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TECHNICAL INFORMATION REPORT
(T.I.R.)
FOR
AMBERWOOD II
KING COUNTY, WASHINGTON
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Prepared by: Gina R. Brooks P.E. '--'r� -
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Date: May,2005 c;s;E�� ;w
Revised: Octo6er,2005 fSL� _�v�t��'�'
January,2006
Core No.• 04027 �x���Es 2-'�0-�"�1
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ENGINEERlNG PLANNING SURVEYING
328�
AMBERWOOD II '
TABLE OF CONTENTS I
l. Project Overview I
2. Conditions and Requirements Sumr��ary �!,
3. Off-Site Analysis I
4. Flow Control and �'�'ater Qualit�� Facilit;� �� ���
�
5. Conveyance System Analysi� and I�e�i �!
�
6. Special Rep� � ',
7. Other Permi
8. ESC Analysis anci l�esigr ''
9. Bond uantities Facilit � , _ . _ _ . __;,:: '
Q � y
lO.Operations and Maintenance Manual
1. PROJECT OVERVIEW:
The 4.24-acre Amberwood II property is located at 6135 NE 4�' Street just east of Rosario
Avenue NE in Renton,Washington(see the attached Vicinity Map). The property is
currently occupied by a single residence and several lazge outbuildings. Ground cover
consists of a combination of impervious surfaces associated with outbuildings and gravel
driveways/parking, along with landscaping,brush, and trees. The property slopes in a
southwesterly direction. No upstream drainage is received by the property.
The proposed project includes constructing 17 single-family residential lots with
associated roadways and utilities. Half-street improvements, including curb, gutter, and
sidewalk,will be made to NE 4�' Street along the property's northern frontage.
Developed drainage within the property will be conveyed to a proposed combination
water quality/detention pond that will be located at the southwest corner of the property.
The pond will discharge via a sheet flows spreader to the adjacent wetlands to the south.
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2. CONDITIONS AND REQUIREMENTS SUMMARY:
Attached on the following pages is a copy of the Hearing Examiner's recommendations.
� ��, ��
January I 8, 2005
OFFICE OF T�IE HEARING EXAMINER
CITY OF RENTON
Minutes
APPLICANT: Steve Beck
Amberwood II LLC
4735 NE 4"' Street
Renton,WA 98059
OWNER: Bales Limited Partnership
PO Box 3015
Renton, �'VA 98056
Amberwood LLC !
4735 NE 4'h Street i
Renton, WA 98059 '
File No.: LUA 04-117,PP, ECF, R
LOCATION: 6135 NE 4`'' Street �
SUMMARY OF REQUEST: Approval for a 17-lot subdivision of a 4.24-acre site intended �'
for detached single-family homes and a Rezone to R-�. �
SUMMARY OF ACTION: Development Services Recommendation: Approve subject to
conditions
DEVELOPMENT SERVICES REPORT: The Development Services Report was received by the
Examiner on November 30,2004.
PUBLIC HEARING: After reviewing the Development Services Report, examining
available information on file with the application, field
checking the property and surrounding area;the Examiner
conducted a public hearing on the subject as follows:
NIINUTES
Tlze following minutes are a summary ojthe Deeember 14, 2009 hearing.
The legal record is recorded on CD.
The hearing opened on Tuesday,December 14, 2004, at 9:01 a.m. in the Council Chambers on the seventh floor
of the Renton City Hall. Parties wishing to testify were affirmed by the Examiner.
The following exhibits were entered into the record:
Exhibit No. 1: Yellow file containing the original Exhibit No. 2: Preliminary Plat with Rezone
application, proof of posting,proof of publication and
other documentation ertinent to this re uest.
Amberwood II Preliminary Plat
File No.: LUA-04-1 l7, PP, ECF, R
January l8, 2005
Page 2
Exhibit 1\'0.3: Preliminarv Grading and Utility Plan Exhibit No. 4: Preliminary Landscapin Plan
Exhibit No. 5: Neighborhood Map Exhibit No. 6: Zonin Ma
Exhibit No. 7: Zoning Map„�ith markings Exhibit No. S: Road profile showing 4' St:zet and
Rosario
The hearing opened with a presentation of the staff report by Susan Fiala, Senior Planner, Uevelopment
Services, City of Renton, 1055 S Grady Way, Renton, Washington 98055. The site is currently zoned
Residential-1 d���elling unit per acre, the applicant is requesting a rezone to R-5 dwelling units per acre. The site
is approximately 4.2 acres and it is located in the east portion of the City of Renton, off NE 4°' Street which
borders the northern property line of the three parcels and one tract site. The eastern boundary is also h�vo
parcels which are within the City of Renton. To the «�est is Rosario Avenue NE which extends and terminates
at NE 3'd Court v�fiich serves.Ambenuood Division I.
This project is vested under the old zoning of R-5 was in effect prior to November ]0, 2004 and that is ��•hat the
applicant is requesting to rezone. The properties that�vere R-5 have been rezoned to R-4. Surrou�:ding the site.
the properties are zoned R-5 and ��rere developed under that zoning designation.
The project was submitted based on approval of the R-5 zoning and with that there is no plat available sho��ing
the current R-1. A basic estimate showed that there could be 3 —4 lots on the 4 acre site and it ��ould be
affected by the access to those }ots��vhich would normally be deducted for densit� as «ell as �vhat ��ould be
provided for the stonn drainage tract.
Staff did not look at the differences between R-4 and R-5 zoning. The categories are very similar,the R-4 does
require a larger lot size of 8,000 square feet compared to the R-5 which requires 7,200 square feet. �Vhen the
ne��� zoning���ent into effect on November 10,there are different methods of calculating lot size as you deduct
the area required for easements and any setbacks are measured from private access easements. Th��R-4 zoning
'� requires additional landscaping along the arterials and non-arterial roads and requires landscaping of h�o trees
' per lot.
This site is designated Residential Low Density(RLD)and both the R-I and R-5 are permitted within this
designation. There has been no public comment with regard to the proposed rezone. The majority of the lots in ��,
the vicinity of the subject site are equal to or smal}er than the lots included with this proposed s�bdivision. The �!
proposed development is subject to code requirements and SEPA imposed mitigation measures that would �
attempt to diminish any potential adverse impacts if the rezone is granted. The majority of the lots in the '
vicinity of this site are equal to or smaller than the lots proposed for this subdivision.
Staff recommends approval of the rezoning of the subject site from R-1 to R-5.
The applicant is proposing 17 lots,based on the approval of the rezone. The net density would be 4.9 du/acre
after the deduction of public rights-of-way as well as private access easements serving three or more lots. NE
3`d Court wil) be extended and a new road extending south from NE 3rd Court terminating in a cul-de-sac of
' which a private access easement���ould serve Lots 11, l2, and 13. Tract A would support the storm drainage
facilities. This is a three-parcel site and Tract 999 from Amberwood Phase I that provides a portion of proposed
i Lot 1 of Amberwood Phase II.
The Environmental Review Committee issued a Determination of Non-Significance—Mitigated fo1�tl�e project,
which included six mitigation measures. No appeals of the determination were filed.
I
Amberwood I1 Preliminary Plat
File No.: LUA-04-117, PP, ECF, R
January l 8, 2005 �
Page 3
A homeowner's association or maintenance agreement is suggested for the development, which would be
responsible for any common i�nprovements and/or tracts within the p1at.
Traffic, Park and Eire Mitigations fees are proposed.
The proposed development complies with the Residential Low Density policies for both land use and housing
elements of the Comprehe�lsive Plan. The maximum per�nitted density in the R-5 zone is 5.0 du/acre.
Minimum density requirements do not apply. After deductions the proposed szte arrives at a net density of 4.9
du/acre. The proposed plat complies�vith density requirements for R-5 zoning_
All lots appear to comply�viti� the standards for dimension, sizes, setbacks and building standards and would be
verified at the time of individual building permit review. There are several single-family residences and
outbuildings on the existing site, staff recommends that the applicant obtain demolition permits and remove all
buildings located on the property prior to recording of the final plat.
Each of the proposed lots satisfies the minimum lot area and dimension requirements ofthe R-5 zone. Lots 1, 6
and 17 would be located at the intersection of public rights-of-way and the proposed radius for each �f these
corner]ots meet code.
Primary access to the site is proposed via NE 4'h Street to Rosario Avenue NE to NE 3`d Court. NE 3`d Court '
�vould extend to the east and be stubbed for future extension. A 26-foot wide access easement�vould provide
access to new Lots 10-13. Lots I- 9 and 14 - l7 would gain access directly to public streets.
Surrounding properties are developed under the R-5 zone, they are single-family residential on lots that are of
similar size. This plat fronts NE 4'h Street which is designated as a major arterial. To insure that these lots are
adequately buffered from the street, staff recommends that the applicant submit a landscape plan providing a
minimum of 5-feet of irrigated landscaping maintained by the HOA and a fence design for review and approval.
The Examiner inquired as to why the entire site was being cleared,why some of the natural vegetation and some
of the larger trees are not being retained. Larger lots should allow saving some of the larger trees.
Ms. Fiala stated that she would check the tree clearing and landscaping plan to see if there are some trees that
could be saved. It appeared that most of the trees are located where the building pads would sit.
The site is located within the boundaries of the Issaquah School District.
The storm drainage system would be located in Tract A�vhich has been designed to meet the Level 2 standazds
and water quality of the 1990 King County surface Water Design Manual. The project drains to Ortin�Hills
Creek. Tract A should be fenced along the entire perimeter and landscaping is to be provided alon�tl�e Tract's
frontage with the cul-de-sac.
The development is witl�in the water service area of Water District 90. The applicant submitted a Certificate of
V�'ater Availability. The District can provide a minimum of 1,000 gpm of avaitable fire flow per fire hydrant.
New water service stubs to each lot must be installed. The site is subject to the East Renton Interceptor Special
assessment District and Sanitary Sewer System Development Charges.
