16.46.050 Provisions for flood hazard protection

16.46.050 Provisions for flood hazard protection.

A. General Standards. In all areas of special flood hazards, the following standards are required:

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 must likewise be anchored to prevent flotation, collapse, or lateral movement, and shall be installed using methods and practices that minimize flood damage. Anchoring methods may include, but are not limited to, use of over-the-top or frame ties to ground anchors. (Reference FEMA’s “Manufactured Home Installation in Flood Hazard Areas” guidebook for additional techniques.)

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. Electrical, heating, ventilation, plumbing, and air conditioning equipment and other service facilities shall be designed and/or otherwise elevated or located so as to prevent water from entering or accumulating within the components during conditions of flooding.

a. All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of flood waters into the system;

b. Water wells shall be located on high ground that is not in the floodway;

c. New and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of flood waters into the systems and discharge from the systems into flood waters; and

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

a. All development proposals, including subdivisions and manufactured home parks, shall be consistent with the need to minimize flood damage;

b. All development proposals, including subdivisions and manufactured home parks, shall have public utilities and facilities such as sewer, gas, electrical, and water systems located and constructed to minimize flood damage;

c. All development proposals, including subdivisions and manufactured home parks, shall have adequate drainage provided to reduce exposure to flood damage; and

d. Where base flood elevation data has not been provided or is not available from another authoritative source, it shall be generated for all development proposals, including subdivisions and manufactured home parks, greater than 50 lots or five acres (whichever is the lesser).

5. Review of Building Permits. Where elevation data is not available, either through the flood insurance study or from another authoritative source, LMC 16.46.040(C)(2), applications for building permits shall be reviewed to assure that proposed construction will be reasonably safe from flooding. The test of reasonableness is a local judgment and includes historical data, high water marks, photographs of past flooding, etc., where available. Failure to elevate at least two feet above the highest adjacent grade in these zones may result in higher insurance rates.

B. Specific Standards. In all areas of special flood hazards where base flood elevation data has been provided as set forth in LMC 16.46.030(B), Basis for Establishing the Areas of Special Flood Hazard, or LMC 16.46.040(C)(2), Use of Other Base Flood Data, the following provisions are required:

a. New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to one foot or more above base flood elevation.

b. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or if used solely for parking, access or storage, shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of flood waters. Designs for meeting this requirement must either be certified by a registered professional engineer or architect or must meet or exceed the following minimum criteria:

i. 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 shall be provided.

ii. The bottom of all openings shall be no higher than one foot above grade.

iii. Openings may be equipped with screens, louvers, or other coverings or devices; provided, that they permit the automatic entry and exit of flood waters.

2. Nonresidential Construction. New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall either have the lowest floor, including basement, elevated to the level of one foot or more above the base flood elevation; or, together with attendant utility and sanitary facilities, shall:

a. Be floodproofed so that below one foot above 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;

c. Be certified by a registered professional engineer or architect that the design and methods of construction are in conformance with accepted standards of practice for meeting provisions of this subsection based on their development and/or review of the structural design, specifications and plans. Such certifications shall be provided to the official as set forth in LMC 16.46.040(C)(3)(b);

d. Nonresidential structures that are elevated, not floodproofed, must meet the same standards for space below the lowest floor as described in subsection (B)(1)(b) of this section;

e. Applicants floodproofing nonresidential buildings shall be notified that flood insurance premiums will be based on rates that are one foot below the floodproofed level (e.g., a building floodproofed to one foot above the base flood level will be rated as at the base flood level).

3. Critical Facility. Construction of new critical facilities shall be, to the extent possible, located outside the limits of the base floodplain. Construction of new critical facilities shall be permissible within the base floodplain if no feasible alternative site is available. Critical facilities constructed within the base floodplain shall have the lowest floor elevated to three feet or more above the level of the base flood elevation at the site. Floodproofing and sealing measures must be taken to ensure that toxic substances will not be displaced by or released into flood waters. Access routes elevated to or above the level of the base floodplain shall be provided to all critical facilities to the extent possible.

