Chapter 14.12
FLOODPLAIN MANAGEMENT1

Sections:

14.12.010    Applicability.

14.12.020    Performance standards – Flood hazard areas.

14.12.030    Allowed uses and activities – Flood hazard areas.

14.12.040    Shallow flooding areas.

14.12.050    Development permit.

14.12.060    Critical area report.

14.12.010 Applicability.

This chapter shall apply to all areas of spe­cial flood hazards within the city. Figure 7, Special Flood Hazard Map2 identifies flood-prone areas mapped by FEMA. The map may be periodically revised by the city to add or remove areas based on additional information.

Areas of special flood hazard shall be determined by consideration of the following:

A. The areas of special flood hazard iden­tified by the Federal Insurance Administration (FIA) in a scientific and engineering report entitled “The Flood Insurance Study for the City” and associated flood insurance rate maps (FIRM) effective April 19, 2005. Such reports and maps are hereby adopted by reference and are on file at City Hall, North Bend, Washing­ton; and

B. Those areas identified by the city based on review of base flood elevation and flood­way data available from federal, state, county, or other valid sources when base flood eleva­tion data has not been provided.

C. In the event of a conflict, the more restrictive provision shall apply.

Note: Per NBMC 14.12.030(E)(2), flood regu­lations for new residential construction apply to areas within the special flood hazard area (SFHA). (Ord. 1243 Exh. B (part), 2006).

14.12.020 Performance standards – Flood hazard areas.

The following standards apply to development proposals and alterations on sites within flood hazard areas:

A. A development proposal shall not increase the base flood elevation unless revisions to the FIRM are approved by FEMA in accordance with 44 CFR 70, and appropriate legal arrangements have been made and documents filed prior to issuance of a construction permit.

B. The following circumstances are presumed to produce no increase in base flood heights and shall not require special studies to establish this fact:

1. Reconstruction or remodeling of existing structures in the floodway where the structure’s footprint is not increased;

2. Development of new residential structures outside the FEMA floodway on lots in existence before November 17, 1998;

3. Substantial improvements to existing residential structures in the floodplain but outside the FEMA floodway;

4. New development or substantial improvement in the area identified as “downtown commercial” per Figure 1-2 of the 2004 North Bend comprehensive plan, which are within the AO-1, AO-2, or AO-3 flood zone; and

5. Minor accessory structures exempt from building permits under the International Building Code.

C. The cumulative effect of any proposed development, where combined with all other existing and anticipated development on the site, shall not reduce the effective base flood storage volume of the floodplain. Except as exempted in subsection B of this subsection, grading or other activity that would reduce the effective storage volume shall be mitigated by creating compensatory storage on-site or off-site if legal arrangements can be made to assure that the effective compensatory storage volume will be preserved over time; provided, however, that no increased upstream or downstream flood hazard shall be created by any fill authorized in the floodplain by this chapter or other applicable chapters.

D. When fill is proposed to achieve elevated construction, a critical area report is required demonstrating that the proposal will not increase the base flood elevation.

E. If grading or other activity will displace any effective flood storage volume, compensatory storage shall be created on-site or off-site, if legal arrangements can be made to assure that the effective compensatory storage volume will be preserved over time, in equivalent volume, at equivalent elevations to that being displaced. Compensatory storage areas must be hydraulically connected to the source of flooding. Alternatively, if feasible, the applicant may provide an increase in side channel habitat as mitigation for floodway alterations.

F. Construction of new residential or commercial or industrial structures is prohibited within the floodway. New construction in nonconforming developments shall meet the construction standards set forth in this chapter.

G. Reconstruction of existing structures within the floodway shall be subject to the requirements of WAC 173-158-170; provided, that reconstruction of existing residential structures between the floodway defined in WAC 173-158-030(8) and the floodway defined in this chapter need only meet the standards for new residential construction set forth in this chapter.

H. Approved alterations shall not block side channel habitats.

I. All construction elevated by pilings must be designed and certified by a professional structural engineer registered in the state of Washington and approved by the city building official.

J. Where the floodway of either Gardiner Creek or Ribary Creek is not identified by the applicant in special studies, the entire floodplain of the site shall be treated as the floodway.

K. An analysis of bioengineering and/or vegetation enhancements will be required when existing levees or dikes are proposed to be repaired or renovated as specified in King County’s Guidelines for Bank Stabilization.

L. Construction materials for residential and nonresidential structures shall meet the following criteria:

1. All new substantial improvement to buildings and structures shall be constructed with materials and utility equipment resistant to flood damage, using methods and products that minimize flood damage; and

2. Electrical, mechanical, plumbing, and other service facilities shall be floodproofed to the flood protection elevation on all new, substantially improved buildings.