If the Hearing Examiner approves tlie rezone classification, staff recommends approval of this plat with
conditions.
Amberwood II Preliminary P1at
File No.: LUA-04-1 17, PP, ECF, R
January 18, 2005
Page 4
Steve Beck, 473�NE 4`h Street, Renton stated the property was originally in King County and zoned R-6 with a
conditional use family run business since 1977. The conditional use came up, the family business applied for
another conditional use,the City of Renton appealed it,the Bales family agreed to file for annexation and come
in under single-family zoning. When filing for annexation,they were cauglit up in the State Court ruling which
tied them for almost a year and a half. They were held to come into the CitJ�of Renton under the R-1 zone. As
many trees as possible will be retained on the proposed site.
Michael Chen, Core Design, Ine., ]471 1 NE 29ih Place, Suite 101, Bellevue, VVA 98007 stated they conc�tr���ith
the staff report. Regarding Condition 4 with the irrigated landscaping would drought tolerant p]anting be
included in place of irrigated landscaping?
The Examiner stated that they might be limited by code. Susan Fiala stated that current code states that it must
be irrigated landscapiiig. The new code effective November 10 does allow for drought resistant, staff would be
willing to look at drought resistant as well.
David Cavton, Engineer Core Design, Inc., 14711 NE 29'h Place, Suite 101, Bellevue, WA 98007 stated that he
would be happ}�to answer any questions regarding storm drainage or utilities. Plans at this time do not show
saving trees, but it is quite possible during building construction to maintain a� �1���n.� ��� p��sihie. The lar�est
trees on the site are on NE 4`h Street in the rear yards of Lots 4 and �.
Kayren Kittrick, Development Services stated thatthe only outstandin� yu��,�iun i� ah��ut tlic �li���u„iun ��uiil�;
on with transportation about a swap of vacating a portion of NE 4'" in exchange for dedicating a partion of NE
4`h,a per square footage straight up svvap,tl�ere are working on it now.
The Examiner called for further testimony reQardin� this pmiect. There ���as no �ne el�e ���ishin�t� speak. and
no further comments from staff. The hearin
FINDINGS,COI�CLL'SIONS & RECO�'
Having reviewed the record in this matter,the Examiner n�>�v nial:cs an�l ent��r; the lull.n��in�:
FINDINGS: 'I
). The applicant, Steve Beck, filed a request for a zoning reclassification of 4.24 acres of property from R-
1 (Single Family Residential - 1 dwelling unit per acre)to R-5 (Single Family Residential - 5 dwelling
units per acre)together�vith a request for a l 7-lot Preliminary Plat.
2. The yello�v file containing the staff report,the State Environmental Policy Act(SEPA}documentation
and other pertinent materials was entered into the record as Exhibit#1.
3. The Environmental Review Committee(ERC),the City's responsible official issued a Determination of
Non-Significance-Mitigated (DNS-M).
4. The subject proposal was review�ed by all departments with an interest in the matter.
5. The subject site is located 6135 NE 4th Street. The subject site is located south of NE 4th and east of
Rosario Avenue NE.
Amben��ood I1 Pretiminar�°Plat
File No.: LUA-04-1 17, PP, ECF, R
January 18, 2005
Page 5
6. The map element of the Comprehensive Plan designates the area in which the subject site is located as
suitable for the development of lo�v density residential uses, but does not mandate such development
without consideration of other policies of the Plan.
7. The subject site is currently zoned R-1 (Single Family - 1 dwellin;unit/acre).
8. The subject site was anneYed to the City with the adoption of Ordinance �064 enacted in 1��larch 2004.
9. The subject site is approximately 42 acres or 184,740 square feet. The subject site is generally
rectangular with a slight jog to the west at the north��est corner of the parcel. The parcel is
approximately 295 feet wide(east to�vest)along NE 4th Street. It is approximately 6] 1 feet deep.
10. The subject site has a slight slope dowm�ard to the south. The site drops about 15 feet over the 600
linear feet presenting a grade of approximately 3 percent.
1]. The applicai�t has proposed removing all trees and other vegetation from the subject site. There are
larger trees located on the site in the northwest corner and the southwest corner.
l2. As noted above, the applicant has requested that the �uhject site he reclassific�! fr��m R-1 to R-� t�
accommodate a 17-lot single-family plat.
13. Access to the subject site would be south i�r���n NI_�: ��th t�� a I-intersecti�,n ��itl� �i n<<v e�utcrl�� ��ten�ion
ofNE 3rd Court. Then a cul-de-sac would be created tl�at runs south to access the majority of the site.
NE 3rd Court would have a stub ending at the eastern edge of the plat to allo�v its eventual ccF�tinuation
further to the east.
l4. A tier of lots would lie between NE 4th Street, a »iajor arterial, and NE 3rd Court. Access �iould be
taken to the south,NE 3rd Court, and no access would be permitted to NE 4th. There would then be a
tier of lots on each side ofthe cul-de-sac roadway. Access for Lots I l, 12, and 13 would be via a
private utility easement located in the southeast corner of the site. The proposed lots�vould range in
size from 7,276 square feet to 9,254 square feet.
l 5. The subject site is located in the Issaquah School District. The City has adopted the Issaquah District's
impact fee for new homes built within the district's boundaries. That fee is$2,937.00 per home.
16. The density for the plat would be 4.9 dwelling units per acre after subtracting roadways.
17. The development will increase traffic approximately 10 trips per unit or approximately 170 trips for the
17 single-family homes. Approximately ten percent of the trips,or approximately 17 additional peak
hour trips�vill be generated in the morning and evening.
18. Stormwater will be contained in a Tract A, which is located in the southwest corner of the subject site.
This will continue to drain to an offsite wetland. The plat witl meet Level 2 standards for storm��vater
control. Staff has recommended that the tract be screened with fencing around its entire perimeter and
landscaping adjacent to the road��vay.
19. The subject site is served by City of Renton sewer utilities and a main runs a]ong NE 4th and along the
west side of the plat and can be extended to serve the site.
20. The subject site is located in Water District 90. The applicant has obtained a certificate of availabi(ity.
Amberwood lI Preliminary Plat
File No.: LUA-04-117, PP,ECF, R
Janoary I 8,2005
Page 6
21. The subject site is basically at the eastern limits of the City. Property to the north and east is generally
low-density single-famity uses in both the City and County. The City zoning near the subject site is
either R-1 like the subject site or is R-4, recently reclassified after the City eliminated the R-5 district
and created the R-4 district. The R-4 district reyuires a minimum lot size of 8,000 square feet whereas
the R-5 zone required a minimum lot size of 7,200 square feet. Staff noted that there are other
differences in things like easement, landscaping and setbacks.
22. As noted above,the subject site is not quite rectangular. 7'he subject site extends slightly to the west
and north creating jogs in those property lines. Rosario Avenue NE will be located along the western I
edge of the site. The applicant and the City are discussing a s��ap of property along NE 4th to create a �'
smooth boundary. The City��'ould vacate approximately as much property along NE 4th Street as the ,
applicant would dedicate. Staff has recommended that the applicant landscape and fence the northern
property line and that a homeowners association maintain this property.
23. Staff has recommended that the applicant plant h�vo trees in t1�e front yard of each 1ot.
24. The City Council has adopted legislation that has eliminated the R-5 Zoning District. In its place the
Council has created the R-4 Zoning District. In this action the zoning of R-5 parcels was changed to R-
4. As noted,there are lot size differences and any parcel that does not meet the current, larger or
changed standards would be considered a legally, non-confonning use. The change occurred on !
November l0, 2004. The applicant submitted the application to change the zoning from R-1 to R-5
prior to that date and,therefore, staff considered the request under the prior standards. Staff indicated
that the application vested the application to the R-5 zoning.
REC011Ti�ZENDATIONS:
Rezone
l. A property�nay, at the discretion of the City Council, be reclassified frozn one zoning district to another
if it generally meets the criteria fo�nd in Section 4-9-180F(2). Those criteria include:
a. The rezone is in the public interest, and
b. The rezone tends to further the presenration and enjoyment of any substantial property rights
of the petitioner, and
c. The rezone is not materially detrimental to the public welfare or the properties of other
persons located in the vicinity thereof, and
d. The rezone meets the review criteria in subsections Flb and Flc ofthis Section. (Amd. Ord.
4794, 9-20-1999)
It also must meet the criteria of 4-9-]80F(1):
b. The property is potentially classified for the proposed zone being requested pursuant to the
polices set forth in the Comprehensive P1an; and
c. At least one of the following circumstances applies:
i. The subject reclassification���as not specifically considered at the time of the last area
land use analysis and area zoning; or
ii. Since the most recent land use analysis or the area zoning ofthe subject property,
authorized public improvements, permitted private development or other circumstances
affecting the subject property have undergone significant and material change_
Amberwood ll Preliminary Plat '
File No.: LUA-04-117, PP, ECF, R
January l 8, 2005
Page 7
For reasons cited below,the City Council should not approve the proposed reclassification of the subject
site from R-1 to R-5.
2. The City Council has substantial discretion wlien it comes to applying zoning categories to properties.
While there are limits to that discretion such as not approving spot zones,their discretion allows them to
achieve uniform standards that are in compliance with the comprehensive plan. There are a few
fundamental concepts in law use law. One of them is that tl�e law frowns on non-conformin� ��ses. It
encourages their early and reasonable termination. (Citations omitted). Therefore, the first question is
why immediately create non-conforming lots? Why zone property R-5, a classification th��t no longer
exists, plat it at tliat density and then immediately change the zoning to R-4 and make the plat's basis
non-confonning. Staff has suggested in its reasoning and analysis of this rezone request that it is
governed by vesting. ln dealing with this rezone request, vesting usually follows zoning and permits an
applicant who l�as already submitted an application to develop or use property in a manner allowed by
that current zoning or the zoning regulations in place wl�en the application was submitted. That is an
applicant may develop the property with the zoning and under regulations that existed when they
submitted their application. This office is not aware of any particular case�vhere this doctrine requires
that zoning that has been eliminated still be applied to a site because an application for a zoning change
was submitted prior to the change. The vesting doctrine generally is not applied outside of land use
regulations that change under zoning and not to the initial zoning itself.