4. Manufactured Homes. All manufactured homes to be placed or substantially improved on sites shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated one foot or more above the base flood elevation and be securely anchored to an adequately anchored foundation system to resist flotation, collapse and lateral movement.

a. All manufactured homes to be placed or substantially improved on sites:

i. Outside of a manufactured home park or subdivision;

ii. In a new manufactured home park or subdivision;

iii. In an expansion to an existing manufactured home park or subdivision; or

iv. In an existing manufactured home park or subdivision on which a manufactured home has incurred “substantial damage” as the result of a flood;

shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated one foot or more above the base flood elevation and be securely anchored to an adequately designed foundation system to resist flotation, collapse and lateral movement.

b. Manufactured homes to be placed or substantially improved on sites in an existing manufactured home park or subdivision that are not subject to the above manufactured home provisions be elevated so that either:

i. The lowest floor of the manufactured home is elevated one foot or more above the base flood elevation; or

ii. The manufactured home chassis is supported by reinforced piers or other foundation elements of at least equivalent strength that are no less than 36 inches in height above grade and be securely anchored to an adequately designed foundation system to resist flotation, collapse, and lateral movement.

5. Recreation Vehicles. Recreational vehicles placed on sites are required to either:

a. Be on the site for fewer than 180 consecutive days;

b. Be fully licensed and ready for highway use, on their wheels or jacking system, be attached to the site only by quick disconnect type utilities and security devices, and have no permanently attached additions; or

c. Meet the requirements of subsection (B)(4) of this section and the elevation and anchoring requirements for manufactured homes.

C. Floodways. Located within areas of special flood hazard established in LMC 16.46.030(B) are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of flood waters which carry debris, potential projectiles, and erosion potential, the following provisions apply:

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

2. Construction or reconstruction of residential structures is prohibited within designated floodways, except for:

a. Repairs, reconstruction, or improvements to a structure which do not increase the ground floor area; and

b. Repairs, reconstruction or improvements to a structure, the cost of which does not exceed 50 percent of the market value of the structure either:

i. Before the repair, or reconstruction, is started; or

ii. If the structure has been damaged, and is being restored, before the damage occurred.

Any project for improvement of a structure to correct existing violations of state or local health, sanitary, or safety code specifications which have been identified by the local code enforcement official and which are the minimum necessary to assure safe living conditions or to structures identified as historic places shall not be included in the 50 percent.

3. If subsection (C)(1) of this section is satisfied, all new construction and substantial improvements shall comply with all applicable flood hazard reduction provisions of this section, Provisions for flood hazard reduction.

D. Wetlands Management. To the maximum extent possible, avoid the short- and long-term adverse impacts associated with the destruction or modification of wetlands, especially those activities which limit or disrupt the ability of the wetland to alleviate flooding impacts. The following process should be implemented:

1. Review proposals for development within base floodplains for their possible impacts on wetlands located within the floodplain.

2. Ensure that development activities in or around wetlands do not negatively affect public safety, health, and welfare by disrupting the wetlands’ ability to reduce flood and storm drainage.

3. Request technical assistance from the Department of Ecology in identifying wetland areas. Existing wetland map information from the National Wetlands Inventory (NWI) can be used in conjunction with the community’s FIRM to prepare an overlay zone indicating critical wetland areas deserving special attention.

E. AE Zones with Base Flood Elevations but No Floodways. In areas with base flood elevations (but a regulatory floodway has not been designated), no new construction, substantial improvements, or other development (including fill) shall be permitted within zone AE on the community’s FIRM, unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood more than one foot at any point within the community.

