HomeMy WebLinkAboutSWP271810 (2)Dw/°'�7�/�/0
c� OL` L. t
CITY OF PXWON
RE C E I V ED
jAN - 6 1994
Et_I!>,D!NG DIVISION
VALLEY MEDICAL CENTER
SOUTH CAMPUS PARKING
STORM DRAINAGE REPORT
LOT NO'S. 2 THROUGH 8
OF ONE VALLEY PLACE
FOR
VALLEY MEDICAL CENTER
BY:
TOUMA ENGINEERS
15668 W. VALLEY HWY.
SEATTLE WA. 98188
�ftucc�c
TABLE OF CONTENTS
I. PROJECT OVERVIEW
II. PRELIMINARY CONDITIONS SUMMARY
III. OFF -SITE ANALYSIS
IV. RETENTION/DETENTION ANALYSIS AND DESIGN
V. CONVEYANCE SYSTEM ANALYSIS AND DESIGN
VI. SPECIAL REPORTS AND STUDIES
VII. BASIN AND COMMUNITY PLANNING AREAS
VIII. OTHER PERMITS
IX. EROSION/SEDIMENTATION CONTROL DESIGN
X. MAINTENANCE AND OPERATIONS MANUAL
I. PROJECT OVERVIEW
This project involves about 2.28 acres in south Renton in Section
31, Township 23 N., Range 5 E., W.M. The developer wants to
improve an existing asphalt and gravel parking lot by paving the
over the existing gravel portions. The site is bounded on the
north by south 43rd st. and the hospital, on the east by Davis
Ave. S., on the south by apartments, and on the west by Highway
167 and the offramp to S 43rd street.
The construction of approximately 185 permanent parking spaces
will be used by the hospital staff and visitors. The project
area has been used for the past 2-3 years as a temporary parking
area, with asphalt driveways and gravelled parking stalls. It is
intended under this application to convert the existing usage to
permanent facilities. There will be no significant grading
employed to convert these facilities to permanent status.
The existing soils for the site as depicted by the soil
conservation soil survey are AgC an Alderwood series soil with
moderate to high runoff potential. See the attached map copy.
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II. PRELIMINARY CONDITIONS SUMMARY
Pre -developed 2.28 acres
The existing parking drains as sheet flow westerly and
northwesterly toward an existing swale situated at the western
boundary of the subject site. No offsite drainage enters the
site because the offsite drainage is intercepted by the existing
drainage system in Davis Ave. S. and bypasses the site. Please
note that when the original plat was developed, a detention pond
was provided and situated to the west of the parking area. This
open detention pond for the plat and is currently functioning.
Post -developed 2.28 acres
The graveled areas of the existing parking lot are proposed to be
paved with asphalt concrete, and additional curbings to be
constructed. An underground pipe conveyance system and catch
basins will be installed to carry the runoff to a regraded bio-
filtration swale. The new storm drain system will be connected
to the existing drain pipes to carry the runoff to the existing
open detention pond and controlled outlet.
The proposed improvements to the parking area are not expected to
increase the peak runoff rate significantly. According to Core
requirement #3, if the peak rate of runoff for the 100 years
storm event does not increase by more than 0.50 cfs between the
pre -developed condition and the post-developded, detention is
exempted.
III. OFF -SITE ANALYSIS
DOWNSTREAM ANALYSIS
Runoff from the proposed site with no off -site tributary area is
directed into an existing underground,storm pipe system to the
west and south sides of the site. The existing westerly storm
drain system consists of an 18" inch storm pipe running from
north to south at an average slope of 0.6%. On the south side of
the site is a 12" diameter storm pipe that carries runoff
directly from Davis Ave S. to the 18" at a slope of 4.36%.
The proposed permanent parking lot site has been draining to the
west as sheet flow across the gravel parking areas and asphalt
driveway areas. The drainage has been entering a bio-swale that
was constructed to directed runoff to a 12" stub from a type 2-
48" catch basin along the west margin of the site. From this
catch basin the runoff flows to the southwest corner of the site
about 434 feet at an average slope of 0.6%. From the southwest
corner of the site the runoff flows in a 24" diameter pipe
southwesterly some 516 feet at an average slope of 12.35% to the
existing detention pond. The existing detention pond was
designed and as -built to have 50,450 cubic feet of storage per
drawings on record with the City of Renton Public Works Dept.