3. Zoning is only justified ifthe request is appropriate. The City Council as noted has almost complete
discretion in tl�e area of zoning as long as it does not attempt to spot zone a parcel. Zoning
classifications are governed by the City Council and their ability to practice it appropriately. The
Council has the right to decide if zoning is appropriate given the parcel, its circumstances, its
surroundings and the comprehensive plan's policies and goals. Seeing that the City Council in its
judgment has determined to eliminate the R-5 zoning District and in its stead create an R-4 zoning
Uistrict, it is probably inappropriate to agree that this site, at this time, should be reclassified to R-5.
The comprehensive plan calls for rural residential or low residential densities on this site. 7fie current
R-1 zoning fulfills that objective. While R-5, at one time was considered appropriate, clea:ly the City
Council in eliminating the R-5 zone determined that it was not compatible with the Comprehensive
Plan. The Council determined that R-4 with its larger lots and unconstrained front yard setbacks
unhampered by easements was more appropriate for the area at the eastern edge of the City. It would
appear that the R-5 zoning that the applicant has requested seeks additional densities that the City
Council has determined are inappropriate for sites that the comprehensive plan designates far rural
residentia) uses. This site has sheet flows that feed a wetland and then a creek. Larger lots preserve the
more natural storm�vater conditions found on lots in this area. There is less pavement in the form of
roads when there are fewer lots and less proportional home footprints on larger lots. The subject site
should not be developed at the R-5 density in light of those characteristics.
4. It is not in the public interest to change the zoning on a property that has a current and valid zoning
category, in this case, R-1 and change it to a category that no longer exists, in this case, R-5. It is not in
the public interest to create a series of lots that immediately become non-conforming.
�. This o�ce would like to take the tact that the City Council should consider R-4 zoning for the subject
site at this juncture. R-4 zoning would probably be appropriate but since the legal notice was for R-5
zoning, it may or may not be an appropriate stance. It might be something that staff and the City
Attorney can consider and reflect upon given a bit of time that allows for further analysis.
Amberwood ll Preliminary Plat
File No.: LUA-04-1 17; PP, ECF, R
January 18, 200�
Page 8
6. For the reasons noted abo��e, a rezone of the� subject site from R-1 to R-� is inappropriate. ,�\ rezone of
the site to R-4 �r�ould be appropriate. First, it would avoid creating immediately non-confarming lots. It
�vould match the R-4 zoning that now attaches to nearby property and would be in keeping with the
Comprehensive Plan's goals and policies of protecting sensitive lands. It would allow just a bit less
intensive reuse of the subject site, lessening stormwater impacts, enlarging lots and limiting the
iinpediment of access easements decreasing front or side yard usability.
7. Clearly, allo��ing more intense use ofthe site than now permilted in the R-1 zone furthers the property
ri�hts of the property o«-ner. Although, the R-] zone does pennit the use of the subject site and is fu11y
compatible with the Comprehensive Plan's low density housing objectives.
S. A rezone of the subject site to R-4 would not be materially detrimental to either the public welfare or
other properties in the area. Again,though, keeping the site R-1 �vould also not prove materially
detrimental to tl�e public�i�elfare or other properties.
9. The Comprehensive Plan would allow either R-1,the current zoning, or R-4, a more intense but still
permitted residential zoning for the subject site. The area is in the eastern or more rural po►-tion of the
City and could be served by either the R-1 or the R-4 zoning.
10. Vl'hen the subject site was recently annexed some of the intrastructure improvements were not available
such as the new roads west of the subject site. R-4 zoning would increase the density potenti3l of the
subject site and take advantage ofthe ne��v infrastructure.
] 1. Therefore, it if were to be determined that the legal issues can be appropriately satisfied by the
published legal notice, it might be appropriate for the City Council to approve the reclassification of the
subject site from R-1 to R-4. A reclassification to R-5 is not justified at this time and should not be
approved.
Prelimina►-ti`Plat
]2. The proposed Preliminary Plat�vould not be appropriate given the above recommendation that the I
subject site be rezoned to R-4 since approximately half of the proposed lots would not meet the 5,000 I
square foot lot standards of the R-4 zone. A change in the plat's proposed number of lots is quite I�
different from the zoning change proposed in this recommendation. A plat's layout, lots and roadways
may be changed as an inherent part of plat review and is incorporated into any]egal notice that involves I�
a public hearing for a plat. So a division ofthe subject site into a similar fashion as that now proposed �I
but that would meet the density requirements and lot area standards of the R-4 zone would be ,
appropriate under the existing legal notice. If such a plat mirrors the current plan and has rectangular ',
lots, lot lines at generally right angles to streets, appropriate access and stormwater containment, it I
would be appropriate. I
13. A plat that meets the density and lot standards of the R-4 zone would serve the public use and interest. I
It would provide additional housing opportunities to the community. It would be in an are::where urban I
services can be provided. It would avoid urban sprawL It would increase the tax base of t'�e City. ',
14. The plat�vould still have to provide an appropriate dedication so that NE 4th Street could Ue developed
with a consistent and safe, non jogging alignment.
1�. Similarly,the plat would ha�re to make appropriate provisions for landscaping and screening the rear of
new lots that ��ould line NE 4th Street to protect the single family ame►iities of those residents.
Amberwood II Preliminary Plat I
File No.: LUA-04-1 17, PP, ECF, R I
January 18, 2005 ,
Page 9 I
16. Aiso,the Comprehensive Plan calls for low-density, larger lots. Part of that objective was to preserve
some of the rural,open or wooded character of this more remote corner of the City. There are trees that �
already add to tl�e character of this community and if protected, could preserve some of that character.
Not every tree on lots in the R-4 zone should be removed so that the entire site is altered to urban �I
standards. Therefore, working`��ith staff,the applicant should preserve some of the larger trees that do
not immediately lie in the way of building pads or road rights-of-way.
l 7. Stormwater containment is still important since the subject site feeds a wetland and ultimately a creek i
system. Those natural features do��nstream of the subject site need to retain their natural flow of water. ,
The pond created though must be screened and fenced to provide for both public safety and to preserve
the property values of homes adjacent to it. Fencing and screening as recommended by staff is
appropriate. '
l 8. �I'he subject site lies within the Issaquah School District and shall pay the appropriate fees �s building
permits are submitted.
19. In conclusion, a plat of the subject site that meets the R-4 zone's criteria«rould be appropriate and could I',
be approved by the City Council if the Council decides it can rezone the subject site to R-4. I
RECONIMENDATIONS: II
The City Co�mcil should deny the request to reclassify the subject site from R-1 to R-� but should
consider reclassifying the subject site from R-1 to R-4 if permissible under the legal notices already
published for this application.
'�he City Coui�cil should approve a Preliminary Plat that meets the zoning standards for the R-4 zone
subject to the following conditions:
1. The applicant shall comply with the conditions imposed by the ERC.
2. The applicant shall dedicate sufficient property to allow a consistent alignment along 4th Street
adjacent to the plat.
3. ln consultation with staff and a certified arborist,the applicant should preserve some oftl�e larger
trees that do not immediately lie in the way of building pads or road rights-of-way.
4. The applicant shall obtain a demolition permit and complete a11 inspections and approvals for all
buildings located on the property prior to the recording of the final plat. The satisfaction of this
requirement is subject to the review and approval of the Development Services Project Manager.
5. A sign shall be installed at the stub road,NE 3�d Ct.,that informs residents of the plat that the road
�vould be extended to the east in the future and carry through-traffic. The sign shall be installed
prior to recording of the final plat.
6. A homeowner's association or maintenance agreement shall be created concurrently with the
recording of the final plat in order to establish maintenance responsibilities for all shared
improvements, including fences, landscaping, utilities, private easements,etc. A draft of the
document(s), if necessar�-, shall be submitted to the City of Renton Development Services Division
Amberwood II Preliminary Plat
File No.: LUA-04-1]7,PP, ECF, R
January l8, 2005
Page 10
for review and approval by the City Attorney and Property Services section prior to recording of the
final ptat.
7. The applicant shall install a modulated,decorative fence,with irrigated ]andscaping alon�;the entire
plat's frontage with NE 4ti' Street. All fencing shall be located and designed to not inte�fere with
sight distances required at the intersections of poblic streets. The applicant shall submit a landscape
plan and fence design to the City's Development Services Division for review and approval prior to
instal lation. The fence and landscaping shall be installed prior to recording of the final plat.
8. The applicant shall install a fence of a quality material (no chain-link, if possible)with a landscaped
visual barrier that includes plant materials which would provide a year-round dense screen within I
three(3)years from the time of planting along the entire perimeter of Tract A(starm drainage �
facility). The applicant shall submit a landscape plan and fence design to the City's Development
Sen�ices Division for review and approval prior to installation. All fences and landscaping shall be
installed prior to recording of the final plat.
9. The applicant shall pay the appropriate Issaquah School District Mitigation Fee of$2,937.00 per I
new single-family lot. The fee shal) be paid prior to building permit approval. I
ORDERED THIS l 8`h day of January 2005.
�.----� , �'
_j[_�__!� (�,,,,`
FRED J. KA AN
HEARING E MIl�'ER
TRANSMITTED THIS ]8'�' day of January 2005 to the parties of record:
Susan Fiala Steve Beck Kayren Kittrick
1055 S Grady VVay 4735 NE 4'h Street 1055 S Grady Way
Renton,WA 98055 Renton,WA 98056 Renton,WA 98055
Michael Chen Uavid Cayton
Core Design,Inc. Core Design,Inc.
