HomeMy WebLinkAboutSWP272313(2) STORM DRAINAGE REPORT
' FOR
DOUG PRELLWITZ
20335 SE 136 TH STREET
ISSAQUAH, WASHINGTON 98027
1
STORM DRAINAGE REPORT
FOR
PRELLWITZ SHORT PLAT
' FILE NO. 639-001-961
' PREPARED BY
TOUMA ENGINEERS z313
6632 SOUTH 191ST PLACE, SUITE E-102 2�
KENT, WA. 98032 �f
(206)251-0665
' February 10, 1996
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9470 !(�
S. R�OfSTE���
2
TABLE OF CONTENTS
' 1. PROJECT OVERVIEW p. 3
11. PRELIMINARY CONDITIONS SUMMARY pp. 4..5
Core& Special Requirements
III. OFF-SITE ANALYSIS pp. 6
' IV. RETENTION/DETENTION ANALYSIS p. 7..9
V. CONVEYANCE SYSTEM ANALYSIS p. I0..I01)
' V1. SPECIAL REPORTS and STUDIES P. I I
VI1. BASIN and COMMUNITY PLANNING AREAS N.A.
VIII. OTHER PERMITS N.A.
IX. EROSION/SEDIMENTATION CONTROL DESIGN P. 11
X. BOND QUANTITIES WORKSHEET P. 11
' X1. MAINTENANCE and OPERATIONS MANUAL P. 11
APPENDICES p. 12
XII. APPENDIX A: Hydrologic Calculations&Detention Pond Sizing
XIII. APPENDIX B: Soils Report
3
I. PROJECT OVERVIEW
The project involves one parcel of land about 1.5 acres. The property is located North of the City of
Renton in the NE Quarter of Section 32, Township 24 North, Range 5 East, W.M. It is bounded on the
1 South by NE 36th Street, on the East by Aberdeen Avenue NE ( Not opened)and along the North and
West boundaries exist large single family parcels. Access to the properly will be via NE 36th, which will
be widened to 20 feet of pavement. Other improvements on NE 36t I include an 8 foot shoulder, a new I
foot deep ditch and a culvert.crossing the plat access road. See sheet 6 of 9 of the plans.
The project area is hilly with an average slope of 12.5%, leading downhill to the Northwest_ According to
the USGS map, see figure 4, the site is made up of Alderwood soils,which are generally stable,
' moderately well drained soils. The soils on the site were claimed to be weather sensitive. Also, a
geolechnical report for the site has been enclosed(Appendix B).
The City of Renton designates the site with the SF zoning. The R-8 zoning allows for a minimum lot size
of 4500 square feet and a maximum density of 8 units per acre. The setbacks allowed in the SF zone are as
follows: front yard setbacks, 15 feet; rear yard setbacks, 25 feet, and side yards setbacks, 5 feet on all
interior lots, and 15 feet on corner lots. The City of Renton Comprehensive Plan designates the site as
' Single-Family Residence which is consistent with present zoning.
The proposed development would create 9 single family lots with a minimum lot area of 4545 square feet.
Excluding the area of Tract "A" which will be designated for retention/detention facilities for the proposed
' plat, and excluding the road area, the dwelling unit density calculates at 6.72 units per net developed
area. Minimal grading will be required in order to prepare the final residential lots.
The area cover consists of alder trees and few mature evergreen trees. The flow of surface water is directed
north and northwesterly to a Swale which directs the(lows toward open ditches along Lincoln Avenue NE;
thence northerly and northwesterly to NE 441h Street and Jones Avenue NE approximately half a mile
downstream of the site.
Traffic circulation and access to the property is proposed to provide vehicular access from NE 36th Street
which connects to either 110th Avenue SE(City of Newcastle Street.Designation)or Lincoln Avenue NE.
The internal street improvements will be constructed in accordance with City's code and regulations.
4
H. PRELIMINARY CONDITIONS SUMMARY
1 The proposed 9 lots are consistent with the R-8 zoning requirements. The proposal has been found in
compliance with the subdivision regulations.
' Fire prevention and police services are available for the site. Water and sanitary sewer will be designed
and provided by the Coal Creek Water and Sewer District.
' Refer to sheet 7 of 9 for free clearing limits.
NE. 36t 1 Street shall be widened to 20 feet of pavement plus an 8 11. shoulder which includes a 4 ft.
' asphalt walkway and a 4 ft_ gravel strip. A new ditch will be dug alongside NE. 36t1n. See plans, sheet 6
of 9.
' CORE REQUIREMENTS
Core Requirement#1. -Discharge at the Natural Location
The developed site runoff will (low from the detention pond to a level spreader,
from which the runoff will flow to the natural discharge location, a swale on the downstream property.
' Core Requirement #2. -Mile analysis
See section 111, this report.
Core Requirement #3. - Runoff control
Water quality protection and stormwater detention are required. The detention pond will be
constructed to provide a 2.5 ft. detention depth, on top of a 3 ft. deep wetpond section,below which a 1 ft.
deep sediment storage will be provided. See section IV, this report.
' Core Requirement #4. -Conveyance system Design
The storm drainage system consists of catch basins and pipes, which have been checked for
peakflow capacity. It.has been found that their capacity far exceeds the expected 100 yr. peakllow. The
roof runoff will be conveyed in 6" underground pipes. All runoff converges to a type 11 catch basin, from
which a 12" pipe leads into(lie detention-wetpond. The outlet pipe from the pond leads to a type 1 catch
basin situated inside a level spreader. A 6" perforated pipe will provide for even distribution along the
bottom of the level spreader. See Section V of this report for calculation of pipe capacities.
Core Requirement #5. -Temporary erosion and sedimentation control
Temporary erosion and sedimentation control shall consist of siltfences, a construction entrance,
1 filter fabric over storm grates, and hydroseeding. See plans, sheets 7 &8 of 9. Because overland flow
will tend to converge on the detention pond, the pond can function as a temporary sediment trap.
Core Requirement #6. -Maintenance and operation
The storm drainage detention system shall be maintained by the properly owners, and the
applicant shall create a homeowner's association. The maintenance involves checking the dead storage of
' the pond and the catch basins for sediments and having the sediments removed.
Core Requirement#7. - Bonds and liability N.A.
' Special Requirement # I. -Critical drainage areas N.A.
Special Requirement#2. -Compliance with an existing Master Drainage Plan (MDP) N.A.
5
1 Special Requirement # 3. -Conditions requiring a MDP. N.A.
Special Requirement #4. - Adopted basin or community plans N.A.
Special Requirement # 5. - Special water quality controls.
' A combination wetpond/detention pond is proposed in lice of biofiltration.
See section I VA of this report.
Special Requirement #G. -Coalescing plate oil/water seperators N.A.
' Special Requirement #7. -Closed depressions N.A.
' Special Requirement #8. -Use of lakes, wetlands or closed depressions for runoff control N.A.
Special Requirement# 9. -Delineation of the 100_vr (loodplain N.A.
Special Requirement #10. - Flood protection Iacilities for type I and type 2 streams N.A.
Special Requirement#1 I. -Geotechnical analysis and report
' A geotechnical report is required. The geotechnical analysis and report has been be prepared and
stamped by a geotechnical engineer, and is included in appendix B of this report.
' Special Requirement #12. - Soils analysis and report N.A.
The geotechnical report shows that the soil type on site is indeed AldcRvood as shown on the
USGS soils map.
G
Ill. OFF-SITE ANALYSIS
From the site the runoff[lows Nortbwest tbru a well defined swale,across private property to Lincoln Av.
The water will continue along Lincoln Av. in a ditch and comes to a 12" culvert that tikes the flow across
Lincoln Av. and into a small creek. If the flow would exceed the capacity of this 12" culvert, then it will
1 continue down the ditch to an inlet structure with a 36"culvert leading to the creek. This creek finally
flows into a storm drain manhole at the corner of Jones Av. and NE 43 St. The detained 100 year peak
(low from the site is 0.37 cis, whereas the existing 100 year peak flow is 0.50 cfs. The downstream
' channels are not expected to erode because all detained peakflows are equal and lower than existing
peakflows. Therefore, no adverse impacts are anticipated. Refer to Section IV, Table 2 for peakflow
comparison.
r
7
IV. RETENTION/DETENTION ASSESSMENT
I. AREAS SUMMARY - WHOLE PROPERTY
Lot areas:
Lot Number Square Feel Acres
tract A 814l 0.19
1 6167 0.14
2 6376 0.15
3 5959 0.14
4 6723 0.15
5 4845 0.1 1
6 5408 0.12
7 5065 0.12
8 4545 0.10
9 5269 0.12
Totals 58,496 1.34
Assume lie total roof area to be 9 x 1,500 SF= 13,500 SF, driveways 9 x 500 SF= 4.500 SF.
IThe on-site pavement and sidewalk surface amounts to 13,379 SF.