M. All new construction shall be anchored to prevent flotation, collapse, or lateral movement of the structure.

N. For all mobile/manufactured homes, all standards for flood hazard protection for residential construction shall apply. All mobile/manufactured homes must be anchored and shall be installed using methods and practices that minimize flood damage. For existing mobile/manufactured homes where the repair/reconstruction of the utilities and pad equals or exceeds 50 percent of the value of utilities and pad before the repair/reconstruction has commenced, all standards for flood hazard protection applicable for residential construction shall apply to the mobile/manufactured home.

O. If a project is worth more than 50 percent of the assessed value (MAI appraised value may be used at owner choice) of the original building it is considered a “substantial improvement.” The building must then be elevated or otherwise brought up to current flood protection codes and other applicable city codes as required. To determine project value, the proposed project value shall be added to permitted additions or expansions to the building over the last 10 years. This provision will run with the property and not the property owner. Projects necessary to maintain the function of an existing building or structure such as electrical, mechanical, plumbing, roofing, siding, or windows shall be tracked for 180 days. Any outstanding permit for work on the building that has not received a final inspection or certificate of occupancy as required by the applicable construction code will be included in the calculation. This provision will run with the property owner and not the property.

P. Additions. Where expansion to an existing building or structure does not increase the building footprint more than 25 percent, up to a maximum size of 500 square feet, and shares a common wall (one full side) with the primary structure, the addition shall not be required to elevate, but must be flood resistant to a minimum of two feet above BFE. Additions will require full adherence to flood regulations if the sum of all improvements over the last 180 days as described in subsection O of this section and additions over the last 10 years exceeds 50 percent of the current assessed value, or exceeds the addition size threshold above. This provision will run with the property and not the property owner.

Q. Accessory Structures. Minor accessory structures (less than 200 square feet) are exempt from International Code building permits and the city of North Bend floodplain permit. Examples of these structures may include: signs, trash enclosures, fences less than six feet in height, and storage sheds. The following standards shall apply to accessory structures in SFHA:

1. Accessory structures shall not be used for human habitation.

2. Accessory structures shall be designed to have low flood damage potential.

3. Accessory structures shall be constructed and placed on the building site so as to offer the minimum resistance to the flow of floodwaters.

4. Accessory structures shall be firmly anchored to prevent flotation that may result in damage to other structures.

5. For new structures or substantial improvements, service facilities such as electrical and heating equipment shall be elevated or floodproofed.

6. Floodway encroachment standards must be met.

R. Recreational Vehicles. Recreational vehicles placed on sites in the SFHA are required to either:

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

2. 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; or

3. Meet the manufactured home elevation and anchoring requirements. (Ord. 1272 § 1, 2007; Ord. 1243 Exh. B (part), 2006).

14.12.030 Allowed uses and activities – Flood hazard areas.

The director may require the preparation of a critical area report for any of the uses and activities described below:

A. Floodways. Installations or structures that are floodway dependent may be located within the floodway; provided, that the devel­opment proposal receives approval from all other agencies with jurisdiction. Such installa­tions or structures include, but are not limited to:

1. Dams or diversions for water sup­ply, flood control, hydroelectric production, irrigation, or fisheries enhancement;

2. Flood damage reduction facilities such as dikes, levees, and pumping stations when necessary to protect the public from an imminent hazard;

3. Stream bank stabilization structures are allowed only if no feasible alternative exists for protecting structures, public road­ways, and flood protection facilities or sole access routes. Bank stabilization projects shall be consistent with WDFW and NMFS guide­lines and applicable sections of this chapter, and shall use bioengineering to the maximum extent possible;

4. Surface water conveyance facilities subject to the requirements of the development standards for streams and wetlands;

5. Boat launches and related recre­ation structures;

6. Bridge piers and abutments when no reasonable alternative is available; and

7. Approved aquatic area or wetland restoration projects to improve natural func­tions including, but not limited to fisheries enhancement projects;

8. Substantial improvements of exist­ing structures, and minor accessory structures exempt from building permits under the Inter­national Building Code, only when in con­formance with NBMC 14.12.020;

9. Prohibited Encroachments. Encroachments in the floodway that are pro­hibited include new construction of residen­tial, commercial or industrial structures. Other development is prohibited 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.