1471 I NE 29`h P1ace, Ste. 101 14711 NE 29"'Place, Ste. 101
Bellevue, WA 98007 Bellevue,WA 98007
TRANSMITTED THIS 18`h day of January 2005 to the following:
Mayor Kathy Keolker-Wheeler Stan Engler,Fire
Jay Covington, Chief Administrative Officer Larry Meckling, Building Official
JuIia Medzegian, Council Liaison Planning Commission
Larry Warren, City Attorney Transportation Division
Gregg Zimmermaii, PBPW Administrator Utilities Division
Alex Pietsch, Economic Development Neil Watts, Development Services
Jennifer Henning, Development Services Janet Conklin, Development Services
Stacy Tucker, Development Services King County Journal
Amberwood ll Preliminary Plat
File No.: LUA-04-117, PP, ECF, R
January 18, 2005 '
Page 11
Pursuant to Title IV, Cljapter 8, Section 100Gof the City`s Code, request for reconsideration must be filed in
�vritin� on or before 5:00 p.m.,February 1,2005. Any aggrieved person feeling that the decision of the
Examiner is ambiguous or based on erroneous procedure, errors of law or fact, error in judgment, or the
discovery of new evideilce which could not be reasonably available at the prior hearing may make a written
req�est for a review by the Examiner�vitl�in fourteen(14)days from the date of the Examiner's decision. This
request shall set forth the specific ambiguities or errors discovered by such appellant, and tlie Examiner may,
after review of the record,take further action as he deems proper.
An appeal to the City Council is governed by Title IV, Chapter 8, Section I 10, �vhich requires that s�Tch appeal
be filed with the City Clerk, accompanying a filing fee of$75.00 and meeting other specified requirements.
Copies of this ordinance are available for inspection or purchase in the Finance Department, first floor of City
Hall. An appeal must be filed in�vritin�on or before 5:00 p.m.,February 1,2005.
If the Examiner's Recommendation or Decision contains the requireinent for Restrictive Covenants, the
executed Co�enants will be required prior to apProvat by City Council or final processine of the file. You
may contact this office for information on formatting cor-enants.
The Appearance of Fairness Doctrine provides that no ex parte(private one-on-one) communications may occur
concerning pending land use decisions. This means that parties to a land use decision may not comr;�anicate in ;
private with any decision-maker concerning the proposal. Decision-makers in the (and use process include both I
the Hearing Examiner and members of the City Council.
All communications concerning the proposal must be made in public. This public communication permits all
interested parties to know the contents of the communication and would allow them to openly rebut the
evidence. Any violation ofthis doctrine would result in the invalidation of the request by the Court.
The Doctrine applies not only to the initial public hearing but to all Requests for Reconsideration as well as
Appeals to the City Council.
I
3. OFFSITE ANALYSIS:
Upstream Tributary Area
There is no upstream area tributary to the subject site.
Downstream Analysis
This offsite analysis was performed on September 15,2004. The site sheet flows to the
south west corner where the surface runoff enters a wetland azea to the south of the
project. This wetland area flows in a well defined low area to an 18-inch culvert under 2nd
Street and then on to another well defined channel to the south west.
No evidence of erosion or flooding was found during this downstream analysis.
�� NOTF: �(rcil ylaps are�cmpiled trom Official Aecords
(aC6 uy� and Field Surveys.They are produc9d 1a�referenca use � 9
�; only and no w2rranty�s �xpress2d ar implieC. � i
�
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�oz � ���a o . ?,° �° Z 60 79 ' oa '� � DOWNSTREAM DRAINAGE MAP #1 �
"° � AMBERWOOD II
sr. ,� � 89.96 �, . ,,,2 ��.90 76 � �❑ _.
3.6? t,��/q� 49J9 o y 92 ,�o WSBe o O �
;�e.< S�5 �a � '77- � CORE PROJECT NO. 04027
o „�o so m (N.E i75 �i � 7d78 �
a TRI�F " 93 - a�7z _ �•�� ' � i '
p 99m 98 a � $ � - 4 fwr �:. 3 � r��.
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t� �, 94 � �sr z� _ = z : � - , -
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4. FLOW CONTROL AND WATER QUALITY FACILITY ANALYSIS AND
DESIGN:
A. Hydraulic Analysis
The drainage analysis was modeled using the King County Runoff Time Series software.
The onsite soils aze Alderwood (AgC), KCRTS group Till per the Soils Map attached on
the following pages. The site is located in the Sea-Tac rainfall region with a location
scale factor of 1.0.
EXISTING CONDITIONS
The site will include the property azea,4.24 acres, plus the area within the NE 4`� Street
Right-Of-Way along the frontage from the proposed back of sidewalk to the property line,
0.05 acre. The existing ground cover consists of a combination of impervious surfaces,
1.44 acres, associated with outbuildings and gravel driveways/parking, along with
landscaping, brush, 1.94 acre, and trees,0.91 acre. Per Table 3.2.2.E in the 1998
KCSWDM, the effective impervious fraction for the site is 0.40 for existing rural areas.
T'he effective impervious area is therefore 0.40*1.44 acres =0.58 acre. Per Table 3.2.2.0
in the 1998 KCSWDM, Pasture will be utilized as the existing condition rather than
Grass for the landscaping and brush since the predevelopment densiry is less than 4
DU/GA. Pasture will also be utilized for the remaining non-effective impervious area.
The following information was used for generating time series and flow frequencies.
EXISTING CONDITIONS Total Area=4.29 acres
(04027ex)
GROUND COVER AREA(acre)
Till-Forest 0.91
Till-Pasture 2.80
Effective Im ervious 0.58
ST 1.0/
ST 1.1 _ ST 1.0 LA 0.8 LA 0.9 LA 1.0 LA 1.2
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� � � g� ; 2� ��re � �� 2 --- SOIL SURVEY MAP
� - ` � � � ; ' � '� 492 I `.\, AMBERWOOD II
_� � ��. CORE PROJECT NO. 04009
� No � 1 �i��\\ �,`•�IP
�,o�ao ��LJ
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CREATING A TIME SERIES FILE EXAMPLE I
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TABLE III-1
EQUIVALENCE BETWEEN SOIL TYPES CLASSIFIED BY U.S. SOIL CONSERVATION
SERVICE AND KING COUNTY RUNOFF TIME SERIES
SCS
SCS Soil Type Hydrologic KCRTS Soil Group Notes
Soil Grou
'�� Alderwood A ,A ,A C Till
ena B,Am C
Arents,Everett Material An B Outwash 1
Beausite BeC,BeD,BeF C Till 2
Bellin azn Bh D T"ill 3
Briscot Br D Till 3
Buckle Bu D Till 4
Earlmont Ea D Till 3
Ed ewidc Ed C Till 3
Everett EvB,EvC,EvD,Ew A/B Outwash 1
Indianola(InC,InA,InD A Outwash 1
Kitsa K B,K C, D C Till
Klaus Ks C Outwash 1
I�eilton e A Outu�ash 1
Newber N B Till 3
Nooksack 1�(k C Till 3
Norma No D Till 3
Orcas Or D Wetland
Oridia Os D Till 3
Ovall OvC,OvD,Ov C TiIl -2
Pilchuck Pc C Till 3
Pu Pu D Till 3
Pu allu B Till 3
Ra ar RaC,RaD,RaC,RaE) B Outwash 1
Renton Re D Till 3
Salal Sa C Till 3
Sammamish(Sh D Till 3
Seattle Sk D Wetland
Shalmr Sm D Till 3
Si Sn C Till 3
Snohomish So,Sr D Till 3
Sultan Su C Till 3
Tukwila u D Till 3
Woodinville o D Till 3
Key to Notes:
1. Where outwash soiLs are saturated or underlain at shallow depth(<5 feet)by gladal till,they should be
treated as till soils.
2. These aze bedrock soiLs,but calibration of HSPF(Hydrological Simulation Program-Fortran)by King
County Surface W ater Management shows bedrock soils to have similar hydrologic response to till soiLs.
3. These are alluvial soils,some of which are underlain by gladal tiIl or have a seasonally high water table.
In the absence of detailed study,these soiLs should be treated as till soils.
4. Buckley soils aze formed on the low permeability Osoeola mudflow. Hydrolog�c response is assumed to
be similar to that for till soiLs.
��
October 20,199� ��� KCRTS User's Gwde 1�-Jr'
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SECTION 3.2 RUNOFF COMPUTATION AI�iD ANALYSIS MEI'HODS
KCRTS Land Cover Types
KCRTS supports four land cover types:forest,pasture,grass,and impervious. T'hese cover rypes shall be
applied as specified in Table 3.2.2.0(below).
TABLE 3.2.2.0 KCRTS COVER GRQUPS AND AREAS UF APPLICATI�N
KCRTS APPLICATION
Cover Group predevelopment Post•Development
Forest All foresUshrub cover, irrespective of All permanent(e.g., protected by
age. covenant or SAO designation) onsite
foresdshrub cover, irrespective of age,
planted at densities sufficient to ensure
80%+canopy cover within 5 years.
Pasture All grassland, pasture land, lawns, and Unprotected forest in rural residential _
cultivated or cleared areas,except for development may be considered half
lawns in redevelopment areas with pasture,half grass.
predevelopment densities in excess of
4 DU/GA..
Grass Lawns in redevelopment areas with All post-development grassland and
predevelopment densities in excess of landscaping and all onsite forested land
4 DU/GA.. not protected by covenant or SASA
designation (except in rural areas as
noted above).
Wetland All delineated wetland areas(except All de(ineated wetland areas (except
cultivated/drained farmland), cultivated/drained farmland).
I
Impervious��� All impervious surfaces, induding All impervious surfaces,including
heavily compacted gravel and dirt compacted gravel and dirt roads, parking
roads, parking areas, etc.,and open areas,etc.,and open water bodies,
water bodies (ponds and lakes). including onsite detention and water
quality ponds. i
�'f Impervious acreage used in KCRTS computations should be the effective impervious area '
(EIA). This is the gross impervious area multiplied by the effective impervious fraction (see
Table 3.2.2.E, p.3-28). Non-effective impervious areas are considered the same as the '
surrounding pervious land cover.
