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Chapter 24.50 Flood Hazard Areas

- Note
(New Chapter substituted by Ordinance No. 160413, effective Jan. 14, 1988.)

24.50.010 Purpose.

The purpose of this Chapter is to protect the public health, safety, and welfare by restricting or prohibiting uses which are dangerous to health, safety, or property in times of flood or which cause increased flood heights or velocities, and by requiring that uses and structures vulnerable to floods be protected from flood danger at the time of initial construction.


24.50.020 General.

(Amended by Ordinance No. 182370, effective November 26, 2008.)

 

A.  The provisions of this Chapter shall regulate development and construction in flood hazard areas identified in Section 24.50.030.

 

B.  Land classified in a flood hazard area may restrict or affect uses and development permitted in one or more of the regular zones listed in Chapter 33.16.  If an inconsistency exists between Chapter 24.50 and other titles of this Code, the more restrictive uses or requirements shall prevail.

 

C.  A structure or the use of a structure or property which was lawful before the original date of this Chapter but which is not in conformity with the provisions of this Chapter may be continued subject to provisions of the State Building Code, regulations for existing structures.

 

D.  The flood protection elevations and the floodway and floodway fringe areas specified by this Chapter, based on the 100‑year flood elevations, are considered reasonable.  Greater flood heights and more extensive floodway fringe areas associated with longer flood frequency occurrences may occur or the flood height and extent of flooding may be increased by human or natural causes, such as log jams, bridge openings restricted by debris, or changes in basin conditions.  Areas within designated drainage districts and those areas not covered by adequate topographic maps may contain unmapped watercourses subject to flooding.  The identification of designated flood hazard areas does not imply that lands outside of such areas will be free from flooding or flood damage.

The City of Portland or any officer or employee thereof, or the Federal Insurance Administration shall not be liable for any flood damages that result from reliance on the provisions or designations of this Chapter or any administrative decision lawfully made thereunder.

 


24.50.030 Flood Related Definitions.

(Amended by Ordinance Nos. 178741, 182370 and 184235, effective November 26, 2010.)  The definitions contained in this Section relate to flood hazard areas and considerations outlined in this Chapter.

 

A.  "Appeal" means a request for a review of the City of Portland’s interpretation of any provision of this ordinance or a request for a variance.

 

B.  "Area of shallow flooding" means a designated AO or AH zone on the Flood Insurance Rate Map (FIRM).  The base flood depths range from 1 to 3 feet; a clearly defined channel does not exist; the path of flooding is unpredictable and indeterminate; and, velocity flow may be evident.  AO is characterized as sheet flow and AH indicates ponding.

 

C.  "Areas of Special Flood Hazard" mean the land in the flood plain within a community subject to a one percent or greater chance of flooding in any given year.  Designation on maps always includes the letters A or V.

 

D.  "Base Flood (100‑year flood)" means the flood having 1 percent chance of being equaled or exceeded in any given year.  Designation on maps always includes the letters A or V.

 

E.  “Basement” means any area of the building having its floor subgrade (below ground level) on all sides.

 

F.  "City Datum" means the reference datum for the City of Portland maps.  The FIRM maps described in Section 24.50.050 are referenced to the North American Vertical Datum (NAVD) of 1988.  To convert NAVD 1988 level to City datum, subtract 2.125 feet from the elevation referenced to NAVD 1988 level.

 

G.  "Development" means any man‑made change to improved or unimproved real estate, including but not limited to buildings, bridges, other structures, and mining, dredging, filling, grading, paving, excavation, fencing, landscaping, drainage facilities, drilling operations, or storage of equipment or material.

 

H.  "Existing manufactured home park or manufactured home subdivision" means a parcel (or contiguous parcels) of land divided into two or more manufactured home lots for rent or sale for which the construction of facilities for servicing the lot on which the manufactured home is to be affixed (including as a minimum, the installation of utilities, either final site grading or the pouring of concrete pads, and the construction of streets) is completed before the original date of this Chapter.

