HomeMy WebLinkAbout03076 - Technical Information Report - Drainage V
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DRAINAGE REPORT
FOR
FIRE STATION #12
CITY OF RENTON
WASHINGTON
Prepared For:
City of Renton
Fire Department
And
Rice Fergus Miller
Architecture & Planning
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Prepared: May 8, 2002 '� 1�
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720 South 348th S[reet Tet 12531 838 6113 Tacoma 12531 927 0619 Civ l Engineering Land Planning
Federal Way. WA 98003 Fax 12531 838 7104 Seattle 1206) 623 5911 P-c�ect Management Public Works
www.esmciviLcom Bremerton 1360)792 3375 Laed Surveying
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DRAINAGE REPORT
FOR !
FIRE STATION #12
CITY OF RENTON
WASHINGTON _
Prepared For:
City of Renton and Rice Fergus Miller
Fire Department Architecture & Planning
1055 S. Grady Way 262 4th Street
Renton, WA 98055 Bremerton, WA 98337
(425) 430-6400 (360) 377-8773
Prepared By:
John S. Chadwell, P.E.
ESM Consulting Engineers, L.L.C.
720 South 348th Street
Federal Way, WA 98003
(253) 838-6113
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720 South 348th Street Tel 12531 839 6113 Tacoma 12531 927 0619 � vi'. ��gineering Land Planning
Federal Way. WA 98003 Fax (253)838 7104 Seattle 1206) 623 5911 Project Management Public Works
www.esmciviLcom Bremerton 1360)792 3375 �3ad Surveying
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Drainage Report for Fire Station #12
May 8, 2002 �
Page 2
TABLE OF CONTENTS
I. TIR Worksheet
II. Existing and Proposed Drainage Features and Construction
III. Core and 5pecial Requirements
IV. On-Site Detention Analysis
V. Level 1 Off-site analysis
Appendices
• Figure 1 —Vicinity Map
• Figure 2 — Soils Map & Description (2 Pages}
• Figure 3 — Hydrologic Soils Group Table
• Figure 4 — 2 Year King County Isopluvial Map
• Figure 5 — 10 Year King County Isopluvial Map
• Figure 6 — 100 Year King County Isopluvial Map
• Figure 7 — SCS Curve Numbers Table
• Figure 8 - Existing & Proposed Hydrology Basin StormShed
Calculations
• Figure 9 - Downstream Analysis Summary Map
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Drainage Report for Fire Station #12
May 8, 2002
Page 3
SECTION I
TIR WORKSHEET
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^ King County Building and Land Development Div(slon
� TECHNICAL (NFORMATION REPORT (T1R) WORKSHEET
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ProjectOwner C'fj' of �Qe��ah � ProjectName F'��L ffGf�On �' /z
Address /OSS' S. (,�ady �wy — Location
Phone �`1ZS) �/3b' Gy00 _ Township 23 tia�f'�,
Praject Engineer Je tin -S• G hadwcll� P.�• R�9e S Ea,r,�
ESM Co�,,J /�in n � zc• Sec;ion 'S�
Company Project Size �2 AC
Addrsss Phone 7ZOS.3y8' �!`�• F�d«�I W�y , ti/A� Upstream Drainage Basin Size � AC
2S3 g38-G�l3
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� Subcivisicn � DOF/G HPA i�1 Shoreline Mar.agement �
� Short Suodivision Q COE 4C4 � Rodcery
, � Grading � �OE Dam Safety � Structural Vaults
� (i Commercial Cj FEMA Floodplain � Other
Q Other � COE Wetlands � HPA
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C� �i Communiry
Drainage Basin �
j EGrf' Ln�Cc WGd�in��0^
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G' River C Flocdplain
� Stream � Wetlands
0 Critical Stream Reacn � SeepslSprings
L_; DepressionsJSwales Cl High Groundwater Table
� Laice Cj Groundwater Recharge
� Staeo Slooes Q Other
� � LakesidelErosion Hazard
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Soil i y Slopes Erosio/n Potential Eresive Veloc;ties
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Page 2 af 2
King County Bufiding and Land Developmertt Divfslon -.
