HomeMy WebLinkAboutORD 4071 . . ' . . .
Amends Ordinance No. 3537, 3592
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CITY OF RENTON, fnTASHINGTON �f`�'S�
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ORDINANCE N0. 4071 �1y3
AN ORDINANCE OF THE CITY OF RENTON , WA�HINGTON
AMENDING SECTION 4-735 OF TITLE IV (BUILDING
REGULATIONS ) OF ORpINANCE N0. 1628 ENTITLED "CODE
OF GENERAL ORDINANCES OF THE CITY OF RENTON"
RELATING TO FLOOD HAZARD, DEFINING FLOOD HAZARD
AREAS , GIVI�iG AUTHORITY TO DEFINE THE LIMITS OF
THE FLOODWAY AND FLOODWAY FRINGE, PRESCRIBING LAND
USE R�GULATIONS WITHIN FLOOD HAZARD AREAS , AND
PRESCRIBING A PENALTY.
THE CITY COUNCIL OF THE CITY OF RENTON , WASHINGTON does
ordain as follows:
SECTION I : Existing Section 4-736 of Title IV (Building
Regulations of Ordinance No. 1628 entitled "Code of General
Ordinances of the City of Renton" is amendec� to read as follows:
A. FINDINGS OF FACT: The City Council of the City Renton
finds that:
1 . The flood hazard areas of the City of Renton are
subject to periodic inundation which results in loss of
life and property , health , and safety hazards ,
disruption of commerce and governmental services ,
extraordinary public expenditures for flood protection
and relief , and impairment of the tax base, all of
which adversely affect the public health , safety, and
general welfare.
2. These flood losses are caused by the cumulative effect
of obstructions in areas of special flood hazards which
increase flood heights and velocities , and when
inadequately anchored , damage us�s in other areas .
Uses that are inadequately floodproofed, elevated , or
otherwise protected from flood damage also contribute
to the flood loss.
B. STATEMENT OF PURPOSE : It is the purpose of this
ordinance to promote the public health , safety , and general
welfare, and to minimize public and private losses due to flood
conditions in specific areas by provisions designed:
1 . To protect human life and health;
2. To zninimize expenditure of public anoney and costly
flood control projects;
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ORDINANCE N0. 4071
3 . To minimize the need for rescue and relief efforts
associated with flooding and generally undertaken at
the expense of the general public;
4. To minimize prolonged business interruptions;
5. To minimize damage to nublic facilities and utilities
such as water and gas mains, electric , telephone and
sewer lines, streets , and bridges located in areas of
special flood hazard;
6. To help maintain a stable tax base by providing for the
sound use and development of areas of special flood
hazard so as to minimize future flood blight areas;
7. To ensure that potential buyers are notified that
property is in an area of special flood hazard; and,
8. To ensure that those who occupy the areas of special
flood hazard assume responsibility for their actions.
C. METHODS OF REDUCING FLOOD LOSSES : In order to
accomplish its purposes , this ordinance includes methods and
provisions for :
l. Restricting or prohibiting uses which are dangerous to
health, safety, and property due to water or erosion
hazards, or which result in damaging increases in
erosion or in flood heights or velocities;
2. Requiring that uses vulnerable to floods, including
facilities which serve such uses, be protected against
flood damage at the time of initial construction;
3 . Controlling the alteration of natural flood plains ,
stream channels , and natural protective barriers, which
help accommodate or channel flood waters ;
4. Controlling filling , grading , dredging , and other
development which may increase flood damage; and
5. Preventing or regulating the construction of flood
barriers which will unnaturally divert flood waters or
may increase flood hazards in other areas.
D. DEFINITIONS: Unless specifically defined below, words
or phrases used in this ordinance shall be interpreted so as to
give them the meaning they have in common usage and to give this
ordinance its most reasonable application.
1. "Appeal " means a request for a review of any action
pursuant to this ordinance, or of the interpretation of
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ORDINANCE NO. 4071
any provision of this ordinance by any �ity official.
The provisions of Chapter 30 , Title IV shall apply.
2. "Area of Shallow Flooding" means a designated AO or AH
Zone on the Flood Insurance Rate Map (FIRM) . The base
flood depths range from one to three feet ; a clearly
defined channel does not exist; the path of flooding is
unpredictable and indeterminate; and, velocity flow may
be evident. AO is characterized as sheet flow and AH
indicates ponding.
3. "Area of Special Flood Hazard" means tk�e land in the
flood plain within a community subject to one percent
or greater chance of flooding in any given year .
Designation on maps always includes the letters A or V.
4. "Base Flood" means the flood having a one percent
chance of being equalled or exceeded in any given year .
Also referred to as the "100-year flood" . Design�tion
on maps always includes the letters A or V.
5. "Development" means any man-made change to improved or
unimproved real estate, including but not limited to
buildings or other structures , mining , dredging ,
filling , grading , paving , excavation or drilling
operations located within the are� of special flood
hazard.
6. "Flood" or "Flood ing" means a general an�l temporary
condition of partial or complete inundation of normally
dry land areas from:
(a) The overflow of inland or tidal waters and/or
(b) The unusual and rapid accumul�ation of runoff of
surface waters from any source.
7. " Flood Insurance Rate Map (FIRM) " means the official
map on which the Federal Insurance Administration has
delineated both the areas of special flood hazards and
the risk premium zones applicable to the community.
8. " Flood Insurance Study" means the official report
provided by the Federal Insurance Administration that
includes flood profiles , the Flood Boundary-Floodway
Map, and the water surface elevation of the base flood .
9. " Floodway" means the channel of a river or other
watercourse and the adjacent land areas that must be
reserved in order to discharge the base flood without
cumulatively increasing the water surface elevation
more than one foot.
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ORDINANCE NO. 4071
10. "Lowest rloor " means the lowest floor of the lowest
enclosed area ( including basement) . An unfinished or
flood resistant enclosure, usable solely for parking of
vehicles, building access or storage, in an area other
than a basement area, is not considered a building ' s
lowest floor , provided that such enclosure is not built
so as to render the structure in violation of the
applicable non-elevation design require?nents of this
ordinance found at Subsection G. 2.a. ii.
11. "Manufactured Home" means a structure, transportable in
one or znore sections , which is built on a permanent
chassis and is designed for use with or without a
permanent foundation when connected to the required
utilities. For flood plain management purposes the
term "manufactured home" also includes park trailers,
travel trailers, and other similar vehicles placed on a
site for greater than 180 consecutive days . For
insurance purposes the term "manufactured home" does
not include park trailers, travel trailers, and other
similar vehicles.
12. "Manufactured Home Park or Subdivision" means a parcel
( or contiguous Parcels ) of land divided into two or
more m�nufactured home lots for rent or sale.
13. "New Construction" means structures for which the
"start of construction" commenced on or after the
effective date of this ordinance.
14. "Start of Construction" includes substantial improve-
ment , and means the date the building permit was
issued , provided the actual start o� construction,
repair , reconstruction, placement or other improvement
was within 180 days of the permit date . The actual
start means either the first placement of permanent
construction of a structure on a site , such as the
pouring of slab or footings, the installation of piles,
the construction of columns , or any work beyond the
stage of excavation; or the placement of a manufactured
home on a foundation. Permanent construction does not
include land preparation, such as clearing , grading and
filling : nor does it include the installation of
streets and/or walkways; nor does it include excavation
for a basement, footings, piers, or foundation or the
erection of temporary forms; nor does it include the
installation on the property of accessory buildings ,
such as garages or sheds not occupied as dwelling units
or not part of the main structure.
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ORDINANCE N0. 4071
15 . " Structure " means a walled and roofed building
including a qas or li�uid storage tank that is
principally above ground.
16. " Substantial Improvement " zneans any repair ,
reconstruction, or improvement of a structure, the cost
of which equals or exceeds 50 percent of the market
value of the structure either :
a. Before the improvement or repair is started , or
b. I f the structure has been damaged and is being
restored , before the damage occurred . For the
purposes of this definition " substantial
improvement" is considered to occur when the first
alteration of any wall , ceiling , floor , or other
structural part of the building commences, whether
or not that alteration affects the external
dimensions of the structure.
The term does not , however , include either ( 1 ) any
project for improvement of a structure to comply with
existing state or local health , sanitary, or safety
code specifications which are solely necessary to
assure safe living conditions, or ( 2 ) any alteration of
a structure listed on the National Register of Historic
Places or � State Inventory of Historic Places.
17. " Variance " means a grant of re1 ief f rom the
requirements of this ordinance which permits
construction in a manner that would otherwise be
prohibited by this ordinance.
E. GENERAL PROVISIONS:
l. LANDS TO WHICH THIS ORDINANCE APPLIES: This ordinance
shall apply to all areas of special flood hazards
within the jurisdiction of the City of Renton.
2. BAS IS FOR ESTABLIS�iING THE AREAS OF Special FLOOD
HAZARD: The areas of special flood hazard identified
by the Federal Insurance Administration in a scientific
and engineering report entitled "The Flood Insurance
Study for the City of Renton," dated May 5, 1981 , with
accompanying Flood Insurance Maps is hereby adopted by
reference and declared to be a part of this ordinance.
The Flood Insurance Study is on file at the Building
and Zoning Department , 200 Mill Ave . So. , Renton ,
Washington 98055.
