9.6707 Development in Floodplains – Provisions for Flood Hazard Reduction

9.6707 Development in Floodplains – Provisions for Flood Hazard Reduction.

(1) General Standards. In all special flood hazard areas, the following standards shall be adhered to:

1. The flood carrying capacity within the altered or relocated portion of said watercourse shall be maintained.

2. Maintenance shall be provided within the altered or relocated portion of said watercourse to ensure that the flood carrying capacity is not diminished.

3. Prior to any alteration or relocation of a watercourse:

a. The City Manager or their designee shall notify adjacent communities, the Department of Land Conservation and Development, and other appropriate state and federal agencies and submit evidence of such notification to the Federal Insurance Administration.

b. The applicant shall notify the Federal Insurance Administration by transmitting a Letter of Map Revision (LOMR) along with either:

(1) A proposed maintenance plan to assure the flood carrying capacity within the altered or relocated portion of the watercourse is maintained; or

(2) Certification by a registered professional engineer that the project has been designed to retain its flood carrying capacity without periodic maintenance.

4. When required under EC 9.6706(2)(h), the applicant shall submit a Conditional Letter of Map Revision (CLOMR).

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 dwellings shall be anchored per section EC 9.6707(2)(c)4.

1. All new construction and substantial improvements shall be constructed with materials 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.

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

b. 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.

c. On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding consistent with the Oregon Department of Environmental Quality.

a. Except as provided in b., below, electrical, heating, ventilation, air-conditioning, plumbing, duct systems, and other equipment and service facilities shall be elevated a minimum of one (1) foot above the Base Flood Elevation.

b. The requirement set out in a., above, does not apply to service equipment (including but not limited to electrical systems, equipment and components; heating, ventilation, air conditioning; plumbing appliances and plumbing fixtures; and duct systems) that is:

(1) Specially designed and installed to prevent water from entering or accumulating within the components and to resist hydrostatic and hydrodynamic loads and stresses, including the effects of buoyancy, during the occurrence of flooding to one (1) foot above the Base Flood Elevation; and

(2) Not electrical, heating, ventilation, air-conditioning, plumbing, duct systems, and other equipment and service facilities being installed as part of a substantial improvement.

1. Underground tanks shall be anchored to prevent flotation, collapse and lateral movement under conditions of the base flood.

2. Above-ground tanks shall be installed at or above the base flood level or shall be anchored to prevent flotation, collapse, and lateral movement under conditions of the base flood.

1. All new land division proposals and other proposed new developments (including proposals for manufactured dwelling parks and land divisions) that are 5 acres or more in size or are 50 lots or more, whichever is the lesser, shall include within such proposals, Base Flood Elevation data.

2. All new land division proposals and other proposed new developments (including proposals for manufactured dwelling parks and land divisions) 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 hazards.

1. When Base Flood Elevation data has not been provided in accordance with section EC 9.6705, the City Manager or designee shall obtain, review, and reasonably utilize any Base Flood Elevation data available from a federal, state, or other source, in order to administer EC 9.6707. All new land division proposals and other proposed new developments (including proposals for manufactured dwelling parks and land divisions) must meet the requirements of EC 9.6707(1)(f).

2. Base Flood Elevations shall be determined for development proposals that are 5 acres or more in size or are 50 lots or more, whichever is lesser in any A zone that does not have an established base flood elevation. Development proposals located within a riverine unnumbered A Zone shall be reasonably safe from flooding; the test of reasonableness includes use of historical data, high water marks, FEMA provided Base Level Engineering data, and photographs of past flooding, etc. When no base flood elevation data is available, the reasonably safe elevation requirement for development proposals with an elevation requirement, within a riverine unnumbered a zone, is at least two (2) feet above the highest adjacent grade. Failure to elevate at least two (2) feet above grade in these zones may result in higher insurance rates.

(h) Structures Located in Multiple or Partial Flood Zones. In coordination with the State of Oregon Specialty Codes:

1. When a structure is located in multiple flood zones on the community’s Flood Insurance Rate Maps (FIRM) the provisions for the more restrictive flood zone shall apply.

2. When a structure is partially located in a special flood hazard area, the entire structure shall meet the requirements for new construction and substantial improvements.

(2) Specific Standards. These specific standards shall apply to all new construction and substantial improvements in addition to the General Standards contained in EC 9.6707(1).