TECHNICAL INFORMATION REPORT (TlR) WORKSHEET
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REFcRENCc L1MIT�TiONiSiTc L.ONS i r��N i
� Ch.4-Oowns;ream Anafysis Nah� �0�'e�
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C Additional Sheats A�tatched
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MIi�VII1JIUl,!{E.71.+ REflUIREMcN�S MINI�IUM ESC r�cG'UIRE.41E�1TS
DURfNG CONSTr�UCT(aN FOLLOWING CONSTAUCTION
� Sedimentation Facilities � Stabilize Exposed Surface r f c�y,
� Stabilizad Ccnstruction Entrance � Remove and Restore Tamporary ESC Facilities
gf Perimeter Runo�f Control �.1 Clean and Remove All Silt and Debns
� C(earing and Grading Restrictions Qr DateS Q Ensure Oparation of Permanent Facilities
� Cover Practicas � F7ag Limits of NGPES
� Constructian Sequence � Other
0 Other '
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I � Grass Lined Channel l� Tank � Infiltraron Method of Analysis
� Pipe System Cj Vauit Q Depression S'�U h�
�' Ooen Channel � Energy Dissapator I� Flow Cispersal Compensa6on�1vlitigation
I � Dry Pond � Wedand Q Waiver o��i�i�minated Site Storage
Q Wet Pond C1 Stream 0 RegionaJ Detention
BnefDescriptionofSysiemOperation Co�/aef�on Gn� COnvG�Gn[G P�P� S'�J�er., �Onneetir.�
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I �'0 eX�.P��^4 .CyJ'�'en A��'e� JJkS,f�n4 t�tbV9� ��I �GJq�'cr .r�,oa��fer
Facility Related Site Limitations C Additional St�eets Attatched
Reterenca Facility Vmitation
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�j Drainage Easament
0 Cast in Placs Vault C Other Q Access Easement
C Retaining Wail � Native Growth Protection Easament
0 Rockery>4'High Q Tract
I � Structural on Steep Slope I� Other
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II or a civil engineer under my supervision have visited the site. Actual
� 9ite conditions a9 observed were incarporated into this waricsheet and the � �
attatchments. To the best of my knowledge the informetion provided \I s-B�OZ J
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here is accurate. � 59^'d0'�� �
Drainage Report for Fire Station #12
May 8, 2002
Page 6
SECTION II
EXISTING AND PROPOSED DRAINAGE FEATURES AND
CONSTRUCTION
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Drainage Report for Fire Station #12
May 8, 2002 �
Page 7
SECTION II
Existing and Proposed Drainage Features and Construction
Existing Conditions
The project site is located on NE 12th Street between Jefferson Ave NE and
Kirkland Ave NE. The project site fronts onto all three streets. The project site
was developed previously as a restaurant. The structure was recently removed,
however the remainder of the site consists of a.c. pavement, curb, gutter, and
sidewalks along with minimal areas of landscaping around the site perimeter. The
site has an existing storm drain conveyance system consisting of six catch basins
which drain into the existing storm drain system in NE 12th Street via two
connections (10"0 and 6" f� pipes). The portions of the site fronting onto the three
streets (curb, gutter and sidewalk) presently drain into the street and the storm
water is picked up in one of three catch basins located along NE 12�' Street.
For simplicity the project site drainage features were calculated from the curb face '
of the frontage roads in order to more fully describe the proposed projects impact,
or in this situation, reduction of impact to drainage conditions.
The existin site covera e is summarized below:
Cover T e Acrea e Percenta e
Buildin s 0.227 Ac. 16.6%
Pavement 0.788 Ac. 57.4%
Walks 0.088 Ac. 6.4%
Landscapin 0.269 Ac. 19.6%
Total 1.37 A.