3. PENALTIFS FOR NONCOMPLIANCE : No structure or land
shall hereafter be constructed , located , extended ,
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ORDINANCE NO. 4071
converted, or altered without full compliance with the
terms of this ordinance and other applicable
regulations . Violation of the provisions of this
ordinance by failure to comply with any of its
requirements ( including violations of conditions and
safeguards established in connection with conditions )
shall constitute a misdemeanor . Any person who
violates this ordinance or fails to comply with any of
its requirements shall upon conviction thereof be fined
not more than Five Hundred Dollars ( $500 . 00 ) or be
imprisoned for not more than 180 days, or both, for
each violation, and in addition shall pay all costs and
expenses involved in the case . Nothing herein
contained shall prevent the City of Renton from taking
such other lawful action as is necessary to �revent or
remedy any violation.
4. ABROGATION AND GREATER RESTRICTIONS: This ordinance is
not intended to repeal , abrogate , or impair any
existing easements , covenants, or deed restrictions.
However , where this ordinance and another ordinance ,
easement , covenant , or deed restriction conflict or
ov�rlap , whichever imposes the more stringent
restrictions shall prevail .
5. INTERPRETATION: In the interpretation and application
of this ordinance, all provisions shall be:
a. Considere�l as minimum requirements ;
b. Liberally construed in favor of the governing
body; and,
c. Deemed neither to limit nor repeal any other
powers granted under State statutes.
6. WARNING AND DISCLAIMEk2 OF LIABILITY: The degree of
flood protection required by this ordinance is
considered reasonable for regulatory purposes an� is
based on scientific and engineering considerations .
Larger floods can and will occur on rare occasions.
Flood heights may be increased by man-made or natural
causes . This ordinance does not imply that land
outside the areas of special flood hazards or uses
permitted within such areas will be free from flooding
or flood damages . This ordinance shall not create
liability on the part of the City of Renton , any
officer or employee thereof, or the Federal Insurance
Administration, for any flood damages that result from
reliance on this ordinance or any administrative
decision lawfully made hereunder .
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ORDI�ANC� N0. 4071
F. ADMINISTRATION:
1. ESTABLISHMENT OF DEVELOPMENT PERMIT:
a. Development Permit Required: A development permit
shall be obtained before construction or
development begins within any area of special
flood hazard established in Subsection E. 2 above.
The permit shall be for all structures including
manufactured homes , as set forth in the
"DEFINITIONS" , and for all development including
fill and other activities, also as set forth in
the "DEFINITIONS" .
b. Application for Development Permit: Application
for a development permit shall be made on forms
furnished by the Building and Zoning Department
and may include, but not be limited to: plans in
duplicate drawn to scale showing the nature ,
location, dimensions, and elevations of the area
in question; existing or proposed structures ,
fill , storage of materials, drainage facilities,
and the location of the foregoing. Specifically,
the following information is required:
i. Elevation in relation to mean sea level of
the lowest floor ( including basement) of all
structures;
ii. Elevation in relation to mean sea level to
which any structure has been floodproofed;
iii. Certification by a registered professional
engineer or architect that the floodproofing
methods for any nonresidential structure meet
the floodproofing criteria in Subsection
G. 2.b; and
iv. Description of the extent to which a
watercourse will be altere�l or relocated as a
result of proposed development.
2. DESIGIVATION OF THE LOCAL ADMINISTRATOR: The Director
of the Building and Zoning Department ( "Building
Official " ) is hereby appointed to administer and
implement this ordinance by granting or denying
development permit applications in accordance with its
provisions.
3. DUTIES AND RESPONSIBILITIES OF THE BUILDING OFFICIAL:
The duties of the Buildinq Official shall include , but
not be limited to:
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ORDINANCE NO. 4071
a. Permit Review:
i. Review all development permits to determine
th�t the permit reguirements of this
ordinance have been satisfied;
ii. Review all development permits to determine
that all necessary permits have been obtained
from those Federal , State , or local
governmental agencies from which prior
approval is required;
iii. Review all development permits to deter�nine
if the proposed development is located in the
floodway. If located in the floodway, to
assure that the encroachment provisions of
Subsection G. 3.a. are met.
b. Use of Other Base Flood Data: When base flood
elevation data has not been provided in accordance
with Subsection E. 2. , 13ASIS FOR ESTABLISHING THE
AREAS OF SPECIAL FLOOD HAZARD , the Building
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 Subsections G. 2. , SPECIFIC
STANDARDS , and G. 3. , FLOODWAYS .
c. Information to be Obtained and Maintained:
i. Where base flood elevation data is provided
throuqh the Flood Insurance Study or required
as in Subsection F. 3.b. , obtain and record
the actual elevation ( in relation to mean sea
level ) of the lowest floor ( including
basement ) of all new or substantially
improved structures, and whether or not the
structure contains a basement.
ii. For all new or substantially improved
floodproofed structures:
(A) Verify and record the actual elevation
( in relation to mean sea level) , and
(B) Mainta in the f_ loodproofing
certifications required in Subsection
F. l.b. iii .
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ORDINANCE N0. 4071
iii . Maintain for public inspection all records
pertaining to the provisions of this
ordinance.
d. Alteration of Watercourses:
i. Notify adjacent communities and the State of
Washington Department of Ecology prior to any
alteration or relocation of a watercourse,
and submit evidence of such notification to
the Federal Insurance Administration.
ii. Require that maintenance is provided within
the altered or relocated portion of said
watercourse so that the flood carrying
capacity is not diminished.
e. Interpretation of FIRM Boundaries : Make
interpretations where needed , as to exact location
of the boundaries of the areas of special flood
hazards ( for example, where there appears to be a
conflict between a mapped boundary and actual
field conditions ) . The person contesting the
location of the boundary shall be given a
reasonable opportunity to appeal the
interpretation as provided in Subsection F. 4.
4. APPEALS; VARIANCE PROCEDURE:
a. Variances:
i. The Board of Adjustment or the Hearing
Examiner , whichever is afforded jurisdiction
under the provisions of Section 4-722 (G) of
the City Code , as amended , shall k�ear and
decide appeals and requests for variances
from the requirements of this ordinance.
ii. In passing upon such an application for a
variance, the Hearing Examiner or Board of
Adjustment , as the case �nay be , shall
consider all technical evaluations , all
relevant factors , standards specified in
other sections of this ordinance , and:
(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;
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ORDINANCE N0. 4071
(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 provide
by the proposed facility to the
community:
(E ) The necessity to the facility of a
waterfront location, where anplicable;
(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 and f lood plain
management prograrn for that area;
(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 public utilities and
facilities such as sewer , gas ,
electrical , and water systems , and
streets and bridges.
iii. Upon consideration of the factors of
Subsection F. 4.a. i. above, and the purposes
of this ordinance , the Hearing Examiner or
Boarc� of Adjustment, as the case may be, may
attach such conditions to the granting of
variances as it deems necessary to further
the purposes of this ordinance.
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ORDINANCE N0. 4071
b. Conditions for Variances:
i. Generally, the only condition under which a
variance from the elevation standard may be
issued is for new construction and
substantial improvements to be erected on a
lot of one- half acre or less in size
contiguous to and surrounded by lots with
existing structures constructed below the
base flood level , providing items (A) - (K )
in Subsection F . 4 . a . iv . have been fully
considered . As the lot size increases the
technical justification required for issuing
the variance increases.
ii. Variances may be issued for the recon-
struction, rehabilitation, or restoration of
structures listed on the National Register of
Historic Places or the State Inventory of
Historic Places , without regard to the
procedures set forth in this section.
iii. Variances sha11 not be issued within a
designated floodway if any increase in flood
levels during the base flood discharge would
result.
iv. Var iances shall only be issued upon a
determination that the variance is the
minimum necessary, considering the flood
hazard, to afford relief.
v. Variances shall only be issued upon:
(A) A showing of good and sufficient cause;
(B) A determination that failure to grant
the variance would result in exceptional
hardship to the applicant;
(C) A determination that the granting of a
variance will not result in increased
flood heights , additional threats to
public safety , extraordinary public
expense , create nuisances, cause fraud
on or victimization o.f the public or
conflict with existing local laws or
or�inances.
vi. Variances as interpreted in the National
Flood Insurance Program are based on the
general zoning law principle that they
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ORDINANCE N0. 4071
pertain to a physical piece of property; they
are not personal in nature and do not pertain
to the structure, its inhabitants , economic
or financial circumstances. They primarily
address small lots in densely populated
residential neighborhoods . As such ,
variances from the flood elevations should be
quite rare.
vii. Variances may be issued for nonresidential
buildings in very li�ited circumstances to
allow a less�r degree of floodproofing than
watertight or dry-floodproofing , where it can
be determined that such action will have low
damage potential , complies with all other
variance criteria except Subsection F. 4.b. i. ,
and otherwise complies with Subsections
G.l .a. and G. l .b. of the �ENERAL STANDARDS
viii.Any applicant to whom a variance is granted
shall be given written notice that the
structure will be permitted to be built with
a lowest floor elevation below 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.
c. Appeals : Pursuant to Chapter 30 , Title IV, of the
City Code, the Hearing Examiner shall hear and
decide appeals when it is alleged there is an
error in any requirement, decision , or determi-
nation made by the Building Official in the
enforcement or administration of this ordinance.
d. Writ of 12eview: Those aggrieved by any decision
of either the Hearing Examiner or Board of
Adj ustment pursuant to this Subsection E. 4. , or
any taxpayer , may , within twenty ( 20 ) calendar
days from the day of the decision, obtain a writ
of certiorari from the King County Superior Court
for the purpose of review of the action taken.
e. Records: The Building Official shall maintain the
records of all appeal actions and report any
variances to the Federal Insurance Administration
upon request.
