19.30.090 Provisions for flood hazard reduction

19.30.090 Provisions for flood hazard reduction.

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

a. All new construction and substantial improvements, including those related to manufactured homes, 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 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. For more detailed information, refer to guidebook, FEMA-85, “Manufactured Home Installation in Flood Hazard Areas.”

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 floodwaters into the systems;

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 floodwaters into the systems and discharges from the systems into floodwaters;

d. On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding, and in accordance with requirements of the Snohomish Health District.

4. Subdivision Proposals and Development. All subdivisions, as well as new development shall:

a. Be consistent with the need to minimize flood damage;

b. Have public utilities and facilities, such as sewer, gas, electrical, and water systems, located and constructed to minimize or eliminate flood damage;

c. Have adequate drainage provided to reduce exposure to flood damage;

d. Where subdivision proposals and other proposed developments contain greater than fifty lots or five acres (whichever is the lesser), base flood elevation data shall be included as part of the application.

B. Specific Standards. In all areas of special flood hazards where base flood elevation data has been provided as set forth in EMC 19.30.030, Basis for establishing the areas of special flood hazard, or EMC 19.30.080.C.2, Use of Other Base Flood Data (In A and V Zones), the following provisions are required:

a. In AE and A1-30 zones or other A zoned areas where the BFE has been determined or can be reasonably obtained, new construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated one foot or more above the BFE. Mechanical equipment and utilities shall be waterproof or elevated least one foot above the BFE.

b. New construction and substantial improvement of any residential structure in an unnumbered A zone for which a BFE is not available and cannot be reasonably obtained shall be reasonably safe from flooding, but in all cases the lowest floor shall be at least two feet above the highest adjacent grade.

c. New construction and substantial improvement of any residential structure in a V, V1-30, or VE zone shall meet the requirements in EMC 19.30.300.

d. Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs must meet or exceed the following minimum criteria:

(1) Have a minimum of two openings with a total net area of not less than one square inch for every square foot of enclosed area subject to flooding.

(2) The bottom of all openings shall be no higher than one foot above grade.

(3) Openings may be equipped with screens, louvers, valves, or other coverings or devices; provided, that they permit the automatic entry and exit of floodwaters.

(4) A garage attached to a residential structure, constructed with the garage floor slab below the BFE, must be designed to allow for the automatic entry and exit of floodwaters.

Alternatively, a registered engineer or architect may design and certify engineered openings.

2. Nonresidential Construction. New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall meet the requirements of subsection B.2.a or b of this section.

a. New construction and substantial improvement of any commercial, industrial or other nonresidential structure shall meet all of the following requirements:

(1) In AE and A1-30 zones or other A zoned areas where the BFE has been determined or can be reasonably obtained, new construction and substantial improvement of any commercial, industrial, or other nonresidential structure shall have the lowest floor, including basement, elevated one foot or more above the BFE, or elevated as required by ASCE 24, whichever is greater. Mechanical equipment and utilities shall be waterproofed or elevated at least one foot above the BFE, or as required by ASCE 24, whichever is greater.

(2) If located in an unnumbered A zone for which a BFE is not available and cannot be reasonably obtained, the structure shall be reasonably safe from flooding, but in all cases the lowest floor shall be at least two feet above the highest adjacent grade.

(3) If located in a V, V1-30, or VE zone, the structure shall meet the requirements in EMC 19.30.300.

(4) Fully enclosed areas below the lowest floor that are subject to flooding are prohibited, or 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 must meet or exceed the following minimum criteria:

(A) Have a minimum of two openings with 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.

(C) Openings may be equipped with screens, louvers, valves, or other coverings or devices; provided, that they permit the automatic entry and exit of floodwaters.

(D) A garage attached to a residential structure, constructed with the garage floor slab below the BFE, must be designed to allow for the automatic entry and exit of floodwaters.

Alternatively, a registered engineer or architect may design and certify engineered openings.

b. If the requirements of subsection B.2.a. of this section are not met, then new construction and substantial improvement of any commercial, industrial or other nonresidential structure shall meet all of the following requirements:

1. Be dry floodproofed so that below one foot or more above the base flood level the structure is watertight with walls substantially impermeable to the passage of water or dry floodproofed to the elevation required by ASCE 24, whichever is greater;

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

3. Be certified by a registered professional engineer or architect that the design and methods of construction are in accordance 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 EMC 19.30.080.C.3.b;

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

3. 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 shall be securely anchored to an adequately anchored foundation system to resist flotation, collapse and lateral movement.

4. Recreational Vehicles. Recreational vehicles placed on sites are required to:

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

b. Comply with EMC Title 17.

5. Enclosed Area Below the Lowest Floor. If buildings or manufactured homes are constructed or substantially improved with fully enclosed areas below the lowest floor, the areas shall be used solely for parking of vehicles, building access, or storage.