Soils
The Soil Conservation Service (SCS) Maps indicate the presence of Alderwood
Arents series soils throughout the project site (Fig. 2). These soils are hydrologic
soils group "C" according to the King Count Surface Water Design Manual.
Rainfall
The design rainfall was obtained from the isopluvial maps in the 1990 King County
Surface Water Design Manual. The 2-year 24-hour design rainfall is 2.0 inches,
the 10-year 24-hour design rainfall is 2.9 inches and the 100-year 24-hour is 3.89
inches. The six-month design storm is calculated as 0.67 inches.
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Drainage Report for Fire Station #12
May 8, 2002
Page 8
Proposed Conditions
The proposed project site plan, developed by Rice Fergus Miller, includes the new
fire station building along with parking areas, drive approaches, new curb, gutter
and sidewalk afong the three road frontages, and landscaped area. This is a
redevelopment project which proposes less than 5,000 s.f. of new impervious
surface subject to vehicular use. In fact the project proposes less impervious
surface than the previous use. For emphasis we note that the project proposes a
site with 0.97 acres of impervious area, while the existing site has 1.10 acres of
impervious area.
The ro osed site covera e is summarized below:
Cover T e Acrea e Percenta e
Buildin s 0.281 Ac. 20.5%
Pavement 0.471 Ac. 34.4%
Walks 0.219 Ac. 16.0%
Landsca in 0.400 Ac. 29.2%
Total 1 .37 A.
The proposed project will collect storm drainage from roof drains, yard drains (if
needed) and catch basins, then conveyed into a water quality tank before being
released to the existing storm drainage system located in NE 12�h Street.
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Drainage Report for Fire Station #12
May 8, 2002 �
Page 9
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SECTION III
CORE AND SPECIAL REQUIREMENTS
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Drainage Report for Fire Station #12
May 8, 2002
Page 10
SECTION III
CORE AND SPECIAL REQUIREMENTS
This Section will describe how the project proposes to meet each of the applicable
Core and Special Requirements.
Core Requirement (1) — Discharge at a Natural Location
The project site currently drains into an existing on-site storm drainage
conveyance system which connects to the existing storm drain in NE 12th Street.
The redevelopment of the site proposes to discharge at the same locations,
utilizing existing storm drain laterals. '
Core Requirement (2) — Off-site Analysis
Upstream - A small portion of ground to the north of the project site drains onto the
site. The area is minimally landscaped and it is included in the existing and �
proposed hydrologic calculations. '�
Downstream — The hydrologic calculations for this proposal demonstrate that the
site will not have any impact to downstream drainage systems, and proposes less
than 5,000 s.f. of new impervious surface (defined as surfaces that increase the
runoff curve number). As such a downstream analysis is not required. No impact
to downstream drainage systems is demonstrated by the reduced peak flow rates
shown in Section IV below.
Core Requirement (3) — Runoff Control
The project is exempt from On-site peak rate runoff control as the proposed
project post-development peak rate runoff is less than the existing condition peak
rate runoff for the 100 year 24 hour design storm. The project is also exempt from
the bio-filtration requirement because the project does not propose 5,000 s.f. or
more of new impervious surface subject to vehicular use.
Core Requirement (4) — Conveyance System
The conceptual level design performed to date assumes that 12-inch minimum
storm drain lines will be used, with 6-inch or 8-inch lines connecting roof drains to
the main storm drain system. The proposed drainage system sizing will be verified
as meeting the requirements of this condition during the final design phase. Once
the hydraulic grade line from the storm drain located in NE 12�h Street is
determined, the on-site conveyance pipes will be sized such that 0.5 feet of
freeboard will exist during a 25-year storm event and that storm structures do not
overtop during the 100-year event. In keeping with the proposed plans to have no
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Drainage Report for Fire Station #12
May 8, 2002 ',
Page 11 '
drainage impacts to the existing storm drain conveyance lines in NE 12th Street,
the existing 6-inch and 10-inch laterals will be used to connect the proposed on-
site storm drainage collection system to the existing storm drain.
