Frequently Flooded Areas are the Areas of Special Flood Hazards identified by the Federal
Insurance Administration and the Federal Emergency Management Agency (FEMA),
respectively, in scientific and engineering reports entitled, The Flood Insurance Study for the
City of Vancouver, Washington, Clark County, 1981, and The Flood Insurance Study for Clark
County, Washington, 1991 and any revisions thereto, with accompanying Flood Insurance Rate
Maps (FIRM) and Flood Boundary-Floodway Maps (FBFM) and any revisions thereto. The
Flood Insurance Study (FIS) is available from the Planning Official. Frequently Flooded Areas
(Areas of Special Flood Hazards or floodplain) include lands within the floodway
and the flood
fringe. (See VMC 20.150.040 Meanings of Specific Words and Terms for definitions for Areas
of Special Flood Hazards, Flood Fringe, Floodplain, Floodway, and Frequently Flooded Areas.)
Final designations shall be based on site conditions and other available data or information
(See
VMC 20.740.020(C)(1)).
When base flood elevation (BFE) data has not been provided in frequently flooded areas
(Zone
A), the Planning Official shall obtain, review, and reasonably utilize any base flood elevation and
floodway data available from a Federal, State or other source in order to administer the
provisions of this chapter. This best available information for flood hazard area identification
shall be the basis for regulation until a new FIRM is issued.
Figure 20.740.120-1
Frequently Flooded Areas/Areas of Special Flood Hazards
Reprinted from
Floodplain Management: A Local Administrator's Guide to the National Flood
Insurance Program, FEMA Region 10
B.
Additional Critical Areas Report Requirements.
In addition to the Critical Areas Report requirements in VMC 20.740.050, the following
information shall be submitted. Elevation data shall reference the NAVD 1988 Datum.
1. Base (100-year) flood elevation in relation to mean
sea level. When base flood elevation
has not been provided or is not available from an authoritative source, it shall be generated by the
applicant for developments which contain at least 50 lots or 5 acres, whichever is less.
2. Elevation in relation to mean sea level, of the lowest
floor (including basement) of all
existing and proposed structures.
3. Elevation in relation to mean sea level to which any
structure’s lowest floor (including
basement) is raised to be at least 1 foot above the base flood elevation or for non-residential
flood-proofed structures, the elevation in relation to mean sea level to which any structure is
flood-proofed.
4. Description of strategies taken to avoid, minimize,
and mitigate unavoidable impacts to
public safety. When the base flood elevation has not been provided or is not available from an
authorized source (VMC 20.740.120A), the Critical Areas Report shall include a discussion of
how and whether the proposed development would be reasonably safe from flooding. Historical
data, high water marks, photographs of past flooding and other available information will be used
as the basis for this discussion and conclusion.
5. Certification, documentation, and demonstration by
a qualified professional of how the
applicable standards of VMC 20.740.120(C) will be met. To support the “no rise” analyses
required in VMC 20.740.120(C)(1), the documentation required in the most recently updated or
amended FEMA Region 10 publication,
Floodplain Management: A Local Floodplain
Administrator’s Guide to the National Flood Insurance Program shall be submitted.
C.
Performance Standards.
Except as noted, the following standards apply to all structures and development (including
substantial improvement, roads, railroads, trails, dikes, levees, or water, sewer, stormwater
conveyance, gas, power, cable, fiber optic or telephone facilities) in all frequently flooded areas.
1. Maintaining Equilibrium.
a. No Designated
Floodway. In areas where the base flood elevation has been provided
(Zones A1-30, AE, AH, or AO), but a regulatory floodway has not been designated, no new
construction, substantial improvement, or other development (including fill) shall be permitted,
unless the applicant has 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 one foot at any point.
b. Floodway.