B. Subdivisions, short subdivisions, mas­ter site plans, contract rezones, site plan/design review; PRDs and binding site plans shall fol­low these requirements:

1. New buildable lots shall contain 5,000 square feet or more of buildable land outside the floodway;

2. Locate and construct all utilities and their facilities in a manner that minimizes flood damage;

3. Provide adequate drainage to reduce exposure to flood damage;

4. Base flood data and flood hazard notes shall be shown on the face of the recorded plat; this may include the floodwater depth, required flood elevations, and the boundary of the base flood and floodway as deemed appropriated by the city; and

5. Where base flood elevation data has not been provided or is not available from another authorized source, it shall be generated for subdivision proposals and other proposed developments that contain at least 50 lots or five acres (whichever is less).

6. The following note shall appear on the face of the recorded documents and shall be recorded on the title of records for all affected lots:

Note: Lots and structures located within flood hazard areas may be inac­cessible to emergency vehicles during flood events. Residents and property owners should take appropriate advance precautions to provide access.

C. Utilities and on-site sewage facilities shall meet the following criteria:

1. All new and replacement utilities including sewage treatment facilities shall be floodproofed to the flood protection elevation;

2. New on-site sewage disposal sys­tems shall be, to the extent possible, located outside the limits of the floodway and may be installed in the flood fringe if no feasible alter­native site is available. On-site sewage dis­posal systems that are located within the flood hazard areas must be sited to avoid impairment of the system during flooding and to avoid contamination from the system during flood­ing;

3. Sewage and manure waste storage facilities shall be floodproofed to the flood protection elevation;

4. Buried utility transmission lines transporting hazardous substances (as defined by the Washington State Hazardous Waste Management Act in RCW 70.105.005) shall be buried a minimum of four feet beneath the maximum depth of scour of the base flood for the entire width of the floodway and shall achieve sufficient negative buoyancy so that any potential for flotation or upward migration is eliminated; and

5. Aboveground utility transmission lines, not including electrical transmission lines, shall only be allowed in the floodway for the transportation of nonhazardous materials, as defined by the State Department of Ecology, where a bridge or other structure is capable of transporting the line.

D. Critical facilities include, but are not limited to, schools, hospitals, police, fire and emergency response installations, nursing homes, wastewater treatment plants, potable water and sanitary sewer system components, and hazardous materials production. Construc­tion of new critical facilities shall only be allowed within the floodplain when no reason­able alternative site is available. Critical facil­ities constructed within the floodplain shall have the lowest floor elevated to three or more feet above the level of the base flood elevation. Floodproofing and sealing measures must be taken to ensure toxic or hazardous substances will not be displaced by or released into flood­waters. Access routes elevated to or above the level of the 100-year frequency flood shall be provided to all critical facilities to the extent possible.

E. New residential construction and sub­stantial improvements within the special flood hazard area (SFHA) shall meet the following criteria:

1. The lowest floor, including base­ment, shall be elevated two feet or more above base flood elevation; and

2. Fully enclosed areas below the low­est floor that are subject to flooding are prohib­ited. The area and rooms below the lowest floor shall be designated to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this require­ment must meet or exceed the following mini­mum criteria:

a. A minimum of two openings shall be provided on opposite walls having a total new 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; and

c. Openings may be equipped with screens, louvers, or other coverings or devices; provided, that they permit the unrestricted entry and exit of floodwaters.

F. New nonresidential construction and substantial improvements of any existing com­mercial, industrial, or other nonresidential structure that requires a building permit shall either elevate the lowest floor, including the basement, a minimum of two feet in the SFHA or more above base flood elevation or flood­proof the structure to the same elevation. If the structure is floodproofed, the following crite­ria are required:

1. The floodproofing must be certified by a professional civil or structural engineer registered in the state of Washington stating that the floodproofing methods are adequate to withstand the flood-depths, pressures, veloci­ties, impacts, uplift forces, and other factors associated with the base flood. After construc­tion, the engineer shall certify that the permit­ted work conforms to the approved plans and specifications;

2. Approved building permits for floodproofed nonresidential buildings shall contain a statement to notify applicants that flood insurance premiums will be based upon rates for structures that are one foot below the floodproofed level. (Ord. 1243 Exh. B (part), 2006).

14.12.040 Shallow flooding areas.

Shallow flooding zones appear on FIRMs as AO zones with depth designations. The base flood depths in these zones range from one to three feet above ground where a clearly defined channel does not exist, or where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is usually characterized as sheet flow. In these areas, the following provisions apply:

A. New construction and substantial improvements of residential structures within AO zones shall have the lowest floor (includ­ing basement) elevated above the highest adja­cent grade of the building site, two feet or more above the depth number specified on the FIRM (at least two feet if no depth number is speci­fied). Where appropriate, such structures shall be elevated above the crown of the nearest road, one foot or more above the depth number specified on the FIRM. Where hazardous velocities are noted on the FIRM, consider­ation shall be given to mitigating the effects of these velocities through proper construction techniques and methods.