Core Requirement (5) —Temporary Erosion and Sedimentation Control
A Temporary Erosion and Sedimentation Control plan will be prepared with the
final construction drawings. At this time it is assumed that a combination of the
following Best Management Practices will be utilized: defined clearing limits, cover
measures, perimeter protection by filter fabric fence, rock construction entrance,
sediment traps and or rock check dams in interceptor ditches, storm drain inlet
protection, and TESC measures maintenance.
Special Requirement (1) — Critical Drainage Areas
The project is located within Aquifer Protection Zone 2. Additional requirements
include:
• Biofiltration Swale — Not required as project does not propose 5,000
s.f. of new impervious surface subject to vehicular use or storage of ,
chemicals.
• Lining of Drainage Ditches — Not applicable as project does not
propose any surface drainage ditches or swales.
• Wetpond — The project does not meet the threshold requirements
for construction of a wetpond as the project will not construct rnore
than one acre of new impervious surface and does not direct
discharge to a receiving body of water or discharge to a type 1 or 3
stream or wetland.
Special Requirement (2j — Compliance with Existing Master Drainage Plan
Not applicable as project is not part of a Master Planned Development.
Special Requirement (3) — Conditions Requiring a Master Drainage Plan
Not applicable as the project does not meet the thresholds for requiring a Master
Drainage Plan.
Special Requirement (4) — Adopted Basin or Community Plans
Not applicable as the project does not lie within an Adopted Basin or Community
Plan.
Special Requirement (5) — Special Water Quality Controls
Not applicable as the project does not propose more than one acre of new
impervious area subject to vehicular use or storage of chemicals.
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Drainage Report for Fire Station #12
May 8, 2002
Page 12
Special Requirement (6) — Coalescing Plate OiUWater Separators
Not applicable as the project does not propose to construct more than 5 acres of
impervious surface.
Special Requirement (7) — Closed Depressions
Not applicable as the project does not drain into a closed depression.
Special Requirement (8) — Use of Lakes, Wetlands or Closed Depressions for
Runoff Control
Not applicable as the project does not drain into a lake, wetland, or closed
depression for runoff control.
Special Requirement (9) — Delineation of 100 Year Floodplain
Not applicable as the project does not contain or abut a stream, lake, wetland or
closed depression.
Special Requirement (10) — Flood Protection Facilities for Type 1 and Type 2
Streams
Not applicable as the project does not contain or abut a Class 1 or 2 stream.
Special Requirement (11) — Geotechnical Analysis and Report
Not applicable as the project does not propose to construct a pond or an infiltration
system.
Special Requirement (12) — Soil Analysis and Report
Not applicable as the existing SCS soils maps are sufficient for determining the
classification of the underlying soils.
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Drainage Report for Fire Station #12
May 8, 2002
Page 13
SECTION IV
ON-SITE DETENTION ANALYSIS
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Drainage Report for Fire Station #12
May 8, 2002
Page 14
SECTION IV
ON-SITE DETENTION ANALYSIS
Existing & Developed Hydrology
The existing hydrology for the project site was analyzed using the "Santa Barbara
Urban Hydrograph" (SBUH) utilizing the StormShed software package (Engenious
Systems). The project meets the exemption for based on 1.2.3-5 . . .
The Arents-Alderwood series soils are hydrologic soil group "C". The detailed
basin input and results summaries are included in the appendices. Due to the
nature of the site being a redevelopment site, which proposes a reduced amount
of impervious area, no on-site detention will be required.
A summa of the eak flow rates is summarized below:
Storm Event Existin Peak Flow Rate Pro osed Peak Flow Rate Chan e
2-Year 0.63 c.f.s. 0.61 c.f.s. -.02
� 10-Year 0.97 c.f.s. 0.94 c.f.s. -.03
' 100-Year 1.34 c.f.s. 1.31 c.f.s. -.03
As noted previously for Core Requirement #3, the proposed project meets the
criteria for exemption from On-Site Peak Rate Runoff Control.