Encroachments, including fill, new construction, replacement structures,
substantial improvements and other development shall be prohibited unless certification by a
qualified professional (in this case, a registered professional engineer) is provided demonstrating
through hydrologic and hydraulic analyses performed in accordance with standard engineering
practice that the proposed encroachment would not result in a net increase in base flood elevation
or flood velocity during the occurrence of the base flood discharge. At a minimum, such “no
rise” analyses shall include a step-backwater analysis and a conveyance compensation analysis as
required in the most recently updated or amended FEMA Region 10 publication,
Floodplain
Management: A Local Floodplain Administrator’s Guide to the National Flood Insurance
Program.
c. Flood Fringe.
Encroachments, including fill, new construction, replacement structures,
substantial improvements and other development shall be prohibited unless a qualified
professional provides certification demonstrating that the proposed project would not result in a
net loss of flood storage capacity.
2. Elevation.
a. Residential Construction. The
lowest floor (including basement) of new residential
structures (including reconstruction) shall be elevated at least 1 foot above base flood elevation.
Structures shall be elevated using means other than fill (such as extended foundation or other
enclosure walls, piles, or columns) whenever feasible.
b. Non-Residential Construction. New
construction and substantial improvement of any
nonresidential structure shall either:
1. Have the
lowest floor, including basement, elevated at least one foot above the base
flood elevation; or
2. Together
with attendant utility and sanitary facilities, shall:
a. Be flood-proofed so that below the level of the lowest floor, 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 Planning Official as set
forth in VMC 20.740.120(E);
d. Nonresidential structures that are elevated, not flood-proofed, must meet the same
standards for space below the lowest floor as described in 20.740.120(C)(5)(e).
c. In areas where the base flood elevation
has not been provided or is not available from an
authorized source (VMC 20.740.120(A) and .120(B)(4)) and the Critical Areas Report
demonstrates to the satisfaction of the Planning Official that the proposed development would be
reasonably safe from flooding, new residential construction and new non-residential construction
that is elevated should be elevated at least 2’ above the highest adjacent grade. Failure to elevate
at least 2’ above the highest adjacent grade may result in higher insurance rates.
3. Enclosed Areas Below the Base Flood Elevation. When
non-fill means of elevation results
in enclosed areas below the base flood elevation, or where existing structures contain enclosed
areas below the base flood elevation:
a. Enclosed areas below the base flood elevation shall be used only for vehicle parking,
building
access, or storage.
b. New or substantially improved enclosed areas below the base flood elevation shall
be
constructed in accordance with VMC 20.740.120(C)(5)(e).
c. Enclosed areas below the base flood elevation shall not be considered to be the lowest
floor
when they are not part of a basement and are newly constructed or substantially improved in
accordance with VMC 20.740.120(C)(5)(e) or were previously constructed in accordance with
the following criteria:
1. Contain a minimum of 2 openings having a total net area of
not less than 1 square inch for
every 1 square foot of enclosed area subject to flooding;
2. The bottom of all openings are no higher than 1 foot above
grade; and
3. Openings permit the automatic entry and exit of floodwaters
even when equipped with
screens, louvers, or other coverings or devices.
d. Crawlspace Construction. Crawlspaces shall not be considered
“basements” for the
purposes of VMC 20.740.120 when constructed according to the following standards. Note that
insurance premiums for structures with below-grade crawlspaces will be higher than those with
the interior elevation at or above the lowest adjacent exterior grade. Crawlspaces constructed at
or above the lowest adjacent exterior grade are preferred. Refer to FEMA Technical Bulletin 11-01, Crawlspace Construction for Buildings Located in Special Flood Hazard Areas (available
from the Planning Official) for more information.