2. DETENTION POND DESIGN
Part of the landscaping and yards will drain off as in the natural state, however, the pond has
been designed for the entire property. The roofs and driveways will drain to the detention pond thru
pipes. The table below shows the surface cover delineation.
' TABLE 1 : BASIN AREAS
AREA SQUARE FEE 7' ACRES CN
' DRAINAGE 13ASIN 84,226 1.93
DEVELOPED 13ASIN:
All Roofs 9*1,500 = 13,500 0.31
All Driveways 9* 500 = 4,500 0.10
Road& Walk in Basin 13,379 0.31
Total Impervious 13,500+4,500+ 13,379 0.72 98
' = 31,379
Landscaping 84,226 -31,379 1.21 86
= 52,847
Total 84.226 1.93
EXISTING BASIN:
Impervious 0 0.00 98
Forest 84,226 1 93 76
Total 84,226 1.93
The detention pond has been designed for the areas shown above. The calculations are presented on pages
A-L.A-17 of appendix A, . The outflow structure has a bottom orifice of 1.14" in diameter at the
' elevation of 205',and a 3.52" wide notch weir at elevation 207.12'. The detention pond has a rip-rap spill
way at 208.5'elevation, its banks end at 209',and has a bottom elevation of 201'with 1'dead storage plus
3' of wetpond. See plans, sheets 2 & 3. Therefore, the detention volume used for peakflow control is
x
' between elevations 205'and 208'. The detention volume necessar} Io match the 10 year existing �cakll v precisely was determined to be 4277 cf.; and when enlarged 50%to provide a faclor of safety, fuel oe
detention volume increased to 5881 cc with the saute outlet structure. 'These volumes are theoretical; the
1 aclual conslrncled pond will detain 6190 cf. of storm water during the 10 year event. Consegnently,
predicted onlllow peak flows are lower Ilan the existing peak flows. The resulting peak flows are shown
in table 2, and they are based on the actual pond geometry as presented in the plans.
TABLF,2 : DETENTION POND PEAK FLOWS
' CFS EXISTING DFVPD• POND OUTFLOW
INFLOW
100 YR 0.50 1.57 0.45
10 YR 0.23 1.05 0.18
2YR 0.06 0.61 0.06
PEAK W.S. VOLUME, cf.
E1,.
I00 Ylt 207.56' 6640
Ill YR 207.41' 6190
2YR 207.09' 5250
3. ACTUAL POND GEOMETRY - PLANS, SllEE'I'3
After several design iterations(lie dctertlion pond geometry that is presented in the plans had an
emergency capacity of 8()1()cf, at w.s. elevation 208. The minimum volume at design w.s. elevation
207.5 was 6422 cf., while file actual pond geontetrj, has a design volume of 6458 cf.; see table 3
below.
V= SUM (dV) = SUM(JAi-r A(i-1)1/2 * lELVi-EE,V(i-I)l
Consideration had to be given to the required wetpond volume too, wilicii is 2259 cf with a minitnuni
depth of 3 ft. A numerical summary follows.
TABLE 3 .- DETENTION POND/WETPOND VOLUMES
SEDIMENT DEAD STORAGE DETENTION VOLUME _
ELV.-FT A-SF dV-CF TOTAL V ELV.-FT A-SF dN-CF TOTAL V
201 819.31 __ 0 205 2106.83
975.135 0
202 1130.96 1103.87
975.135 205.5 2308.65 1103.87
WETPOND 1202.4
ELV.-FT A-SF dV-CCF TOTAL V 2p6 ��� 2�'�
1
202
1296. 38 1130.9E 206'S 2683.E 3602.408
0 1385.27
1274.525 207 2857.48 _ 4987.678
203 1410.09 1274.525 345.3354
204 1684.4
_ 1551.245 _ 207.12 280.11 _ 5333.013
_ 2825.77 _ 379.5637
_ 1695.615 _ 207.25 2941.64 2106.83 4721.385 5712.597__745.7
207.5 3023.9E 6458.297
304A165
207.6 3056.37 6762.313
1247.88E -
208 3183.0E 8010.199
9
4. WATER - WETPOND QUALITY REQUIREMENTS
Q Q
1 Instead of bioGltration, a combined wetpond/detention pond is proposed. For that purpose a
50%safety factor(30%is common)was applied to the detention volume and the required wetpond
volume. The required wetpond volume is the hydrograph volume that results from 1/3 of the 24 hr. 2
' year precipitation. A calculation follows below, showing the required volume to be 2259 cf. The
wetpond shall accomodate 1 ft. of sediment storage and a minimum of 3 ft. water depth above that.
The volume of the wetpond that is proposed is 4721 cf. above the 1 ft. depth, as is shown in Table 3.
The exstra 2462 cf. is a bonus resulting from the required detention volume on top: At 2.5 ft. deep,
' the bottom area of the detention portion needed to be 2107 sf., and the wetpond portion below is
required to be 3 ft. deep. Thus we have a wetpond that should by itself provide ample water quality
control.
•
c3BUH/SCS METHOD F'•OF" COMPUTING RUNOFF HYDR[:1GRAPH
STORM OPTIONS:
1 --• r:i. . TYPE--•1 A
-- 7-DAY DESIGN ST"OI�;M
3 -• STORM DATA FILE
.OU
SPECIFY STORM OPTION: .32 ^'' AVA11144- C;rORM
1 .
S. C. S. TYPE:-1A RAINFE-ll..l__ DISTRIBUTION
' ENTER F REQ(YEAF ) , DURATION(HOUF ) , PREC I P( I NG ES)
1 p 24 y 0. 67
------------------------------------------------------------------------
aF�t aF x a�xa�x S. C. S. TYPE••-•1A DISTRIBUTION �� �>E��x �a���� x �•>F�� ►� x �
tt tt x x 1—YEAR :2 4--HOUR S`F't:JRICI �..K..�..�. • 67" TOTAL PREC I P r ��•�••�•� �••�•�*•
ENTER: �A(PERV)+, «-�N(PE:RV) , A( I MPE RV) , CN( I MPERV) , TC FOR BASIN NO. 1
1 r.s:i �LIE, (l, •7:�, ':3f3, tI•. /
DATA PR I NT--•OU•T
' AREA(ACRES) PERVIOUS IMPERVIOUS T C(M I NU•T'E_S)
A i:N A (:hl
1 . 9 1 .2 86. 0 . 7 98. 0 i 4. 7
PEAK--Q(CF='S) T-PEAK(1•• RS) VOL(C U-FT) s
• 10 7. 67 1506 K
ENTER Ed: 3 Cpath 3 f i 1 en ame C . ext 3 FOR STORAGE OF COMPU•T'EyW HYDROGRAPH:
dviyrhyd
' SFEC:I FY: C: CONTINUE, N -- NEWSTORM, P PRINT, S •-•• STOP
' 10
V. CONVEYANCE SYSTEM ANALYSIS
1 1. POND EMERGENCY OVERFLOW
According to King County SWM design manual, p.4.4.4-2, a spillway of the minimum width of 6'
with a head of 0.2'allows a flowrate of 1.86 cfs; which is greater than 1.57 cfs, the 100 year
' undetained peakflow. The spillway is a trapezoidal broadcrested weir with 3:1 side slopes and a
discharge coefficient of 0.60. The calculation is as follows: Q=3.21 (LH'n+2.41-1111)1 H=0.2,L=
6,_>Q= 1.86 cfs.
' 2. STORM DRAIN PIPES
Applying the manning equation to full flow in pipes, table 4 below shows the rninimurn slopes for a
12"diareter pipe to convey at least the 100 yr. developed-undetained peak flow of 1.57 cfs. Both of
the pipes have a greater slope, sothat they convey over 1.57 cfs. See plans, sheet 2. The capacity of
the pipe into the pond is 7.67 cfs. At 1.57 cfs this pipe has a flow depth of 4.5"and a flow velocity of
6.64 fps. See figure V.2-1.
TABLE 4 : PIPE CAPACITIES
CPEP CAPACITY- - _. _.. . IQ_--1.49/n"A'_R"(2/3) ' S"(11/2)
-_- FULL FLOW, SO THAT_R -A/P=D/4
Showing minimum slopes for IZ'pipes--_ -� -- ---._---- - - -_-- - __ _--_ _ ---
n L(ft)-- S -q-t-fl) R (fps) A(sf) --
0.012 57 O.U()?_U 1 0.25 2.20 0.79 1.73 smooth wall
_ 0.0_24 _ 57 0.0070 11 0.25 2.06 0.79 1.62 single wall
Actual _....._..__-.,
0.012 76.4 6A3-0- 1 0.25 9.77 0.79 7.00-1711 smooth wall
Showing minimum slopes for G"pipes
0.012 _ __ _O.U150 -_0.5U U.13 3.l10 0.20 0.75 smooth wall
0.024 48 0.0150 0.50 0.13 1.90-6.201 0.37 single wall
3. CULVERT
The proposed culvert along NE 36th St.,crossing under the plat access road, has a slope of 0.0747 and it
is to be a 12"diameter CPEP. This is located at the top end of the basin so the peakflow will be less than
' 1.57 cfs., see above. The normal flow capacity will be greater than 7.67 cfs. as shown in table 4.