Access to the pond and restrictor are via the Crestwood
Apartments to the south of our project. From the restrictor the
runoff outfalls in a 12 pipe about 34' to a riprapped outfall.
The runoff flows about 60 feet to a 30 inch culvert under SR-167.
This leads to an excavated channel which joins the Springbrook
Creek drainage and then the "P" channel system and eventually to
the Black River Pump Station.
There were no restrictions observed during the field
investigation of the downstream facilities. The existing
detention pond is overgrown with brush and blackberry bushes. No
specific flooding problem was noted in the field nor noted during
discussions about the storm system condition with the Cities
staff.
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IV. RETENTION/ DETENTION ANALYSIS AND DESIGN
Please note as mentioned in the analysis above that a storm water
detention system was designed and constructed for this plat.
This detentin pond was visited and appears to be functioning
properly. There should be no further need to provide for
detention as the plat and detention were constructed in about
1982-83 under the City of Renton's number 3-1-151. As a
precaution the following calculations are provided only to show
that the anticipated peak runoff rate will not increase
appreciably. The detention calculations on the following pages
indicate that the runoff from the site is below the threshold of
Q.5cfs increase for a 100 years storm event between the existing
condition runoff and the post developed runoff. With this
determination in mind, under Core requirement number 3 the
proposed improvements would be exempt from detention. The other
requirements for the site improvements, such as bio-filtration,
conveyance, etc. are discussed later in this report.
REFERENCE DATA SHEET
FOR
SOUTH CAMPUS PARKING
PRE -DEVELOPED CONDITIIONS
TOTAL AREA........
PERVIOUS -ASPHALT
GRAVEL
LANDSCAP
POST -DEVELOPED CONDITIONS
TOTAL AREA........
PERVIOUS -LAWN
IMPERVIOUS -ROOFS
2.28 ACRES
0.82 ACRES CN= 98_.00
0.76 ACRES CN= 89.00
0.70 ACRES CN= '90.00
2.28 ACRES
0.70 ACRES CN= 90.00
1.58 ACRES CN= 98.00
-F W 1OOY
,as
kl
L 9470
�EXF'IRES 6/22/23
TIME OF CONCENTRATION - PRE-DEVELOPED-
T3. = 40/((7)(.0251,'2)(60)) = 0.60 min.
T2 = 210/((20)(.0381'2)(60)) = 0.90 min.
T3 = 380/((15)(.0141/2)(60)) = 3.57 min.
TOTAL = 5.07 min.
TIME OF CONCENTRATION - POST -DEVELOPED
T3_
= 35/((7)(.0251/2)(60))
_ .53
min.
T2 =
125/((20)(.0561/2)(60))
_ .44
min.
T3 =
34/((20)(.02971'2)(60))
_ .16
min.
T4 =
187/((20)(.005X/2)(60))
= 2.20
min.
T, =
10/((20)(.011,2)(60))
_ .08
min.
Ts =
235/((15)(.0051Z2)(60))
= 3.69
min
TOTAL
7.08 min.
`j!- �TI ►4GHr 0 (=TFN7-1UN C_!4LC'CfL6 rl0/��
S ILA- i-C H l_ uou) im 6, CRLLvI 1_Li-170M 0 r
N`1 u2v G1✓A-PH- .
SBUH/SCS METHOD FOR COMPUTING RUNOFF HYDROGRAPH
STORM OPTIONS:
1 — S.C.S. TYPE —IA
•••- 7—DAY DESIGN STORM
-- STORM I:1ATA FILE:
SPECIFY STORM OPTION:
I
S.C.S. TYPE —IA RAINFALL DISTRIBUTION
ENTER: FREG? (YEAR) , DURAT I ON C HOUR) , PREC I P (INCHES )
2,24f2
S.C.S. TYPE —IA DISTRIBUTIOPJ
#.. .... ;_-...YEAR 24—HOUR STORM 2. i 0" TOTAL_. PRECIP.