 

I.  "Expansion to an existing manufactured home park or manufactured home Subdivision" means the preparation of additional sites by the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including the installation of utilities, either final site grading or the pouring of concrete pads, and the construction of streets).

 

J.  "FIA" means Federal Insurance Administration.

 

K.  "Flood Hazard Area" means any area which has been identified as subject to flooding. 

 

L.  “Flood Insurance Study” means the official report provided by the Federal Insurance Administration that contains information regarding flooding, discusses the engineering methods used to develop the Flood Insurance Rate Maps (FIRMs), includes flood profiles, and the water surface elevation of the base flood.

 

M.  "Flood Insurance Rate Map (FIRM)" means the official map on which the Federal Insurance Administration has delineated the areas of special flood hazards.

 

N.  "Flood or flooding" means a general and temporary condition of partial or complete inundation of normally dry land areas from the overflow of inland or tidal waters, and/or the unusual and rapid accumulation of runoff of surface waters from any source.

 

O.  "Flood protection elevation" means the water surface elevation of the base flood plus a freeboard allowance.

 

P.  "Floodplain" means the channel of watercourse and adjacent land areas which are subject to inundation by the base flood.

 

Q.  "Floodproofing" means any combination of structural and nonstructural additions, changes, or adjustments to structures which reduce or eliminate flood damage to real estate or improved real property, sanitary, and water facilities, structures, and their contents.

 

R.  "Floodway" means the channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than one foot.  The actual floodway boundaries are computer activated and approximate.  These boundaries are depicted on the FIRM.  Boundaries for other watercourses may be subject to identification by the Sewage System Administrator.  The width of the floodway for unidentified watercourses should not be less than 15 feet.

 

S.  "Flood fringe area" means any area lying outside the floodway which is subject to flooding by a base flood and for which water surface elevations and floodway and flood fringe boundaries have been determined by a Flood Insurance Study and are shown on the FIRMs.  Boundaries for unidentified watercourses may be subject to identification by the Sewage System Administrator.

 

T.  "Freeboard" means an additional height above the base flood level to account for factors that may contribute to flood heights greater than the height calculated for a selected size flood and floodway conditions, such as filling in the floodway fringe, wave action, effect of urbanization of the watershed, map inaccuracies, irregular stream cross sections, irregular constructions at bridges, and the uncertainties of flood discharge computations.

 

U.  "Lowest Floor" means the lowest floor of the lowest enclosed area (including basement).  An unfinished or flood resistant enclosure, usable solely for parking of vehicles, building access or storage, in an area other than a basement area, is not considered a building’s lowest floor, provided that such enclosure is not built so as to render the structure in violation of the applicable non‑elevation design requirements of this ordinance found at Section 24.50.060 F.2. 

 

V.  "Manufactured home" means a structure transportable in one or more sections, which is built on a permanent chassis and is designed for use with or without a permanent foundation when connected to the required utilities.  For flood plain management purposes, the term “manufactured home” also includes park trailers, travel trailers, and other similar vehicles placed on a site for greater than 180 consecutive days.  For insurance purposes, the term “manufactured home” does not include park trailers, travel trailers, and other similar vehicles.

 

W.  "New construction" means structures for which the start of construction commenced on or after the effective date of this Chapter.

 

X.  "New manufactured home park or manufactured home subdivision" means a parcel (or contiguous parcels) of land divided into two or more manufactured home lots for rent or sale for which the construction of facilities for servicing the lots on which the manufactured home is to be affixed (including as a minimum, the installation of utilities, either final site grading or the pouring of concrete pads and the construction of streets) is completed on or after the original date of this Chapter. 