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
FIGURE 4.3.411 CIRCULAR CHANNEL RATIOS
' Experiments have shown that o varies slightly with depth.
This figure gives velocity and flow rate ratios for varying n(solid line)
and constant n (broken line) assumptions.
' -- 1.2
1.1
1.0
Y V/V full
♦ .7 d 0168
a
.6
0f0full ♦ I
.4
.3
- - - - - .2
.1
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
RATIO OF FLOW DEPTH TO DIAMETER (d/D)
f.C. 5. )
' J
4.3.4-19 1/90
II
VI. SPECIAL REPORT'S and STUDIES: Geotechnical Report
' A geotechnical report has been included in Appendix B. Findings include that on avarage the
soil consists of 1 ft. dark organic top soil,followed by 3 ft. medium dense sand, followed by a very dense
glacial compacted sand. Liquefaction was deemed impossible. The only concerns were the potential
erosion of the loose top layer, and the possibility of perched water due to the low permeability of the
substratum.
VI1. BASIN and COMMUNITY PLANNING AREAS
' VI11. OTHER PERMITS
' IX. EROSION/SEDIMENTATION CONTROL
Sec Section 11, core requirement 5.
' X. BOND QUANTITIES WORKSHEET
' XI. MAINTENANCE and OPERATIONS MANUAL
Every dry season(August- September)cl►eck the detention pond for sediment accumulation, and
have sediments removed if more than 0.5 ft. of sediment has accumulated.
a
' 12
XII. APPENDIX A
Hydrologic Calculations & Detention Pond Design
' I. RUNOFF CALCULATIONS
TIME OF CONCENTRATION CALCULATION p. A-I
SITE BASIN MAI' p A-3
' p. A-4
USGS SOIL TYPE MAI'
HYDROLOGIC SOIL GROUP TABLE p. A-5
CN NUMBERS IDENTIFIED p. A-fi
' 2 YEAR PEAKFLOW CALCULATION; EXISTING& DEVELOPED p• A-7
10 YEAR PEAKFLOW CALCULATION; EXISTING& DEVELOPED p• A-8
25 YEAR PEAKFLOW CALCULATION; EXISTING& DEVELOPED p. A-9
100 YEAR PEAKFLOW CALCULATION; EXISTING&DEVELOPED p. A-10
ISOPLUVIALS pp. A-I L.14
' 2. DETENTENTION POND DESIGN
-15
CALCULATION PROCEDURE p. . A-1
G..17
THEORETICAL CALCULATION PRINTOUT pp.
NOTCH WEIR DESIGN p. A 1R
STAGE-DISCHARGE CALCULATION p. A- 0
STAGE - STORAGE CALCULATION p. . A-21..22
2, 10& 100 YR. DEVELOPED DETAINED PEAKFLOWS pp. -2
i
1
1
Developer] Sllh TC
�HEEI j lTr� 0.42 {i_'na)"0.8/(P2'0.5'S"C).4)
f -�- ----- -
--- - .
-�.F'2(tn) i T(min.)
- ( 74.62.1 0.15l 0.m! 2i 4.15
- --
( -I o! '(_ ' 0.00
I ISO
} L (11) 1 k
f
- ---- -- --.SFIAL.L.n1N 1�1().1�4! 271 0.0285 t)S�
_..+---- �------t-- — 0.03
CHANNEII 401 42it _ 0.2251 _...�
"11ME or- coNCENTRATIUN
! (Existing Site Tr, I I --
( .. ..
iSll[ [ l �Eit� 0.41 0.1303i 11 Fi'i
1
1
1
' AI-2
' KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TABLE 3.5.2C "n" AND "k" VALUES USED IN'TIME CALCULATIONS FOR HYDROGRAPHS
'n,'Sheet Flow Equation Manning's Values(Fox the Initial J(In h of Pavel)
' Smooth surfaces(concrnte,asphalt,gravel,or lobe hard packed sell) 0.011
Fallow fields or Ionise soil surface(no residue) 0.05
' Cullivated sop with residue cover(s<= 0.20 B/11) 0.06
Cultivated son will,residue cover(S>0.20 fl/ft) 0.17
Short prairie grass and lawns 0.15
Dense grasses 0.24
Bermuda grass 0.41
Range(natural) 0.13
' Woods or forest with light underbrush 0.40
Woods or forest with dense underbrush 0.90
*Manning values for sheet How only,from Ovedon and Meadows 1976(See TR-55. 1986)
' 'k'Values Used In Travel Ttme/Time of Concentration Calculations
Shallow Concentrated Flow (After the Initial 300 H.of sheet How,R -0.1) k.
' t. Forest with heavy ground liner and meadows(n-0.10) 3
2. Brushy ground with some trees(n-0.060) 5
' 3. Fellow or minimum tillage cultivation(n-0.040) 6
4. High grass(n =0.035) 9
S. Short grass,pasture and lawns(n-0.030) 11
' 6, Nearly bare ground(n-0.025) 13
7. Paved and gravel areas(n-0.012) 27
' Channel Flow(Intennitlent)(At the"Going of vl%lUe etwinnels R-0 2) - -_------_-k,
1. Forested swale with heavy ground litter(n =0.10) 5
' 2. Forested drainage course/ravine with defined channel bed(n=0.050) 10
3. Rock-lined waterway(n=0.035) 15
4. Grassed waterway(n-0.030) 17
' 5. Eanh-lined waterway(n=0.025) 20
6. CMP pipe(n-0.024) 21
7. Concrete pipe(0.012) 42
' 9--Other waterways and pipes--,--- --- ------- 0.508/n
' Ckinnel Flow(Can1111u00e stream,R _ 0A)- ----- k�
9. Meandering stream with some pods(n =0.040) 20
10. Rock-Ilned stream(n-0.035) 23
' 11. Grass lined stream(n-0.030) 27
12. Other streams,man-made channels and pipe 0.807/n'•
' **See Chapter 5,Table 5.3.6C for additional Mannings'n values for open channels
' 3.5.2-7 1/90
3
209 zo9•# 27
�;. 56.,moa�°' BASIN MAP
215
'9 2, �� # �y •4i" FF = 217 I
1 sq. 5,044
r ` 5040 sq.ft I
�9 0.jP acres
0.19 cres 2 .4 acre3`
6,11: sq.ft.
acres EXISTING FLOW LINE
`Fr 221
FT, RO S N
�'�
21,'SSF� 0r�4sa I 0,19 , DEVELOPED FLOW LINE
' 5,,065 sgry
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j 6,183 sq.ft.
\ i 0.14 acres.
223 I
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acr
127 �° r
- 9Qoo, •s IMPERVIOUS SUBBAS111v
DEVELOPED CONDITIONS
ti 0 5,490 sq.`t.
5,303 s .ft. R-25'
acre
a;, 3 227s
s rs
`'6`a BASIN BOUNDARY
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4„ i1�7;tgY 't„ Ilq«;,', r' .,�,i„ '• II x'`„ AgG, •,: •'-.�II.. 1 f, , , • -
a�k �i+;���,[ 1 den yC�i�A' "� - - +b:� ,.. �1 I =::: �.••_ '-,J • I r c ;, `I: _
;�.�`�`� .k 1 �' r<�� �z '. �InC ! t vJ4kF v, .,✓''AkF Ev
• .I `/w ✓' 1 '
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Y7 d GRA VET 1
r t�t{l6�{t.. Fvx�0� � • Q' •• t .'•. '_. — - — , `= Py. r ., ;y,, wT ' •� _ 9," t.
���..+ri� � 1 �--_ . - r�l r�' J1kF^ +Ifk'•,�f = C� rr, '" � �' S � ,
�q,. ('� \ InA i•i_ .+ r, i_". _ _ "I• p � ` � ' !�. _ ABC `i
�19;;
r �, `{y s a ° • ._�_:.,t- s n BM;111 t>'y"' 1 r t,`�•. r
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�
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if
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lu° 1 7
i `i � ✓
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J � �r L• !1!S t I i 1= �l{ Af4IC i.� �t ,.
� �1 ' •�J„�'t lir „ "1 �g 7 Z , ' . ., , ', j t �JS� R ry Iri �w1' 1.• ndC' i ' !.
1
Ev
Plant' .*. �z r + '� •� ',;f=, Jl / iSiJ 3Ji� � _
RENTON 1.9 Mi. 12r30rr (Joins sheet 1 1) R d( 10'
RENTON 1.7 MI-
' Scalf, 1:24 000
tFz t,a O l 2 MiIP;
--1 3000 2000 1000 --O ----— — 1000 {0000 I PPI
A - 5
K I N <i (' O U N 'I' Y, W A S 11 I N (; 'I' () N, S 11 R FA C I s W A '1' I R 1) F' S I (i N h 1 A N U A L
' (2) CN values can he area weighted when they apply to pervious areas of similar CN's (within 2.0
CN points). I lowever, high CN areas should not be combined with low CN areas (unless the
low CN area,; are less than 1 5% of the suhbasin). In this case, separate hydrographs should be
generated and surruned to form one hydrograph.