G. PROVISIONS FOR FLOOD HAZARD REDUCTION:
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ORDINANCE NO. 4071
l . GENERAL STANDARDS : In all areas of special flood
hazards, the following standards are require�:
a. Anchor.ing:
i. All new construction and substantial
improvements shall be anchored to prevent
flotation , collapse, or lateral movement of
the structure.
ii. All manufactured homes must likewiae be
anchored to prevent flotation , collapse or
lateral movement , and shall be installed
using methods and practices that minimize
flood damage. Anchoring methods may include,
but are not limited to, use of over-the-top
or frame ties to ground anchors ( Reference
FEMA ' s "Manufactured Home Installation in
Flood Hazard Areas" guidebook for additional
techniques) .
b. Construction Materials and Methods :
i. All new construction and substantial
improvements sha11 be constructed with
materials and utility equipment resistant to
flood damage.
ii. All new construction and substantial
improvements shall be constructed usinq
methods an� practices that minimize flood
damage.
iii. Electrical , heating , ventilation , plumbin� ,
and air-conditioning equipment and other
service facilities shall he designed and/or
otherwise elevated or located so as to
prevent water from entering or accumulating
within the components during conditions of
flooding .
c. Utilities:
i. Al1 new and replacement water supply systems
shall be designed to minimize or eliminate
infiltration of .flood waters into the system;
ii. New and replacement sanitary sewage systems
shall be designed to mini�nize or eliminate
infiltration of flood waters into the systems
and discharge from the systems into flood
waters; and
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ORDINANCE N0. 4071
iii . On-site waste disposal systems shall be
located to avoid impairment to them or
contamination from them during flooding .
d. Subdivision Proposals :
i. All subdivision proposals shall be consistent
with the need to minimize flood damage;
ii. All subdivision proposals shall have public
utilities and facilities such as sewer , gas,
electrical , and water systems located and
constructed to minimize flood damage;
iii. Al1 subc3ivision proposals shall have adeguate
drainage provided to reduce exposure to flood
damage; and
iv. Where base flood elevation data has not been
provided or is not available from another
authoritative source, it shall he generated
for subdivision proposals and other proposed
developments which contain at least 50 lots
or 5 acres (whichever is less) .
e. Review of Building Perznits : Where elevation data
is not available either through the Flood
Insurance Study or from another authoritative
source (Subsection F. 3 .b . ) , applications for
building permits shall be reviewed to assure that
proposed construction will be reasonably safe from
flooding. The test of reasonableness is a local
judgment and includes use of historical data, high
water marks, photographs of past flooding , etc . ,
where available. Failure to elevate at least two
feet above grade in these zones may result in
higher insurance rates.
2. SPECIFIC STANDARDS : In all areas of special flood
hazards where base flood elevation data has been
provided as set forth in Subsection E. 2. , BASIS FOR
ESTABLISHING THE AREAS OF SPECIAL FLOOD HAZARD , or
Subsection F. 3.b. , Use of Other Base Flood Data, the
following provisions are reguired:
a. Residential Construction:
i. New construction and substantial improvement
of any residential structure shall have the
lowest floor , including basement, elevated to
or above base flood elevation.
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. . .
ORDINANCE N0. 4071
ii . Fully enclosed areas below the lowest floor
that are subject to flooding are prohibited,
or shall be designed to automatically
equalize hydrostatic flood forces on exterior
walls by allowing for the entry and exit of
floodwaters . Designs for meeting this
requirement must either be certified by a
registered professional engineer or architect
or must meet or exceed the following minimum
criteria:
(A) A minimu.m of two (2 ) openings having a
total net area of not less than one
square inch for every square foot of
enclosed area subject to flooding shall
be provided.
(B) The bottom of all openings shall be no
higher than one foot above grade.
(C) Openings may he equipped with screens,
louvers, or other coverings or devices
provided that they permit the automatic
entry and exit of flood�waters.
b. Nonresidential Construction: New construction and
substantial improvement of any commercial ,
industrial or other nonresidential structure shall
either have the lowest floor , including basement,
elevated to the level of the base flood elevation;
or , together with attendant utility and sanitary
facilities, shall :
i. Be floodproofed so that below the base flood
level the structure is watertight with walls
substantially iznpermeable to the passage of
water;
ii. Have structural components capable of
resisting hydrostatic and hydrodynamic loads
and effects of buoyancy;
iii. 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 an� plans.
Such certifications shall be provided to the
Building Official .
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ORDINANCE N0. 4071
iv. Nonresidential structures t�at are elevated,
not floodproofed , must meet the same
standards for space below the lowest floor as
described in Subsection G. 2.a. ii.
v. A�plicants floodproofing nonresidential
buildings shall be notified that flood
insurance premiums will be based on rates
that are one foot below the floodproofed
level ( e .g . , a bui ld ing constructed to the
base flood level will be rated as one foot
below that level) .
c. Manufactured Homes: All manufactured homes to he
placed or substantially improved within Zones A1-
30 , AH , and AE shall be elevated on a permanent
foundation such that the lowest floor of the
manufactured home is at or above the base flood
elevation and be securely anchored to an
adequately anchored foundation system in
accordance with the provisions of Subsection
G. l.a. ii .
3. FLOODWAYS : Located within areas of special flood
hazard established in Subsection E . 2 . are areas
designated as floodways . Since the floodway is an
extremely hazardous area due to the velocity of flood
waters which carry debris , potential projectiles, and
erosion potential , the following provisions apply:
a. Prohibit encroachments , including fill , new
construction, substantial improvements , and other
development unless certification by a registered
professional engineer or architect is provided
demonstrating that encroachments shall not result
in any increase in flood levels during the
occurrence of the base flood discharge.
b. If �ubsection G . 3 . a . is satisfied , all new
construction and substantial improvements shall
comply with all applicable flood hazard reduction
provisions of this ordinance.
SECTION II : Severabilit � : The invalidity or
unconstitutionality of any provision or section of this ordinance
shall not render any other provision or section of this ordinance
unconstitutional or invalid.
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ORDINANCE NO. 4071
SECTIO� III : Effective Date : This ordinance shall be
effective upon its passage , approval and thirty �ays after
publication.
PASSED BY THE CITY COUNCIL on lst day of June , 1987.
��������
Maxine Motor , City Clerk
APPROVED BY THE MAYOR on lst day of June , 1987.
i'
��
��.,-�- �.u/ �� f�.�-C.�r,-3a,,�,,-
Thomas W. Trimm, Mayor Pro tem
Approved as to form:
Lawre e . , i rney
Date of Publication : June 5 , 1987
DK: 03: 4/6/87:dk
17
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CITY OF RENTON, �::�.::.::::.:�:
W A H I `�
S NGTON ���� `�
KING COUNTY
�
:
NOVENIBER 5, 1980
federal emergency management agency
federal insurance administration
COMMUNITY NUMBER-530088
T�BLE OF CONTENTS
Yage
1.0 INTRODUCTION. . . . . � . . . . . . . . . . . . . . . . . . . . . . . . .
y . . . . . . . . . . . . . . . . . . . . . . _l.
1.1 Purpose of Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.
1.2 Coordination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Authority and Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . < . _l
a
2.0 AREA STUDIED. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I
' 2.1 Scope of Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2.2 Community Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3 Principal Flood Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Flood Protection Measures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.0 ENGINEERING M�THODS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Hydrologic Analyses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 Hydraulic Analyses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . e 10
4.0 FLOOD PLAIN MANAGFMENT APPLICATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4,1 F'lood Boundaries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2 Floodways. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . < . . . J.3
5.0 INSURANCE APPLICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1 Reach Determinations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ]_9
5.2 Flood Hazard Factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.3 Flood Insurance Zones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.4 Flood Insurance Rate Map Description. . . . . . . . . . . . . . . . . . . . . . o ?.1
6.0 OTHER STUDIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
s
7.0 LOCATION OF DATA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
8.0 BIBLIOGRAPHY AND REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
i
TABLE OF CQNTEN"rS (Cont'd)
Page
3�IGURES
Fi_gur� ]� - vicinity Nfap. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Figd�re 2 -- F'loodway Schematic, » . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
w
�'ABL�S
Tabl� I - Sununary of d�ischarges. e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
'I'able 2 �- F_Loodway Data. . . . . . . � . . . . . . . . . . . . . . . . . . . . . . . . . . . . o . . . . . . . . . . . 15
Tak�le 3 - F'�c�r�c' In,>urance Zone Data. . . . . . . . . . . . . . . . . . . s . . . . . . . . . . e . . . . . 21
EX�iI B I TS
Exhibit 1 - Flcx�cl Profil.es
Green River Panel O1P
(�eda� River Panels 02P-03P
i�iay C'.�eek Panels 04P-05P
Sprinc}brook Creek Panels 06P-07P
k31a�k River Panel 08P
��nibit 2 - E':Lo�� L3oundary and �']_ooc�way Map Index
I•'lo�� Boundary ai��3 F7_oc�dway Map
r�t�..�z_;f4f.:� �t��;=az��a•rF�s��:
T�'lc_x>t1 7n:�.;_�;e,cc= I<ate Map Iridex
Fl:�cict 1;,�,��:�r;c�� �2atF Map
�
ii
FLOOD INSURANCE STUDY
1.0 INTRODUCTION
l.l Purpose of Study
The purpose of this Flood Insurance Study is to investigate the
existence and severity of flood hazards in the City of Renton,
King County, Washington, and to aid in the administration of the
National Flood Insurance Act of 1968 and the Flood Disaster Protectior7
Act of 1973. Initial use of this information will be to convert
` Renton to the regular program of flood insurance by the Federal
Insurance Administration. Further use of the information will
be made by local and regional planners in their efforts to promote
' sound land use and flood plain development.