 

Y.  “Start of construction” includes substantial improvement, and means the date the building permit was issued, provided the actual start of construction, repair, reconstruction, placement or other improvement was within 180 days of the permit date.  The actual start means either the first placement of permanent construction of a structure on a site, such as the pouring of slab or footings, the installation of piles, the construction of columns, or any work beyond the stage of excavation; or the placement of a manufactured home on a foundation.  Permanent construction does not include land preparation, such as clearing, grading and filling; nor does it include the installation of streets, walkways, sanitary sewers, storm sewers, and/or drainage facilities; nor does it include excavation for a basement, footings, piers, or foundation or the erection of temporary forms; nor does it include the installation on the property of accessory buildings, such as garages or sheds not occupied as dwelling units or not part of the main structure. 

 

Z.  “Structure or accessory structure” means, for the purposes of this Chapter, a walled and roofed building including a gas or liquid storage tank that is principally above ground.

 

AA.  “Substantial Damage” means damage of any origin sustained by a structure whereby the cost of restoring the structure to its before damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred.

 

BB.  "Substantial Improvement" means any repair, reconstruction, or improvement of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure, either:

 

1.   Before the improvement or repair is started, or

 

2.   If the structure has been damaged, and is being restored, before the damage occurred.  Substantial improvement is considered to occur when the first alteration of any wall, ceiling, floor, or other structural part of the building commences, whether or not that alteration affects the external dimensions of the structure.

 The term does not, however, include either:

 

a.  Any project for improvement of a structure to comply with existing State or local health, sanitary, or safety code specifications which are solely necessary to assure safe living conditions, or

 

b.  Any alteration of a structure listed on the National Register of Historic Places or the State Inventory of Historic Places. 

 

CC.  “Variance” means a grant of relief from the requirements of this ordinance which permits construction in a manner that would otherwise be prohibited by this ordinance. 

 

DD.  “Water surface elevation” means the height of the water surface of the base flood for any point along the longitudinal course of a stream. 

 

EE.  “Watercourse” means a channel in which a flow of water occurs, either continuously or intermittently, and if the latter, with some degree of regularity.  Watercourses may be either natural or artificial.


24.50.040 FIA Study and Flood Hazard Maps.

(Amended by Ordinance Nos. 173979, 176955, 178741, 182671 and 184235, effective November 26, 2010.)  The following study and maps in this Section are hereby adopted and declared to be a part of this Chapter.

 

A.  Flood Insurance Study is the official scientific and engineering report entitled “Flood Insurance Study for City of Portland, Oregon: Multnomah, Clackamas and Washington Counties”, dated November 26, 2010 prepared by the Federal Insurance Administration (FIA) under agency agreement with the Portland District Corps of Engineers.  The latest edition of the report, along with accompanying FIRMs, are on file with the Bureau of Development Services.

 

B.  Flood Insurance Rate Maps (FIRMs) are the official maps entitled “The Flood Insurance Rate Maps (FIRMs) for City of Portland, Oregon: Multnomah, Clackamas and Washington Counties”, dated either October 19, 2004 or November 26, 2010, whichever is more current, on which the Federal Insurance Administration has delineated the areas of flood hazards along with the 100-year (base flood) and 500-year flood boundaries, the floodway zone boundaries and the 100-year flood elevations.

 

C.  Water Features Map is the official map, dated May, 1981, or latest edition, compiled by the Bureau of Planning and Sustainability delineating certain watercourses which are subject to special flood hazard and drain 30 acres or more.

 

D.  When base flood elevation data has not been provided by the FIA study, the Sewage System Administrator may obtain, review, and reasonably utilize any base flood elevation and floodway data available from a federal, state, or other source.  This data shall be utilized only after technical review and approval of the Sewage System Administrator.

 

E.  The "Title 3 Water Quality and Flood Management Area Map," as adopted by Metro Council on June 18, 1998, is the official map which identifies areas as "February 1996 Flood Inundation."  The identified areas are subject to the regulations of this Title.