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Drainage Report for Fire Station #12
May 8, 2002 �
Page 15
SECTION V
LEVEL 1 OFF-SITE ANALYSIS
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Drainage Report for Fire Station #12
May 8, 2002
Page 16
SECTION V
LEVEL 1 OFF-SITE ANALYSIS
As noted previously under "Core Requirment #2" a detailed Level 1 Off-site
analysis is not required. This is based on the "no-impact" nature of the proposal,
which includes a reduction in total impervious surface, a reduction in impervious
surface subject to vehicular use, a reduction in vehicle trips (vs. pre-existing
restaurant), and a reduction in peak storm flow rates.
Though a detailed Level 1 Off-site analysis is not required, the following
description is provided as additional information. The existing on-site storm drain
collection system connects to the existing storm drain in NE 12�' Street via a 10-
inch and a 6-inch CMP lateral. For reasons of maintaining no impact to
downstream storm drains, we are proposing to use the two existing laterals. The
existing storm drain in NE 12th Street is a 36-inch CMP. The 36-inch storm drain
line continues west in NE 12�h Street at slopes varying from 0.32% to 7.6%.
Approximately 1,550 feet downstream of the site, at Edmonds Ave NE the storm
flows proceed south in the storm drain system. A map of the downstream analysis
area is in the appendices.
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Drainage Report for Fire Station #12
May 8, 2002
Page 17
- APPENDICES
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�rlrents Alderwood Material � Some areas are up to 30 percent inciuded soils
' that are similar to this soil material, but either
� shallower or deeper over the compact substratum;
rents, Alderwood material consists of Alderwood i and some areas are S to 10 percent very gravelly
o s that have been so disturbed through urban- j Everett soils and sandy Indianola soils .
z��ion that they no longer can be classified with � . Runoff is medium, and the erosion hazard is
he Alderwood series. T'hese soils, however, have � moderate to severe.
a similar features. The upper part of the soil, This soil is used for urban development. Ca-
o depth of 20 to 40 inches, is brown to dark- pability unit IVe-2; woodland group 3d2.
ruWn gravelly sandy loam. Below this is a grayish-
rown, consolidated and impervious substratum. Arents, Everett material (An) .--'Ihis is a level
1 �s generally range from 0 to 15 percent. to gently sloping, dark-brown gravelly or very
hese soils are used for urban development. gravelly sandy loam. It is very similar to Everett
gravelly sandy loam (see Everett series) , but it
has been disturbed and altered through urban de-
^ents, Alderwood material, 0 to 6 percent slopes velopment. Multicolored very gravelly coarse sand
y ) .--In many areas this soil is level, as a is at a depth of 8 to 40 inches. Areas are common- ,
.��lt of shaping during construction for urban ly rectangular in shape, and range from 1 to 120
icilities. Areas are rectangular in shape and acres in size.
u � from 5 acres to about 400 acres in size. Representative profile of Arents, Everett mate-
:presentative profile of Arents, Alderwood rial, in a homesite, 440 feet west and 100 feet
i�__:ial, 0 to 6 percent slopes, in an urban area, north of the center of sec. 11, T. 24 N., R. 6 E.:
,300 feet west and 350 feet south of the northeast
�; �r of sec. 23, T. 25 N., R. 5 E. : 0 to 8 inches, dark-brown (7.5YR 3/4) gravelly
sandy loam, brown (7.SYR 5/4) dry; massive;
1 26 inches, dark-brown (lOYR 4/3) gravelly soft, very friable, nonsticky, nonplastic;
sandy loam, pale brown (lOYR 6/3) dry; few roots; 30 percent gravel content;
massive; slightly hard, very friable, non- slightly acid; clear, smooth boundary. 8 to
sticky, nonplastic; many roots; medium acid; 14 inches thick.