1. All crawlspaces (those at or above the lowest adjacent exterior grade or below grade)
shall be
constructed according to the following standards:
a. The building must be designed and
adequately anchored to resist flotation, collapse, and
lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including
the effects of buoyancy. (Hydrostatic loads and the effects of buoyancy can usually be addressed
through the required openings discussed in VMC 20.740.120(C)(3)(d)(1)(B).) Because of
hydrodynamic loads, crawlspace construction is not recommended in areas with flood velocities
greater than 5’ per second unless the design is reviewed by a qualified design professional, such
as a registered architect or professional engineer. Other types of foundations are recommended
for these areas.
b. The crawlspace must have openings
that equalize hydrostatic pressures by allowing for
the automatic entry and exit of floodwaters. The bottom of each flood vent opening can be no
more than 1’ above the lowest adjacent exterior grade. For guidance on flood openings, see
FEMA Technical Bulletin 1-93,
Openings in Foundation Walls.
c. Portions of the building below the
base flood elevation must be constructed with
materials resistant to flood damage. This includes not only the foundation walls of the
crawlspace used to elevate the building, but also any joists, insulation, or other materials that
extend below the base flood elevation. The recommended construction practice is to elevate the
bottom of joists and all insulation above the base flood elevation. For more detailed guidance on
flood-resistant materials see FEMA Technical Bulletin 2-93,
Flood-Resistant Materials
Requirements.
d. Any building utility systems within
the crawlspace must be elevated above the base flood
elevation or designed so that floodwaters cannot enter or accumulate within the system
components during flood conditions. Ductwork, in particular, must either be placed above the
base flood elevation or sealed from floodwaters. For further guidance on the placement of
building utility systems in crawlspaces, see FEMA Publication #348,
Protecting Building
Utilities from Flood Damage.
2. Additional standards for constructing
below-grade crawlspaces:
a. The interior grade of a crawlspace
below the base flood elevation must not be more than
2’ below the lowest adjacent exterior grade.
b. The height of the below-grade crawlspace,
measured from the interior grade of the
crawlspace to the top of the crawlspace foundation wall must not exceed 4’ at any point.
c. Provide an adequate drainage system
that removes floodwaters from the interior area of
the crawlspace.
d. The velocity of floodwaters at the
site should not exceed 5’ per second for any
crawlspace. For velocities in excess of 5’ per second, other foundation types should be used.
4. Property Damage. Development shall not result in adverse
impacts to other properties
either upstream or downstream.
5. Construction Materials and Methods.
a. Construction methods and practices shall minimize flood damage.
b. Construction materials and utility equipment shall be resistant
to flood damage.
c. All structures and development shall be elevated on a permanent
foundation and securely
anchored to an adequate foundation system to prevent flotation, collapse, or lateral movement
and shall be installed or placed using methods and practices that minimize flood damage. For
manufactured homes (mobile, modular, designated, and new) follow the guidance in FEMA-85,
Manufactured Home Installation in Flood Hazard Areas.
d. 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 a base flood event.
e. Fully enclosed areas below the lowest floor that are subject
to flooding are prohibited unless
designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the
entry and exit of flood waters. Designs for meeting this requirement must be certified by a
qualified professional (in this case, a registered professional engineer or architect).
6. Drainage. Drainage paths around structures and on slopes
shall be adequate to guide
floodwaters around and away from proposed structures and adjacent properties.
7. Water.
a. Water wells are prohibited in the
floodway. In the flood fringe, water wells shall be
constructed to withstand a 100-year flood without adversely impacting groundwater quality
(WAC 173-160-171).
b. All new and replacement water
supply systems shall be designed to minimize or
eliminate infiltration of flood waters into the system.
8. Waste.
a. New and replacement
sanitary sewage systems shall be designed to minimize or
eliminate infiltration of flood waters into the systems and discharge from the systems into flood
waters.
b. On-site waste
disposal systems are prohibited in the floodway. In the flood fringe they
shall be located to avoid flood damage to them or release of contaminants from them during a
base flood event.
9. Subdivisions.
a. All subdivisions
shall be designed:
1. To ensure that no structures for human habitation are located in the floodway even
though lots may extend into the floodway;
2. To avoid placement of any structures in the flood fringe;
3. Where it is not possible to design a subdivision in a manner to avoid placement of
any structures in the flood fringe, the subdivision shall be designed to minimize potential flood
damage.
b. All subdivisions shall have facilities
such as sewer, gas, power, cable, fiber optic,
telephone, stormwater and water systems located and constructed to minimize flood damage.
c. All subdivisions shall have adequate drainage provided to
reduce exposure to flood damage.