24.50.050 Flood Hazard Areas and Flood Protection Elevations.

(Amended by Ordinance Nos. 173979, 178741 and 182370, effective November 26, 2008.)  Flood hazard areas shall contain all lands located within the Floodway boundary, Flood Zones within the Flood fringe areas, and other identified Flood Zones.  Identified Flood Zones are depicted on the National Flood Insurance Rate Map (FIRM).  Both identified and unidentified Flood Hazard areas along with flood protection elevations are described in the following.  Figure 1 illustrates the basic flood hazard areas and elevations.

 

  (See Figure 1 at the end of Title 24)

 

A.  Columbia River FIRM Flood Zone AE.  These flood zones represent areas for which base flood elevations are determined.  The flood protection elevation shall be the base flood elevation plus one foot of freeboard.  The nominal one-foot increase for freeboard reflects the relatively wide flood plain of the Columbia River.  In the vicinity of the confluence of the Columbia and Willamette Rivers, the Columbia River floodplain shall be considered to be east of the westerly floodway fringe boundary of the Columbia Slough.

 

B.  Multnomah Drainage District No. 1 and Peninsula Drainage District No. 2 FIRM Zone AH.  This flood zone represents isolated areas of shallow flooding (1 to 3 feet in depth, resulting from upslope runoff) for which base flood elevations are determined.  In the case of unidentified watercourses occurring within the boundaries of the Drainage Districts, the base flood elevation shall be estimated by procedures described in paragraph G. below.  The flood protection elevation shall be the base flood elevations plus one foot of freeboard.

 

C.  Columbia River FIRM Flood Zone A.  These flood zones represent areas for which base flood elevations are not determined.  The flood protection elevation shall be either the grade at the adjacent flood fringe boundary or the crown of the nearest street, whichever is higher, plus one foot of freeboard.

 

D.  Willamette River FIRM Flood Zone AE.  These flood zones represent areas for which the base flood elevations are determined.  The flood protection elevation shall be the base flood elevation plus two feet of freeboard.

 

E.  Johnson Creek, Fanno Creek and Crystal Springs Creek FIRM Flood Zone AE.  This flood zone represents area for which the base flood elevations are determined.  The flood protection elevation shall be the base flood elevation plus two feet of freeboard.

 

F.  Johnson Creek FIRM Flood Zone AH.  This flood zone represents areas of shallow flooding depth (1 to 3 feet) for which base flood elevations are determined.  The flood protection elevation shall be the base flood elevation plus two feet of freeboard.

 

G.  Johnson Creek FIRM Flood Zone AO.  This flood zone represents areas of shallow flooding depth (1 to 3 feet) for which the depths of flooding are determined.  The flood protection elevation shall be the depth of flooding shown on the FIRM map plus two feet of freeboard above the highest adjacent grade.

 

H.  Johnson Creek, Fanno Creek, Tryon Creek, and Crystal Springs Creek FIRM Flood Zone A. These flood zones represent areas for which base flood elevations are not determined.  The flood protection elevation shall be the base flood elevation plus two feet of freeboard.  Base flood elevations shall be calculated in accordance with paragraph I. below.

 

I.  Unidentified Watercourse Flood Zones.  These watercourses, generally draining one acre or more, are not identified in a Federal Insurance Study and may not be identified on the Water Features map.  The flood protection elevation shall be the base flood elevation plus two feet of freeboard.  The width of the floodway shall not be less than 15 feet.  The floodway boundary, flood fringe boundary, and flood protection elevation data shall be based upon watercourse geometry, slope, channel roughness, effect of obstructions, backwater and other factors which affect flood flow.  The requisite flood hazard data, maps, and sections shall be obtained and developed by procedures approved by the Sewage System Administrator.  When appropriate and necessary data are available, the flood protection elevation and floodway and flooding fringe boundary data may be provided by the Sewage System Administrator.  If pertinent hydrologic data and topographic data are not available, inaccurate, or outdated, and where substantial alterations or relocations of a watercourse are involved, the Sewage System Administrator may require the permit applicant to secure a registered engineer and surveyor to develop and supply the requisite flood hazard data, maps, and sections.