abrupt, smooth boundary. 23 to 29 inches 8 to 60 inches, grayish-brown and light olive-brown
thick. (2.5Y 5/2 and 5/4) very gravelly coarse
� `- 60 inches, grayish-brown (2.5Y 5/2) weakly � sand, light gray and light yellowish brown
consolidated to strongly consolidated glacial � (2.5Y 7/2 and 6/4) dry; single grain; loose,
till, light brownish gray (2.5Y 6/2) dry; nonsticky, nonplastic; few roots; 55 percent
common, medium, prominent mottles of yellowish gravel and 10 percent cobblestone content;
brown (lOYR 5/6) moist; massive; no roots; medium acid. ,
medium acid. hlany feet thick.
The upper part of the soil ranges from dark
The upper, very friable part of the soil extends brown to olive brown and from gravelly sandy loam
� ^ depth of 20 to 40 inches and ranges from dark to very gravelly loamy sand. The substratum ranges
a sh brown to dark yellowish brown. from black to olive b mwn.
ne areas are up to 30 percent included soils 'Ihis soil is somewhat excessively drained. The
at are similar to this soil material, but either effective rooting depth is 60 inches or more.
a"�wer or deeper over the compact substratum; Permeability is rapid, and available water capacity
d �me areas are 5 to 10 percent very gravelly is low. Runoff is slow, and the erosion hazard
e tt soils and sandy Indianola soils. is slight.
This Arents, .4lderwood soil is moderately well This soil is used for urban development. Ca-
a�nAd. Permeability in the upper, disturbed soil pability unit IVs-1; woodland group 3f3.
t ial is moderately rapid to moderately slow,
p� iing on its compaction during construction. Beausite Series
e substratum is very slowly permeable. Roots
nP*�ate to and tend to mat on the surface of the
n; lidated substratum. Some roots enter the The Beausite series is made up of well-drained
b� �atum through cracks. Water moves on top of soils that are underlain by sandstone at a depth
e substratwn in winter. Available water capacity of 20 to 40 inches. These soils formed in glacial
7^��r. Runoff is slow, and the erosion hazard is deposits. They are rolling to very steep. Slopes
i� „ are 6 to 75 percent. The vegetation is alder, fir,
'1 s soil is used for urban development. Ca- cedar, and associated brush and shrubs. The annual
�ility unit IVe-2; woodland group 3d2. precipitation is 40 to 60 inchos, and the mean
annual temperature is about 50 F. The frost-free
season ranges from 160 to 190 days. Elevation is
F nts, Alderwood material, 6 to 15 percent � 600 to 2,000 feet.
�F" (AmC) .--This soil has convex slopes. rlreas In a representative profile, the surface layer
� rectangular in sliape and range from 10 acres to and the upper part of the subsoil are dark-brown
�u 450 acres in size.
KING COUNTY, WASHINGTOM, SURFACE WATER DESIGN MANUAL
(2) CN values can be area weighted when they apply to pervious areas of simiiar CN's (within 20
�„ CN points). However, high CN areas shouid not be combined with low CN areas (unless the
low CN areas are less than 1596 of the subbasinl. In this case, separate hydrographs should be
� generated and summed to form one hydrograph.
FIGURE 3.5?A HYDROLOGIC SOIL GROUP OF THE SOILS PY KING COUNTY
HYDROLOGIC I-fYDF10LOG(C
SOIL �ROUP GROUP' SOIL GROUP Gr�OUP'
Alderwood C Orcas Peat D
' Arents, Ald2rw C Oridia D
Arents, Everett Material B Ovall C
Beausite C PlchucSc C
i Belling�am D Puget D
I Briscot D Ptryallup S
8uckley D Ragnar 8
Coastal Beaches Variable ftenton D j
�arimQnt Silt �oam D Riverwash Varrab(e I
Edgewick C Salal C
�verett A/B �Sammamish D
Indianola A Seattle D
Kitsap C Shacar D
Klaus C Si Sitt C i
Mixed Allwial land Variable Snohomish 0 !