6. Appurtenant Structures (Detached Garages and Small Storage Structures). For A Zones (A, AE, A1-30, AH, AO):

a. Appurtenant structures used solely for parking of vehicles or limited storage may be constructed such that the floor is below the BFE, provided the structure is designed and constructed in accordance with the following requirements:

(1) Use of the appurtenant structure must be limited to parking of vehicles or limited storage;

(2) The portions of the appurtenant structure located below the BFE must be built using flood resistant materials;

(3) The appurtenant structure must be adequately anchored to prevent flotation, collapse, and lateral movement;

(4) Any machinery or equipment servicing the appurtenant structure must be elevated or floodproofed to or above the BFE;

(5) The appurtenant structure must comply with floodway encroachment provisions in subsection D.1 of this section (No Rise Standard);

(6) The appurtenant structure must be designed to allow for the automatic entry and exit of floodwaters in accordance with subsection B.1.d of this section;

(7) The structure shall have low damage potential;

(8) If the structure is converted to another use, it must be brought into full compliance with the standards governing such use; and

(9) The structure shall not be used for human habitation.

7. Detached garages, storage structures, and other appurtenant structures not meeting the above standards must be constructed in accordance with all applicable standards in subsection B.1 of this section.

8. Upon completion of the structure, certification that the requirements of this section have been satisfied shall be provided to the floodplain administrator for verification.

C. AE and A1-30 Zones with Base Flood Elevations but No Floodways. In areas with BFEs (but a regulatory floodway has not been designated), no new construction, substantial improvements, or other development (including fill) shall be permitted within zones A1-30 and 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.

D. Floodways. Located within areas of special flood hazard established in EMC 19.30.030 are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of floodwaters that can carry debris and increase erosion potential, the following provisions apply:

1. No Rise Standard. 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 encroachment would not result in any increase in flood levels during the occurrence of the base flood discharge.

2. Residential Construction in Floodways. Construction or reconstruction of residential structures is prohibited within designated floodways, except for repairs, reconstruction, or improvements to a structure that do not increase the ground floor area; and repairs, reconstruction, or improvements to a structure, the cost of which does not exceed fifty percent of the market value of the structure, either before the repair or reconstruction is started or, 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 that have been identified by the local code enforcement official and that are the minimum necessary to assure safe living conditions, or to structures identified as historic places, may be excluded in the fifty percent.

a. For all substantially damaged residential structures, other than farmhouses, located in a designated floodway, the floodplain administrator may make a written request that the Department of Ecology assess the risk of harm to life and property posed by the specific conditions of the floodway. Based on analysis of depth, velocity, flood-related erosion, channel migration, debris load potential, and flood warning capability, the Department of Ecology may exercise best professional judgment in recommending to the local permitting authority repair, replacement, or relocation of a substantially damaged structure consistent with WAC 173-158-076. The property owner shall be responsible for submitting to the local government and the Department of Ecology any information necessary to complete the assessment. Without a favorable recommendation from the Department for the repair or replacement of a substantially damaged residential structure located in the regulatory floodway, no repair or replacement is allowed per WAC 173-158-070(1).

b. Before the repair, replacement, or reconstruction is started, all requirements of the NFIP, the state requirements adopted pursuant to Chapter 86.16 RCW, and all applicable local regulations must be satisfied. In addition, the following conditions must be met:

(1) There is no potential safe building location for the replacement residential structure on the same property outside the regulatory floodway.

(2) A replacement residential structure is a residential structure built as a substitute for a legally existing residential structure of equivalent use and size.

(3) Repairs, reconstruction, or replacement of a residential structure shall not increase the total square footage of floodway encroachment.

(4) The elevation of the lowest floor of the substantially damaged or replacement residential structure is a minimum of one foot higher than the BFE.

(5) New and replacement water supply systems are designed to eliminate or minimize infiltration of floodwater into the system.

(6) New and replacement sanitary sewerage systems are designed and located to eliminate or minimize infiltration of floodwater into the system and discharge from the system into the floodwaters.

(7) All other utilities and connections to public utilities are designed, constructed, and located to eliminate or minimize flood damage.

4. All Other Building Standards Apply in the Floodway. If subsection D.1 of this section (No Rise Standard) is satisfied, or construction is allowed pursuant to subsection D.2 of this section, all new construction and substantial improvements shall comply with all applicable flood hazard reduction provisions of this section.

5. Critical Facility. Construction of new critical facilities shall be, to the extent possible, located outside the limits of the SFHA (one-hundred-year floodplain). Construction of new critical facilities shall be permissible within the SFHA if no feasible alternative site is available. Critical facilities constructed within the SFHA shall have the lowest floor elevated three feet above BFE or to the height of the five-hundred-year flood, whichever is higher. Access to and from the critical facility should also be protected to the height utilized above. Floodproofing and sealing measures must be taken to ensure that toxic substances will not be displaced by or released into floodwaters. Access routes elevated to or above the level of the BFE shall be provided to all critical facilities to the extent possible.

6. Livestock Sanctuaries. Elevated areas for the purpose of creating a flood sanctuary for livestock are allowed on farm units where livestock is allowed. Livestock flood sanctuaries shall be sized appropriately for the expected number of livestock and be elevated at least one foot above the BFE to protect livestock. Proposals for livestock flood sanctuaries shall meet all procedural and substantive requirements of this chapter. (Ord. 3766-20 § 9 (Exh. A), 2020.)