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(A) Where special flood hazard areas have not been defined within the community or a base flood elevation has not been provided, all plans and permits for proposed construction of subdivisions, placement of manufactured homes, or other development shall be consistent with the need to ensure that building sites will be reasonably safe from flooding (44 CFR Part 65.2 defines “reasonably safe from flooding” as base flood waters will not inundate the land or damage structures...and that any subsurface waters related to the base flood will not damage existing or proposed buildings). The test of reasonableness is a local judgment and includes historical data, high water marks, photographs of past flooding, and the like.
(B) Building lots shall have adequate buildable area outside of regulatory floodways.
(C) Where base flood elevation has not been provided, it shall be generated for subdivision proposals and other proposed developments (including proposals for manufactured home parks and subdivisions) greater than 50 lots or five acres (whichever is the lesser).
(D) Site improvements, subdivisions, and manufactured home parks shall have public utilities and facilities such as sewer, gas, electric, and water systems located and constructed to minimize or eliminate flood damage and infiltration of flood waters into the systems. Replacement public utilities and facilities such as sewer, gas, electric, and water systems, shall likewise be sited and designed to minimize or eliminate damage and infiltration of flood waters.
(E) New and replacement water supply systems shall be designed to minimize or eliminate infiltration of flood waters into the systems. New and replacement sanitary sewerage systems shall be designed to minimize or eliminate infiltration of flood waters in the systems and discharges from the systems into flood waters. Onsite waste disposal systems shall be located to avoid functional impairment to them or contamination from them during flooding.
(F) Subdivision proposals and other proposed new development, including manufactured home parks, shall have adequate drainage provided to reduce exposure to flood hazards as provided in 44 CFR Part 60.3(a)(4). In AO and AH Zones, drainage paths shall be provided to guide flood water around and away from proposed structures.
(Ord. 527, passed 1-14-2013)
(A) Requirements.
(1) Except as provided in division (B), encroachments, including fill, new construction, substantial improvements, fences, or other development are prohibited in the regulatory floodway unless certification by a registered professional civil engineer is provided demonstrating through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that such encroachment will not result in any increase in flood levels during the occurrence of the base flood discharge.
(2) If division (A)(1) is met, any fill permitted to be placed in the regulatory floodway shall be designed to be stable under conditions of flooding, including rapid rise and rapid drawdown of flood waters, prolonged inundation, and flood-related erosion and scour.
(3) Upon demonstration of no other alternative, applicants shall obtain a conditional letter of map revision (CLOMR) from FEMA before an encroachment, including fill, new construction, substantial improvement, fences, or other development, in the regulatory floodway is permitted that will cause any increase in the base flood elevation unless the development causes a temporary encroachment and the conditions in division (B)(1) below are satisfied. Upon completion of the project, but not later than six months after the project completion, a letter of map revision shall be submitted to FEMA to reflect the changes on the FIRM and/or FIS.
(B) Exceptions.
(1) Temporary encroachments in the regulatory floodway for the purposes of capital improvement projects (including bridge construction/repair) must have a development permit issued. This includes ensuring that all other required permits and permissions are obtained from federal, state, and local agencies.
(a) The permit should stipulate the days and dates the structure or other development will be on site. If a longer period is required, a new permit should be issued.
(b) A flood warning system for the project should be in place to allow equipment to be evacuated from the site and placed outside the floodplain.
(c) Placement of equipment in the floodway should be restricted to only that equipment which is absolutely necessary for the purposes of the project. All other accessory equipment and temporary structures (for example, construction trailers) shall be restricted from the floodway. Structures should be placed on site so that flood damages are minimized. The community may want to consider such things as anchoring construction trailers in case evacuation isn’t practical.
(d) The following conditions shall be included in the permit:
1. Identification of the temporary changes to the floodplain under a 1% chance flood event (100-year flood);
2. Identification of all insurable structures affected by any increase in BFE during a 1% chance flood event (100-year flood);
3. Written notification to the applicant that they may be liable for any flood damages resulting from the temporary structure; and
4. The length of time the structure or encroachment will be allowed.
(e) No CLOMR/LOMR will be required because there is no need to modify the FIRM due to the temporary condition of the encroachment, but the community should disclose to all owners of insurable structures and all applicants for permits in the affected area that there is an increased risk of flooding for the duration of the temporary encroachment.