- --------- — ——
FIGURE 3.5.2A HYDROLOGIC SOIL GROUT'OF I III;SOILS IN KING COUNTY
' I IYDROLOGIC I JYDROLOGIC
SOIL GROUP GROUP* SOIL GROUP GROUP*
�!;P Alderwood (C;? Orcas Peat D
Arents, Alderwood Material C Oridia D
Arents, Everett Material B Ovall C
Beausite C Pilchuck C
Bellingham D Puget D
t Briscot D Puyallup B
Buckley D Ragnar B
Coastal Beaches Variable Renton D
Earlmont Silt Loam D Riverwash Variable
' Edgewick C Salal C
Everett A/0 'Sammarnish D
Indianola A Seatile D
Kitsap C Shacar D
' Klaus C Si Silt C
Mixed Alluvial Land Variable Snohomish D
Neilson A Sultan C
Newberg B Tukwila D
' Nooksack C Urban Variable
Normal Sandy Loam D Woodinville D
' HYDROLOGIC SOIL GROUP CLASSIFICATIONS
A. (Low runoff potential). Soils having high infiltration rates, even when thoroughly wetted, and consisting
' chielly of deep, well-to-excessively drained sands or gravels. These soils have a high rate of water
transmission.
B. (Moderately low runoff potential). Soils having moderate infiltration rates when thoroughly wetted, and
' consisting chiefly of moderately fine to moderately coarse textures. These soils have a moderate rate of
water transmission.
O (Moderately high runoff potentiai). Soils having slow infiltration rates when thoroughly wetted, and
consisting chiefly of soils with a layer that impedes downward movement of water, or soils with moderately
' fine to fine textures. These soils have a slow rate of water transmission.
D. (High runoff potential). Soils having very slow infiltration rates when thoroughly wetted and consisting
chielly of clay soils with a high swelling potential, soils with a permanent high water table, soils with a
hardpan or clay layer at or near the surface, and shallow soils over nearly Impervious material. These soils
have a very slow rate of water transmission.
* From SCS, TR-55, Second Edition, June 1986, Exhibit A-1. Revisions made from SCS, Soil Interpretation
Record, Form #5, September 1988.
1
3.5•2-2 11/92
' KIN (; COlIN '1' Y, WASIIIN (; 'I' C) N, Stlltl' nc' I? WA '1' GR UI: SIGN MANUA1,
'1'A111 E 3 5.211 SCS IVASHING' ON IZUN01 1, CURVF,NUMBERS
' SCS WESTERN WASHINGTON RUNOFF CURVE NUMBERS (Published by SCS In 1982)
' -- — —_ Runoff curve numbers for selected agricultural, suburban and urban land use for Type1A
rainfall distribution, 24-hour storm duration.
CURVE NUMBERS BY
' — -- — -- HYDROLOGIC SO L GROUP
LAND USE DESCRIPTION A B D
Cultivated land(1): winter condition 86 91 94 95
' Mountain open areas J low growing brush and grasslands 74 82 89 92
Meadow or pasture: 65 78 85 89
' Wood,or forest land: undisturbed or older second growth 42 64 76 81
Wood or forest land: young second growth or brush 55 72 '81 1 66
Orchard: with cover crop 81 88 92 94
' Open spaces, lawns, parks, golf courses, cemeteries,
landscaping.
good condition: grass cover on 75%
or more of the area 68 80 8 90
' fair condition: grass cover on 50%
to 75% of the area 77 85 90 92
Gravel roads and parking lots 76 85 89 91
' Dirt roads and parking lots 72 82 87 89
Impervious surfaces, pavement, roofs, etc. 98 98 98 98
Open water bodies: lakes, wetlands, ponds, etc. 100 100 100 100
' Single Family Residential (2)
Dwelling Unit/Gross Acre % Impervious (3)
' 1.0 DU/GA 15 Separate curve number
1.5 DU/GA 20 shall be selected
2.0 DU/GA 25 for pervious and
2.5 DU/GA 30 impervious portion
3.0 DU/GA 34 of the site or basin
' 3.5 DU/GA 38
4.0 DU/GA 42
4.5 DU/GA 46
5.0 DU/GA 48
' 5.5 DU/GA 50
6.0 DU/GA 52
6.5 DU/GA 54
7.0 DU/GA 56
' Planned unit developments, % impervious
condominiums, apartments, must be computed
commercial business and
' industrial areas. -- ------ _---- - '- --------- — ---
(1) For a more detailed description of agricultural land use curve numbers refer to National Engineering
Handbook, Section 4, Hydrology, Chapter 9, August 1972.
' (2) Assumes roof and driveway runoff is directed into street/storm system.
(3) The remaining pervious areas (lawn) are considered to be in good condition for these curve numbers.
' i(An 3.5.2-3 1 1/92
`� . / i ` T
TYPE—IA RAINFALL DISTRIBUTION
Nl"ER'; F R':EW(YEAR) , DUR*:AT I ON(HOUR) , PREi_I P( I Ni_HES)
-----------------------------------------------------------------
� a�x S. C. S. TYPE-1A DISTRIBUTION
2—YEAR 24—HOUR STORM ***..*. 2. 00" TOTAL PR'EC:I P.
----------- ---_------__.___—..._..--_..._--_-..___._..._._____._..._"._..._----_-- _---_--...---_—___._-__-..-._—
NTER: A(PER'V) , CN(PER�:V) , A( I MPERV) , C:N( I MNERV) , TC FOR BASIN NO. I.
P93
F; \HYD\639001 >1
UC. S. TYPE—IA RAINFALL_ DISTRIBUTION
ENTER: FREQ(YEAR:) , DURATION(HOUR) , PREC:I P( I NC:HES)
24
r..... 'L---...----------.....-..-._...-......--_...---......---_.._..._._-•....___--. -_-_.•-_••___--..._._..-- __•__...-_.-_- -
� S. C. S. TYPE-IA DISTR='IBUTION * * * * * * *
2-YEAR 24--•HOUR~.: STORM 2. i 0" TOTAL PR'EC I P.
----•----------_-_-----..._..-..-_-__--._-__...___--_---........-_-----._____..-----_--•--------------
ENTER: A DERV) , C:N(PE RV) , A( I MPER'V) , CN( I MPER'V) , TC FOR BASIN NO. 1
11 . 93v76, 0198t27. 7
DATA PRINT-OUT:
' AREA(ACRES) PERVIOUS IMPERVIOUS TC:(I"I I NUTES)
A CN A )'N
1 . 9 1 . 9 76. 0 . 0 98. 0 27. 7
'., PEAK*--Q(C:FS) T-FEAR::(HR::S) VOL(CU—FT)
. (_)G 0. 50 2892
LATER 1d: J Cpath J f i I enameC . ext J FOR STORAGE OF COMPUTED HYDROG APH:
X2Y. HYD
FILE ALREADY EXIST; OVERWRITE (Y ��r N) -
r
SPECIFY: C -- CONTINUE, N -- NR_WSTOR=.M, P - PR I NT, S "- STOP
.--__.._._.__...__.--".____.-_"--_----___- --..-----_-...-_____.-..---..:------__--_----__-
NTER: A(PER'V) , C:N(PER'V) , A( I MPER'V ) , CN( I MPERV) , TC FOR BASIN NO. 2
1 .21 , 86, U. 72, 9S, 4. 7
1
,DATA PRINT—OUT:
AREA(AC:R;;ES) PERVIOUS IMPERVIOUS TC(MINUTES)
A 11.1N A )_N
1. 9 1 . 2 86. 0 . 7 98. 0 4. 7
' PEAR::—O(i:FS) T—PEAK(HRS) VOL(CU..._FT.)