1.2 Coordination
On April 8, 1976, streams selected for detailed analysis were
identified in a meeting attended by representatives of the com-
munity, the original study contractor, and the Federal Insurance
Administration.
On July 13, 1979, the results of the work were reviewed at an
intermediate coordination meeting attended by representatives
of the city, the study contractor, and the Federal Insurance Admin-
istration.
The results of this study were reviewed at a final community coordi-
nation meetinq held on May 5, 1980. Attending the meeting were
representatives of the Federal Insurance Administration, the study
contractor, and the city. No problems were raised at the meeting.
1.3 Authority and Acknowledgments
The source of authority for this Flood Insurance Study is the
National Flood Insurance Act of 1968, as amended.
The hydrologic and hydraulic analyses for this study were perforrned
by Tudor Engineering Company, for the Federal Insurance Administra-
tion, under Contract No. H-4025. This work, which was completed
in July 1979, covered all significant flooding sources affecting
. the City of Renton.
- 2.0 AREA STUDIED
2.1 Scope of Study
This Flood Insurance Study covers the i.ncorporated area of the
City of Renton, King County, Washington. The study area is shown
on the Vicinity Map (Figure 1) .
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Floods caused by overflow of Green River, Cedar River, May Creelc,
and Springbrook Creek which includes the Black River were studied
in detail.
A small area of King County located north of State Highway 900
has not been included in this study.
Those areas studied by detailed methods were chosen with consider-
ation given to all proposed construction and forecasted development
through 1984.
2.2 Community Description
The City of Renton, in western King County in central-w�stern
Washington is situated 11 miles southeast of Seattle on the south
' shore of Lake Washington. It is bordered by the Citi.es of Kent
to the south and Tukwila to the west. The remaining area is bordered
by the unincorporated areas of King Countye
Many Indians were living in this region before the arrival oF
the settlers. Because of the abundance of food in the rivers
and the fertility of the delta, it had long been tt�e home of the
Duwamish Tribe. They engaged in agricultizre, fishing, and the
harvesting of wild berries which abounded in the region. In 1852,
the Oregon Territorial Legislature created King Caunty and named
it in honor of William King, Vice President of the United States
from 1852 to 1856.
In 1853, Henry and Diana Tobin became the first residents of Renton.
They built a homestead on a donation land cl.aim between the banks
of the Cedar and Black Rivers. Later, settlers chose to name
their town, Renton, after the founder of the f?rst sawmill.
Coal mining played an important role in the development of Renton.
The coal was discovered accidentally while land was being clea�ea
not far from the present site of Renton. At orie time there were
16 profitably operating mines in the immediate vicinity. i:n 19?8,
over 1.3 million tons of soft coal were mined and bil_lions of
tons of proven deposits still remain. Lumbcr �n� millin� were
important early industries, also.
The Town of Renton was platted in 1876, gained city incorporation
in 1901, and thereby became part of Washington Territery. �or_l�]
• War II brought a tremendous change to the city. Production of
war planes at the Boeing plant in Renton reached six a da}� as
population swelled from 4,000 to 16,000 (Refererice 1) . Ttie popula-
' tion in 1976 was 27,800 (Reference 2) .
In 1962, damaging floodflows from Green River came under the control
of Howard A. Hanson Dam. At that time, �3reen River valley Lf:�:•�>>;ae
an aLtractive area `�r indus�r i�.]. d�•.^?:��:i..er L. The economy .. .
3
i
Renton includes a variety of industries, services, and businesses
but is dominated by the Boeing Airplane Company. In 1976, the
company employed nearly 11,000. Other major employers include
Pacific Car and Foundry Company (1,685) and the Renton School
District (1,096) (Reference 2.) . i
Renton was originally built in the lowlands between the Cedar
and Green Rivers, but has gradually spread into the surrounding ;
hills. The elevations range from less than 10 feet to approxi- �
mately 450 feet. The commercial center of the city is located
north and west of Interstate Highway 405, on both sides of Cedar
River. Residential development has spread primarily along the
ascending ground east of Cedar River, and includes extensive areas •
outside the corporate limits. The flood plain areas of Renton
were originally farmland, a use which predominated until the early �
1960s. Urban development has displaced agriculture to the extent '
that the Green River valley is among the fastest growing urban
employment centers in the Puget Sound region (Reference 3) . Agricultural
and noncommercial pastureland account for only 18 percent of the
land use in the east Green River watershed. In King County, approxi-
mately 26.40 acres of prime agricultural land have been industrialized
(Reference 4) , including land in the Renton area of the Green
River valley.
Land use throughout the May Creek watershed is primarily open
space with scattered houses, most of which have been built back �
from the creek.
Land use in the Springbrook Creek basin is primarily residential
on the valley slopes, with major industrial development on the
flatlands adjacent to Green River.
Renton at one time was primarily in the Cedar River drainage basin.
It has since expanded into four watersheds; Green River, Cedar
River , May Creek, and Springbrook Creek. �
Green River meanders from north to south and is extremely flat.
It varies in elevation from 23 feet to 27 feet over a distance '
of approximately 2 miles.
Cedar River enters Lake Washington at Renton and drains approxi-
mately 186 square miles. The higher portions of the basin are
rugged and densely forested. Elevations within the basin range
from 14 feet at Renton to over 5000 feet at the headwaters. Major .
tributaries to the north of Renton include Rex River, which flows
northwesterly into the upstream end of Morse Lake, and Taylor �
Creek, which flows northerly to join Cedar River near Selleck. .
The slope of Cedar River within the study area is steep, approxi-
mately 19 feet per mile. Channel velocities generally range from
5 to 10 feet per second.
4
May Creek flows thr�ugh the northern portion o£ Renton into Lake
Washington, and drains approximately 13 square miles. The north
side of the water�hed i� foreste�, except near the mouth. The
south side is becoming increa.singly urbanized. The drainage basin,
especially the southern section, has been significantly affected
by glaciatzon. Retreating glaci�rs have created hog�, lakes,
irregular channel slopes, and unusual drainage patterns. In the
middle of the creek� channelizatie;n has heen user� to improve drain-
age. Elevations throughout the basirz range Erom "l0 feet n�ar
the mouth to approximatel�y 150U feet at. �he hiqhest point. The
slope of the creek bed throuyh the study reach �.s very steep,
• approximately 64 feet per mi1e. The 1Q0-year fl.00d plain varies
in width from 20 to 260 feet, with anticipa�ed chanriel velocities
of up to 15 feet per sec�nd. Niay Creek c�rains both Lake Kathleen
• and Lake 13oren ]_ocated to the west of Renton. `I'he main tributary
is Honey Creek which enter.s from the west at River Mile 2.0.
Springbrook Creek drains the southwestern portion af Renton, and
enters Green River through Black River. Upstrearn from Renton,
Springbrook Creek is joined by Mill Creek and together they drain
approximately 22 square miles, including mosc of the City of Kent.
Elevations throughout the basin range from 13 feet near the mouth,
to over 450 feet at the headwaters.
Glacial activity dramatically influenced the terrain of the Puget
Sound region until recent times. The area has been repeated]_y
occupied by glaciers advancing from British Columbia. The last
glaciation (Vashon) took place about 13,500 years ago. It is
estimated this glacier was approximately 3000 feet thick at Renton.
During this period, most west-trending valleys were filled with
glacial drift (jumbled boul.ders, gravel, and sand) while preexisting
north-trending valleys like Green River were scoured deeper.
As the ice retreat.ed to the north, the Strai.ts of Juan de Fuca
became ice-free, and the ocean once more covered the Green River
valley. This embayment slowly filled with �lluvzum carried by
the White, Green, and Cedar Rivers, creatinc� a flood plain with
a series of bogs and swamps. These alluvial deposits vary from
a few feet thick near the hillsides to 400 to 500 feet thick in
the central lowland area. This alluviur� £orms some of the most
fertile sail in the Pacif�c Northwest. Glacial deposits from
the Vashon glaciation are the chief components of the uplands
and vary from 25 to 200 feet in thickness.
� The climate of the region is predominantly a mid-latitude, west
coast, marine type, because most of the air masses that reach
. the Puget Sound area originate over the Pacific Ocean. In late
fall and winter these masses are moist and approximately the same
temperature as the ocean surface. Orographic lifting and cooling
as air masses move inland result in cloudiness and widesgread
precipitation throughout King County. RPnton experiences approxi-
mately 39 inches of annual rainfall, of which 5� percent of the
5
annual precipitation falls in the 4-month period, October through
January, and 75 percent occurs in the 6 months of October through
March. Average annual snowfall is 8.6 inches. During the warmest
summer months, afternoon temperatures are in the 73°F to 80°F
range. Temperatures reach 90°F on the average of 2 days per year.
In winter, afternoon temperatures range from 40°F to 50°F. The
Japan Current generally moderates winter temperatures but each
year temperatures below freezing occur on an average of 16 nights
(Reference 5) .
2.3 Principal Flood Problems
Minor flooding occurs almost annually, especially during the winter ,
months as a result of heavy rainfall. The flood impact is more
severe due to the effects of urbanization. Rapid increases in
construction of roads, housing, and parkinq lots accelerate the .
amount of runoff reaching the valley floor. Industrial landfills
in the val.ley are frequently located with little regard for natural
drainage patterns.