Neiiton A Sultan C
Newoerg B Tukwila D
Nooksack C Urban Variable
� Normal Sandy Loam D Woodinville 0
I-EYOROLCG(C SOIL GROUP CL.�,SSIFICATIONS
A. (Low runoif potential). Soils having high infiltration rates, even when thoroughly wetted, and consisting
cniefly of deep, well-to�xcessivefy drained sands or gravels. These so�7s have a high rate of water
transmission.
B. (Moderately low runoff potential). Soils having moderate infiftration rates when thoroughly werted; and
consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of
water transmission.
C. (Moderately high runoff potentiai�. So�s having slow in�i tration rates when thoroughly wetted, and
consisting chiefly of so�is with a layer that impedas downward movement of water, or sods with moderdtely
"ne to fine textures. These so�is have a slow rate of water uansmission.
D. (High runoff potential). Soils having very siow infdtration rates when tho�oughfy wetted and consisiing
chiefly of ciay soils with a high swelling potential, so�is with a permanent high water table, sods with a
hardpan or clay layer at or near the surface, and shatlow soils over nearly impervious material. These saas
have a very slow rate of water transmission.
' From SCS, TR-55, Second Edition, June 1986, Exhibic A-1. Revisio�s made from SCS, Soi! Interpretation
Record, Form �5, September t988.
1
.
� 3.�.2-2 II/92
KING COUNTY, WASHINGTON, 5 URFACE WATER D ESIGN MAYUAL
� FIGURE 3.5.1C 2-YEAR 24-HOUR ISOPLUVIALS
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f ,.3.4�` ISOPLUVIALS OF 2-YEAR 24HOUR I �►� ' ' � ` 35
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KING COUNTY, WAS HINGTON, S URFACE WATER DESIGN MANUAL
E FIGURE 3.S.IE 10-YEAR 24-HOUR IS�PLLJVIALS
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FIGURE 3.S.1H 100-YE�R 24-HOUR ISOPLUVIALS
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KING COUivTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TABLE 3.5'B SCS WESTERN WASHINGTON R[Ji�lOFF CURVE NUMBERS
. ��
SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS in 1982�
Fiunoff curve numbers tor selected agricuitural, suburban and urban land usa for Type tA
rainfail distribution, 24-hour storm duration.
CIJRVE NUMBEAS BY
HYDROLOGIC S GROUP
LAND USE DESCAIPTION A 8 C 0
Cultivated land(1): winter condRion 86 91 94 95
Mountain open areas: low growinq orush and grasslands 7a 82 89 92
Meadow or pasture: I FS 78 85 89
Wood or `oresi lana: undisturbed or older second growth 42 64 16 81
Wood or `ores; land: young second gtowtn or brush �� 72 8� 86
Orchard: with cover crop 81 88 92 94
Open saaces, lawns, parks, golf courses, cemeceries.
lands:,aping.
good condRion: grass cover on 75%
or more oi;he area 68 3C O 90
fair condrtion: grass cover on 50°,6
ro 75% of the area 77 85 � 92
Gravel raads and parking lots 76 85 89 91 �
Dirt roads and parking lots ' 72 82 87 89 (r
� t
impervious surraces, r,avement, roofs, etc. 98 98 98 98
Cpen water bodies: lakes, wetlands, ponds, 2tc. I t 04 1 CO 0 t 0o
� Sinqle Family Residentia! (Z)
Dwelling Unit/Gross Ac;e � Impervious (3)
1.0 DU/GA 15 Separate curve numher
t.5 OU/GA 20 shall be selected
2.0 DU/GA 25 for pervious and
2.5 DU/CA 30 impervious portian
3.o DU/GA 3a ot the site or basin
3.5 DU/GA �8
a.0 DU/GA a2
a.s au/�,� as
s.o ou/�� �
5.5 DU/GA 50 .
6.0 DU/CaA 52
0.5 DU/GA �4
7.0 DU/Gr, 5&
Planned unit developments. °6 impervious
condominiums, apartments, must be camputed
commercial business and
industnal areas.