10. Residential Development.
a. In the Floodway.
1. New construction or reconstruction
of residential structures including placement of
manufactured homes(mobile, modular, designated, and new) and other structures for human
habitation is prohibited.
2. Existing residential structures
are non-conforming (see VMC 20.740.120(C)(14)), but
may be repaired or improved, provided:
a.
The repair or improvement does not increase the ground floor area of the
structure; and
b.
The repair or improvement does not result in adverse impacts to other properties
either upstream or downstream; and
c.
The cost of the repair or improvement does not exceed 50% of the market value of
the structure either:
i.
Before the start of repair or improvement where there is no damage to the
structure; or
ii.
Before flood or other damage to the structure occurred.
b. In the Flood Fringe. New construction,
reconstruction, repair, or improvement of
residential structures including placement of manufactured homes (mobile, modular, designated,
and new) and other structures for human habitation may be allowed in the flood fringe.
1. New Construction and Reconstruction.
New residential construction and reconstruction
shall meet all the provisions of this chapter, including the elevation standards of VMC
20.740.120(C)(2) and (3). In particular, manufactured home development must meet the
standards of VMC 20.740.120(C)(5)(c).
2. Repair or Improvement. All
provisions of this chapter (including the elevation standards
of VMC 20.740.120(C)(2) and (3)), all state and local health, sanitary, safety codes, and where
applicable, historic preservation codes shall be met when the cost of repair or improvement of an
existing residential structure exceeds 50% of the market value of the structure either:
a. Before the
start of repair or improvement where there is no damage to the structure; or
b. Before flood
or other damage to the structure occurred.
11. Recreational Vehicles. Recreational vehicles shall
be located outside the floodway and
shall either:
a. Be on the
site for fewer than 180 consecutive days;
b. Be fully
licensed and ready for highway use, on its wheels or jacking system, attached
to the site only by quick disconnect-type water, sewer, stormwater, gas, power, cable, fiber optic,
telephone, and security devices, and have no permanently attached additions; or
c. Meet the
requirements of VMC 20.740.120(C)(2) and (3) and (C)(5)(c).
12. Critical Facilities. Critical facilities housing vulnerable
populations and emergency
services shall be prohibited in the floodway. In the flood fringe, construction of new critical
facilities shall be prohibited unless the applicant demonstrates that no feasible alternative site is
available; and either:
a. The lowest
floor, entrances, egresses, and to the extent feasible access routes are
elevated to 3 feet above the base flood elevation or to the elevation of the 500-year flood,
whichever is lower; or
b. The applicant
demonstrates that other measures would ensure that in the event of a
flood, the facility would remain safe and fully operational and that potentially harmful materials
would not be displaced by or released into floodwaters. Such measures shall be conditions of
approval of the Critical Areas Permit.
13. Alteration of Watercourse.
a. The planning official shall notify
adjacent communities and the state coordinating agency,
Washington State Department of Ecology, prior to any alteration or relocation of a watercourse,
and submit evidence of such notification to the Federal Insurance Administration.
b. Alteration or relocation of a watercourse
shall be allowed only after:
1. Certification by a qualified professional that the
alteration or relocation:
a. Is the only feasible alternative
or is part of a restoration project approved by the
appropriate state or federal agencies;
b. Will not diminish the flood-carrying
capacity of the watercourse;
c. Will not block side channels;
d. Will be accomplished using soft armoring
techniques wherever possible;
e. Will avoid to the extent possible
and then minimize and mitigate removal of vegetation
including downed woody vegetation; and
2. The applicant provides assurance
acceptable to the planning official of maintenance of
the relocated channel such that the flood carrying capacity of the watercourse is not diminished.
14. Floodway Development.
a. Structures for Human Habitation.
Structures for human habitation are prohibited in the
floodway. Such structures include but are not limited to residential development (See VMC
20.740.120(C)(10)), development sites within subdivisions, recreational vehicles, and critical
facilities housing vulnerable populations or emergency services.
b. On-Site Waste Disposal Facilities.