The following four factors were considered in specifying the above land cover types to be used in
hydrologic analysis with KCRTS:
• Cover types are applied to anticipate ultimate land use conditions. For example,probable clearing
of woodland after development is nominally complete suggests that the post-development land use be
specified as grassland(either pasture or grass)unless the forest cover is protected by covenant.
• In areas of redevelopment,there are often significant changes between the predevelopment and post-
development efficiencies of the drainage system. For example,in conversion of low density
residential areas to higher densiry land use, impervious areas prior to redevelopment may not be
efficiently connected to a drainage system(e.g.,downspouts draining to splash blocks,ditched instead
of piped roadway systems). These problems are addressed by defining an"et�ective impervious
fraction"for existing impervious areas and by generally requiring predevelopment grasslands to be
modeled as pasture land.
9/1/98 1998 Surface Water Design Manual
3-26
SECTION 3.2 RUNOHF COMPiTI'ATION AND ANALYSIS MB71-IODS
TABLE 3.2.2.D PERCENT 1MPERVIOUS COVERAGE FQR EXISTING RESIDENTIAL AREAS
Dwelling Units/Gross %Impervious��� Dwelling Units/Gross %Impervious
Acre Acre
1.0 DUIGA 15�2� 4.5 DU/GA 46
1.5 DU/GA 20 5.0 DU/GA 48
2.0 DU/GA 25 5.5 DU/GA 50
2.5 DU/GA 30 6.0 DU/GA 52
3.0 DU/GA 34 6.5 DU/GA 54
3.5 DU/GA 38 7.0 DU/GA 56 I
4.0 DU/GA 42 7.5 DU/GA 58 II
For PUDs,condominiums, apartments,commercial businesses,and • ,
industrial areas, percent impervious coverage must be computed.
Notes: I'!
�'� Includes streets and sidewalks.
��� These figures should be adjusted by the effective impervious fraction given in Table 3.2.2.E, if
applicable. Values from Table 3.22.E may be interpolated as necessary.
TABLE 3.2.2.E EFFECTIVE L'�iPERVIOUS FRACTION���
Land Use Predevelopment Post-Devetopment
Commercial, Industrial, or Roads with Collection System 0.95 1.00
Multi-Family or High Density Single Family�2} (>4 DU/GA) 0.80 1.00�3�
Medium Density Single Family�2�(4 DU/GA) 0.66 1.00�3�
Low Density Single Family��(1 DU/GA) 0.50 1.00�3�
Rura1�2�(< 1 DU/GA) 0.40 1.00�3�
GraveVDirt Roads and Parking Lots, Roads without 0.50 0.50 -
Collectio�System
Notes:
�'� The effecfive impervious fraction is the fraction of actual total impervious area connected to the
drainage system. These figures should be used in the absence of detailed surveys or physical
inspection (e.g.,via pipe,channel,or short sheet flowpath).
��� Figures for residential areas indude roadways.
"� Where downspout infiltration is used, roofs are not counted as impervious area when sizing the flow
control facility. Roofs are considered grass where downspouts are dispersed in rural residential
devefopment, or where dispersed flowpaths exceed 50 feet in urban residential development(see
Section 5.1.2 for limitations on roof downspout dispersion).
9/1/98 1998 Surface Water Design Manual
3-28
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Flow Frequency Analysis
Time Series File:04027ex.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS} Period
0.355 4 2/09/Ol 15:00 0.677 1 100.00 0 .990
0.212 7 1/05/02 16:0a 0.375 2 25.00 0.960
0.375 2 2/27/03 7:0a 0.358 3 10.00 Q.90�
0.157 8 8/26/04 2:00 0.355 4 5.OQ 0.800
0.217 6 1/05/05 8:OQ 0.337 5 3 .0a 0.667
0.358 3 1/18/06 16:00 0.217 6 2.00 0.500
�.337 5 11/24/06 3:00 0.212 7 1.30 0.231
0.677 1 1/09/08 6:00 0.157 8 1.10 0.091
Computed Peaks 0.577 50.00 0.98�
DEVELOPED CONDITIONS
The developed site will consist of 17 single family residences with associated roadway
and utilities.
The maximum impervious area per lot was calculated using the criteria in the 1998 King
County Surface Water Design Manual page 3-27 and K.C.C.21A.12.030. T'he proposed
development is urban residential. The site is R-5 zoning. In K.C.C.21A.12.030,there is
no listing for R-5 zoning. The maximum impervious area per lot therefore is assumed to
range from R-4 zoning of 55%to R-6 zoning of 70%. The average lot size is 7,913
square feet. The average maximum impervious area per lot would therefore range from
R-4 zoning with 4,352 square feet of impervious area per lot to R-6 zoning with 5,539
square feet of impervious area per lot. Per the 1998 King County Surface Water Design
Manual page 3-27,the maaLimum impervious area per lot would either be 4,000 square or
the maximum impervious area as stated in K.C.C.21A.12.030,whichever is less. The
impervious area per lot will therefore, be equal to 4,000 square feet since it is less than
the other impervious areas as stated in K.C.C.21A.12.030.
Im rvious Area Delineation
Onsite road and sidewalk 29,952 sf
Impervious area of lots(17*4,000 sfl 68,000 sf
Total impervious area 97,952 sf(2.25 acres)
The input used for the KCRTS analysis is summarized in the table below:
DEVELOPED CONDITIONS Total Area=4.29 acres
(04027d)
GROUND COVER AREA(acre)
Till-Grass (Landsca in ) 2.04
Im ervious 2.25
21 A.12.030 A. Densities and dimensions - residential zones
RESIDENTIAL
Z nuwLL urts�w uasnw
0
N �E RES�FNiiA1
E
S
STAFtDARDS RA-25 RA-5 RA-10 RA-20 UN ihi R-4 X-6 R-8 ii-12 R-t8 R-24 R-AS-
(771
Bzsa Dentlty: 02 0.2 0.1 OAS 02 1 4 6 8 12 18 24 4a
DwNling dWx dWx duhc dWac dWx dWx Mdac dWx dWae tlWae dulac dWx dWae
Unwws lr1 (�
{��
�vm o.�ny:
o.a o.a e e �2 �s n 3s n
. DwalBng IA�WAtn dufae duFx dufx dWsc dWx dufx tlWx dWae dufx
��� (� �) �
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� 1��1 1�� �+� (�8? (�� t��l 1+8)
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(b)
runmwm s.a �ss rt �as n 1]5 R 135 h u a as n ao a x rt ao tt w n son so n so n '
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ai ';
°pn�"""'d°°� soa aoe� mrt mn mee zna �on �ort �on �on �on �orc �ox
sNDaac
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�)
Mlnlowm Inhfior S R tOR 10![ 10 R S}! 5 ft S 1t 5}I S R S R 5 tt 5 R 5 tt
swback la} (9) i91 I91 fn frl I�ol 1�01 (�a1 (�ol
f�l{1el
Bas�Helght 10 R 40 it 40 h �0 h JS A 35 ft 35 R 35 R 35 tt 60 h 60 h 6D R 60 R
(4) +5 R �S R 80 R 80 R !0 ft
CuF I��1 ful (�4) (�41
Mah�mo 25X 20X 14:C 12SX �OX 30X 55% 70X TY.G LS% 85X 8iX 90l,
� re�pe�vious 1��1 I�n h�) h�l 1'�t) (��l
Suffaea: (�9} (19) (19j (19)
?nc�ntagsl�
12-2 (King County 6-00)
Flow Frequency Analysis
Time Series File:04027d.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) Period
0.728 5 2/09/O1 2:00 1.50 1 100.00 0.990
0.573 8 1/05/02 16:00 0.879 2 25.00 0.960
0.879 2 2/27/03 7:00 0.869 3 10.00 0.900
0.598 7 8/26/04 2:0� �.771 4 5.00 0.800
0.726 6 10/28/04 16:00 0.728 5 3.00 0.667
0.771 4 1/18/06 16:00 0.726 6 2.00 0.500
0.869 3 10/26/06 0:00 0.598 7 1.30 0.231
1.50 1 1/09/08 6:00 0.573 8 1.10 0.091
Computed Peaks 1.29 50.�0 0.980
B. Detention Routing Calculations
Per the Hearing Examiner's Recommendations, Level 2 Flow Control shall be utilized to
mitigate for increase storm drainage flows created from the developed site. A '',
combination water quality/detention pond will be constructed at the southwest corner of ',
the subject property. All stormwater facilities will be sized according to the 1998 i
KCSWDM. '
The Pond (04027pd.rdf� was sized based on the 1998 KCSWDM and KCRTS Computer
Software Reference Manual. See attached KCRTS printouts and attached Pond Volume
Calculation spreadsheet on the following pages. The live storage portion of the Pond has
a volume of 32,814 CF at El. 500 which exceeds the required 30,794 CF.
The length of the sheet flow spreader was designed based on the sheet flow spreader
detail on page 4-31 in the 1998 KCSWDM. Per the KCSWDM detail, 50 feet of sheet
flow spreader can handle 0.5 cfs of flow. Per the KCRTS printouts on the following
pages, the 100-yeaz outflow from the pond is 0.87 cfs. Therefore, a sheet flow spreader
of length 87 feet would handle the 0.87 cfs of flow.
Retention/Detention Facility �do�-�L'7(JL.I.i��
r - -
Type of Facility: Detention Pond
Side Slope: 2 .50 H:lV
Pond Bottom Length: 98.00 ft ,
Pond Bottom Width: 51.00 ft '!
