For all land use actions that could result in development of the Flood Plain Corridor, the following is required in addition to any requirements of AMC 15.10.
A. Standards for Fill in Flood Plain Corridor Lands.
1. Fill shall be designed as required by the Oregon Structural Specialty Code (OSSC), and Oregon Residential Specialty Code (ORSC), where applicable.
2. The toe of the fill shall be kept at least ten feet outside of floodway channels, as defined in AMC 15.10, and the fill shall not exceed the angle of repose of the material used for fill.
3. The amount of fill in the Flood Plain Corridor shall be kept to a minimum. Fill and other material imported from off the lot that could displace floodwater shall be limited to the following.
a. Poured concrete and other materials necessary to build permitted structures on the lot.
b. Aggregate base and paving materials, and fill associated with approved public and private street and driveway construction.
c. Plants and other landscaping and agricultural material.
d. A total of 50 cubic yards of other imported fill material.
e. The above limits on fill shall be measured from April 1989, and shall not exceed the above amounts. These amounts are the maximum cumulative fill that can be imported onto the site, regardless of the number of permits issued.
4. If additional fill is necessary beyond the permitted amounts in subsection 18.3.10.080.A.3, above, then fill materials must be obtained on the lot from cutting or excavation only to the extent necessary to create an elevated site for permitted development. All additional fill material shall be obtained from the portion of the lot in the Flood Plain Corridor.
5. Adequate drainage shall be provided for the stability of the fill.
6. Fill to raise elevations for a building site shall be located as close to the outside edge of the Flood Plain Corridor as feasible.
B. Crossings. A crossing of any waterway identified on the official maps adopted pursuant to section 18.3.10.070 Official Maps (e.g., for streets, property access or utilities) must be designed by an engineer. Stream crossings shall be designed to the standards of AMC 15.10, or where no floodway has been identified, to pass a 100-year flood without any increase in the upstream flood height elevation. The engineer shall consider in the design the probability that the crossing will be blocked by debris in a severe flood, and accommodate expected overflow. The crossing shall be at right angles to the stream channel to the greatest extent possible. Fill for stream crossings shall be kept to the minimum necessary to achieve property access, but is exempt from the limitations in subsection 18.3.10.080.A, above.
C. Elevation of Non-Residential Structures. Non-residential structures shall be flood-proof to the standards in AMC 15.10 to one foot above the elevation contained in the maps adopted by AMC 15.10, or up to the elevation contained in the official maps adopted by section 18.3.10.070 Official Maps, whichever height is greater. Where no specific elevations exist, then they must be flood-proofed to an elevation of ten feet above the stream channel on Ashland, Bear or Neil Creek; to five feet above the stream channel on all other Riparian Preservation Creeks identified on the official maps adopted pursuant to section 18.3.10.070; and three feet above the stream channel on all other Land Drainage Corridors identified on the official maps adopted pursuant to section 18.3.10.070.
D. Elevation of Residential Structures. All residential structures shall be elevated so that the lowest habitable floor shall be raised to one foot above the elevation contained in the maps adopted in AMC 15.10, or to the elevation contained in the official maps adopted pursuant to section 18.3.10.070 Official Maps, whichever height is greater. Where no specific elevations exist, then they must be constructed at an elevation of ten feet above the stream channel on Ashland, Bear, or Neil Creek; to five feet above the stream channel on all other Riparian Preservation Creeks identified on the official maps adopted pursuant to section 18.3.10.070; and three feet above the stream channel on all other Land Drainage Corridors identified on the official maps adopted pursuant to section 18.3.10.070, or one foot above visible evidence of high flood water flow, whichever is greater. An engineer or surveyor shall certify the elevation of the finished lowest habitable floor prior to issuance of a certificate of occupancy for the structure.
E. Structure Placement. To the maximum extent feasible, structures shall be placed on other than Flood Plain Corridor Lands. In the case where development is permitted in the Flood Plain Corridor area, then development shall be limited to that area which would have the shallowest flooding.
F. Residential Structure Placement. Existing lots with buildable land outside the Flood Plain Corridor shall locate all residential structures outside the Corridor Land, unless 50 percent or more of the lot is within the Flood Plain Corridor. For residential uses proposed for existing lots that have more than 50 percent of the lot in Corridor Land, structures may be located on that portion of the Flood Plain Corridor that is two feet or less below the flood elevations on the official maps, but in no case closer than 20 feet to the channel of a Riparian Preservation Creek identified on the official maps adopted pursuant to section 18.3.10.070. Construction shall be subject to the requirements in subsection 18.3.10.080.D, above.
G. New Non-Residential Structures. New non-residential uses may be located on that portion of Flood Plain Corridor Lands that equal to or above the flood elevations on the official maps adopted in section 18.3.10.070 Official Maps. Second story construction may be cantilevered or supported by pillars that will have minimal impact on the flow of floodwaters over the Flood Plain Corridor for a distance of 20 feet if it does not impact riparian vegetation, and the clearance from finished grade is at least ten feet in height. The finished floor elevation may not be more than two feet below the flood corridor elevations.
H. Building Envelopes. All lots modified by property line adjustments, and new lots created from areas containing Flood Plain Corridor Land, must have building envelopes containing buildable area of a sufficient size to accommodate the uses permitted in the underling zone, unless the action is for open space or conservation purposes. This section shall apply even if the effect is to prohibit further division of lots that are larger than the minimum size permitted in the zoning ordinance.
1. Habitable basements are not permitted for new or existing structures or additions located within the Flood Plain Corridor.
2. Non-habitable basements, used for storage, parking, and similar uses are permitted for residential structures but must be flood-proofed to the standards of AMC 15.10.
J. Hazardous Chemicals. Storage of petroleum products, pesticides, or other hazardous or toxic chemicals is not permitted in Flood Plain Corridor Lands.
K. Fences. Fences shall be located and constructed in accordance with subsection 18.3.11.050.B.3. Fences shall not be constructed across any waterway or stream identified on the official maps adopted pursuant to section 18.3.10.070 Official Maps. Fences shall not be constructed within any designated floodway.
L. Decks and Other Structures. Decks and structures other than buildings, if constructed on Flood Plain Corridor Lands and at or below the levels specified in subsections 18.3.10.080.C and D, shall be flood-proofed to the standards contained in AMC 15.10.
M. Local Streets and Utilities. Local streets and utility connections to developments in and adjacent to the Flood Plain Corridor shall be located outside of the Flood Plain Corridor, except for crossing the Corridor, except as provided for in chapter 18.3.11 Water Resources Overlay, or in the Flood Plain Corridor as outlined below.
1. Public street construction may be allowed within the Bear Creek Flood Plain Corridor as part of development following the adopted North Mountain Neighborhood Plan. This exception shall only be permitted for that section of the Bear Creek Flood Plain Corridor between North Mountain Avenue and the Nevada Street right-of-way. The new street shall be constructed in the general location as indicated on the neighborhood plan map, and in the area generally described as having the shallowest potential for flooding within the corridor.
2. Proposed development that is not in accord with the North Mountain Neighborhood Plan shall not be permitted to utilize this exception.