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POL Government Elected Officials Auditor Griffin-Valade Charter, Code & Policies City Code & Charter Online Code & Charter Title 24 Building Regulat Chapter 24.50 Flood Hazard Areas
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.

 


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)