Pond Bottom Area: 4998. sq. ft
Top Area at 1 ft. FB: 9852. sq. ft
0.226 acres
Effective Storage Depth: 4.50 ft
Stage 0 Elevation: 495.50 ft
Storage Volume: 30794. cu. ft
0.707 ac-ft
Riser Head: 4.50 ft
Riser Diameter: 12.�0 inches
Number of orifices: 3
Full Head Pipe
Orifice # Height Diameter Discharge Diameter
(ft) (in) (CFS) (in)
1 a.00 1.63 0.152
2 2.50 1.75 0.117 4.0
3 3.25 1.90 0.109 4.0
Top Notch Weir: None
Outflow Rating Curve: None �
Stage Elevation Storage Discharge Percolation Surf Ar�a
(ft) (ft) (cu. ft) (ac-ft) (cfs) (cfs) (sq. ft i
0.00 495.50 0. 0.000 0.000 0.00 4998 .
0.02 495.52 100. 0.002 0.009 0.00 5013 .
0.03 495.53 150. 0.003 0.013 0.00 5020.
0.05 495.55 251. 0.006 0.016 0.00 5035.
0.07 495.57 352. 0.008 0.019 0.00 5050.
0.08 495.58 402. 0.009 0.021 0.00 5058.
0.10 495.60 504. 0.012 0.023 0.00 5073.
' 0.12 495.62 605. 0.014 0.025 0.00 5088. ,
0.14 495.64 707. 0.016 0.026 0.0� 5103.
0.24 495.74 1221. 0.028 0.035 0.00 5178. '
0.34 495.84 1743. 0.040 0.041 0.00 5254. '
0.44 495.94 2272. 0.052 0.047 0.00 5331. '
0.54 496.04 2809. 0.064 O.a52 0.00 5408.
0.64 496.14 3354. 0.077 0.057 0.00 5485.
0.74 496.24 3906. 0.090 0.061 0.00 5563.
0.84 496.34 4466. 0.1�3 0.065 0.00 5641.
0.94 496.44 5034. �.116 0.069 0.00 5720.
1.04 496.54 5610. 0.129 0.073 0.00 5800.
1.14 496.64 6194. 0.142 0.076 0.00 5880.
1.24 496.74 6786. 0.156 0.080 0.00 5960.
1.34 496.84 7386. 0.170 0.083 0.00 6041.
1.44 496.94 7994. 0.184 0.086 0.00 6123 .
1.54 497.04 8611. 0.198 0.089 0.00 6205.
1.64 497.14 9235. 0.212 0.092 0.00 6287.
1.74 497.24 9868. 0.227 0.094 0.00 6370.
1.84 497.34 10509. 0.241 0.097 0.00 6453.
1.94 497.44 11159. 0.256 0.100 0.00 6537.
2.04 497.54 11817. 0.271 0.102 0.00 6622 . %
2.14 497.64 12483. 0.287 0.105 0.00 6707. 'i
2.24 497.74 13158. 0.302 0.107 0.40 6792. ,
2.34 497.84 13842. 0.318 0.109 0.00 6878. �
2.44 497.94 14534. 0.334 0.112 0.00 6965 . '�
2.50 498.00 14953. 0.343 0.113 0.�0 7017.
2 .52 498.02 15094. 0.347 0.114 0.00 7034. '
2.54 498.04 15235. 0.350 0.117 0.00 7052 . '
2.55 498.05 15305. 0.351 0.120 O.Oa 7060.
2.57 498.07 15447. 0.355 0.125 0.00 7078.
2 .59 498.�9 15588. 0.358 0.131 0.40 7095.
2.61 498.11 15730. 0.361 0.138 0.00 7113.
2 .63 498.13 15873. 0.364 0.146 0.00 7130.
2.65 498.15 16016. 0.368 0.148 0.00 7148.
2 .75 498.25 16735. 0.384 0.160 0.00 7236.
2 .85 498.35 17463. 0.401 0.170 0.00 7324.
2 .95 498.45 18200. 0.418 0.178 0.00 7413.
3.05 498 .55 18946. 0.435 0.186 0.00 7503.
3.15 498.65 19700. 0.452 0.194 Q.00 7593.
3 .25 498.75 20464. 0.470 0.201 0.00 7683.
3.27 498.77 20618. 0.473 0.2�3 0.00 7701.
3.29 498.79 20772. 0.477 0.207 0.00 7720.
3.31 498.81 20927. 0.480 0.212 0.00 7738.
3.33 498.83 21082. 0.484 �.218 O.QO 7756.
3.35 498.85 21237. 0.488 0.226 0.40 7774.
3 .37 498.87 21393. 0.491 0.235 0.00 7793.
3 .39 498 .89 21549. 0.495 0.245 0.00 7811.
3 .41 498 .91 21705. 0.448 0.250 0.00 7829.
3.43 498.93 21862. 0.502 0.254 0.00 7847.
3.53 499.�3 22651. 0.520 0.270 0.00 7939.
3.63 499.13 23450. 0.538 0.285 0.00 8032.
3.73 499.23 24258. 0.557 0.298 0.00 8125.
3.83 499.33 25075. 0.576 0.310 0.00 8218.
3.93 499.43 259a1. 0.595 0.322 0.00 8312 .
4 .03 499.53 26737. 0.614 Q.333 0.0� 8406.
4 .13 499.63 27582. 0.633 0.343 0.00 8501.
4.23 499.73 28437. 0.653 0.353 0.40 8597.
4.33 499.83 29302. �.673 0.363 0.00 8693.
4.43 499.93 30176. 0.693 0.372 0.00 8789.
4.50 500.00 30794. 0.707 0.379 0.00 8857.
4.60 500.10 31684. 0.727 0.696 Q.00 8954.
4.70 500.20 32584. 0.748 1.270 0.00 9052.
4.80 500.30 33494. 0.769 2.01a 0.00 9150.
4.90 500.40 34414. 0.790 2 .800 Q.00 9249.
5.00 500.50 35344. 0.811 3 .100 O.Oa 9348.
5 .10 500.60 36284. 0.833 3 .360 0.00 9448.
5.2� 5�0.70 37234. 0.855 3.600 0.00 9548.
5.3� 500.80 38194. 0.877 3.830 0.00 9649.
5.40 500.90 39164. 0.899 4.040 0.0� 9750.
5.50 501.00 40144. 0.922 4.240 0.00 9852.
5.60 501.10 41134. 0.944 4.430 0.00 9954.
5.70 501.20 42134. 0.967 4.620 0.00 1Oa57.
5.80 501.30 43145. 0.990 4.790 0.00 10160.
5_90 501.40 44166. 1.014 4 .960 0.00 10264.
6.00 501.50 45198. 1.038 5.130 0.00 10368.
6 .1a 501.6� 46240. 1.062 5.280 0.00 10473.
6.20 501 .70 47293. 1.086 5.440 �.00 10578.
6 .30 501.80 48356. 1.110 5.590 0.00 106c
6.40 501.90 49429. 1.135 5.730 0.00 1079U.
6.50 502.00 50514. 1.16Q 5.870 0.00 10897.
Hyd Inflow Outflow Peak Storage
Target Calc Stage Elev (Cu-Ft) (Ac-Ft)
1 1.50 ******* 0.87 4.63 500.13 31959. 0.734
2 0.73 0.37 0.35 4.17 499.67 27931. 0.641
3 0.73 ******* 0.31 3.86 499.36 25294. 0.581
4 0.77 ******* 0.29 3.65 499.15 23593. 0.542
5 0.88 ******* 0.25 3.43 498.93 21866. 0.502
6 0.45 ******* 0.16 2.76 498 .26 16835 . 0.386
7 0.57 ******* 0.10 2.03 497.53 11764 . 0.270
8 0.60 ******* 0.08 1.40 496.90 7754 . 0.178
----------------------------------
Route Time Series through Facility
Inflow Time Series File:04027d.tsf
Outflow Time Series File:04027out
Inflow/Outflow Analysis
Peak Inflow Discharge: 1.49 CFS at 6:00 on Jan 9 in Year 8
Peak Outflow Discharge: 0.871 CFS at 10:00 on Jan 9 in Year 8
Peak Reservoir Stage: 4.63 Ft
Peak Reservoir Elev: 500.13 Ft
Peak Reservoir Storage: 31959. Cu-Ft
. 0.734 Ac-Ft
Flow Duration from Time Series File:04027out.tsf
Cutoff Count Frequency CDF Exceedence_Probability
CFS % g �
0.005 43049 70.204 70.204 29.796 a.298E+00
0.015 3571 5.824 76.027 23 .973 U.240E+00
0.024 3315 5.406 81.433 18 .567 0.186E+00
0.034 2999 4.891 86.324 13 .676 0.137E+00
0.044 2564 4.181 90.506 9.494 0.949E-01
0.054 1764 2.877 93.382 6.618 0.662E-01
0.063 1282 2.091 95.473 4.527 0.453E-01
0.073 877 1.430 96.903 3 .�97 0.31QE-01
0.083 597 0.974 97.877 2.123 0.212E-01
0.093 464 0.757 98.633 1.367 0.137E-01
0.102 339 0.553 99.186 0.814 0.814E-02
0.112 199 0.325 99.511 0.489 0.489E-02
0.122 50 0.082 99.592 0.408 0.408E-02
0.132 11 0.018 99.610 0.390 0.390E-02
0.141 12 0.020 99.630 0.370 0.370E-02
0.151 40 0.065 99.695 0.305 0.305E-02
0.161 30 0.049 99.744 0.256 0.256E-02
0.171 22 0.036 99.780 0.220 0.220E-02
0.180 16 0.026 99.806 0.194 0.194E-02
0.19Q 18 0.029 99.835 0.165 0.165E-02
Q.20a 30 0.049 99.884 0.116 0.116E-02
a.210 14 0.023 99.907 a.093 0.930E-03
0.219 3 0.005 99.912 0.088 0.881E-03
0.229 4 0.007 99.918 �.082 �.815E-03
0.239 3 0.005 99.923 0.077 0.766E-03
0.249 3 0.005 99.928 0.072 0.718E-03
0.255 4 0.007 99.935 0.065 0.652E-03
0.268 6 0.010 99.945 0.055 0.554E-03
0.278 5 0.008 99.953 0.047 0.473E-03
0.288 6 0.010 99.962 0.038 Q.375E-03
0.297 4 0.007 99.969 0.031 0.310E-03
0.307 5 0.008 99.977 0.023 0.228E-03
0.317 4 0.007 99.984 0.016 0.163E-03
0.327 2 0.003 99.987 0.013 0.130E-03
0.336 3 0.005 99.992 0.008 0.815E-04
0.346 3 0.005 99.997 a.003 0.326E-04
Duration Comparison Anaylsis
Base File: �4027ex.tsf
New File: 04027out.tsf
Cutoff Units: Discharge in CFS
-----Fraction of Time----- ---------Check of Tolerance-------
Cutoff Base New �Change Probability Base New oChange
0 .109 � 0.66E-02 0.56E-02 -15.3 � 0.66E-02 0.109 0.106 -2.3
0.129 ( 0.46E-02 0.39E-02 -14.2 I 0.46E-02 0.129 0.113 -12.7 i
0.150 � 0.33E-�2 0.31E-02 -5.9 I 0.33E-02 0.150 0.148 -1.5 I
0.170 � 0.23E-02 0.22E-02 -5.6 � 0.23E-02 0.170 0.167 -2.1
0.191 � 0.16E-02 0.16E-02 0.0 � 0.16E-02 0.191 0.191 0.0