During periods of excessive precipitation, surface and subsurface
runoff from the steep valley walls cause significant rises in
groundwater elevations in the valley floor. This creates open
ponding in topographically depressed areas. The condition is
further aggravated by floodflow and corresponding high elevations
on Green River, which prevents natural drainage of subsurface
water. In other areas, the overlying soils are relatively imper-
meable and runoff collects in ponds perched above the water table.
Renton is not subject to flooding from Green River due to discharge
control at Howard A. Hanson Dam, diking, and other flood-control
measures. However, Springbrook Creek, a tributary to Black River
through the P-1 pumping station, does cause flooding problems
within the dikes to the east of Green River.
Cedar River is channelized through Renton and has the capacity
to convey the 100-year return flood for most of its length. The
lower 1-mile reach of the Cedar River channel was stabilized in
1912. Only minor overbank flows and negligible flood damage were
experienced during the December 1933 flood in Renton. However,
extensive flooding occurred upstream. Since that flood, King
County has provided extensive riprap bank protection, bulkheads,
cleanings, and snag removal upstream of Renton.
Flood damage on May Creek occurs mainly at the mouth where a lumber '
mill has been built on the small delta there. Upstream of Inter-
state Highway 405, May Creek flows generally within a canyon.
Flooding problems in this reach are the result of surface runoff '
and ground-water seepage from the steep canyon walls rather than
excessive overflow of May Creek.
6
Flooding from� Springbrook Creek within the corporate limits is
due in part to overburdened channels and ponding upstream of under-
sized culverts. However, large areas are inundated because of
ponding behind the P-1 pumping station. The station is limited
to a maximum discharge of 300 cfs when Green River is at flood
stage. Landfill for development in the area has reduced natural
storage capabilities and further aggravated this type of flooding
problem.
The most recent flood occurred on December 3, 1975. Discharges
and recurrence intervals for Green River, Cedar Creek and May
, Creek were 12,100 cubic feet per second (cfs) , 10-, 500-year;
8,800 cfs, 50-year; and 510 cfs, 15 year, respectively.
. 2.4 Flood Protection Measures
The U.S. Army Corps of Engineers operates Howard A. Hanson Dam
at Eagle Gorge, north of King County, on upper Green River. Since
1962, the dam has provided approximately a 500-year level of protec-
tion against overbank flooding by Green River. The dam is a rockfill
embankment approximately 235 feet high with a gated spillway and
a maximum reservoir elevation of 1222 feet. Stored water is released
as soon as possible after a flood to prepare for the possibility
of a second flood. When the Auburn gage (No. 12113000) is expected
to reach 12,000 cfs, dam operators allow runoff over the spillway.
At that point, they regulate further releases in order to maintain
no more than 12,000 cfs at Auburn. Protection of flood plain
lands is afforded by channelization and diking. Along Green River,
a total of 12 miles of levees have been constructed. The King
County Division of Hydraulics is responsible for dike maintenance.
Since the adoption of enabling legislation by the State of Washington
in 1945, the state and King County have combined to control river-
bank erosion.
The channelizing of Cedar River now allows it to convey the 100-
year return flood. Since the 1933 flood, King County has provided
Cedar River with extensive riprap bank protection, bulkheads,
cleanings, and snag removal upstream of Renton. Within the study
reach, most of the channel of May Creek is in its natural condition.
The lower 1000 feet have been channelized to alleviate flooding
problems at the mouth caused by excessive deposition.
Floodflows on Springbrook Creek are discharged into Black River,
� just upstream of the P-1 pumping station located approximately
1 mile downstream of Interstate Highway 405. This pumping station,
constructed in 1972, is operated and maintained by King County.
� It performs the dual function of preventing Green River backwater
from entering and inundating the low-lying east valley lands.
Also, it pumps water from relatively low elevations on Black River
into Green River at higher elevations. The pumping station is
part of a 1965 Watershed Work Plan designed by the U.S. Soil Conser-
vation Service with the cooperation of King County. It includes
7
a system of integrated drainage channels known as P-channels.
It is expected that construction of these P-channels will continue
and extend as far south as Orillia.
Under Chapter 86.16 of the Revised Code of Washington, Green River
is in Flood Control Zone 2 and Cedar River is in Flood Control
Zone 3. Pursuant to the statute, flood plain management in these
zones is administered by county and city authorities, Specific
provisions for flood plain management, designed to reduce flood
damage to urban developments, have been formulated jointly by
King County, the City of Renton, and the other municipalities
located in the Green River valley. These provisions require all ,
new urban developments in flood-prone areas to floodproof against
8-�t� flood conditions. To..In$e-��-t��--�1Qod-proofing require-
ments, deve �rs must raise�he ground surface to an elevation ,
� 1.0 foot above he predicted wa«� ��~f ce cau d by the 100-year
� flood.
Flood forecasting and protection is facilitated by an agreement
between the U.S. Army Corps of Engineers, Seattle District, and
King County whereby the former will advise the King County Division
of Hydraulics when a flow of 10,000 cfs in Green River is expected
to reach Auburn. The Division of Hydraulics has agreed to monitor
river conditions and to be responsible for encroachments on the
safe carrying capacity of the existing levees.
3.0 ENGINEERING METHODS
For the flooding sources studied in detail in the community, standard
hydrologic and hydraulic study methods were used to determine the flood
hazard data required for this study. Flood events of a magnitude which
are expected to be equalled or exceeded once on the average during any
10-, 50-, 100-, or 500-year period (recurrence interval) have been selected
as having special significance for flood plain management and for flood
insurance premium rates. These events, commonly termed the 10-, 50-,
100-, and 500-year floods, have a 10, 2, 1, and 0.2 percent chance,
respectively, of being equalled or exceeded during any year. Although
the recurrence interval represents the long term average period between
floods of a specific magnitude, rare floods could occur at short intervals
or even within the same year. The risk of experiencing a rare flood
increases when periods greater than 1 year are considered. For example,
the risk of having a flood which equals or exceeds the 100-year flood
(1 percent chance of annual occurrence) in any 50-year period is approxi-
mately 40 percent (4 in 10) , and, for any 90-year period, the risk increases '
to approximately 60 percent (6 in 10) . The analyses reported here reflect
flooding potentials based on conditions existing in the community at
the time of completion of this study. Maps and flood elevations will '
be amended periodically to reflect future changes.
8
3.1 Hydrologic Analysis
Hydrologic analyses were carried out to establish the peak dis-
charge-frequency relationships for floods of the selected recur-
rence intervals for each stream studied in detail in the community.
On Green River, releases are controlled by Howard A. Hanson Dam
engineers so as not to exceed a discharge of 12,000 cfs at the
City of Auburn for all recurrence floods ug to the 500-year event
(Reference 6) .
The U.S. Army Corps of Engineers, Seattle District, had previously
� carried out a hydrologic study to derive recurrence flood peaks
on Cedar River (Reference 4) . Historzc streamflow data for this
river was obtained from two Cedar River gages, both operated and
� maintained by the U.S. Geological Survey. One gage at the mouth
in Renton (gage no, 12-1190) , has been in operation continually
since 1945. The other, (gage no. 12-1175) , near Landsburg, has
been in operation at its present site since 1948.
Flood-frequency data for May Creek was based on discharge records
at a U.S. Geological Survey streamflow gaging station at the mouth
of May Creek. The gage (no. 12-1196) , located at the Lake Washington
Boulevard bridge, has a period of record from 1964 to the present.
Analysis of streamflow data was performed in accordance with the
standard log-Pearson Type YII method outlined by the U.S. Water
Resources Council (Reference 7) .
There are no streamflow records available for Springbrook Creek
and Black River. Hydrologic analysis for this drainage basin
was performed by the U.S. Soil Conservation Service using synthetic
hydrograph methodology (Reference 8) and the TR-20 computer program
(Reference 9) . Results of this study were reviewed and incorpor-
ated into a computerized runoff-routing model developed by the
study contractor to utilize the U.S. Soil Conservation Service
synthetic hydrograph method. Hydroqraphs representing the 10-
and 100-year return storms runoff were generated and routed through-
out the study reach, The 24-hour precipitation volume for the
expected 10- and 100-year return storm was obtained from the National
Oceanic and Atmospheric Administration Precipitation-Frequency
Atlas (Reference 10) . It was compared with precipitation gage
records at Seattle-Tacoma International Airport. Intensity distri-
bution was also based on the Seattle-Tacoma International Airport
• rainfall records. The 50- and 500-year floods are not within
the scope of this study, therefore, discharges were not computed
for these recurrence in�ervals.
The expected 8-day, 1D0-year return storm precipitation volume
was used to determine the extent of surface ponding in low-lying
areas.
9
Peak discharge-drainage ar.ea relationships for Green River, Cedar
River, May Creek, and Springbrook Creek are shown in Table 1.
3.2 Hydraulic Analyses
Analyses of the hydraulic characteristics �f streams in the commu-
nity were carried out ta provide estimates of the elevations of
floods of the selected recurrence intervals along each stream
studied in the communit�.
Water-surface elevations throughout the May Creek and Springbrook
Creek study reaches were computed using the U.S. Army Corps of
Engineers HEC-2 step-backwater computer program (Reference 11) . '
The U.S. Army Corps of Engineers, Seattle District, had previously
developed 10- and 100-year water-surface elevations having field '
surveyed the physical data for Gr_een and Cedar Rivers. Cross
section and bridge data for May and Springbrook Creeks were field
surveyed (References 4 and 6) .