(a) Flood Openings. All new construction and substantial improvements with fully enclosed areas below the lowest floor (excluding basements) are subject to the following requirements. Enclosed areas below the Base Flood Elevation, including crawl spaces shall:

1. Be designed to automatically equalize hydrostatic flood forces on walls by allowing for the entry and exit of floodwaters;

2. Be used solely for parking, storage, or building access;

3. Be certified by a registered professional engineer or architect or meet or exceed all of the following minimum criteria:

a. There shall be a minimum of two openings;

b. The total net area of non-engineered openings shall be not less than one (1) square inch for each square foot of enclosed area, where the enclosed area is measured on the exterior of the enclosure walls;

c. The bottom of all openings shall be no higher than one (1) foot above grade;

d. Openings may be equipped with screens, louvers, valves, or other coverings or devices provided that they shall allow the automatic flow of floodwater into and out of the enclosed areas and shall be accounted for in the determination of the net open area; and

e. All additional higher standards for flood openings in the State of Oregon Residential Specialty Code shall be complied with when applicable.

1. Attached garages may be constructed with the garage floor slab below the Base Flood Elevation (BFE) in riverine flood zones, if the following requirements are met:

a. If located within a floodway the proposed garage shall comply with the requirements of EC 9.6707(2)(d);

b. The floors shall be at or above grade on not less than one side;

c. The garage shall be used solely for parking, building access, and/or storage;

d. The garage shall be constructed with flood openings in compliance with EC 9.6707(2)(a) to equalize hydrostatic flood forces on exterior walls by allowing for the automatic entry and exit of floodwater;

e. The portions of the garage constructed below the BFE shall be constructed with materials resistant to flood damage;

f. The garage shall be constructed in compliance with the standards in EC 9.6707(1); and

g. The garage shall be constructed with electrical and other service facilities located and installed so as to prevent water from entering or accumulating within the components during conditions of the base flood.

2. Detached garages must be constructed in compliance with the standards for appurtenant structures in EC 9.6707(2)(c)6 or non-residential structures in EC 9.6707(2)(c)3, depending on the square footage of the garage.

(c) Riverine Special Flood Hazard Areas with Base Flood Elevations. In addition to the general standards listed in EC 9.6707(1), the following specific standards shall apply in Riverine special flood hazard areas with Base Flood Elevations (BFE):

1. Before Regulatory Floodway. In areas where a regulatory floodway has not been designated, no new construction, substantial improvement, or other development (including fill) shall be permitted within Zones A1-30 and AE on the community’s Flood Insurance Rate Map (FIRM), unless it is demonstrated through hydrologic and hydraulic analyses, performed in accordance with standard engineering practice, 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 (1) foot at any point within the community.

a. New construction, conversion to, and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to a minimum of one (1) foot above the Base Flood Elevation (BFE). When no base flood elevation data is available, the reasonably safe elevation requirement for development proposals with an elevation requirement, within a riverine unnumbered a zone, is at least two (2) feet above the highest adjacent grade.

b. Enclosed areas below the lowest floor shall comply with the flood opening requirements in EC 9.6707(2)(a).

a. New construction, conversion to, and substantial improvement of any commercial, industrial, or other non-residential structure shall:

(1) Have the lowest floor, including basement elevated at or above the Base Flood Elevation (BFE) or, when no base flood elevation data is available, the reasonably safe elevation requirement for development proposals with an elevation requirement, within a riverine unnumbered A zone, is at least two (2) feet above the highest adjacent grade; or

(2) 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; and

(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 are in accordance with accepted standards of practice for meeting provisions of this section based on their development and/or review of the structural design, specifications and plans. Such certifications shall be provided to the City.

b. Non-residential structures that are elevated, not floodproofed, shall comply with the standards for enclosed areas below the lowest floor in EC 9.6707(2)(a).

c. Applicants floodproofing non-residential buildings shall be notified that flood insurance premiums will be based on rates that are one (1) foot below the floodproofed level (e.g. a building floodproofed to the base flood level will be rated as one (1) foot below.)

a. Manufactured dwellings to be placed (new or replacement) or substantially improved that are supported on solid foundation walls shall be constructed with flood openings that comply with EC 9.6707(2)(a);

b. The bottom of the longitudinal chassis frame beam shall be at minimum one (1) foot above Base Flood Elevation;

c. Manufactured dwellings to be placed (new or replacement) or substantially improved shall be anchored to prevent flotation, collapse, and lateral movement during the base flood. Anchoring methods may include, but are not limited to, use of over-the-top or frame ties to ground anchors and;

d. Electrical crossover connections shall be a minimum of twelve (12) inches above Base Flood Elevation (BFE).

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

a. Be on the site for fewer than 180 consecutive days and be fully licensed and ready for highway use, 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

b. Meet the requirements of EC 9.6707(2)(c)4, including the anchoring and elevation requirements for manufactured dwellings.