 

J.  Metro Flood Management Areas.  Flood 1996 inundation areas shown on Metro Title 3 Water Quality and Flood Management Area Maps shall have a flood protection elevation which provides two feet of freeboard above the Flood 1996 level.  Flood 1996 inundation areas adjacent to Columbia River FIRM Flood Zone AE, Multnomah Drainage District No. 1, Peninsula Drainage District No. 2 Firm Zone AH and Columbia River FIRM Flood Zone A shall have freeboard of one foot.

 


24.50.060 Provisions for Flood Hazard Reduction.

(Amended by Ordinance Nos. 165678, 169905, 172209, 173979, 176955, 178741, 182370 and 184235, effective November 26, 2010.)  In all flood hazard areas defined in Section 24.50.050, the following provisions are required:

 

A.  Permits.  All permit applications shall be reviewed to determine whether proposed building sites will be reasonably safe from flooding.  A development or building permit shall be obtained before construction or development begins within any area of flood hazard.  Such applications for permits shall include the following specific information:

 

1.  Elevation of lowest floor, including basement, for all structures and floodproofed elevations for nonresidential structures.

 

2.  Elevation of lowest point of bridge structures.

 

3.  Existing and proposed topography of the site taken at a contour interval (normally 1 foot) sufficiently detailed to define the topography over the entire site and adjacent watercourses subject to flooding.  Ninety percent of the contours shall be plotted within 1 contour interval of the true location.

 

4.  All necessary permits obtained from the federal and state governmental agencies from which prior approval is required.

 

5.  Where elevation data is not available either through the Flood Insurance Study or from another authoritative source (Section 24.50.050 G.), 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 use of any available hydrological data, drainage basin hydrology, historical data, high water marks, photographs of past flooding, etc., where available.  Failure to elevate at least two feet above grade in these zones may result in higher insurance rates.

 

B.  Elevation reference.  The survey reference datum for finished lowest floor including basement, floodproofed elevations, and finished site grades shall be either the North American Vertical Datum of 1988 or City of Portland datum, whichever is appropriate.  When approved by the City Engineer, a local onsite survey reference datum may be adopted for FIRM Zones A and Unidentified Watercourse Flood Zones.  The survey reference datum shall be indicated on all relevant plan and Section drawings, and the certified Flood‑Elevation Certificate.

 

C.  Certification of elevations and floodproofing.  All finished elevations as specified hereunder shall be certified on a FEMA (FIA) Elevation Certificate by a licensed surveyor secured by the permittee, and made part of the permit records.

 

1.  As‑built elevation of lowest floor including basement, of all new or substantially improved structures;

 

2.  As‑built floodproofed elevation of all new or substantially improved nonresidential structures;

 

3.  As‑graded elevation of lowest grade within 25 feet of structures;

 

4.  As‑graded elevation of lowest crawl space grade, as applicable.

All floodproofing materials and methods for nonresidential structures shall be certified by a licensed professional engineer or architect as meeting the criteria in Section 24.50.060 F7.

 

D.  Floodway.  Encroachments into the floodway by development and structures defined in Section 24.50.020 are prohibited unless it is demonstrated by technical analysis from a registered engineer that the development will result in no increase in the base flood elevation.  In areas where a regulatory floodway has not been designated, no new construction, substantial improvement or other development (including fill) shall be permitted within Zone AE, 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 1 foot at any point within the community.  Technical analysis shall be reviewed and approved by the Sewage System Administrator.  However, the minimum width of the floodway shall not be less than 15 feet.

 

E.  Alteration of watercourses.  The Bureau of Development Services shall:

 

1.  Notify adjacent communities and the Department of Land Conservation and Development prior to any alteration or relocation of a watercourse as identified in the Flood Insurance Study and Flood Insurance Rate Map, and submit evidence of such notification to the Federal Insurance Administration.

 

2.  Require that maintenance is provided within the altered or relocated portion of said watercourse so that the flood carrying capacity is not diminished.

