16.55.280 Flood Hazard Management.
(1) Policies.
(a) Recognize and protect the hydrologic functions of floodplains by limiting the use of structural flood hazard reduction measures except where they are necessary to protect existing development and where non-structural flood hazard reduction measures are infeasible.
(b) Ensure developments subject to damage or that could result in loss of life do not locate in areas of known flood hazards unless it can be demonstrated by the project proponent that the development is sited, designed and engineered for long-term structural integrity, and that life and property on and off-site are not subject to increased hazards as a result of the development.
(c) Limit new development or uses in shoreline jurisdiction, including subdivision of land, that would likely require structural flood hazard reduction measures.
(2) Regulations.
(a) Development in floodplains shall avoid significantly or cumulatively increasing flood hazards. Development shall be consistent with this SMP, including Section 16.55.250 (Environmental Protection) and Section 16.55.380 (Frequently Flooded Areas) as well as applicable guidelines of the Federal Emergency Management Agency and an approved flood hazard management plan.
(b) The channel migration zone (CMZ) is considered to be that area of a stream channel which may erode as a result of normal and naturally occurring processes and has been mapped consistent with WAC 173-26-221(3)(b). The Channel Migration Zone Maps are available for review in the City Department of Community Development. Applicants for shoreline development or modification may submit a site-specific CMZ study if they believe these conditions do not exist on the subject property and the map is in error. The CMZ study must be prepared consistent with WAC 173-26-221(3)(b), and may include, but is not limited to, historic aerial photographs, topographic mapping, flooding records, and field verification. The CMZ study must be prepared by a licensed geologist or engineer with at least five years of applied experience in assessing fluvial geomorphic processes and channel response.
(c) The following uses and activities may be authorized within the CMZ or floodway, provided they are also consistent with Section 16.55.380 (Frequently Flooded Areas):
(i) Actions that protect or restore the ecosystem-wide processes or ecological functions or development with a primary purpose of protecting or restoring ecological functions and ecosystem-wide processes.
(ii) New development or redevelopment landward of existing legal structures, such as levees, that prevent active channel movement and flooding.
(iii) Existing and ongoing agricultural activities provided that no new restrictions to channel movement are proposed.
(iv) Development of new or expansion or redevelopment of existing bridges, utility lines, public stormwater facilities and outfalls, and other public utility and transportation structures, including trails, where no other feasible alternative exists or the alternative would result in unreasonable and disproportionate costs. (For the purposes of this Section, “unreasonable and disproportionate” means that locations outside of the floodway or CMZ would add more than 20% to the total project cost. Other methods to determine unreasonable and disproportionate cost may be used on a case-by-case basis with approval of the SMP Administrator. [20% has been used as a threshold by WSDOT and the Federal Department of Justice for ADA standards]) Where such structures are allowed, mitigation shall address adversely impacted functions and processes in the affected shoreline.
(v) New or redeveloped measures to reduce shoreline erosion, provided that it is demonstrated that the erosion rate exceeds that which would normally occur in a natural condition, that the measures do not interfere with fluvial hydrological and geo-morphological processes normally acting in natural conditions, and that the measures include appropriate mitigation of adverse impacts on ecological functions associated with the river or stream.
(vi) Water-dependent installations which by their very nature must be in the floodway.
(vii) Modifications or additions to an existing nonagricultural legal use, provided that channel migration is not further limited and that the modified or expanded development includes appropriate protection of ecological functions.
(viii) Repair and maintenance of existing legally established use and developments, provided that channel migration is not further limited, flood hazards to other uses are not increased, and significant adverse ecological impacts are avoided.
(ix) Uses and developments allowed in the floodway under Section 16.55.380 (Frequently Flooded Areas) provided they are otherwise consistent with all provisions of Part VII (Shoreline Critical Areas Policies and Regulations) and other requirements of this SMP.
(d) Flood hazard reduction measures shall not result in channelization of normal stream flows, interfere with natural hydraulic processes such as channel migration, or undermine existing structures or downstream banks.
(e) New development in shoreline jurisdiction, including the subdivision of land, shall not be permitted if it is reasonably foreseeable that the development or use would require structural flood hazard reduction measures within the channel migration zone or floodway.
(f) New public and private structural flood hazard reduction measures:
(i) Shall not be approved, unless a scientific and engineering analysis demonstrates the following:
(aa) That they are necessary to protect existing development;
(bb) That nonstructural measures, such as buffers and setbacks, land use controls, wetland restoration, dike removal, use or structure removal or relocation, biotechnical measures, and stormwater management programs are not feasible;
(cc) That adverse effects upon adjacent properties will not result relative to increased floodwater depths and velocities during the base flood or other more frequent flood occurrences;
(dd) That the ability of natural drainage ways to adequately drain floodwaters after a flooding event is not impaired;
(ee) That the proposal has been coordinated through the appropriate diking district where applicable, and that potential adverse effects upon other affected diking districts have been documented; and,
(ff) That adverse impacts on ecological functions and priority species and habitats can be successfully mitigated so as to assure no net loss.
(ii) Shall be consistent with an approved comprehensive flood hazard management plan.
(iii) Shall be placed landward of associated wetlands and designated shoreline buffers, except for actions that increase ecological functions, such as wetland restoration, or when no other alternative location to reduce flood hazard to existing development is feasible as determined by the SMP Administrator.
(g) New public structural flood hazard reduction measures, such as levees, shall dedicate and improve public access pathways unless public access improvements would cause unavoidable health or safety hazards to the public, inherent and unavoidable security problems, unacceptable and unmitigable significant adverse ecological impacts, unavoidable conflict with the proposed use, or a cost that is disproportionate and unreasonable to the total long-term cost of the development.
(h) In those instances where management of vegetation as required by this SMP conflicts with vegetation provisions included in state, federal or other flood hazard agency documents governing City-authorized, legal flood hazard reduction measures, the vegetation requirements of this SMP will not apply. However, the applicant shall submit documentation of these conflicting provisions with any shoreline permit applications, and shall comply with all other provisions of this Section and this SMP that are not strictly prohibited by the approving flood hazard agency.
(i) The removal of gravel or other riverbed material for flood management purposes shall be consistent with Section 16.55.530 (Dredging and Dredge Material Disposal) and be allowed only after a biological and geo-morphological study shows that extraction has a long-term benefit to flood hazard reduction, does not result in a net loss of ecological functions, and is part of a comprehensive flood management solution. (Ord. 21-15 §6, 2021; Ord. 16-3 §29, 2016).