement manufactured homes and additions to manufactured homes in A, A1-30, AH, and AE zones shall:

• A. Be elevated so that the lowest floor is one foot above the base flood elevation; or

• B. If no elevation is determined, lowest floor, including basement, shall be elevated above the highest adjacent grade at least as high as the depth number specified in feet plus one foot, or at least three feet if no depth number is specified;

• C. Be securely anchored to a permanent foundation system to resist flotation, collapse or lateral movement.

• (Ord. 419 § 5.4, 1987; Ord. 715 (part), 2010; Ord. 853, 2021)

All recreational vehicles placed in Zones A1-30, AH, and AE will either:

• A. Be on the site for fewer than one hundred eighty consecutive days; or

• B. 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

• C. Meet the permit requirements of Chapter 17.16 and the elevation and anchoring requirements for manufactured homes in Section 17.12.040.

• (Ord. 715 (part), 2010; Ord. 853, 2021)

Located within areas of special flood hazard established in Section 17.04.060 are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of floodwaters which carry debris, potential projectiles, and erosion potential, the following provisions apply:

• A. Until a regulatory floodway is adopted, no new construction, substantial development, or other development (including fill) shall be permitted within Zones A1-30 and AE, unless hydrologic and hydraulic analyses signed and sealed by a qualified professional engineer are submitted and demonstrate that the cumulative effect of the proposed development, when combined with all other development, will not increase the water surface elevation of the base flood more than one foot at any point within the city of Patterson.

• B. Prohibit encroachments, including fill, new construction, substantial improvements, and other development, unless certification by a registered professional engineer or architect is provided demonstrating through hydrologic and hydraulic analysis in accordance with standard engineering practice that encroachments shall not result in any increase in flood levels during the occurrence of the base flood discharge.

• C. If subsections A and B of this section are satisfied, all new construction and substantial improvements shall comply with all other applicable flood hazard reduction provisions of this chapter.

(Formerly 17.12.050; Ord. 419 § 5.5, 1987; Ord. 715 (part), 2010; Ord. 853, 2021)

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City of Patterson, CA

FLOOD HAZARD AREAS

§ 17.16.010

§ 17.16.030