�.211 � 0.12E-02 0.90E-03 -26.7 � 0.12E-02 0.211 0.198 -6.3
0.232 � 0.90E-03 0.77E-�3 -14.5 � 0.90E-03 0.232 0.218 -5.8
0.252 � 0.72E-03 0.68E-03 -4.5 � 0.72E-03 0.252 0.250 -1.0
0.273 ( 0.54E-03 0.52E-03 -3.0 � 0.54E-03 0.273 0.271 -0.7
0.293 � 0.34E-03 0.34E-03 0.0 � 0.34E-03 0.293 Q.294 0.2
0.314 I 0.20E-03 0.16E-03 -16.7 � 0.20E-03 0.314 �.311 -0.8
0.334 � 0.13E-03 0.98E-04 -25.0 � 0.13E-03 0.334 0.329 -1.7
0.355 � 0.49E-04 O.00E+00 -100.0 ( 0.49E-04 0.355 0.342 -3 .6
Maximum positive excursion = 0.006 cfs ( 2.2%)
occurring at 0.286 cfs on the Base Data:04027ex.tsf
and at 0.292 cfs on the New Data:04027out.tsf
Maximum negative excursion = 0.020 cfs (-14.7%)
occurring at 0.135 cfs on the Base Data:04027ex.tsf
and at 0.115 cfs on the New Data:04027out.tsf
PON D
VOLUME CALCULATIONS
CORE PROJECT NO. 04027
PROJECT NAME: AMBERWOOD II
LEVATIO INCREMENT TOTAL LIVE
VOLUME VOLUME VOLU
SF CF CF CF
491.0 1389 0
1,735
492.0 2081 1,735
5,849
494.0 37b8 7,584
2,005
494.5 4251 9,589
0
494.5 4414 9,589 j
4,837 �
495.5 5260 14,426 0
2,737
496.0 5688 17,163 2,737
13,177
498.0 7489 30,340 15,914
16,900
500.0 9411 47,240 32,814
Pond Overflow Elevations I
The riP mary overflow for the pond is the riser pipe within the control structure. The
water surface elevation above the riser for the 100 year developed flow is calculated
assuming all orifices are plugged. To pass the 100-year retum period storm, 1.50 cfs,
through a 12" overflow riser will require 0.29 feet of head per the following equation: Q
=9.739DH3�2 or 1.54=9.739(1)H3�2. The primary overflow elevation would therefore,be
equal to the elevation of the top of the riser plus the amount of head required to pass the
100-year return period storm, Elev. 500.00+0.29 feet=Elev. 500.29.
The secondarv overflow for the pond is the jailhouse weir located on the control structure
catch basin. To pass the 100-year return period storm at 0.29 feet of head, a minimum
2.97-foot wide jailhouse weir will be required. T'he jailhouse weir is analyzed as a notch
weir using the following equation:
Q=C (L-0.2H)H3i2
where Q =flow (1.50 cfs)
C = 3.27 +0.40H/P
H =head above weir(0.29 ft� Use Same Head as Req'd Head Over Riser)
P=depth of storage at weir(Elev. 500.00—Elev. 495.50=4.50 feet)
L= length of the riser(ft)
An emergency overflow spillway will be installed within the pond. The spillway will be
sized based on the equation listed on page 5-32 in the 1998 King County Surface Water
Manual. The emergency overflow spillway will be located at the primary and secondary
overflow elevation 500.29. To pass the 100-year return period storm at 0.2 feet of head, a
minimum 4.7-foot wide spillway is necessary. Since the required minimum spilllway
width is 6 feet, the spillway will be installed with a length of 6 feet.
L= (Qi�l(3.21H3��)) - (2.4H)
L= (1.50/(3.21(0.2)3�2)) - (2.4(0.2))=4.7 feet� 6 feet (MIN.)
C.Water Quality Volume Calculations
Basic Water Quality Treatment shall be utilized to mitigate for the developed storm
drainage flows. The wetpond/dead storage portion of the Pond will satisfy this
requirement. The required volume will be designed per KCSWDM Section 6.4.1.1. 'The
following variables were used in the calculation:
Volume Factor(fl =3
Rainfall =0.039 feet or 0.47 inches
Area=developed basin
Where A;= area of impervious surface (s fl
Atg = area of till soil covered with grass (s�
Atf= area of till soil covered with forest (s fl
Ao= area of outwash soil covered with grass or forest(s�
Vr= [0.9A; +0.25At�+O.IA�f+O.OIAa) * (R/12)
Vb= fl�`Vr
Vb= 3*[(0.9)(2.25)+(0.25)(2.04}]0.039 * (43560sf/ac) = 12,920 CF
The dead storage portion of the Pond has a volume of 14,426 CF which exceeds the
required 12,920 CF. See Pond Volume Calculations spreadsheet in Section 4B of this
report.
6.4.1 WETPONDS—BASIC AND LARGE—METHODS OFANALYSIS
FIGURE 6.4.1.A PRECIPITATION FOR h1EAN ANNUAL STORM IN INCHFS(FEE'1�
ST 1.0/ � 1.2
ST 1.1 - ST 1.0 � 0.8 LA. 0.9 � 1.0
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•..c� Rivedlake 0.47" � ' �
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— Major Road (0.03 9' ) 0.52" �!-. J--� \
(0.043' � 0.65' �
NOTE:Areas east of the eastemmost isopiwial should use 0.65 �.5 6" (0.0 5 4' ) I
inches unless rai�all data is available for the location of iMerest (0.04 7' ) !
N The mean amual stortn is a oonceplual stam fouid �
by dviding the amual predpilation Dy the rotal r�unber
d stam eve�ts per year
result,generates targe amounts of runoff. For this application, till soil types include Buckley and '
bedrock soils,and alluvial and outwash soils that have a seasonally high water table or are underlain at
a shallow depth(less than 5 feet)by glacial till. U.S. Soil Conservation Service(SCS)hydrologic soil
groups that are classified as till soils include a few B,most C,and all D soils. See Chapter 3 for
classification of specific SCS soil types.
1998 Surface Water Design Manual 9/1/98
.6-69
5. CONVEYANCE SYSTEM ANALYSIS AND DESIGN:
The conveyance system for the site was designed for both the 25-year return period storm
and the 100-year return period storm. The flows generated from the 25-year return period
storm and the 100-year return period storm were input into backwater analysis
spreadsheets to confirm adequate sizing. Conservatively and for simplicity, total KCRTS
15-minute time step flows from the entire site were substituted into each pipe segment
except from Inlet 11 to CB 10,to confirm adequate sizing. See attached KCRTS Flow
Frequency Analysis (04027d15.ts�on the following pages. The 15-minute time step
flows for the entire site for the 25-yeaz and 100-year return periods are 2.47 cfs and 3.69
cfs consecutively. Since the pipe size between Inlet 11 and CB 10 was reduced to 8" due
to water/storm drainage vertical conflicts, it was simply and conservatively assumed that
the 8" pipe segment carries 25°Io of the total site flow. The 15-minute time step flows for
Inlet 11 to CB 10 for the 25-year and 100-year return periods are 0.62 cfs and 0.92 cfs
consecutively.
The tailwater elevations within the pond was derived from the KCRTS outfall
information. The tailwater elevations for the 25-year and 100-year return periods are El.
499.67 and El. 500.13 consecutively.
T'he backwater analysis was performed to ensure that during the 25-year design storm, the
headwater elevation in each structure dces not exceed an elevation equal to 0.5' less the
rim and during the 100-year design storm, the m�imum water surface elevation either
does not exceed rims or exceedance of a rim would be allowed if the topography of the
basin would allow the overflow to be conveyed to the next downstream catch basin or if
the topography could ensure that ponding would not cause structural damage.
During the 25-year,the headwater elevations do not exceed 0.5' less the rim. During the
100-year, headwater elevations exceed the rims on CB 10 and CB 11. Overtlow from
these catch basins will simply drain downstream to the west and discharge into the next
downstream catch basins. The conveyance system is therefore, adequately sized.