. 61 r. 67 0 367
Ld: ] [pathJfi1ename[ . exLJ FUk SlukAUE UF CUU|'UTED HYDROGRAPH:'
HYD#H�
E ALREADY EXIST; OVERWRITE (Y or N)
i ` '
��PECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP
��
~~
TORM OPTIONS:
-I - S. C. S. TYPE-IA
- 7-DAY DESIGN STORM
- STORM DATA FILE -
I
SPECIFY STORM OPTION:
I.C. S. TYPE-IA RAINFALL DISTRIBUTION
' NTER: FREQ(YEAR) , DURATION(HOUR) , PRECIP( INCHES) '
0, 24, 2" 9
.��
! '
S. C. S. TYPE-IA DISTRIBUTION ********************
/
******** 10-YEAR 24-HOUR STORM **** 2. 90" TOTAL PRECIP. *********
______________________________________________________________________
INTER';
(PERV) , CN(PERV) , A( IMPERV) , CN( IMPERV) , TC FOR BASIN NO. 1
,.�3,bn�\
DATA PRINT-OUT:
IAREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
A CN A CN
1 ° 9 1 . 9 76. 0 . 0 98. 0 27. 7
`
PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT)
./ . 23 8. 00 6619
INTER [d: ] [path] filename[ . ext ] FOR STORAGE OF COMPUTED HYDROGRAPH:
ILE ALREADY EXIST; OVERWRITE (Y or� N) ?
|��
��
��
. SPECIFY: C ` - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP
---------------------------------------------------------------------
� ENTER: A(PERV) , CN(PERV) , A( IMPERV) , CN( IMPERV) , TC FOR BASIN NO. 2
� 21, 86, 0. 72, 98, 4. 7
^
",,TA PRINT-OUT:
N� AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
A CN A CN
1 . 9 1 . 2 86. 0 . 7 98. 0 4. 7
N� PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT)
mm 1 . 05 7. 67 13903
NTER
[path] filename[ . ext ] FOR STORAGE OF COMPUTED HYDROGRAPH:
'
U
C. S. TYPE-1A RAINFALLREQ TER: F (YEAR) , DURATION(HOUR) , PRECIP( INCHES)
25, 24, 3. 42
___________ ____
S. C. S. TYPE-1A DISTRIBUTION ********************
25-YEAR 24-HOUR STORM **** 3. 42" TOTAL PRECIP. *********
_....._....._....._.....-...._-....................... _____-....................... ............. _....._..............._............ ....__.......... .................................. ............................................
NTER: A(PERV) , CN(PERV) , A( IMPERV) , CN( IMPERV) , TC FOR BASIN NO. 1
1 . 93, 76, 0, 98, 27. 7
ATA PRINT-OUT:
AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
N� A CN A CN
1 . 9 1 . 9 76. 0 . 0 98. 0 27. 7
PEA K-Q(CFS) T-PEAK(HRS) VOL(CU-FT)
. 36 7. 83 9116
[path ] filename[ . ext ] FOR STORAGE OF COMPUTED HYDRO8RAPH:
OF1LE ALREADY EXIST; OVERWRITE (Y or N) ?
IFIECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP
C
_______________________________________
NTER: A(PERV) , CN(PERV) , A( IMPERV) , CN( IMPERV) , TC FOR BASIN NO 2
.
^ . 21 , 86, 0. 72, 0098, 4. 7
NTER: A(PERV) ' CN(PERV) , A( IMPERV) , CN( IMPERV) , TC FOR BASIN NO. 2
. 21 , 86, 0. 72, 98, 4. 7
ATA PRINT-OUT:
~~ AREA(ACRES) PERVIOUS IMPERVIOUS TC(I'll INUTEIS)
A CN A CN
N� 1 . 9 1 . 2 86. 0 . 7 98. 0 4. 7
PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT)
1 7. 67 17236
ENTER Ed: ][path] filename[ . ext. ] FOR STORA8E OF COMPUTED HYDROGRAPH:
N�lLE ALREADY EXIST; OVERWRITE (Y or N) ?
ECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP
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KING COUNTY_WAS NINGTON,-SURFACE WATER DESIGN MANUAL
FIGURE i° .1C 2-YEAR 24`1IOUR 1SOPLUVIAL5
Jf
}
2.9 rl
ILj
wya? ..
1 r W •
em
U
( 1�01S
• -1
N
•
ry o,� _ ��•� -�' _ _ •�--. (\ M�l
2-YEAR 24-HOUR PRECIPITATION — 35
ISOPLUVIALS OF 2-YEAR 24-HOUR
TOTAL PRECIPITATION IN INCHES
----------
--a 5-6 7 8 Mllsi >. 1
' 1-300,000 3.5.1-8 1/90
A - )z
KING COUNTY, WAS 11 INGTON, S URFACE WATE.R -DESIGN MAN U A 1,
FIGURE 3.5.1E 10-YEAR 24-IIOUR ISOPLUVIALS
2.1
22
,23
24
40-r"
2S
wow
26
27
29
3.0 —3
L V11
t I An ,� / � • ,~
mofc
3?
Mm
33 41
Tr
4
I tn-
4 .....
V
T�,A
10-YEAR 24-HOUR PRECIPITATION
3.4-00' ISOPLUVIALS OF 10-YEAR 24-HOUR
TOTAL PRECIPITATION IN INCHES
0 2 2 3 4 5 6 7 R Miles
---- 3.5.1- 0 3y1/90 4.0
1-300.000
1 A - 13
KING COUNTY, W ASHINGTON, SURFACE W ATE It U.ESI0N MANUAL
FIGURE 3.5.1F 25-YEAR 24-IIOUR ISOPLUVIALS _
-29
30
51
...., is
z
5.5
'fl
•_ '�-. 1 I� 1 1. -
Dow
25-YEAR 24-HOUR PRECIPITATION
4•y 5 p�l
3.4 ISOPLUVIALS OF 25-YEAR 24-HOUR _ 4
TOTAL PRECIPITATION IN INCHES
0 1 2 3 4 5 6 7 8 Mlles
' 1. 300.000
1 A �4
-
KING COUNTY, WASIIINGTON. SURFACE WATER DESIGN MANUAL
FIGURE 3.5.111 100-YEAR24-1110URISOPLUVIALS
J'm
1 .4
r\-,. 4M
nk
14
Poo
Mi
46
17
cb
1b. I- . .. / / - 11 6.5
100-YEAR 24-HOUR PRECIPITATION 0.0
3.4 ISOPLUVIALS OF 100-YEAR 24-HOUR 5.5
TOTAL PRECIPITATION IN INCHES
0 1 2 3 4 5 6 7 a Miles
3.5.1-13 Q1
1
1- 300,000 V 1/90
' DETENTION POND DESIGN CALCULATIONS:
' First design iterations of orifice sizes and elevations were done to get peak outflows as close as
possible to existing peak (lows. This first calculation was based on a regular trapezoidal pond with
3:1 sides. The 10 year developed hydrograph was used to get a design volume at (lie design water
surface elevation.
Secondly, the trapezoidal pond was enlarged 50%, and used to route the t0, 2& 100 year
hydrographs of the developed conditions, using the same outlet structure as in the first calculation.
' The result is lower peakllows and larger detention volumes. Of interest is that all peakflows are now
at or below existing pcalkflows, which is what we want.
' Unfortunately, the designed top orifice could not physically fit below the riser rim so that a notch weir
was designed with the same stage-discharge properties. Another exception is that.the pond is not
trapezoidal, and had to be iteratively drawn and measured to have a similar stage-storage
relationship.
' Finally the actual stage-storage and stage-discharge relationships were calculated for the pond as
represented by the plans. This data was then used to route the 2, 10, & 100 yr. developed condition
' hydrographs through the pond, resulting in the peak outflows and peak stages that were reported i❑
Section IV, Table 2.
A - 16
�1
ENTER: POND SIDE SLOPE (HOR I Z. COMPONENT)
ENTER: EFFECTIVE STORAGE DE::P.F H( f t ) BEFORE:: OVERFLOW
ILTERJ
Ed: 3 Ew ath3 f ilencameE . ext _I OF-PRIMARY DESIGN INFLOW HYDROGRAF'H:
DVIOY. HYD
.I MARY DES ON INFLOW PEAK 1 . 05 CF•S
ENTER PRIMARY DESIGN RELEASE RA`I"E( f s) :
VaJ
EFL: NUMBER OF INFLOW HYDRC:aGRAPHS TO BE:. TESTED STE:D FOR PERFORMANCE (5 MAXI MUM? :
TER E d: 3 E path 3 f i 1 ename E . ex t _i OF HYI:)R(:7i_:iR(1F'H 1 .
DV2Y. HYD
fE'_R TARGET RELEASE RATE: (r. •f s) :
1106
TEFL: Ed i 3 Epath 3 f i l enameL . ext ] OF HYDROGRAPH 2:
100Y. HYD
TER TARGET RELEASE RATE(c f s) :
0. 00
LTER: NUMBER OF ORIFICES, R I SER--.HEAD( f t ) , R I'SER-...D I AMETEK( i n
r_
SER OVERFLOW DEPTH FOR PRIMARY PEAK INFLOW -= . 23 FT
SPECIFY ITERATION DISPLAY: Y -._ YES, N •- NO
SPECIFY: R - REVIEW/REVISE INPUT, C: -- CONTINUE
11ITIAL STORAGE VALUE FOR ITERATION PURPOSES: 5550 C:U--FT
TTOM ORIFICE: ENTER .0--MAX (c fs:)
1106
DIA. = 1 . 18 INCHES
P ORIFICE: ENTER HE:I GHT( f t i
12
A. = 3. 19 INCHES
]JRFORMANCE: INFLOW TARGET-OUTFLOW ACTUAL-OUTFLOW PK -STAGE STORAGE
ES I GN HYD: 1 . 05 . 23 . 23 2. 50 4277
TEST HYD 1 : . 61 . 06 . 10 2. 10 3550
TEST HYD 1 . 57 . 50 1 . 21 2. 71 47 0
0 iQT t7PTr, F- 9 STF)P
i �
ENLARGEMENT OPTION: ALLOWS FDR lNCREASIN6 STORAGE AT A SPECIFIED
N� STAGE HE|GHT, TO PROVlUE A FACTOROF SAFETY.