New on-site waste disposal facilities are prohibited in
the floodway.
c. Other Development in the Floodway.
Where other development is allowed in the
floodway under VMC 20.740.120(C)(1), the standards of VMC 20.740.120(C)(2)-(13) shall also
apply.
D.
Minor Exceptions.
The applicant may seek a minor exception from the standards required for development
in
frequently flooded areas. Minor exceptions as interpreted in the National Flood Insurance
Program are based on the principle that they pertain to a physical piece of property. Such minor
exceptions apply to the land and are not personal in nature, do not pertain to the structure, its
inhabitants, or economic or financial circumstances.
In addition to the standards contained herein, minor exceptions for development in frequently
flooded areas shall be processed as Type II decisions in accordance with the provisions of VMC
20.740.070(A), except that minor exceptions to the elevation standards may exceed the 10%
limit.
1. Minor Exception Allowed for Historic Structures. Minor
exceptions 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 complying with the provisions
of VMC 20.740.120(D)(2) and (D)(3). Any such minor exception shall be documented in
accordance with the provisions of VMC 20.740.120(D)(4) and 20.740.120(E)(2).
2. Factors to Consider. The following factors shall be
considered in determining whether to
grant a minor exception:
a. The danger that materials may be swept onto other lands to
the injury of others;
b. The danger to life and property due to flooding or erosion
damage;
c. The susceptibility of the proposed facility and its contents
to flood damage and the effect of
such damage on the individual owner;
d. The importance of the services provided by the proposed facility
to the community;
e. The necessity to the facility of a waterfront location, where
applicable;
f. The availability of alternative locations for the proposed
use which are not subject to
flooding or erosion damage;
g. The compatibility of the proposed use with existing and anticipated
development;
h. The relationship of the proposed use to the comprehensive
plan;
i. The safety of access to the property in times of flood for
ordinary and emergency vehicles;
j. 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; and
k. The costs of providing governmental services during and after
flood conditions, including
maintenance and repair of facilities such as sewer, gas, electrical, stormwater, and water systems,
and streets and bridges.
3. Minor Exception Approval Criteria. A minor exception
for development in frequently
flooded areas may be granted only if the applicant demonstrates that the requested action
conforms to all of the general minor exception approval criteria set forth in VMC 20.740.070(B)
and the following additional criteria:
a. Demonstration that the factors set forth in VMC 20.740.120(D)(2) have been considered.
b. Granting the minor exception will not result in increased flood heights or velocities,
additional
threats to public safety, significantly increased property damage potential, extraordinary public
expense, or conflict with existing local laws or ordinances.
4. Notices Required when Minor Exception Approved.
a. Minor Exception to the Elevation Standard. The planning official shall issue a written
notice to
any applicant to whom a minor exception to the elevation standard is granted that the structure
will be permitted to be built with a lowest floor elevation below that normally required with
respect to 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.
b. Minor Exception for Historic Structures. The planning official shall issue a written
notice to
any applicant to whom a minor exception is granted under VMC 20.740.120(D)(1) that the minor
exception was granted and the reasons for which it was granted.
E.
Information to be Obtained and Maintained.
1. For all new and substantially improved structures and
development, the planning official
shall complete Section B of a current elevation certificate and obtain and record on that
certificate:
a. For elevated (rather than flood-proofed) structures and development, the actual (as-built)
elevation in relation to mean sea level of the lowest floor (including basement), and whether or
not the structure contains a basement.
b. For non-residential, flood-proofed structures, the elevation to which the structure
was flood-proofed. All flood-proofing certifications shall also be maintained.
c. Maintain all records pertaining to development in frequently flooded areas subject
to the
provisions of this chapter, VMC 20.740, for public inspection.
2. Records of Minor Exception Actions. The planning official
shall keep records of all minor
exception actions and report any approved minor exceptions to the Federal Insurance
Administration upon request.
3. Records of Appeal Actions. The planning official shall
keep records of all appeal actions.
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