Locations nf selected cross sections used in the hydraulic analyses
are shown on the Flood Profiles (Exhibit 1) . For stream segments
for which a floodway is computed (Section 4.2) , selected cross
section locations are also sh�wn on the Flood Boundary and Flood-
way Map (Exhibit 2) .
Channel- and overbank-roughness coefficients are based on field
inspection. Values used in this study are listed below:
Stream Channel Overbank
Green River 0.030 - 0.055 0.090 •- 0.150
Cedar River Oo026 - O.Q54 0.035 - 0.099
May Creek 0.045 - 0.055 0.080 - 0.150
Springbrook Creek Qo038 - 0.045 0.100 - 0.150
The U.S. Army Corps of Engineers has previously determined the
starting water-surface elevations for Green River and Cedar River
(References 4 and 6) .
Starting water-surface elevation for May Creek is controlled by
Lake Washington. On Springbrook Creek, starting water-surface
elevation is dependent on the storage-elevation curve upstream
from the P-1 pumping station (Black River) . In order to arrive .
at an accurate estimate for the starting water-surface elevation,
the hydrograph at the mo�th was routed through the pump station
using pumping criteria and a maximum discharge of 300 cfs. The •
routing was done using an in-house computer program incorporating
the Modified Puls routing techniques.
10
Table 1. Summary of Discharges
Discharges
Flooding Source Drainage Area (Cubic Feet Per Second
and Location (Square Miles) 10-Year SU-Year 100-Year 500-Year
Green River
At Renton 450 12,0001 12,0001 12,0001 12,0001
Cedar River
At Mouth 186 5,950 8,550 9,810 13,000
May Creek
At Mouth 12.7 480 795 870 1,015
Springbrook Creek
At Mouth 21.9 5852 N/A 1,1052 N/A
Downstream of Confluence With
r Mill Creek 16.0 680 N/A 1,020 N/A
�
1Discharges Constant Due to Controlled Release From Howard A. Hanson Dam
2Decrease in Discharges Due to P-1 Pumping Plant Pumping 300 Cubic Feet Per Second Into Green River
During Flood Stages
Flood profiles were drawn showing computed water-surface elevations
to an accuracy of 0.5 foot for floods of the selected recurrence
intervals (Exhibit 1) . Only the 10-year and 100-year flood elevations
are shown for Springbrook Creek and Black River because of the
limited scope of this study.
The Black River profile, upstream to the P-1 pumping station,
was developed by projecting the water-surface elevations taken
from the confluence with Green River, as flat backwater from Green
River (Reference 12) . The 10- and 100-year elevations at Earlington
Golf and County Club Foot Bridge on Springbrook Creek were projected
downstream to the P-1 pumping station to complete the profile.
At the P-1 pumping station, the water from the Springbrook Creek- '
Black River system is pumped up to the elevation of Green River.
Results of the Green River study (Reference 6) show that the 10-, '
50-, 100-, and 500-year water-surface elevations through Renton
are represented by a single water-surface profile of controlled-
discharge releases at Howard A. Hanson Dam. This profile was
taken from the Flood Insurance Study for King County (Reference
6) . Flood Hazard areas caused by high water on Green River, as
shown in this study, are based on the previously developed profile
and information from topographic maps obtained from Renton (Refer-
ence 13) .
The hydraulic analyses assumed unobstructed flow. The flood eleva-
tions are considered valid only if bridges and culverts remain
unobstructed.
Ponding elevations were derived using the runoff-routing computer
model described in Section 3.1, together with pumping criteria
and elevation-storage curves developed from field surveys, and
information from topographic maps (Reference 13) .
All elevations are referenced to the National Geodetic Vertical
Datum of 1929 (NGVD) . Elevation reference marks used in the study
are shown on the maps.
4.0 FLOOD PLAIN MANAGEMENT APPLICATIONS
A prime purpose of the National Flood Insurance Program is to encourage
State and local governments to adopt sound flood .plain management pro-
grams. Each Flood Insurance Study, therefore, includes a flood boundary
map designed to assist communities in developing sound flood plain manage- .
ment measures.
4.1 Flood Boundaries .
In order to provide a national standard without regional discrimi-
nation, the 100-year flood has been adopted by the Federal Insurance
Administration as the base flood for purposes of flood plain manage-
12
ment measures. The 500-year £lood is employed to indicate addition-
al areas of flood risk in the community. For each stream studied
in detail, the boundariPs of the 100- and 500-year floods have
been delineated using the flood elevations determined at each
cross section; between cross sections, the boundaries were inter-
polated using topographic maps at a scale of 1:24Q0, with a contour
interval of 5 feet (Reference 13) .
For the detailed study of Green River, the flood boundary delin-
eated is representative of the 10-, 50-, 100-, and 500-year floods.
, For Springbrook Creek, only the 100-year flood boundary has been
delineated.
_ In cases wher_e the 100- and 500-year flood boundaries are close
together, only the 100-year flood boundary has been shown.
Flood boundaries for the 100� and 500-year floods are shown on
the Flood Boundary and Floodway Map (Exhibit 2) ,
Approximate flood boundaries in some portions of the study area
were taken from the Federal Insurance Administration's Flood Hazard
Boundary Map (Reference 14) ,
Small areas within the flood boundaries may lie above the flood
elevations and, therefore, not be subject to flooding; owing to
limitations of the map scale, such areas are not s:�own.
Similarly, small areas wYiich may be subject to shalZow ponding
due to runoff or high ground-water elevations may not be shown.
4.2 Floodways
Encroachment on flood plains, such as artificial fill, reduces
the flood-carrying capacity and increases flood heights, thus
increasing flaod hazards in areas beyond the encroachment itself.
One aspect of flood plain management involves balancing the economic
gain from flood plain ��velopment against the resulting increase
in flood hazard. For purposes of the National Flood Insurance
Program, the concept of a floodway is used as a tool to assist
local communities zn thzs aspect of flood plain management. Under
this concept, the area of the 100-year flood is divided into a
floodway and a floodway fringe. The floodway is the channel of
' a stream, plus any adjacent flood plain areas, that must be kept
free of encroachment �n order that the 100-year flood be carried
without substantzal incr.eas�s iri flood heights. As minimum standards,
� the Federal Tnsurance Administration limits such increases in
flood heights to 1.0 foot, provided that hazardous velocities
are not produced.
7_3
The floodways developed in this study wer.e initially computed
on the basis of equal-conveyance reduction from each side of the
flood plain. Further refinement was made using field observations,
hydraulic principles, and a topographic map (Reference 13) .
For Springbrook Creek, there were areas of backwater ponding up-
stream of roadway culverts where floodway requirements were com-
puted based on storage routing criteria. The 100-year ponding
water-surface elevations were established using reservoir routing
by Modified Puls techniques. The floodway encroachment limits
were then determined by reducing the width of the flood plain
to obtain the required surcharge for each ponding area upstream .
of the culvert. The flow with the increased elevation was then
routed through the culvert. No cross section widths, areas, or
velocities are shown for these ponding areas. .
No floodway was computed for Black River since the area upstream
from the P-1 pumping station to the confluence of Springbrook
Creek was considered a reservoir suitable to receive the overflow
from Springbrook Creek.
The results of these computations are tabulated at selected cross
sections for each stream segment for which a floodway is computed
(Table 2) .
As shown on the Flood Boundary and Floodway Map (Exhibit 2) , the
floodway boundaries were determined at cross sections; between
cross sections, the boundaries were interpolated. In cases where
the floodway and 100-year flood boundaries are close together,
only the floodway boundary has been shown.
The area between the floodway and the boundary of the 100-year
flood is termed the floodway fringe. The floodway fringe thus
encompasses the portion of the flood plain that could be completely
obstructed without increasing the water-surface elevation of the
100-year flood more than 1.0 foot at any point. Typical relation-
ships between the floodway and the floodway fringe and their signi-
ficance to flood plain development are shown in Figure 2.
14
BASE FLOOD -
FLOODING SOURCE FLOODWAY WATER SURFACE ELEVATION
SECTION MEAN WITHOUT WITH INCREASE
TANCE 1 W�DTH AREA VELOCITY ��U��ORY� FLOODWAY I FLOODWAY
CROSS SECTION DIS (FEEZ') {SF�� �FSECOND R (FEET NGVD} .