ENTER: STORAGE-INCREASE(%) , STAGE-HElGHT' ft )
N�50, 2. 5
PERFORMANCE: INFLOW TARGET-QUTFLOW ACTUAL-OUTFLOW PK-STAGE STORAGE
N� DESIGN HYD: 1 . 05 . 23 . 18 2. 34 5881
N� TEST HYDC. 2. 11 5160
TEST HYD 2: 1 . 57 . 50 . 43 2. 56 6620
ISPEC I FY: D - DOCUMENT, k ADJUST ORIF, E - ENLAR6E, IS STOP
D
FERFORMANCE: INFLOW TARGET-OUTFLOW AC T UAL-OUTFLOW PK-STA8E STORAGE
DESIGN HYD: 1 . 05 . 23 . 18 2. 34 5881
TEST HYD 1 . 61 . 06 . 06 2. 11 5160
TEST HYD 2: 1 . 57 . 50 ' 43 2. 56 6620
TRUCTURE DATA: R/D-POND (3. 0: 1 SIDE SLOPES)
�RISER-HEAD POND-BOTTOM-AREA TOP-AREA(@lrF. B. ) STOR----DEPTH GiORAG E-VOLUME
2. 50 FT 1
1815. 9 SQ-FT 455. 3 SQ-FT 2. 50 FT 6422 CU-FT
LUBLE ORIFICE RESTRICTOR: DIA( INCHES) HT(FEET) Q-MAX (CFS)
BOTTOM ORIFICE: 1 . 18 . 00 . 060
' TOP ORIFICE: 3. 19 2. 12 . 170
ROUTIN8 DATA:
TAGE(FT) DISCHARGE(CFS) STORAGE(C(J-FT) PER` -AREA(SQ-FT)
m� . 00 ' . 00 . 0 . 0
. 25 . 02 471 . 1 . 0
. 50 . 03 977. 3 . 0
N� . 75 . 03 1519. 5 . 0
1 . 00 . 04 2099. 1 . 0
1 . 25 . 04 2717. 1 . 0
N� 1 . 50 . 05 33746 0
1 ^ 75 05 4072 7 ^
2. 00 . 05 4812. 6 . 0
2. 12
. 16 5595. 4 . 0
2. 50 . 23 6422. 2 . 0
2. 60 . 56 6765. 6 . 0
N� 2. 70 1 . 14 7116. 2 0
N� 2^ 80 1 89 7474^ 1 ^
^ . 0
2. 90 2. 70 7839. 6 . 0
3. 00 3. 00 8212. 5 . 0
AVERAGE VERTICAL PERMEABILITY: . 0 MINUTES/INCH
�NPECIFY: F - FILE, PRINT IF/OF, STOP
`-
t TTER
[d: ] [path] filename[ . extJ JFOR STORAGE OF ROUTING DATA:
ND2. DAT
ECIFY: F - FILE, N - NEWJOB, P - PRINT IF/OF, R - REVISE, S - STOP
��
' A - 18
TOUMA ENGINEERS JOD
SIIrET Sao. __. _ _.-__._._ --_ or... —_—_--
' CALCUI_ATM DY _._._..------_._.____.-- __.-_-. DATE__.._.....--_._-_--
CIIECKFD DY
' SCALE --- -- ------ ....--- -
I j
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' _ ORIFICE 1.18 INCFI WEIR _ 0.2931=L, P= 2.12 TOTAL
C — H Q H h i C IQ CFS
0.62 2 0.053 ! 6 0.05
A 2.12 0.0551--- 212 0 3.27 —0 0.06
0.007594 2.25 0.057 2.25 0.13 3.295 0.041 0.1 U
2.5 0.060 2.5 0.38 3.342 0.170 0.23
1 2.6 0.061 2.6 0.48 3.361 0.220 0.61
3 U U65 i 3 0.88 3.436 0.332 3.16
1 RISER WEIR 3.141593 =L, P= 2.5
H C Q
2.5 _ 0 _ _3.270 0.000
2.6 0.1 _ 3.286 0.324
ORIFICE 12 INCH
` C H jh_ . Q
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3 0.5 _ 3
2.76
03853981
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SEUIMEN T UEAU STORAGE UE_-i ENTION VOLUME
ELV.-FT A-SF dV-CF TOTAL V ELV.-FT A-SF TOTAL V
2U 1 819.31 _ U 205 2106.83 U
1
__.._. � 975.135- -- -----1103.87
- - __-_-- _--- -_--
-202- 1130.96 _ - _-9 75.135 2U5.5 2308.65 1103.87
1202.4
WETPONU _. . . 206 2500.95 _ 2306.27
1296 136
2U6.S -2683.6 36U2 4U8
202 113U.9G 0 1385.27
1274.525 207 2857.48 4987.678
2U3 1418.09L_- 1274.5251-- 345.3354 _
1551.245 207.12 2898.11 5333.013
1 204 1684.4 - _ 2825.77 _- 379.5837
1895.615 207.25 2941.64� 5712.597
205 2106.83' 4721.3Ej� _ 745.7
207.5 3023.96 - 6458.297
304.0165
207.6 3056.37 6762.313
1247.886
?.U8 3183.06 i 8016.199
-- -- - - �_�--- --1--
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~~
_
' XIII. APPENDIX B
Geotechnical Report
1
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SUBSURFACE EXPLORATION, GEOLOGIC HAZARD AND
GEOTECHNICAL ENGINEERING REPORT
1
_ PRELLWITZ SHORTPLAT
Renton, Washington
1
1
prepared for
MR. DOUG PRELLWITZ
1
' Project No. 960902
October 25, 1996
k, a ounce
ENGINEERING, INC.
�IlLiilffi11�.6111i1FnfWintlllYY�ICii6YTJicLLT4^WAI :J'-'"L--•••rF MleFW1161M14YJ:N
i
1
Geo
,Source
i EPI GMEERIPI G, 1PI C.
GE0TECHNICAL ENGINEERING
I
I ,October 25 1996
O
Project No. 960902
1
SUBSURFACE EXPLORATION , GEOLOGIC HAZARD AND
GEOTECHNICAL ENGINEERING REPORT
PRELLWITZ SHORTPLAT
1 1200 BLOCK OF NE 36th STREET
RENTON, WASHINGTON
1
I. PROJECT AND SITE CONDITIONS
1
■ INTRODUCTION
7 Port P
'his re resents the results of' our subsurface exploration, geologic hazard and
geotechnical engineering study for the above mentioned project. The proposed lot layouts
and approximate locations of the explorations accomplished for this study are presented on
the Site and Exploration Plat, Figure 1. In the event that any changes in the nature, design
or lot locations of the houses are planned, the conclusions and recommendations contained
in this report should be reviewed and modified, or verified, as necessary.
Our study was to address potential geologic hazards from seismic and erosion
considerations. We were also asked to address the concern of liquefaction. It was our
opinion that slope stability was not considered an issue due to the low slope angles present
on the site.
Authorization
Written authorization to proceed with this study was granted by Mr. Doug Prellwitz,
owner. Our study was accomplished in general accordance with our scope of work/contract
letter dated August 29, 1996. This report has been prepared for the exclusive use of Mr.
i
1 -
Doug Prellwitz and his agents, for specific application to this site. Within the limitations of
' scope, schedule and budget, our services have been performed in accordance with generally
accepted geotechnical engineering and engineering geology practices in effect in this area at
the time our report was prepared. No other warranty, expressed or implied is made. Our
observations, findings, and opinions are a means to reduce the risks inherent to property
development.
■ SITE DESCRIPTION
The property was situated in the 11200 block of NE 36th Street in Renton, Washington.
The 250 foot by 300 foot rectangular parcel gently sloped down toward the northwest at an
approximate slope of 6H:1V (horizontal:vertical). Total elevation change across the
property was on the order of 48 feet. Vegetation consisted of scattered deciduous and
evergreen trees with moderate undergrowth. Nine lots are proposed with one extra area for
stormwater control (Tract A).
' ■ SUBSURFACE EXPLORATION
' Our field study included excavating six exploration pits to gain information about the site.
All of tilt, pits were excavated with a tractor-mounted backhoe and were continuously
logged by a geotechnical engineer/geologist from our firm. The various types of sediments
' as well as the depths where characteristics of the sediments changed are indicated on the
exploration logs presented in the Appendix. Tile depths indicated on the logs where
conditions changed' may represent gradational variations between sediment types in the
field. Our explorations were approximately located on a topographic survey prepared by
Touma Engineers of Kent, Washington.