 

F.  Special flood hazard areas.

 

1.  General.  All new construction and substantial improvements shall be anchored to prevent flotation, collapse or lateral movement of the structure.

 

2.  Residential construction. 

 

a.  New construction and substantial improvement of any residential structure shall have the lowest floor, including basement, elevated to or above flood protection elevation.  Floodproofing of “lowest floor” space is not permitted. 

 

b.  Fully closed areas below the lowest floor that are subject to flooding are prohibited or shall be used solely for parking of vehicles, building access or limited storage and be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing 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:

 

(1)  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;

 

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

 

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

 

(a)  Fills required to elevate the lowest floor to the flood protection level shall comply with Chapter 24.70.  Fill selection and placement shall recognize the effects of inundation from floodwaters on slope stability, fill settlement, and scour.  The minimum elevation at the top of the fill slope shall be at the base flood level.  Minimum distance from any point of the building perimeter to the top of the fill slope shall be either 25 feet or twice the depth of fill at that point, whichever is the greater distance. 

 

(b)  Piling foundations required to elevate the lowest habitable floor to the flood protection level shall comply with Section 1809 and 1808 of the Structural Specialty Code.  Pilings shall be spaced no more than 10 feet apart, and reinforcement shall be provided for piling more than 6 feet above the ground level.

 

3.  Subdivision proposals.

 

a.  All subdivision proposals shall be consistent with the need to minimize flood damage;

 

b.  All subdivision proposals shall have public utilities and facilities such as sewer, gas, electrical and water systems located and constructed to minimize flood damage;

 

c.  All subdivision proposals 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 subdivision proposals and other proposed developments which contain at least 50 lots or 5 acres (whichever is less).

 

4.  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 the flood protection elevation, or, together with attendant utility and sanitary facilities, shall:

 

a.  Be floodproofed so that below the flood protection elevation 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 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 Bureau of Development Services.

 

d.  Nonresidential structures that are elevated, not floodproofed, must meet the same standards for space below the lowest floor as described for residential structures.

 

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 constructed to the base flood level will be rated as one foot below that level).

 

5.  Manufactured homes.  All manufactured homes to be placed or substantially improved within Zones AO, AH and AE shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is at or above the flood protection elevation and be securely 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 (Refer to FEMA’s "Manufactured Home Installation in Flood Hazard Areas” guidebook for additional techniques).

 

6.  Utilities.  All new and replacement water supply and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of flood waters into the systems and discharges from the sanitary sewage systems into flood waters.  On‑site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding.

 

7.  Construction materials and methods.  All new construction and substantial improvements shall be constructed with materials and utility equipment resistant to flood damage, using methods and practices that minimize flood damage.  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.

 

8.  Balanced Cut and Fill Required.  In all Flood Management Areas of the City not addressed by Section 24.50.060 G, balanced cut and fill shall be required.  All fill placed at or below the base flood elevation shall be balanced with at least an equal amount of soil material removal.  Soil material removal shall be within the same flood hazard area identified in Section 24.50.050 A. through I.

 

a.  Excavation shall not be counted as compensating for fill if such areas will be filled with water in non-storm winter conditions.

 

b.  Temporary fills permitted during construction shall be removed.

 

9.  Tank anchoring.  Tanks containing hazardous materials must be anchored to prevent flotation if they are located in areas of special flood hazard or flood management areas.

 

10.  Uncontained hazardous materials as referred to in Section 101 (14) of the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (42 U.S. Section 9601 et seq.) (CERCLA), section 502 (13) of the Clean Water Act and any other substances so designated by the Director of the Bureau of Development Services are prohibited in flood management areas.

 

11.  AH/AO Zone Drainage.  Adequate drainage paths shall be provided around structures on slopes to guide floodwaters around and away from proposed structures.