6. Appurtenant Structures. Relief from elevation or floodproofing requirements for residential and non-residential structures in riverine flood zones may be granted for as that meet the following requirements:

a. Appurtenant structures located partially or entirely within the floodway shall comply with requirements for development within a floodway found in EC 9.6707(2)(d);

b. Appurtenant structures shall only be used for parking, access, and/or storage and shall not be used for human habitation;

c. Appurtenant structures on properties within the special flood hazard area shall be limited to one-story structures less than 600 square feet in size;

d. The portions of the appurtenant structure located below the Base Flood Elevation shall be built using flood resistant materials;

e. The appurtenant structure shall be adequately anchored to prevent flotation, collapse, and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy, during conditions of the base flood;

f. The appurtenant structure shall be designed and constructed to equalize hydrostatic flood forces on exterior walls and comply with the requirements for flood openings in EC 9.6707(2)(a);

g. Appurtenant structures shall be located and constructed to have low damage potential;

h. Appurtenant structures shall not be used to store toxic material, oil, or gasoline, or any priority persistent pollutant identified by the Oregon Department of Environmental Quality unless confined in a tank installed in compliance with EC 9.6707(1)(e); and

i. Appurtenant structures shall be constructed with electrical, mechanical, and other service facilities located and installed so as to prevent water from entering or accumulating within the components during conditions of the base flood.

(d) Floodways. Located within the special flood hazard areas established in EC 9.6705 are areas designated as floodways. Since the floodway is an extremely hazardous area due to the velocity of the floodwaters which carry debris, potential projectiles, and erosion potential, the following provisions apply:

1. Encroachments, including fill, new construction, substantial improvements, and other development are prohibited within the adopted regulatory floodway unless:

a. Certification by a registered professional civil engineer is provided demonstrating through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that the proposed encroachment shall not result in any increase in flood levels within the community during the occurrence of the base flood discharge; or

b. A Conditional Letter of Map Revision (CLOMR) is applied for and approved by the Federal Insurance Administrator, and the requirements for such revision as established under Volume 44 of the Code of Federal Regulations, section 65.12 are fulfilled.

2. If the requirements of EC 9.6707(2)(d)1 are satisfied, all new construction, substantial improvements, and other development shall comply with all other applicable flood hazard reduction provisions of EC 9.6707.

(e) Standards for Shallow Flooding Areas. Shallow flooding areas appear on FIRMs as AO zones with depth designations or as AH zones with Base Flood Elevations. For AO zones, the base flood depths range from one (1) to three (3) 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. For both AO and AH zones, adequate drainage paths are required around structures on slopes to guide floodwaters around and away from proposed structures.

1. Standards for AH Zones. Development within AH Zones must comply with the standards in EC 9.6707(1), 9.6707(2) and 9.6707(2)(e).

2. Standards for AO Zones. In AO zones, the following provisions apply in addition to the standards in sections EC 9.6707(1) and 9.6707(2)(e).

a. New construction, conversion to, and substantial improvement of residential structures and manufactured dwellings within AO zones shall have the lowest floor, including basement, elevated above the highest grade adjacent to the building, to or above the depth number specified on the Flood Insurance Rate Maps (FIRM) (at least two (2) feet if no depth number is specified). For manufactured dwellings the lowest floor is considered to be the bottom of the longitudinal chassis frame beam;

b. New construction, conversion to, and substantial improvements of non-residential structures within AO zones shall either:

(1) Have the lowest floor (including basement) elevated above the highest adjacent grade of the building site, to or above the depth number specified on the Flood Insurance Rate Maps (FIRMS) (at least two (2) feet if no depth number is specified); or

(2) Together with attendant utility and sanitary facilities, be completely floodproofed to or above the depth number specified on the FIRM or a minimum of two (2) feet above the highest adjacent grade if no depth number is specified, 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 the effects of buoyancy. If this method is used, compliance shall be certified by a registered professional engineer or architect as stated in EC 9.6707(2)(c)3.a.

c. Recreational vehicles placed on sites within AO Zones on the community’s Flood Insurance Rate Maps (FIRM) shall either:

(1) Be on the site for fewer than 180 consecutive days, and

(2) Be either:

(A) Fully licensed and ready for highway use, 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

(B) Meet the elevation requirements of EC 9.6707(2)(e)2.a, and the anchoring and other requirements for manufactured dwellings of EC 9.6707(2)(c)4.

d. In AO zones, new and substantially improved appurtenant structures must comply with the standards in EC 9.6707(2)(c)6.

e. In AO zones, enclosed areas beneath elevated structures shall comply with the requirements in EC 9.6707(2)(a).