' The conclusions and recommendations presented in this report are based on the exploration
pits completed for this study. The number, location, and depth of the explorations were
completed within site and budgetary constraints. Because of the nature of exploratory work
below ground, extrapolation of subsurface conditions between field explorations is
necessary. It should be noted that differing subsurface conditions may sometimes be
present due to the random nature of deposition and the alteration of topography by past
grading and/or filling. The nature and extent of variation from the field explorations may
not become fully evident until construction. If variations become known, it may be
necessary to re-evaluate specific recommendations in this report and make appropriate
' changes.
' ■ SUBSURFACE CONDITIONS
he
ield
ns
Subsurface conditions at the project' sile were l'the sites and erred fom tpast fexperience lrinl�he accomplished for this study, visual reconnaissance of
area. The overall geology of the site is an upper layer of relatively loose sand underlain by
Vashon-age glacial sand. This is discussed in more detail below.
3
Stratigraphy
A thin layer of organic topsoil covered the site, ranging in thickness from 4 to 16 inches.
' Beneath the topsoil the native soils consisted of about 3 to 4 feet of loose to medium dense,
dry to damp, tan, clayey, silty, fine sand. The roots from the trees penetrated into this
layer.
' Natural soils underlying the loose sands consisted of glacially-compacted, very dense,
Y g
damp, gray-tan, gravelly, silty, fine to medium sand with some cobbles. This material was
' overrun by several thousand feet of ice during the last glacial advance which resulted in a
compact soil possessing high strength and low compressibility, and relatively low
permeability characteristics. This material is very similar to the glacial Tills found in the
' Puget Sound region.
' Hydrology
No surface water was encountered at the time of our field work.
Ground water seepage was not encountered in our exploration holes at the time of our field
study, however, perched water may be encountered during wet periods of the year atop the
' very dense, silty sand. Perched water occurs when surface water infiltrates down through
surficial permeable soils and becomes trapped or "perched" atop the very dense, silty sands
which have a comparatively low permeability. It should be noted that fluctuations in the
' level of the ground water may occur due to the time of the year and variations in rainfall.
1
4
October 25, 1996
' Project No. 960902
' II. GEOLOGIC HAZARDS AND MITIGATIONS
' The followingdiscussion of potential geologic hazards and mitigations are based on the
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geologic, slope, and potential ground water conditions anticipated on the site. The areas of
' concern to be addressed include seismic (including liquefaction), and erosion (including
sediment transport).
' ■ SEISMIC HAZARDS AND MITIGATION
Earthquakes occur in the Puget Lowland with great regularity. fortunately, the vast
majority of these events are small and are usually not felt by man. However, large
earthquakes do occur as evidenced by the 1949, 7.2 magnitude event and the 1965, 6.5
' magnitude event. The 1949 earthquake appears to have been the largest in this area during
recorded history. Evaluation of earthquake return rates indicate what to expect within the
life of the structure (50 to 100 years): an earthquake of magnitude between 5.5 and 6.0 will
' likely occur within the next 8 to 12 years; longer ranging, an earthquake of magnitude 6.6
to 7.2 will likely occur within the next 50 to 100 years. The City usually requires that
engineering design be for a 100-year seismic event.
' On this site, there are 2 types of potential geologic hazards associated with large seismic
events: 1) surficial ground rupture and 2) the ground motion response. We were also asked
' to address the potential for seismically induced liquefaction. The potential for each of the
hazards to adversely impact the site is discussed below.
Surficial Ground Rupture
' Generally, the largest earthquakes which have occurred in the Puget Sound area are sub-
crustal events with epicenters ranging from 50 to 70 kilometers in depth. No surficial
faulting or earth rupture as a result of deep seismic activity has been documented, to date,
' in the tri-county Region. it is our opinion based on existing geologic data that the risk of
surface rupture impacting the site is low.
' Ground Motion Response
Based on the encountered site stratigraphy, local geology and visual reconnaissance of the
' site, it is our opinion that any earthquake damage to a proposed structure founded on the
recommended bearing strata, and following our foundation and drainage recommendations,
would be caused by the intensity and acceleration associated with the event and would not
s
■
be compounded by the site geology. Because of this fact, we recommend that seismic
' design of a house follow the minimum requirements of UBC standards.
Liquefaction Potential
■ Four conditions are required for a site to have a liquefaction potential; 1) The soils must
consist of a uniform sand with a grain size distribution falling within a specific narrow
' range, 2) the sand must be in a loose condition, 3) the sand must be saturated (be below the
water table), and the earthquake must have a duration of at least 20 seconds. The risk of
liquefaction for this site is considered non-existent. The grain size distribution of the
' existing sand does not fall within the specified range, it is medium dense below 3 feet and
the sloping, very dense layer would drain by gravity, thereby precluding any rise in a water
table.
'
■ EROSION ION HAZARDS AND MITIGATION
' The surficial, loose, sand represents a moderate erosion hazard. The loose nature of the
sand will allow it to be eroded by rain. The erodability of the underlying, very dense sand
' is considered low.
To mitigate and reduce the erosion hazard and offsite sediment transport potential, we
' recommend the following:
• Soils which are to be reused around the site should be stored in such a manner as
' to reduce erosion. Protective measures may include, but are not necessarily
limited to. covering with plastic sheeting or the use of hay bales and/or silt
fences.
' • In order to reduce the potential for erosion, we recommend that clearing not be
p g
' done on the sloping areas unless they are replanted and stabilized. They must
also be protected during the interim by plastic sheeting or other means. Straw
mulching over hydroseeding, fiber-reinforced hydroseeding, or other approved
' means should be used to re-establish ground cover.
• All storm water from impermeable surfaces, including paved or concrete
' driveways and roofs, should be directed into a tightlined City-approved storm
water system which discharges away from slopes. Uncontrolled discharge on
sloping areas may promote erosion.
■
■
■
■
r,
October 25, 1996
' Project No. 960902
III. DESIGN RECOMMENDATIONS
■ INTRODUCTION
Our exploration indicates that, from a geotechnical standpoint, the parcel is suitable for
single family residences provided the risks discussed are accepted and the recommendations
' contained herein are properly followed. The distribution of foundation loads of the wood-
frame structures are expected to be typical; no concentrated loads are anticipated. Because
our explorations indicate that the uniform, very dense sands (about 3 to 4 feet in depth) are
' capable of providing suitable building support, spread footing foundations may be utilized.
■ SITE PREPARATION
Site preparation of planned building and road/ arking areas should include removal of all
P P P g P
trees, brush, debris and any other deleterious material. Additionally, the upper organic
' topsoil should be removed and the remaining roots grubbed. Areas where loose surficial
soils exist due to grubbing operations should be considered as fill to the depth of
disturbance and treated as subsequently recommended for structural fill placement. We
recommend that road areas be proofrolled with a loaded dump truck to identify any soft
spots; soft areas should be overexcavated and backfilled with structural fill.
' Loose sands should be stripped down to the underlying medium dense or very dense sands.
Since the density of the soil is variable, random loose/soft pockets may exist and the depth
and extent of stripping can best be determined in the field by the Geotechnical Engineer.
Because of the many variables which can affect the required depth of stripping, it is our
opinion that it is inappropriate to give exact stripping depths. It is important to understand
' that the quantity of soils to be stripped can increase dramatically due to rain-softening and
equipment disturbance. In all actuality, the amount of stripping will probably be greater
than estimated from the exploration logs.
' ■ STRUCTURAL FILL
There is a possibility that structural fill will be necessary to establish desired grades. All
references to structural fill in this report refer to subgrade preparation, fill type, placement
and compaction of materials as discussed in this section.
1
After overexcavation/stripping has been performed to the satisfaction of the Geotechnical
' Engineer, the upper 12 inches of exposed ground should be recompacted to 90 percent of
the Modified Proctor Maximum Density using ASTM:D 1557 as the standard. If the
subgrade contains too much moisture, adequate recompaction may be difficult or impossible
' to obtain and should probably not be attempted. In lieu of recompaction, the area to
receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break
between the new fill and the wet subgrade.
' After recompaction of the exposed ground is tested and approved, or a free-draining rock
course is laid, structural fill may be placed to attain desired grades. Structural fill is
' defined as non-organic soil, acceptable to the Geotechnical Engineer, placed in maximum 8
inch loose lifts with each lift being compacted to 95 percent of the Modified Proctor
Maximum Density using ASTM:D 1557 as the standard. The top of any above-grade
' compacted fill upon which a building will be founded should extend horizontally outward a
minitnum distance of 5 feet beyond the outer edge of the perimeter footings before sloping
' down at an angle of 2H: IV (horizontal:vertical).
The contractor should note that any proposed fill soils must be evaluated by GeoSource
Engineering prior to their use in fills. This would require that we have a sample of the
material 72 hours in advance to perform a Proctor test and determine its compaction curve
which is required for field testing. Soils in which the amount of fine-grained material
' (smaller than No. 200 sieve) is greater than approximately 5 percent (measured on the
minus No. 4 sieve size) should be considered moisture-sensitive. Use of moisture-sensitive
soil in structural fills should be limited to favorable dry weather conditions. The onsite
' soils generally contained significant amounts of silt and are considered moisture-sensitive.