 

G.  Johnson Creek Flood Zones - Special Provisions.  In addition to other requirements of this chapter the following requirements shall apply within designated portions of the Johnson Creek Flood Zones:

 

1.  All Johnson Creek Flood Zones

 

a.  Balanced cut and fill.  Within all areas of the Johnson Creek Flood Zones, all new fills below the base flood elevation shall be accompanied by an equal amount of excavation on the same site so that the storage capacity of the floodway and floodway fringe is retained.

 

b.  Mitigation payment allowed in lieu of balanced cut and fill.  After September 1, 1998 residential properties within the area of the 100 year floodplain, but outside of the floodway and Flood Risk Area, and bounded by I-205 on the west, SE 142nd Avenue on the east, and the Springwater Corridor Trail on the south, may elect to pay into the Johnson Creek Fill Mitigation Bank in lieu of creating a balanced cut and fill.  The amount of the payment shall be determined by the Bureau of Environmental Services.

 

2.  Johnson Creek Flood Risk Area.  The following provisions shall apply within the Johnson Creek Flood Risk Area, as established in Chapter 33.535 of the City Code:

 

a.  Balanced cut and fill.  The requirements of subsection G.1. above, shall apply within the Johnson Creek Flood Risk Area.

 

b.  Reduction in flooding capacity prohibited.  Structures, fill or other development shall only be allowed in the Johnson Creek Flood Risk Area when they are designed so that there is no significant reduction in the storage capacity of the floodway and floodway fringe and there is no significant impediment to the passage of flood waters.

 

c.  Exceptions to Section 24.50.060 G.2.:

 

(1)  One story detached accessory buildings used as tool and storage sheds, playhouses and similar uses, provided the floor area does not exceed 120 square feet.

 

(2)  Parking garages accessory to one and two family structures, provided the floor area does not exceed 300 square feet.

 

(3)  Fences which do not prevent the flow of water.

 

d.  Buildings designed to meet all of the following criteria shall be presumed to comply with Section 24.50.060.G.2.:

 

(1)  At least 50% of perimeter walls located at, or below, the base flood elevation shall remain open and unenclosed;

 

(2)  At least 25% of each perimeter wall located at, or below, the base flood elevation shall remain open and unenclosed; and

 

(3)  The footprint of all portions of the building located at, or below, the base flood elevation shall not exceed 15% of the footprint of the building located above the base flood elevation.

 


24.50.065 Recreational Vehicles located in Areas of Special Flood Hazard or Base Flood Zones.
 
(Added by Ordinance No. 180330, effective August 18, 2006.)
 
A.  Any recreational vehicle placed on a site located in either an Area of Special Flood Hazard or in the base flood zone shall:
1.  Meet the elevation and anchoring requirements for manufactured homes;
 
2.  Be on the site for fewer than 180 consecutive days; or
 
3.  Be fully licensed and ready for highway use.  As used in this section, “ready for highway use” means that the vehicle is on its wheels or jacking system, is attached to the site only by quick disconnect type utilities and has no permanently attached additions.
B.   For the purpose of this section, “recreational vehicle” means any vehicle which is:
1.   Built on a single chassis;
 
2.   400 square feet or less when measured at the largest horizontal projection;
 
3.  Designed to be self propelled or permanently towable by a light duty truck; and
 
4.  Designed primarily not for use as a permanent dwelling but as temporary living quarters for recreational, camping, travel or seasonal use.

24.50.070 Appeals and Variances.
(Amended by Ordinance No. 178741, effective October 19, 2004.)
 
A. Appeals. Any person aggrieved by a requirement, decision, or determination made pursuant to the administration of this Chapter may appeal such action to the Building Board of Appeal in accord with Chapter 24.10.
 