(2) If the temporary encroachment results in an increase in flood levels during the occurrence of the base flood discharge, a CLOMR is not required to be obtained when:
(a) The project is limited as to duration with the days and dates that the structure or other development will be on site specified in the development permit. If a longer period is required, a new permit should be issued;
(b) All other accessory equipment and temporary structures (for example, construction trailers) are restricted from the regulatory floodway;
(c) The project limits placement of equipment and material in the regulatory floodway to that which is absolutely necessary for the purposes of the project;
(d) Structures shall be placed on site so the flood damages are minimized;
(e) The project includes a flood warning system sufficient to allow equipment to be evacuated from the regulatory floodway and placed outside the area of special flood hazard in the event of imminent flood;
(f) The project applicant identifies insurable structures affected by any increase in base flood elevation. The community should disclose to all owners of insurable structures and all applicants for permits in the affected area that there is an increased risk of flooding for the duration of the temporary encroachment; and
(g) The project applicant is provided with written notification that they may be liable for any flood damages resulting from the temporary encroachment.
(3) Projects for stream habitat restoration may be allowed without certification by a registered professional civil engineer provided:
(a) A development permit is obtained prior to initiating development activities;
(b) The project qualifies for a Department of the Army, Portland District Regional General Permit for Stream Habitat Restoration (NWP-2007-1023);
(c) A qualified professional (a registered professional engineer; staff of NRCS; the county; or fisheries, natural resources, or water resources agencies) has provided a feasibility analysis and certification that the project was designed to keep any rise in 100-year flood levels as close to zero as practically possible given the goals of the project;
(d) No structures would be impacted by a potential rise in flood elevation; and
(e) An agreement to monitor the project, correct problems, and ensure that flood carrying capacity remains unchanged is included as part of the local approval.
(Ord. 527, passed 1-14-2013)
(A) In areas within Zones A1-30 and AE on the community's FIRM with a base flood elevation but where no regulatory floodway has been designated, new construction, substantial improvements, or other development (including fill) shall be prohibited, 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.
(B) Applicants of proposed projects that increase the base flood elevation more than one foot shall obtain from FEMA a conditional letter of map revision (CLOMR) before the project may be permitted. As soon as possible, but no later than six months after project completion, an application for a letter of map revision (LOMR) shall be submitted by the applicant to FEMA. The applicant is responsible for paying any costs associated with the CLOMR and LOMR process.
(Ord. 527, passed 1-14-2013)
(A) When special flood hazard areas have been provided by FEMA on flood insurance rate maps, but base flood elevations have not been provided, the Floodplain Administrator shall:
(1) Require that a base flood elevation be generated whenever development is proposed on greater than 50 lots or five acres (whichever is the lesser); or
(2) If 50 lots or less, or five acres or less (whichever is the lesser), obtain, review, and reasonably utilize scientific or historic base flood elevation and floodway data available from a federal, state, or other source, in order to administer this chapter. If base flood elevations are not available, and are not required to be generated, division (C) below shall apply.
(C) In special flood hazard areas without base flood elevations, the following shall apply:
(1) No encroachments, including structures or fill, shall be located in an area of special flood hazard within an area equal to the width of the stream or 50 feet, whichever is greater, measured from the ordinary high water mark, unless a base flood elevation is developed by a licensed professional engineer; or
(2) The lowest floor of any building or structure, including the bottom of the longitudinal chassis frame beam of the manufactured dwelling, shall be elevated a minimum of three feet above highest adjacent grade. Below grade crawlspaces are prohibited.
(Ord. 527, passed 1-14-2013)
Buildings and structures, including manufactured dwellings, within the scope of the state specialty codes, including repair of substantial damage and substantial improvement of existing buildings and structures, shall be designed and constructed in accordance with the flood-resistant construction provisions of these codes, including, but not limited to, the Residential Specialty Code, the Manufactured Dwelling Installation Specialty Code, and the Structural Specialty Code.