Green River 27.1 27.2 27.1 �.�
A 11,845 150/1102 2609 4.6
g 13,100 185f1402 2857 4.2 27.5 27.5 27.5 �.�
1 2 . _ _
Feet Above Cor�aorate Limits �v7idth/Wi�th 'tiithin Cor�c�rate Limits
�EDERAL EMERGENCY MANAGEMENT AGENCY ��OQpW�Y DA�A
—� Federai insurance Administration ,
�
°° CITY 4f REHT�H, WA
� GREEH RIYER
'T' (KING CQ.�
� , . � �
� �
FLOODING SOURCE FLQODWAY
BASE FLOQD
WATER SURFAC� ELEVATION
Z WIDTH S AREA N VEL�ITY REGtJLATdI2Y( WIT'HpUT � WI'I'H I INCREASE
CROSS SEC'I'ION DISTANCE FLt�ODWAY FI�t}ODWAY
(FEET} (SQUARE (FEET PER
FEET) SECOIVD} (FEET NGVB)
Cedar River
A 0.025 i5$ 128Q 7.7 15.Q 15.0 15.0 0.0
B 0.462 144 180 10.0 18.9 1�.9 18.9 0.0
C 0.767 157 1510 6.5 23.7 23.7 23.7 0.0
D 1.1�4 156 1020 9.G 25.7 25.7 25.7 0.0
�' 1.261 120 95d 10.3 27,5 27.5 27.5 d.0
F 1.337 135 1030 9.5 28.5 28.5 28.5 0.0
G 1.489 154 1110 8.8 30.6 30.6 30.G 0.0
H 1,679 114 950 �0.3 32.5 32.5 32.5 0.0
I 1.83Q 135 1180 8.3 35.5 35.5 35.5 0.0
J 1.960 221 1360 7.2 37.3 37.3 37.3 0.0
K 2.038 135 1280 7.7 38.4 38.4 38.=� O.Q
L 2.090 115 1210 8.1 39.5 39.5 39.5 ' t7.0
P�i 2.160 103 1160 8.5 4d.7 40.7 40.7 0.0
N 2.320 110 1490 6.6 C=3.4 43.4 43.4 0.0
a 2.470 142 15Q0 6.5 45.2 45.2 45.2 0.0
P 2,730 141 1210 8.1 49.5 49.5 49.5 � 0.0
Q 2.900 130 1310 7.5 52.6 52.6 52.6 0.0
R 2.960 14p 1220 8.1 53.6 53.6 53.6 ' 0.0
S 3.020 150 1070 9.1 55.4 55,4 55.4 0.0
T 3.250 21q 169d 5.8 60,9 b0.9 61.0 0.1
U 3.370 196 1310 7.5 b2.8 62.8 62.9 0.1
I
�Miles Above Mouth
� FEDERAL EMERGENCY MANAGEMENT AGENCY �IO�DW�Y D�T�
a Federal Insurance Administration
°° CITY Of RENT�H, WA
� .
�
N (KINS CO.� CEDAR RIYER
FLOODING SOURCE FLOODWAY BASE FLOOD
WATER SURFACE ELEVATION
SECTION MEAN WITHOUT WITH �,
CROSS SECTION DISTANCE� WIDTH AREA VELOCITY REGUL.�TORYI FLOODWAY I FLOODWAY I INCREASE �
(FEET) (SQUARE (FEET PER
FEET) SECOND) (FEET NGVD)
May Cre�k
A 0.14 34 158 5.5 21.0 21.0 21.5 0.5
B C.16 60 239 3.6 21.8 21.8 22.2 0.4
C 0.24 42 99 8.8 23.3 23.3 23.3 0.0
D 0.25 42 110 7.9 25.7 25.7 25.7 0.0
E 0.31 31 121 7.2 29.0 29.0 29.2 0.2
F 0.39 40 150 5.8 32.5 32.5 33.0 0.5
G 0.46 28 �7 10.0 35.8 35.$ 35.8 0.0
F-I fJ.52 23 123 7.1 40.0 40.0 40.n O.G
I 0.57 45 165 5.3 41.E 4Z.3 42.5 0.7
J G.63 31 $9 9.7 45.3 45.3 45.3 0.0
K 0.78 33 133 6.5 55.2 55.2 55.2 0.0
L Q.94 79 143 6.1 64.7 64.7 �4.7 0.0
Ni 1.09 33 113 7.7 76 .4 76.4 76.E 0.2
N 1.25 39 128 6.6 85.4 �S.S 55.4 0.0
0 1.36 32 89 9.6 �3.1 93.1 93.2 0.1
P 1.39 40 172 4.9 95.6 95.6 96.0 0.4
Q 1.41 33 90 9.5 95.f3 95.8 95.8 0.0
R 1.42 33 111 7.7 96.4 96.4 96.4 0.0
S 1.46 30 95 8.9 99.8 99.8 99.9 0.1
T 1.54 22 91 9.3 106.�3 106.8 106.5 C.1
U 1.56 8 68 12.5 112.2 112.2 7_12.2 0.0
V i.61 43 283 2.9 114.2 114.2 115.1 0.9
W 1.74 2i $I 9.9 120.9 120.9 120.9 0.0
X 1.83 38� 170 4.8 125.0 125.0 125.7 0.7
Y 1.96 52` 101 8.0 135.8 I35.8 135.8 0.0
Z 2.02 42 130 6.3 140.4 14Q.4 I�0.5 0.1
1Miles Above Mouth LFiood;aay Lies Ent__rely Outside Corporate Limits
� , . ._ .. . . . .. ; ..,, ., ., , . .:.. . .
� FEDERALEMERGENCY MANAGEMENiAGEIVCY
� Federal Insurance Administration - f LOODWAY DATA
°° CI�'l� Of RENTON, W�
� .
�
N �KiNc co.� MAY CREEK
. . . � � � � � .. �. � , . �. � � . , � ,�. � . . , . . i
F�'LOODING SOUP.CE FLC}ODWAY BA�F FLOOD
WATLR SURFACE ELEVATIUN
_- --. .---..... .. _......_ _ _
_ - .___ _
. � �E�TION MEAN �WITHOUT � WITN �
CRU7S SEC:TION D?STF.^IC.:F_:l' `'"IPlN I AREA VELOCITY REc;ULATORY gj,(�(�DWAY FLOODWAY =NCREASE
{?�I�:ETt ; ;�Q���E {FEE'T PER
i F'EET) SECOND) (FEET IQGVD)
Springbrook Greek �
k 0.238 81 ` 616 2.l 14.9 14.9 14.9 0.0
� 0.581 I50 r 706 i.8 15.(l 15.0 15.1 G'.l
C 0.730 68 � 472 2.7 15.1 15.1 15.4 0.3
D 0.?87 6& 482 2.6 15.2 15.2 15.5 Q.3
E 0.859 58 467 2.7 15.4 15.4 15.$ 0.4
F 1,254 50 ' 439 2.9 15.8 15.8 16.3 0r5
G 1.487 $3 ( 63£3 2.0 1b.J 16.0 ib.6 0.6
H 1. b24 25 � 297 4.b 16.0 1.6.0 16.? 0.7
I 1.987 63 581 2.1 16.6 I.6.b 17.4 Q.8
�J 2..565 44 325 3.$ 17.0 17.0 17.9 0.9
K 2.605 43 383 3.2 1.7.3 17.3 18.2 0.9
L 2.672 56 � 476 2.6 17.4 17.� 18.3 0.9
- M 2.76Q 88 881 1.4 ].7.6 17.6 18.5 0.9
1Miles Above Mouth
FEDERA���Eal nsu a ce Admin�MEN7 AGENCY � � ct oODw �
� G
a istration 1"L IiAY DATA
°° CITIf �F RENTON, WA
� ,
�' �K��� �Q�a ! SPRlN�BROOK CREEK
�
II - . . 1fi0�Yt�-AR F=L,Ot)t>Ft.tlitU �
4
�� F�4QDWAY 6�.,, ,,,_I ,�-IGODWAY�
FLC;t?DWAY' � FRINGE
FRINGE
.. ' STRhAUI � �
�CHANfVEL�
�
FI.Od� E�EVAI'IQtV WNEN
C4NFINED WI"7NIN FL,OO�WAY
' ENCROACI#MENi' � � ' ENCR(7—A�C--HMENT
' ��� ':;�:�" C ',� SUP,CHARGE� I � :���1 :�.. I
�'��j:;:ji,:%;:;w:;:}};:u;%,v,:k*iri•}ei;I;:;i;l;l,",;' oA� s—'"' —_—_= g
A }::�:�}: '
..;...�.::::�.}.. •..::.�:::.
..,.;..... :.a..� •.e•rrr::::•:•
., .....� .,.: vr�..... ..
, . , ,.__:,,,. .�
...,_. ,.. . .—-- —_.
AREA OF FLOOCI PI�AIN THAT C�'.-'U�-D � FLOC)D ELEVAT10t`3
BEFOREENCROACHMENT
BE 11SED �OR C1EVE�OPMENT f3Y ��y F�ppp p�AlN
RAISING GROUND
�tIVE A8 IS THE Fl�C?4D EIEVA't'IQN SEFC}RE 4h1C`iOA�NM�lVY.
�INE CO IS THE FLOOD EI.EVATION AFTER ENCRCACHMENT.
'SURCHARGE IS NOT TO EXCEED 1.0 FOQT it=�R REC2UiREMEM1lTi OR LESSER AMOUNT IF SPECIFIED$Y STATE. J
Fic�ure 2. Fl�ociway 5chemat:ic
5.0 TNSURANCE AP:PLICATIJN
In order ta estabiish actuar ial insuran�e rates; t�ae Fec3eral Tnsurance
Administratian has develaped a process c.o transfo�m the data from the
engineering stucly into �la�d insurance criteria. This process includes
the determinatiara of reaches, Flood Hazard Factor_s, �nd flood insurance
zone desiqnations for each fl.00ding source studied in detail affecting
Rentan.
5.1 Reach neterminatir�n�
Reaches are de��rtec� as lengths of watercourses having relatively
the �ame floo� hazazdF based on th� average weightec� difference
in wa�.er-suzLaaU el�vwt�.ons 1����een the 10- and t00-year floads.
