Trinity County Municipal Code Art. III Flood Hazard Overlay (fho) Zoning District

The following areas shall be zoned flood hazard overlay (FHO) zoning district:

All of those lands as designated on the Federal Emergency Management Agency's (FEMA) flood insurance rate (FIRM) maps as zone AO or AH (areas of shallow flooding), or lands designated as zone A which are not included in a flood hazard (FH) zoning district.

(Ord. No. 315-776A, § 1, 10-20-09)

All uses permitted in the underlying zone shall be permitted in the flood hazard overlay (FHO) zoning district provided, however, that a floodplain development permit shall be obtained prior to commencement of construction and issuance of any other county entitlement.

(Ord. No. 315-776A, § 1, 10-20-09)

The following standards shall be applied to any development proposed within a flood hazard overlay zoning district or within a special flood hazard area within which development is permitted by this chapter.

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, and certified per subsection (A)(3).

2. All manufactured homes shall meet the anchoring standards of subsection (F)(2).

3. All standards in subsection (A)(1) and (A)(2) shall be certified by a registered professional architect or engineer.

B. Construction Materials and Methods.

1. All new construction and substantial improvements shall be constructed with flood resistant materials as specified in FEMA Technical Bulletin TB 2-93, and utility equipment resistant to flood damage.

2. All new construction and substantial improvements shall be constructed using methods and practices that minimize flood damage.

3. All new construction and substantial improvements 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. All new construction and substantial improvements within zones AH or AO shall be constructed so that there are 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 residential structures shall have the lowest floor, including basement,

a. In A, AE, AH, and A1-30, elevated not less than two feet above the base flood elevation. Nonresidential structures may meet the standards in subsection (C)(2).

b. In an AO zone, elevated above the highest adjacent grade to a height equal to or exceeding two feet above the depth number specified in feet on the FIRM, or elevated at least four feet above the highest adjacent grade if no depth number is specified.

Upon the completion of the structure, the elevation of the lowest floor, including basement, shall be certified by a registered civil engineer or licensed land surveyor, and verified by the county building inspector, to be properly elevated. Such certification, or verification, shall be provided to the floodplain administrator.

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

a. Be flood proofed so that below the elevation recommended under subsection (C)(1), 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 standards of this subsection are satisfied. Such certification shall be provided to the floodplain administrator.

3. All new construction and substantial improvements of structures with fully enclosed areas below the lowest floor (excluding basements) that are used solely for parking of vehicles, building access or storage, 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 shall follow the guidelines in FEMA Technical Bulletin TB 1-93 and TB 7-93 and must meet the following minimum criteria:

a. Have a minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding. 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. Buildings with more than one enclosed area must have openings on exterior walls for each area to allow flood water to directly enter; and

b. Be certified by a registered civil engineer or architect.

4. Manufactured homes shall also meet the standards in subsection F.

5. This subsection applies to buildings with crawl spaces up to two feet below grade. Below-grade crawl space construction in accordance with the requirements listed below will not be considered basements.

a. The building must be designed and adequately anchored to resist flotation, collapse and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy. Crawl space construction is not allowed in areas with flood velocities greater than five feet per second unless the design is reviewed by a qualified design professional, such as a registered architect or professional engineer;

b. The crawl space is an enclosed area below the BFE and, as such, must have openings that equalize hydrostatic pressures by allowing for the automatic entry and exist of floodwaters. For guidance on flood openings, see FEMA Technical Bulletin 1-93;

c. Portions of the building below the BFE must be constructed with materials resistant to flood damage. This includes not only the foundation walls of the crawl space used to elevate the building but also any joists, insulation, or other materials that extend below the BFE;

d. Any building utility systems with the crawl space must be elevated above the BFE or designed so that floodwaters cannot enter or accumulate within the system components during flood conditions; and

e. Requirements for all below-grade crawl space construction, in addition to the above requirements, to include the following:

i. The interior grade of a crawl space below the BFE must not be more than two feet below the lowest adjacent exterior grade (LAG), shown as D in figure 3 of Technical Bulletin 11-01;

ii. The height of the below-grade crawl space, measured from the interior grade of the crawl space to the top of the crawl space foundation wall must not exceed four feet (shown as L in figure 3 of Technical Bulletin 11-01) at any point;

iii. There must be an adequate drainage system that removes floodwaters from the interior area of the crawl space within a reasonable period of time after a flood event, not to exceed seventy-two hours; and

vi. The velocity of floodwaters at the site should not exceed five feet per second for any crawl space. For velocities in excess of five feet per second, other foundation types should be used.

D. Standards for Utilities.

1. All new and 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 be located to avoid impairment to them or contamination from them during flooding.

3. All disposal fields for on-site waste disposal systems shall be located outside of the one hundred-year flood zone.

E. Standards for Manufactured Homes. All new and replacement manufactured homes (including manufactured homes located in new and existing parks), substantial improvements and additions to manufactured homes shall:

1. Be elevated on a permanent foundation system such that the lowest floor is not less than two feet above the base flood elevation;

2. Be securely anchored to a permanent foundation system designed to resist flotation, collapse or lateral movement, and installed in accordance to FEMA Publication 85 entitled "Manufactured Home Installation in Flood Hazard Areas"; and

3. Upon 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 county building inspector to be properly elevated. Such certification and verification shall be provided to the floodplain administrator.

F. Standards for Recreational Vehicles. All recreational vehicles placed on sites within zones A1-30, AH, AE and A on the county's flood insurance rate map will either:

1. Be on site for fewer than one hundred eighty 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

2. Meet the permit requirements of Article VI of this chapter and the elevation and anchoring requirements for manufactured homes in subsection F.

G. Floodplain Encroachments. Since floodways are an extremely hazardous area due to the velocity of flood waters which carry debris, potential projectiles, and erosion potential, the following provisions apply:

1. Areas without a Regulatory Floodway (Includes all flood zones): All fill and other encroachments shall be certified by a registered professional engineer or architect to not increase the base flood elevation more than twelve inches. Such certification shall be provided to the floodplain administrator.

2. Areas with a Regulatory Floodway: Within an adopted regulatory floodway, the County of Trinity shall prohibit encroachments, including fill, new construction, substantial improvements, and other development, unless certification by a registered civil engineer is provided demonstrating that the proposed encroachment shall not result in any increase in flood levels during the occurrence of the base flood discharge.

3. If subsections (G)(1) and (2) are satisfied, all new construction, substantial improvement, and other proposed new development shall comply with all other applicable flood hazard reduction provisions of this section.

(Ord. No. 315-776A, § 1, 10-20-09)