�I
Flow Frequency Analysis
Time Series File:04�27d15.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak - - Peaks - - Rank Return Prob
(CFS) (CFS) Period
1.07 6 8/27/O1 18:00 3 .69 1 100.00 0.990
0.799 8 1/05/02 15:00 2.47 2 25.00 0.960
2.47 2 12/08/02 17:15 1.56 3 10.00 0.900
0.863 7 8/23/04 14:30 1.52 4 5.00 0.800
1.56 3 11/17/04 5:00 1.33 5 3.00 0.667
1.33 5 10/27/OS 10:45 1.07 6 2.00 0.500
1.52 4 10/25/06 22:45 0.863 7 1.30 0.231
3 .69 1 1/09/08 6:30 0.799 8 1.10 0.091
Computed Peaks 3.28 50.00 0.980
I3ACKWATER CALCULATIONS
OD NAME: AMDF.RWOOD II PREPARED BY: G.Brooks I
OB NUMBER: IW027 DESIGN STORM: 23 YEAR
ENTRANCE ENTRANCE EXIT OUTLN;T INLET APPROACH BEND JIINCTION
P�E P�E MANNING'S OUTLET INLET PIPE FLOW VELOCITY TAQ.WATER FRICTION HGL HF,AD HEAD CONTROL CONTROL VELOC[TY IiEAD HEAD HEADWATER
FROM TO FLOW LENGTH DIA. n ELEVATION ELEVATION AREA VELOCITY HEAD ELEVATION LOSS ELEVATION LOSS LOSS ELEVATION ELEVATION IIEAD LOSS LOSS ELEVATION
CB CB CFS EET IN VALUE IFF.F.71 FEET) 5 FT T/SEC (FEET FEET FEE (FEET) FEET FEE EET FEE EET EET FEE EE'1� RN1 EL
4A 4 2.47 4U 12 0.012 497.50 4y8.50 0.79 ?14 11.15 499.67 O.16 4'�9.R? 0.08 015 SOLLOA 499.50 U.1S 0,01 0.0U 499.92 501.92
4 5 2.47 103 12 0.012 49R.50 502.31 OJ9 3.14 0.15 49Y92 0.42 503.?I O.UB O.1S 501.54 SU39i 0.15 0.01 0,08 503.48 506.11
5 6 2.47 30 l2 QU12 50231 502.61 U.79 3.14 015 503.48 0.12 503.61 0.08 0.15 503.84 SU3.61 0.00 0.00 0.00 503.84 SW.11
5 7 2.47 135 l2 0.012 502.}1 505.18 0.79 3.14 0.13 .503.4R 0.55 506.18 O.OR 0.15 506.41 S06.1R 0.15 O.UO O.OR 50634 SIlAO
7 R 2.47 30 12 0.012 505.18 507.13 0.79 3.14 II.1.5 506.34 0.12 508.13 0.08 0.15 508.36 SOA.13 0.00 0.00 0.00 SU836 511.40
7 9 2.47 I16 12 0.012 505.18 505.76 IIJ9 3.14 0.15 SOG.34 0.47 506.81 0.08 0.15 507.04 5p6J6 0.15 0.2U O.OR 507.18 51329
9 10 2.47 136 12 0.012 303.76 5p(.44 0.79 i.14 0.15 507.I8 U.55 507.73 0.08 U.15 307.96 507.44 OAS 0.20 0.00 SOA.II 510.03
IU 11 0.62 30 8 0.012 507.63 507.78 035 1.7R 0.05 SOS.II 0.07 SOA.45 0.02 0.05 508.52 508.45 0.00 O.W 0.(10 508.52 S1U.Ui
9 12 2.47 55 12 0.012 50576 511.42 OJ9 3.14 0.15 507.IR 012 512.42 O.OR 0.15 512.65 312,42 0.15 U.2U n.an SI2J0 514J2
12 13 2.47 30 12 11.012 SIL42 511.72 0.79 3.14 0.15 512J0 O.12 512.82 p.OR 0.15 S13A5 512J2 0.00 0.00 0.00 SI3.05 S14.72
BACKWATER CALCOLA'1'IONS �I
OB NAME: AMBERWOOD II PREPARED BY: C.6rooks I
UNNUMBF;R: 04027 DES[GNSTORM: 100 YEAR
ENTRANCE ENTRANCE EXIT OUTLET INLET APPROACH BEND JUNC7'ION
P�E P�E MANNING'S OUTLET INLET P�E FLOW VELOOITY TAILWATER FRICTION fIGL �F�AD HEAD CONTROL CONTROL VELOCITY HEAD HEAD HEADWATER
FROM TO FLOW LENGTH DIA. n ELEVATION ELEVATION AREA VELOCITY HEAD ELEVATION LOSS ELEVATION LOSS I,OSS ELEVATION ELEVAT[ON HEAD LOSS LOSS ELEVATION
CB CB (CFS) (FEET (W VAU1F. (FEE7� (FEE'1� (5 N7'/SEC) (FEE'1� (FEE1) (FEE'I� (FEE'1� FEET) (NF.ET) (FEET) (FEE� (FEE'I) (FEET) (FF.F.7'1 (FEE'I) RIM EL
4A 4 3.69 40 12 0.012 4I3.30 498.50 0.79 4.70 0.34 500.13 036 500.49 0.17 034 501.01 49y99 0.34 0.02 0.(� SW.68 301,92
4 5 3.69 103 12 0.012 498.50 50231 OJ9 4,70 0.34 500.68 0.93 503.31 0.17 034 503.R2 507.84 U34 O(i3 0.19 50371 SW.11
5 6 3.69 30 I2 0.012 502.31 502.61 0.'79 4.70 034 503J1 0.27 503.99 O.t7 0.34 504.50 SU4.I5 0.00 0,00 0.00 504.50 SOG,11
5 7 3.69 135 12 U.012 502.31 SOS.IA 0.99 4.70 034 SU371 1.22 506.IR 0.17 034 506.69 506J2 034 0.00 0.19 SU5.56 511.40
7 R 3.69 30 12 U.012 SOS.IR 507.13 0.79 4.70 034 S(K.,56 0.27 508.13 O.17 0.34 5p8,64 SOA.63 0.00 0.00 Q(� 508.65 .511.40
7 9 3.69 116 12 0.012 5p5.i8 SOS76 0.79 490 034 506.56 LUS SOZAI 0.17 034 508.13 5p7.i1 0.34 O.d3 0.19 508.43 517.29
9 IU 3.6H 136 12 0.012 SOSJ6 906,44 0.7`I 4J0 034 508.43 1.23 5119 f,l, 0.17 034 510.17 507.99 U.l l 0.43 0.00 510.52 510.03
10 ll 0.92 30 8 D.1112 507.63 507JR 0.35 2.64 0.11 510.52 0.15 510.67 0.05 U.11 S1U.83 SOAAS 0.00 0.00 QOU 5111.N3 510.03
9 12 3.69 55 12 OAt2 SOSJ6 511,42 OJ9 4J0 0.34 508.43 U.SU 512,42 0.17 034 512.93 51292 U34 0.45 0.00 513.04 514.72
12 13 3.69 3(1 12 0.012 S11.42 511.72 D.7�i 4J0 034 S13.04 027 513.32 0.17 034 513.R3 513.26 0.00 UAU o.nn 513.R3 514J2
6. SPECIAL REPORTS AND STUDIES:
Included in this section is the postmaster approval.
' � 5-19-285 2: 13PM FROM RENTON HIGHLANDS d25 2287150 p. �
MAY.19.2005 9'SBA�'1 CORE DESIGTV I�'1� N0.933 P.2
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7. OTHER PERMITS:
Permits from Water District 90 is required for the water design.
8. ESC ANALYSIS AND DESIGN:
Design of the erosion/sedimentation control plan was completed in conformance with
Core Requirement#5 per the 1998 KCSWDM. Compliance with the 7 minimum
requirements are summarized below. ,
1. Clearing Limits: Clearing limits have been delineated on sheet C2.01 of the civil
plans. The clearing limits extend only to those areas that will be disturbed during
construction of the subject project.
2. Cover Measures: The ErosionlSedimentation Control Notes listed on sheet C2.01
of the civil plans specify specific times at which temporary and permanent cover
measures will be installed.
3. Perimeter Protection: Per sheet C2.01 of the civil plans, silt fence will be used for
perimeter protection. Silt fence will be installed along the perimeters of those
areas that will be receiving silt-laden runoff.
4. Traffic Area Stabilization: A construction entrance will be installed at the
entrance to the project site. See sheets C2A1 and C2.31 for location of
construction entrance and detail.
5. Sediment Retention: A portion of the detention/water quality pond will be used
for sediment retention. Sediment retention will be designed per the 1998
KCSWDM Appendix D.
Surface Area:
Q,o(04027d.ts fl =0.87 cfs
SA=2080 sf/cfs * Qlo
SA=2080 sf/cfs * 0.87 cfs = 1,810 SF
SA Provided at Elev. 499.0= 5,244 SF> 1,810 SF � OK
Riser Diameter:
The same riser diameter will be used as was designed for the primary overflow
within the control structure for the pond. Riser will be 12".
Emer�ency Overflow Spillway:
The emergency overflow spillways as designed in Section 4B of this report will be
installed as part of the erosion/sedimentation pond.
Dewatering Orifice:
A�-AS�2h�o.s/(10.6*3600Tg0.5)
D =24(Aa/3.14)o.s
Ao= 5,244(2*3.5)o.s/(10.6*3600*24*32.2o.$) =0.003 sf
D=24(0.003/3.14)°'S =0.7" Use 1"
6. Surface Water Control: Interceptor swales will be used to direct all sediment-
laden runoff to the sediment pond. See sheets C2A1 and C2.31 for location of
swales and details.
7. Dust Cantrol: A note on sheet C2.01 addresses the procedure for dust control
should soils become too dry.
I
9.BOND QUANTITIES,FACILITY SUIVIIVIARIES,AND DECLARATION OF
COVENANT:
A bond quantities worksheet and facility summary will be completed as required by the
City when engineering plans have been approved. A Declaration of Covenant is not
applicable since all drainage facilities will be public.
10. OPERATIONS AND MAINTENANCE MANUAL:
A maintenance and operations manual is not required since all drainage facilities will be
public.