F. Zone VE Standards. New structures, substantial improvements and recreational vehicles shall meet the following provisions:

1. All new construction and substantial improvements in zone VE on the community’s FIRM shall be elevated on pilings and columns so that:

i. Residential Buildings. The bottom of the lowest horizontal structural member of the lowest floor (excluding the pilings or columns) is elevated one foot or more above the base flood level.

ii. Nonresidential Buildings. The bottom of the lowest horizontal structural member of the lowest floor (excluding the pilings or columns) is elevated one foot or more above the base flood level or meets the elevation requirements of ASCE 24, whichever is higher; and

b. The pile or column foundation and structure attached thereto is anchored to resist flotation, collapse and lateral movement due to the effects of wind and water loads acting simultaneously on all building components. Wind and water loading values shall each have a one percent chance of being equaled or exceeded in any given year (100-year mean recurrence interval).

c. A registered professional engineer or architect shall develop or review the structural design, specifications and plans for the construction, and shall certify that the design and methods of construction to be used are in accordance with accepted standards of practice for meeting the provisions of subsections (F)(1)(a)(i) and (ii) of this section.

2. Obtain the elevation (in relation to mean sea level) of the bottom of the lowest structural member of the lowest floor (excluding pilings and columns) of all new and substantially improved structures in zone VE on the community’s FIRM and whether or not such structures contain a basement. The floodplain administrator shall maintain a record of all such information.

3. All new construction within zone VE on the community’s FIRM shall be located landward of the reach of mean high tide.

4. Provide that all new construction and substantial improvements within zone VE on the community’s FIRM have the space below the lowest floor either free of obstruction or constructed with nonsupporting breakaway walls, open wood latticework, or insect screening intended to collapse under wind and water loads without causing collapse, displacement, or other structural damage to the elevated portion of the building or supporting foundation system. For the purposes of this section, a breakaway wall shall have a design safe loading resistance of not less than 10 and no more than 20 pounds per square foot. Use of breakaway walls which exceed a design safe loading resistance of 20 pounds per square foot (either by design or when so required by local or state codes) may be permitted only if a registered professional engineer or architect certifies that the design proposed meets the following conditions:

a. Breakaway wall collapse shall result from water load less than that which would occur during the base flood; and

b. The elevated portion of the building and supporting foundation system shall not be subject to collapse, displacement, or other structural damage due to the effects of wind and water loads acting simultaneously on all building components (structural and nonstructural). Maximum wind and water loading values to be used in this determination shall each have a one percent chance of being equaled or exceeded in any given year (100-year mean recurrence interval).

c. If breakaway walls are utilized, such enclosed space shall be useable solely for parking of vehicles, building access, or storage. Such space shall not be used for human habitation.

5. Prohibit the use of fill for structural support of buildings within zone VE on the community’s FIRM.

6. Prohibit manmade alteration of sand dunes within zone VE on the community’s FIRM which would increase potential flood damage.

7. All manufactured homes to be placed or substantially improved within zone VE on the community’s FIRM on sites:

a. Outside of a manufactured home park or subdivision;

b. In a new manufactured home park or subdivision;

c. In an expansion to an existing manufactured home park or subdivision; or

d. In an existing manufactured home park or subdivision on which a manufactured home has incurred “substantial damage” as the result of a flood; shall meet the standards of subsections (F)(1) through (6) of this section and manufactured homes placed or substantially improved on other sites in an existing manufactured home park or subdivision within zone VE on the FIRM shall meet the requirements of subsection (A)(4) of this section.

8. Recreational vehicles placed on sites within V or VE zones on the community’s FIRM shall either:

a. Be on the site for fewer than 180 consecutive days; or

b. Be fully licensed and ready for highway use, on its wheels or jacking system, attached to the site only by quick disconnect type utilities and security devices, and have no permanently attached additions; or

c. Meet the requirements of subsections (F)(1) and (3) of this section and the anchoring requirements for manufactured homes (subsection (A)(1)(b) of this section). (Ord. 3370 § 2, 2020; Ord. 3285 § 2, 2018; Ord. 2274 § 4, 1999; Ord. 1701 § 8, 1989; Ord. 1462 § 5, 1985)