This c3ifference dc�e� Yzot have a v�r iatian greatez than tha� indica-
ted in th�: followinc� table tor more t.han 20 pezcent af the reach:
�1v�rage L:i��erc.�ce F3etween
10- and 1fl0-Year �'loc�ds Var iatian
Less than 2 feet 0.5 foot
2 �0 7 fe�t 1.0 foot
l,1 to 12 feet 2..0 feet
More �.han I� feet 3.7 fbet
19
The locations of the reaches determined for the flooding sources
of Renton are shown on the Flood Profiles (Exhibit 1) and summar-
ized in Table 3.
5.2 Flood Hazard Factors
The Flood Hazard Factor (FHF) is the Federal Insurance Administra-
tion device used to correlate flood information with insurance
rate tables. Correlations between property damage from floods
and their FHF are used to set actuarial insurance premium r.ate
tables based on FHFs from 005 to 200.
The FHF for a reach is the average weighted difference between •
the 10- and 100-year flood water-surface elevations expressed
to the nearest one-half foot, and shown as a three-digit code.
For example, if the difference between water-surface elevations •
of the 10- and 100-year floods is 0.7 foot, the FHF is 005; if
the difference is 1.4 feet, the FHF is 015; if the difference
is 5.0 feet, the FHF is 050. When the difference between the
10- and 100-year water-surface elevations is greater than 10.0
feet, accuracy for the FHF is to the nearest foot.
5.3 Flood Insurance Zones
After the determination of reaches and their respective Flood
Hazard Factors, the entire incorporated area of the City of Renton
was divided into zones, each having a specific flood potential
or hazard. Each zone was assigned one of the following flood
insurance zone designations:
Zone A: Special Flood Hazard Areas inundated
by the 100-year flood, determined by
approximate methods; no base flood
elevations shown or Flood Hazard Factors
determined.
Zone AH: Special Flood Hazard Areas inundated
by types of 100-year shallow flooding
where depths are between 1.0 and 3.0
feet; base flood elevations are shown,
but no Flood Hazard Factors are deter-
mined.
Zones A1, A2, A4, A5, Special Flood Hazard Areas inundated ,
and A7 by the 100-year flood, determined by
detailed methods; base flood elevations
shown, and zones subdivided according .
to Flood Hazard Factors.
20
ELEVATION DIFFERENCE2 FLOOD BASE FLOOD
1 BETWEEN 1% (100-YEAR) FLOOD AND
FLOQDING SOURCE PANEL HAZARI� ZONE ELEVATION 3
10% 2% 0.2 a FACTOR tFEET IJGVD)
(IO-YEAR} (50-YEAR) (500-YEAR}
Green River4
Reach 1 0044 4.Q 0.0 0.0 005 Al Varies - See Map
� Cedar River
� Reach 1 0002 -2.3 -0.7 2.0 025 A5 Varies - See Map
Reach 2 0002,0003 -3.6 -0.9 1.9 035 A7 Vari2s - See Map
Reach 3 0003 -2.3 -0.9 1.2 025 AS Varies - See Map
May Creek
Reach 1 OOQl -1.2 -Q.18 1.59 O10 A2 Varies - See Map
5pringbrook Creek
Reach 1 0002,0004 -2.0 N/A N/A 02Q A4 Varies - See Map
Ponding Area 0004 N/A N/A N/A N/A AH 16
Black River
Reach 1 Q002 -2.0 NjA NjA 02Q A4 Varies - See Map
---_
-
4
1Flood Insurance Rate Map Panel 2Weighted Average �Rounded to Nearest Foat I�ata Based on Regulated Flow
From Howarc2 A. Hanson L?am
` _ - __ - - - .,.,.
FEDERA FedeEai�su a ceAdr��irr�tratN� ��oQ� IN�URAN�'G L ,
� ME �AGENCY �
m «r oNE aa�a
°° C1�'l� OF' RENTOH, W� . , . � . � �
_ �
- "' (KIN6 CO.a GREEN RIYER-CEDAR RIYER-MA`� CREEK-SPRINGBROOK CREEK-BLACK RIVER
� -
� � � ��� � , � � , �� ��� � �� �� � � �� � � . ,�� ���� ������, � �„�,�.� � � ��� � ���
Zane B: Areas between the Sgecial Flood Hazard
Areas and the limits of �he 5Q0-year
flood, including areas o� the 500-year
flood plain that are protected fram
the lOQ-year flaod by dike, levee,
or other water control structure; also
areas subject to certain types af 100-
year shallow flaoding where depths
are less than 1.4 foat; and areas subject
ta 100-year floading from sources with
drainage areas less than 1 square mile.
Zone B is not subdivided.
Zone C: Areas of minimal f.looding. �
The flood elevation differences, Flaad Hazard Factors, flood insur- .
ance zones, and base flood elevations for each flooding source
studied in detail in �he c�mmunity are summarized in Tab1e 3.
5.4 Fload Insurance Rate Map Description
The Flood Insurance Rate Map for Renton is, for insurance purpases,
the principal result af th� Flaad Insurance Study. This map tAUblished
separately) contains the official delineation of flaad insurance
zones and base flood elevatian lines. Base flood elevation lines
show the locations of the expected whale-foot water-surface eleva-
tions of the base (100-year) flood. This map is developed in
accardance with the latest flood insurance map preparatian guide-
lines published by �he Federal Insurance Administratian.
b.0 OTHER STUDI�S
The F'ederal Insurance Administration published a F2oad Insurance Study
{Reference 6) in March 1976, which covered the unincorporated areas
of King Cnunty, including those areas affected by Creen and Cedar Rivers
adjoining Renton.
The Federal Insurance Administratian is canducting Flood Insurance Studies
for the adjacent Cities of Kent {Reference 15} and Tukwila (Reference 12} .
'These studies are in general agreement with this study.
The Federal Insurance Administratian has previously published a Flood
Hazard Boundary Map for the City of Renton (Reference 16) . However,
this study represents a more detailed analysis.
The U.B. Army Corps of Engineers, Seattle District, alsa published a
Flaod Plain Informatian repart (Reference 4} on Cedar River through
Ftenton in March 1969. Da�a from this repart have been incarporated �
into this study.
22
The U.S. Soil Conservation Service has conducted extensive studies (Refer-
ence 17) in the Green River valley. Its work t�as been directed primarily
toward determining criteria pertinent to the design of flood-control
drainage channels and associated structures. These studies have been
mainly concerned with the effects of future land use and development
of runoff patterns, rather than existing flood-hazard conditions.
This study is authoritative for the purposes of the National Flood Insur-
ance Program; data presented herein either supersede or are compatible
with all previous determinations.
7.0 LOCATION OF DATA
Survey, hydrologic, hydraulic, and other pertinent data used in this
study can be obtained by contacting the Insurance and Mitigation Division,
• Federal Emergency Management Agency, Federal Regional Center, 130 228th
Street, SW. , Bothell, Washington 98011.
8.0 BIBLIOGRAPHY AND REFERENCES
1. Greater Renton Chamber of Commerce, Renton History, unpublished
2. Greater Renton Chamber of Commerce, An Economic Profile of Renton,
Washington, 1976
3. Puget Sound Committee, "The Green River Valley Discussion Paper,"
presented at Puget Sound Governmental Conference, Seattle, Washington,
March 1975
4. II.S. Department of the Army, Corps of Engineers, Seattle District,
Flood Plain Information, Cedar River, Renton, Washinqton, Seattle,
Washington, March 1969
5. U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, Climatography of the United States, No. 60-45,
Climate of Washington, Silver Spring, Maryland, February 1960,
Revised April 1965
6. U.S. Department of Housing and Urban Development, Federal Insurance
Administration, Flood Insurance Study, King County, Washington,
(Unincorporated Areas) , March 1976
7. U.S. Water Resources Council, Hydrology Committee, "Guidelines
, for Determining Flood Flow Frequency," Bulletin 17, 1976
8. U.S. Department of Agriculture, Soil Conservation Service, Enyineer-
, ing Division, National Engineering Handbook, Section 4, Hydrology,
January 1971
9. U.S. Department of Agriculture, Soil Conservation Service, Engineer-
ing Division, Technical Release 20, Computer Program For Hydrology
May 1975
23
10. U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, Atlas 2, Precipitation - Frequency Atlas of the
Western United States, vol. IX, 1973
11. U.S. Department of the Army, Corps of Engineers, Hydrologic Engi-
neering Center, No. 723-X6-L202A, HEC-2 Water-Surface Profiles,
Generalized Computer Program, Davis, California, November 1976
12. Federal Emergency Management Agency, Federal Insurance Administra-
tion, Flood Insurance StudX, City of Tukwila, Washington, unpublished
13. Aerial Mapping Company, Topographic Ma�, 1:2400, Contour Interval
5 feet: Renton, Washington (1968) �
14. U.S. Department of Housing and Urban Development, Federal Insurance
�dministration, Flood Hazard Boundary Map, City of Renton, King •
County, Washington, Scale 1:9600, June 7, 1974
15. Federal Emergency Management Agency, Federal Insurance Adminis-
tration, Flood Insurance Study, City of Kent, Washington, unpublished
16. U.S. Department of Housing and Urban Development, Federal Insur-
ance �dministration, Flood Hazard Boundary Map, City of Renton,
Washinaton, June 7, 1974 (Revised November 7, 1975)
17. U.S. Department of Agriculture, Soil Conservation Service, Draft
Environmental Impact Statement, East Side Green River Watershed,
King County, Washington, Spokane, Washington, May 1977
24
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*PANEL NOT PRINTED - AREA OF MINIMAL FLOOD HAZARDS
COMMUNITY -PANEL NUMBERS
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EFFECTIVE Ta
MAY 51 1981
federal emergency management agency
federal insurance administration