16.15.340 Zero-rise and FEMA floodway development standards and alterations

16.15.340 Zero-rise and FEMA floodway development standards and alterations.

The following standards apply to development proposals and alterations on sites within the zero-rise and FEMA floodways:

(1) The standards that apply to the zero-rise flood fringe also apply to the zero-rise floodway. The more restrictive standards apply where there is a conflict;

(2) A development proposal shall not increase the base flood elevation except as follows:

(a) Revisions to the flood insurance rate map are approved by FEMA, in accordance with 44 CFR 65, to incorporate the increase in the base flood elevation; and

(b) Appropriate legal documents are prepared and recorded in which all property owners affected by the increased flood elevations consent to the impacts on their property;

(3) If post and piling construction techniques are used, the following are presumed to produce no increase in base flood elevation and a critical areas report is not required to establish this fact:

(a) New residential structures outside the FEMA floodway on lots in existence before November 27, 1990, that contain less than 5,000 square feet of buildable land outside the zero-rise floodway;

(b) Substantial improvements of existing residential structures in the zero-rise floodway, but outside the FEMA floodway, if the footprint is not increased; or

(c) Substantial improvements of existing residential structures that meet the standards for new residential structures in Article III of this chapter;

(4) When post or piling construction is not used, a critical areas report is required in accordance with CMC 16.15.110 demonstrating that the proposal will not increase the base flood elevation;

(5) During the flood season from September 30th to May 1st the following are not allowed to be located in the zero-rise or FEMA floodway:

(a) All temporary seasonal shelters, such as tents and recreational vehicles; and

(b) Staging or stockpiling of equipment, materials or substances that the Floodplain Administrator determines may be hazardous to the public health, safety, or welfare;

(6) New residential structures and substantial improvements to existing residential structures or any structure accessory to a residential use shall meet the following standards:

(a) Locate the structures outside the zero-rise and FEMA floodway;

(b) Locate the structures only on lots in existence before November 27, 1990, that contain less than 5,000 square feet of buildable land outside the zero-rise floodway; and

(c) To the maximum extent practical, locate the structures the farthest distance from the channel, unless the applicant can demonstrate that an alternative location is less subject to risk;

(7) Public and private utilities are only allowed if:

(a) The Floodplain Administrator determines that a feasible alternative site is not available;

(b) A waiver is granted by the Department of Public Health of Seattle-King County for new on-site sewage disposal facilities;

(d) Aboveground utility transmission lines, except for electrical transmission lines, are only allowed for the transport of nonhazardous substances; and

(e) Underground utility transmission lines transporting hazardous substances are buried at a minimum depth of four feet below the maximum depth of scour for the base flood, as predicted by a civil engineer, and achieve sufficient negative buoyancy so that any potential for flotation or upward migration is eliminated;

(8) Critical facilities, except for those listed in subsection (9) of this section, are not allowed within the zero-rise or FEMA floodway; and

(9) Structures and installations that are dependent upon the zero-rise floodway are allowed in the zero-rise floodway if the development proposal is approved by all agencies with jurisdiction and meet the development standards for the zero-rise floodway. These structures and installations may include, but are not limited to:

(a) Dams or diversions for water supply, flood control, irrigation or fisheries enhancement;

(b) Flood damage reduction facilities, such as levees, revetments and pumping stations, provided:

(i) That the new structural flood hazard reduction measures are only allowed where demonstrated to be necessary;

(ii) Nonstructural methods are infeasible and mitigation is provided to achieve no net loss, such facilities must be located landward of associated wetlands and buffer areas except where no alternative exists;

(c) Stream bank stabilization structures only if a feasible alternative does not exist for protecting structures, public roadways, flood protection facilities or sole access routes. Bank stabilization projects must meet the standards of the stormwater manuals adopted in CMC Title 13 and use bioengineering techniques to the maximum extent practical. An applicant may use alternative methods to the guidelines if the applicant demonstrates that the alternative methods provide equivalent or better structural stabilization, ecological and hydrological functions and salmonid habitat;

(d) Surface water conveyance facilities;

(e) Boat launches and related recreation structures;

(f) Bridge piers and bridge widening structures; provided, that the new abutments and piers are aligned with existing piers and abutments;

(g) Culvert replacements that upgraded to current fish passage standards; and

(h) Approved stream or wetland restoration projects including, but not limited to, fisheries enhancement projects. (Ord. 12-20 § 2 (Exh. A); Ord. 06-17 § 3 (Exh. A))