B. Variances. If variances from requirements of this Chapter are requested, all relevant factors and standards specified in other sections of this Chapter shall be considered, as well as the following:
1. The danger that materials may be swept into other lands to the injury of others;
 
2. The danger to life and property due to flooding or erosion damage;
 
3. The susceptibility of the proposed facility and its contents to flood damage and the effect of such damage on the individual owner;
 
4. The importance of the services provided by the proposed facility to the community;
 
5. The necessity to the facility of a waterfront location, where applicable;
 
6. The availability of alternative locations, not subject to flooding or erosion damage;
 
7. The compatibility of the proposed use with existing anticipated development;
 
8. The relationship of the proposed use to the Comprehensive Plan and Floodplain Management Program for that area;
 
9. The safety of access to the property in times of flood for ordinary and emergency vehicles;
 
10. The expected heights, velocity, duration, rate of rise, and sediment transport of the flood waters and the effects of wave action, if applicable, expected at the site;
 
11. The costs of providing governmental services during and after flood conditions including maintenance and repair of public utilities and facilities such as sewer, gas, electrical, and water systems, and streets and bridges; Upon consideration of the factors listed above and the purposes of this Chapter, such conditions may be attached to the granting of variances as deemed necessary.
C. Conditions for variances.
1. Generally the only condition under which variance from the elevation standard may be issued is for new construction and substantial improvements to be erected on a lot of 1/2 acre or less in size contiguous to and surrounded by lots with existing structures constructed below the base flood level, providing items (1-11) have been fully considered. As the lot size increases, the technical justification required for issuing the variance increases.
 
2. Variances shall not be issued within designated floodway if any increase in flood levels during the base flood discharge would result.
 
3. Variances may be issued for the reconstruction, rehabilitation or restoration of structures listed on the National Register of Historic Places or the State Inventory of Historic Places, without regard to the procedures set forth in this Section.
 
4. Variances shall only be issued upon a determination that the variance is the minimum necessary, considering the flood hazard, to afford relief.
 
5. Variances shall only be issued upon:
a. A showing of good and sufficient cause,
 
b. A determination that failure to grant the variance would result in exceptional hardship to the applicant, and
 
c. A determination that the granting of a variance would not result in increased flood heights, additional threats to public safety, extraordinary public expense, create nuisances, cause fraud on or victimization of the public, or conflict with existing local laws or ordinances.
6. Any applicant to whom a variance is granted shall be given written notice that the structure will be permitted to be built with a lowest floor elevation below the base flood elevation and that the cost of flood insurance will be commensurate with the increased risk resulting from the reduced lowest floor elevation.
 
7. Variances as interpreted in the National Flood Insurance Program are based on the general zoning law principle that they pertain to a physical piece of property; they are not personal in nature and do not pertain to the structure, its inhabitants, economic or financial circumstances. They primarily address small lots in densely populated residential neighborhoods. As such, variances from the flood elevations should be quite rare.
 
8. Variances may be issued for nonresidential buildings in very limited circumstances to allow a lesser degree of floodproofing than watertight or dry-floodproofing, where it can be determined that such action will have low damage potential, complies with all other variance criteria except 24.50.070 C.1. and otherwise complies with Section 24.50.060 F.1. and 24.50.060 F.7.

Figure 1 (24.50)

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Title 24 Building Regulat
Chapter 24.10 Administration and Enforcement
Chapter 24.15 Definitions
Chapter 24.20 Special Inspections
Chapter 24.25 Movings of Buildings
Chapter 24.30 Home Occupations
Chapter 24.35 Historical Buildings
Chapter 24.40 Use of and Projections Over Public Streets and Property
Chapter 24.45 Parking and Driveway Surfaces
Chapter 24.50 Flood Hazard Areas
Chapter 24.51 Wildfire Hazard Zones
Chapter 24.55 Building Demolition
Chapter 24.60 Fences
Chapter 24.65 Sidewalk Vault Openings
Chapter 24.70 Clearing, Grading and Erosion Control
Chapter 24.75 Uniform Building Address System
Chapter 24.80 (Repealed)
Chapter 24.85 Seismic Design Requirements for Existing Buildings
Chapter 24.90 Manufactured Dwelling Installation and Accessory Structures, Manufactured Dwelling Parks, Recreation Parks, Recreational Park Trailer Installation and Accessory Structures
Chapter 24.95 (Repealed)