In addition they should not be used for backfilline directly against walls. Construction
equipment traversing the site when the soils are wet can cause considerable disturbance. If
' fill is placed during wet weather or if proper compaction cannot be obtained, a select import
material consisting of a clean, free-draining gravel and/or sand should be used. Free-
draining fill consists of non-organic soil with the amount of fine-grained material limited to
5 percent by weight when measured on the minus No. 4 sieve fraction.
Geotechnical Construction Monitoring
A representative from our firm should inspect the stripped subgrade and be present during
placement of structural fill to observe the work and perform a representative number of in-
place density tests. In this way, the adequacy of the earthwork will be evaluated as filling
progresses and any problem areas may be corrected at that time. It is important to
understand that taking random compaction tests on a part-time basis will not confirm the
' uniformity or acceptable performance of a fill. As such, we are available to aid the owner
in developing a suitable monitoring and testing program.
x
■ FOUNDATIONS
' Spread footings may be used for building support when founded on the lower very dense
natural sands. The upper sands are loose and variable for the most part and we recommend
that footings bear on the lower, very dense sand layer. The following design strategy
summary is discussed in more detail below:
' Design Strategy Summary
' • 16 inch wide continuous footings or 24"x24" for isolated pads up to 2
story high (including any daylight basement).
• 2000 psf (pounds per square foot) allowable bearing pressure for footing
' design on very dense, lower sand stratum.
18 inches minimum depth below final grade to bottom of footings.
• 4 inch diameter, rigid PVC (ASTM:D-2729) footing drains.
' We recommend that an allowable bearing pressure of 2,000 pounds per square foot (psf) be
utilized for design purposes, including both dead and live loads. An increase of one-third
' may be used for short-term wind or seismic loading. Perimeter footings should be buried at
least 18 inches into the surrounding soil for frost protection; interior footings require only
12 inches burial. However, all footings must penetrate to the prescribed bearing stratum
' and no footing should be founded in or above loose or disturbed soils. To limit total
settlements, all continuous footings should have a minimum width of 16 inches for 2-story
structures (including daylight basements) and 24 inches for pad footings. Brick facing must
' be supported by an extension of the footings to reduce the potential of differential settlement
between the brick and wood structure.
' It should be noted that the area bounded by lines extending downward at l H:l V
(horizontal:vertical) from any footing must not intersect another footing or intersect a filled
area which has not been compacted to at least 95 percent of ASTM:D 1557. In addition, a
1.5H: 1V line extending down from any footing must not daylight because sloughing may
eventually undermine the footing. Thus, footings should not be placed near the edge of
' steps or cuts in the bearing soils.
Anticipated settlement of footings founded on the lower, very dense sand, with footing
' excavations inspected and approved by us, should be on the order of 1 inch. Differential
settlements are expected to be less than 1/2 inch. However, disturbed soil not removed
from footing excavations prior to footing placement, could result in increased settlements.
' All footing areas must be inspected by GeoSource Engineering prior to placing concrete, to
verify 1) that the bearing soils have not been loosened during excavation, 2) that the design
bearing capacity of the soils has been attained, and 3) that construction conforms with the
recommendations contained in this report. Such inspections may also be required by the
governing municipality. Perimeter footing drains should be provided as discussed under the
' section on Drainage Considerations.
1
' ■ FLOOR SUPPORT
Slab-on-grade floors may be used over structural fill or pre-rolled medium dense natural
' ground. Floors should be cast atop a minimum of 4 inches of washed granulithic material
or pea gravel to act as a capillary break. They should also be protected from dampness by
an impervious moisture barrier or otherwise sealed. We recommend bar reinforcement
' instead of wire mesh.
' ■ DRAINAGE CONSIDERATIONS
Dense sands sometimes have ground water originating from rain which infiltrates into the
' upper looser sediments and flows above the denser sand at depth. Any excavations for
basements may have flow in them at times.
' All retaining, basement and footing walls should be provided with drains at the footing
elevations. Drains should consist of ASTM 2729 rigid, perforated PVC pipe surrounded by
washed pea gravel and constructed with sufficient gradient to allow gravity discharge away
' from the houses. In addition, all basement walls should be backfilled with clean, free-
draining sand. Roof and surface runoff should not discharge into the footing drain system
but should be handled by a separate, rigid tightline drain. In planning, exterior grades
' adjacent to walls should be sloped downward away from the structures to achieve surface
drainage. We also recommend that the back side of any basement wall be waterproofed
instead of dampproofed.
1
1
1
10
■ PROJECT DESIGN AND CONSTRUCTION MONITORING
At the time of this report, site grading, structural plans, and construction methods have not
been finalized. We are available to provide additional geotechnical consultation as the
' project design develops and possibly changes from that upon which this report is based. We
suggest that GeoSource Engineering perform a geotechnical review of the grading,
drainage, and building plans prior to final design completion. In this way, our earthwork
' and foundation recommendations may be properly interpreted and implemented in the
design.
' We are also available to provide geotechnical engineering and quality control monitoring
services during construction. The integrity of the foundations depend on proper site
' preparation and construction procedures. In addition, engineering decisions may have to be
made in the field in the event that variations in subsurface conditions become apparent.
Additional consultation, Plan Review and Construction Monitoring services are not part of
' this current scope of work. if these services are desired, please let us know and we will
prepare a cost proposal.
' We have enjoyed working with you on this study and are confident that these
recommendations will aid in the successful development of your site. If you should have
any questions, or require further assistance, please do not hesitate to call.
Sincerely,
GeoSource Engineering, Inc.
' pPO75Q %/9G
s'S�nl�'Al.�
exNinrs 3 T¢T97
Gary T. Lobdell, P.E., P.G.
' Principal
960902.n c c
' � T
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2 2 87
^T 112' R%'BAR do AP NE 36th STREET
�—
LEGAL DESCRIP jJOPI � o
F EDEN
LOT 9, BLOCK 4, HILLMAN'S C.U., LAKE WASHINGTON ;;ARDEN O SE(
DIVISION NO. 7. ACCORDING TO THE PLAT THEREOF, ACCORDED IN
PRELL WITZ SHORTPLA T
' Renton, Washingtion
' Scale of Feet
I I SITE AND EXPLORATION PLAN- FIG. 1
0 25 50 100
' NORTH
- LEGEND - GeoSource
' ❑ EP-1 Exploration pit and ENGINEERING, INC.
approximate location.
' Survey by Touma Engineers, Inc. 960902 OCT 1996
X
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12
EXPLORATION PIT LOGS
' Prellwitz Shortplat
Renton, Washington
' Project No. 960902
' EXPLORATION PIT NO. 1
Depth (ft) Soil Description
' 0.0-0.4 Loose, moist, black, topsoil.
0.4-3.8 Loose to medium dense, dry-damp, tan, clayey, silt, fine sand with roots to 3
r feet.
3.8-6.0 Very dense, damp, gray-tan, gravelly, silty, fine to medium sand with some
t cobbles.
No Seepage.
No Caving.
EXPLORATION PIT NO. 2
Depth (ft) Soil Description
' 0.0-0.9 Loose, moist, black, topsoil.
0.9-3.9 Loose to ►nedium dense, dry, tan, clayey, silt, fine sand.
3.9-6.5 Very dense, damp, gray-tan, gravelly, silty, fine to medium sand with some
' cobbles.
No Seepage.
No Caving.
EXPLORATION PIT NO. 3
'
Depth (ft)._ Soil Descri tion
' 0.0-1.0 Loose, moist, black, topsoil.
1.0-2.8 Loose, dry, tan, clayey, silt, fine sand.
2.8-4.3 Very dense, damp, gray-tan, gravelly, silty, fine to medium sand with some
' cobbles.
No Seepage.
' No Caving.
13
EXPLORATION PIT NO. 4
Depth (ft) Soil Description
' 0.0-1.3 Loose, moist, black, topsoil.
1.3-3.9 Loose to medium dense, dry-damp, tan, clayey, silt, fine sand.
' 3.9-5.7 Very dense, damp, gray-tan, gravelly, silty, fine to medium sand with some
cobbles.
No Seepage.
No Caving.
EXPLORATION PIT NO. 5
Depth (ft) Soil Description
0.0-l.0 Loose, moist, black, topsoil.
1.0-3. 1 Loose to medium dense, dry-damp, tan, clayey, silt, fine sand.
3. 1-5.0 Very dense, damp, gray-tan, gravelly, silty, fine to medium sand with some
' cobbles.
No Seepage.
No Caving.
' EXPLORATION PIT NO. 6
Depth (ft) Soil Description
0.0-1.0 Loose, moist, black, topsoil.
' 1.0-3. 1 Loose to medium dense, dry-damp, tan, clayey, silt, fine sand.
3. 1-5.0 Very dense, damp, gray-tan, gravelly, silty, fine to medium sand with some
' cobbles.
No Seepage.
No Caving.