(Ord. 527, passed 1-14-2013)
(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. Hydrostatic loads and the effects of buoyancy can usually be addressed through the required openings stated in division (B) below. Because of hydrodynamic loads, crawlspace construction is not recommended 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. Other types of foundations are recommended for these areas.
(B) The crawlspace is an enclosed area below the base flood elevation and, as such, must have openings that equalize hydrostatic pressures by allowing the automatic entry and exit of flood waters. The bottom of each flood vent opening can be no more than one foot above the lowest adjacent exterior grade.
(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 crawlspace used to elevate the building, but also any joists, insulation, or other materials that extend below the BFE. The recommended construction practice is to elevate the bottom of joists and all insulation above BFE.
(D) Any building utility systems within the crawlspace must be elevated above BFE or designed so that flood waters cannot enter or accumulate within the system components during flood conditions. Ductwork, in particular, must either be placed above the BFE or sealed from flood waters.
(E) The interior grade of a crawlspace below the BFE must not be more than two feet below the lowest adjacent exterior grade.
(F) The height of the below-grade crawlspace, measured from the interior grade of the crawlspace to the bottom of the structural support of the next higher floor must not exceed four feet at any point.
(G) There must be an adequate drainage system that removes flood waters from the interior area of the crawlspace. The enclosed area should be drained within a reasonable time after a flood event. The type of drainage system will vary because of the site gradient and other drainage characteristics, such as soil types. Possible options include natural drainage through porous, well-drained soils and drainage systems such as perforated pipes, drainage tiles, or gravel or crushed stone drainage by gravity or mechanical means.
(H) The velocity of flood waters at the site should not exceed five feet per second for any crawlspace. For velocities in excess of five feet per second, other foundation types should be used.
(Ord. 527, passed 1-14-2013)
In all special flood hazard areas, recreational vehicles that are an allowed use or structure under Chapter 155 must either:
(A) Be placed on the site for fewer than 180 consecutive days;
(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) Shall:
(1) Meet the development permit requirements of §§ 153.32 and 153.50 through 153.61, the manufactured home requirement in the Oregon Manufactured Dwelling Installation Specialty Code, and be elevated on a permanent foundation such that the bottom of the vehicle chassis is elevated to or above base flood elevation; and
(2) Be securely anchored to an adequately anchored foundation system to resist flotation, collapse and lateral movement. Methods of anchoring may include, but are not limited to, use of over-the-top or frame ties to ground anchors. Permanently placed recreational vehicles shall, in addition, meet the requirements of § 153.61(A).
(Ord. 527, passed 1-14-2013)
(A) Temporary structures placed in the floodway. Relief from no-rise evaluation, elevation, or dry flood-proofing standards may be granted for a non-residential structure placed during the dry season (June through October) and for a period of less than 90 days. A plan for the removal of the temporary structure after the dry season or when a flood event threatens shall be provided. The plan shall include disconnecting and protecting from water infiltration and damage all utilities servicing the temporary structure.
(B) Temporary storage (temporary storage does not include hazardous materials) in the floodway. Temporary storage of goods and materials is allowed in the floodway for a period of less than 90 days within the dry season (June through October).
(Ord. 527, passed 1-14-2013)
(A) Construction of new essential facilities shall be, to the extent possible, located outside the limits of the special flood hazard area. Construction of new essential facilities shall be permissible within the special flood hazard area if no feasible alternative site is available. Flood-proofing and sealing measures must be taken to ensure that toxic substances or priority organic pollutants as defined by the Oregon Department of Environmental Quality will not be displaced by or released into flood waters. The lowest floor shall be elevated three feet above the base flood elevation or to the height of the 500-year flood, whichever is higher. Access routes elevated to or above the level of the base flood elevation shall be provided to all essential facilities to the maximum extent possible.
(B) New essential and new special occupancy structures may not be constructed in the Tsunami Inundation Zone. If an exception is granted then the Coastal High Hazard Area construction standards shall apply.
(Ord. 527, passed 1-14-2013)
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