B. New construction and substantial improvements of nonresidential structures that require a building permit within AO zones shall either:

1. Have the lowest floor (including basement) elevated above the highest adjacent grade of the building site, one foot or more above the depth number specified on the FIRM (at least two feet if no depth number is speci­fied). Where appropriate, such structure shall be elevated above the crown of the nearest road, one foot or more above the depth number specified on the FIRM; or

2. Together with attendant utility and sanitary facilities, be completely flood proofed to or above that level so that any space below that level is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. If this method is used, compliance shall be certified by a registered professional engineer or architect as defined under qualified professional. Where hazardous velocities were noted on the FIRM, consider­ation shall be given to mitigating the effects of these velocities through proper construction techniques and methods; or

3. Require adequate drainage pads around structures on slopes to guide flood-waters around and away from proposed struc­tures. (Ord. 1243 Exh. B (part), 2006).

14.12.050 Development permit.

A. A flood development permit shall be obtained before new construction, substantial improvement, or “development” begins within any area of special flood hazard established in NBMC 14.12.010, except for minor accessory structures which are exempted from building permits in the International Building Code as provided in NBMC 14.12.020. An applicant will need to obtain a floodplain permit in addi­tion to other development permits when new construction or substantial improvements are proposed, and/or when proposed modifica­tions will impact flood elevation. The city encourages property owners to use flood resis­tant materials and elevate new portions even when a flood permit does not enforce this activity. The permit shall be for all structures including mobile and manufactured homes or nonlicensed recreational vehicles on-site for more than 180 days, as set forth in NBMC 14.12.020 and for all other development including fill and other activities, also as set forth in NBMC 14.12.030 and 14.12.040. Application for a development permit shall be made on forms furnished by the director and may include but not be limited to plans in duplicate drawn to scale showing the nature, location, dimensions, and elevations of the area in question, existing or proposed struc­tures, fill, storage of materials, drainage facili­ties, and the location of the foregoing. These documents will be maintained by the city for inspection of all records pertaining to the pro­visions of these critical areas regulations. Spe­cifically, the following information is required for critical areas review. The floodplain permit will require additional and more extensive information as identified on the application information sheet.

1. The base flood elevation (BFE) in relation to the lowest floor (including base­ment) of all structures located in the AE zone or within the ZO zone. Identify the highest adjacent natural grade next to the building prior to construction;

2. Proposed floodproofing elevation in relation to the BFE or highest adjacent nat­ural grade next to the building prior to con­struction;

3. Certification by a registered profes­sional engineer or architect that the flood­proofing methods for any nonresidential structure meet the floodproofing criteria in NBMC 14.12.030(F);

4. A description of the extent to which a watercourse will be altered or relocated as a result of a proposed development;

5. The accuracy of said elevation as proposed and as built shall be certified by a licensed professional engineer and/or a profes­sional land surveyor; and

6. All development permits for the site must be reviewed to ensure all necessary per­mits have been obtained from those federal, state, or local governmental agencies from which prior approval is required.

Adjacent communities and the Department of Ecology must be notified prior to any alter­ation or relocation of a watercourse, and evi­dence of such notification must be submitted to the Federal Insurance Administration. (Ord. 1243 Exh. B (part), 2006).

14.12.060 Critical area report.

The director may waive a critical area report when existing mapping and flood insur­ance study is determined to be adequate. When a critical area report is required the following shall be included:

A. A critical area report for flood hazard areas shall be prepared by an engineer or hydrogeologist, licensed in the state of Wash­ington, with expertise analyzing geologic, hydrogeologic and surface and ground water flow systems, and who has experience prepar­ing reports for the relevant type of hazard.

B. In addition to the requirements of Chapter 14.05 NBMC, critical area reports required for flood hazard areas shall include the following information:

1. On the site map:

a. The dimensioned location of all proposed development in the floodplain;

b. The location of the floodway where it has been delineated on the most recent flood insurance study map (FIRM) or by spe­cial studies for Gardiner or Ribary Creeks; where basin plans have been completed and adopted. The location of the floodplain and floodways shall be based upon the hydrologic and hydraulic analysis; and

c. Identification of all proposed structures and grading within the floodplain.

2. In the report:

a. Identify how the boundaries of the floodways and floodplain were deter­mined; and

b. Establish the elevation of the lowest floor of all new or substantially improved structures proposed in the existing floodplain, utilizing the North American Ver­tical Datum of 1988. (Ord. 1243 Exh. B (part), 2006).

1

Prior legislation: Ords. 951 and 1088.


2

See city website for current version.