�
(1) For a more detailed descnption or agnculturat lana use curve numbers refer to National Engineenng
Handbook, Section a, Hydrology, Chapter 9, August 1972.
{2) Assumes roof and driveway runo'rf is directed into street/storm system.
(3) The remaining pervious areas (lawn) are considered to be in qood condition for these curve numbers.
r
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� 3.�.�-3 11/9_
Existing Condition Event Summary:
BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event
------- (cfs) (hrs) (ac-ft) ac /Loss
Existing Condition 0.63 7.83 0.1876 1.37 SBUH/SCS kc24hr 2 yr
Existing Condition 0.97 7.83 0.2877 1.37 SBUH/SCS kc24hr 10 yr
Existing Condition 1.34 7.83 0.3991 1.37 SBUH/SCS kc24hr 100 yr
Drainage Area: Existing Condition
Hyd Method: SBUH Hyd Loss Method: SCS CN Number
Peak Factor: 484.00 SCS Abs: 0.20
Storm Dur: 24.00 hrs Intv: 10.00 min
Area CN TC
Pervious 0.2690 ac 90.00 0.08 hrs
Impervious 1.1030 ac 98.00 0.08 hrs
Total 1.3720 ac
Supporting Data:
Pervious CN Data:
Landscaping 90.00 0.2690 ac
Impervious CN Data:
Buildings 98.00 0.2270 ac
Pavment 98.00 0.7880 ac
Walks 98.00 0.0880 ac
Pervious TC Data:
Flow type: Description: Length: Slope: Coeff: Travel Time
Fixed Assumes 5 min. 0.00 ft 0.00% 5.0000 5.00 min
Impervious TC Data:
Flow type: Description: Length: Slope: Coeff: Travel Time
Fixed Assumes 5 minutes 0.00 ft 0.00% 5.0000 5.00 min
Redeveloped Condition Event Summary:
BasinlD Peak Q Peak T Peak Vol Area Method Raintype Event
------ (cfs) (hrs) (ac-ft) ac /Loss
Redeveloped Cond 0.61 7.83 0.1800 1.37 SBUHlSCS kc24hr 2 yr
Redeveloped Cond 0.94 7.83 0.2790 1.37 SBUH/SCS kc24hr 10 yr
Redeveloped Cond 1.13 7.83 0.3369 1.37 SBUHlSCS kc24hr 25 yr
Redeveloped Cond 1.31 7.83 0.3896 1.37 SBUH/SCS kc24hr 100 yr
Redeveloped Cond 0.13 7.83 0.0427 1.37 SBUH/SCS kc24hr 6-month
Drainage Area: Redeveloped Condition
Hyd Method: SBUH Hyd Loss Method: SCS CN Number
Peak Factor: 484.00 SCS Abs: 0.20
Storm Dur: 24.00 hrs Intv: 10.00 min
Area CN TC
Pervious 0.4000 ac 90.00 0.08 hrs
Impervious 0.9710 ac 98.00 0.08 hrs
Total 1.3710 ac
Supporting Data:
Pervious CN Data:
Landscaping 90.00 0.4000 ac
Impervious CN Data:
Buildings 98.00 0.2810 ac
Pavment 98.00 0.4710 ac
Walks 98.00 0.2190 ac
Pervious TC Data:
Flow type: Description: Length: Slope: Coeff: Travel Time
Fixed Assumes 5 min. 0.00 ft 0.00% 5.0000 5.00 min
Impervious TC Data:
Flow type: Description: Length: Slope: Coeff: Travel Time
Fixed Assumes 5 minutes 0.00 ft 0.00% 5.0000 5.00 min
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