--------------------------------------------------------------------------
ENTER: A(PERV), CN(PERV), A(IMPERV), CN(IMPERV), TC FOR BASIN NO. I
1 . 4S, S9, . S2, 9S, J. 07
DATA PRINT—OUT:
AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
A CN A CN
2.3 1.5 89.0 .8 98.0 5.1
PEAK—Q,(CF S ).. T--PEAK (HRS) VOL (CU—FT )
. 80 !} 7.67 1072
ENTER C d: 1 C path 3 f i 1 ename E- . e x t 1 FOR STORAGE OF COMPUTED HYDROGRAPH:
lE2YR
SPECIFY: C — CONTINUE, N -... NEWSTORM, P — PRINT, S — STOP
is
----------------------------------------------------------------------
ENTER : A ( DERV) , CN ( DERV) , A (I MPERV) , CN (I MPERV) , TC FOR BASIN NO. 2
. 7, 'fit,, I.. 58, 'a8, 7. 08
DATA PRINT—OUT:
AREA t: ACRES) PERVIOUS IMPERVIOUS TC (M I NUTE-.S )
A CN A CN
2.3 .7 90.0 16.
PEAK—U(CFS) T—PEAK(HRS) VOL(CU—FT)
93 7.83 12955 Q
ENTER Cd:7CpathlfilenameC.e t1 FOR STORAGE OF COMPUTED HYDROGRAPH:
i D'2 YR
SPECIFY: C — CONTINUE, N — NEWSTORM, P -- PRINT, S —. STOP
N
STORM OPTIONS:
1 - S.C.S. TYPE -IA
2 - 7-DAY DESIGN STORM
3 - STORM DATA FILE
SPECIFY STORM OPTION:
1
S.C.S. TYPE -IA RAINFALL DISTRIBUTION
ENTER: FREQ(YEAR), DURATION(HOUR), PRECIP(INCHES)
10,24,2.9
______________________________________________________________________
******************** S.C.S. TYPE -IA DISTRIBUTION ********************
********* 10-YEAR 24-HOUR STORM **** 2.90" TOTAL PRECIP. *********
______________________________________________________________________
ENTER: A(PERV), CN(PERV), A(IMPERV), CN(IMPERV), TC FOR BASIN NO. 1
1.46,89,.82,98,5.07
DATA PRINT-OUT:
AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
A CN A CN
2.3 1.5 89.0 .8 98.0 5.1
PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT)
1.34 7.67 17534
-
ENTER [d:][path]filename[.ext] FOR STORAGE OF COMPUTED HYDRO6RAPH:
1E10YR
SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP
C
____________________________________________________________________
ENTER: A(PERV), CN(PERV), A(IMPERV), CN(IMPERV), TC FOR BASIN NO. 2
.7,90,1.58,98,7'08
DATA PRINT-OUT:
AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
A CN A UN
2.3 .7 90.0 1.6 98.0 7.1
PEAK-Q(CFS) T-PEAK(HRS) VOL(CU-FT)
1.45 7.83 20112
' �J
ENTER [d:][path]filename[.ext] FOR STORAGE OF COMPUTED HYDROQRAPH:
1D10YR
SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP
WAR
r
/
/
-`
/ --__-
L
STORM OPTIONS:
1 - S.C.S. TYPE -IA
2 - 7-DAY DESIGN STORM
3 - STORM DATA FILE
SPECIFY STORM OPTION:
1
S.C.S. N ALL DISTRIBUTION
ENT YEAR), lDURATION(HOUR), PRECIP(INCHES)
10{�
__________________________________________________________________
******************** S.C.S. TYPE -IA DISTRIBUTION ********************
********* 100 YE 24-HOUR STORM **** 3.90^`TOTAL PRECIP. *********
'
______________________________________________________________________
ENTER: A(PERV), CN(PERV), A(IMPERV), CN(IMPERV), TC FOR BASIN NO. 1
1.46,89,.82,98,5.07 ' -
DATA PRINT-OUT:
'
AREA(ACRES) PERVIOUS IMPERVIOUS TC(MINUTES)
A CN A CN
2.3- 1.5 89.0 .8 98.0 5.1
ENTER Ed:1EpathJfz1enameL.ext1 FOR STORAGE OF COMPUTEDI
HYDROGRAPH:
1E100YR
SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - ST P
C
______________________________________________________ _______________
ENTER: A(PERV), CN(PERV), A(IMPERV), CN(IMPERV), TC FOR BASIN NO. 2
.7,90,1.58,98,7.08 (
DATA PRINT-OUT:
AREA(ACRES)
2.3
PEAK-Q(CFS)
, on
PERVIOUS
A CN
.7 90.0
T-PEAK(HRS)
IMPERVIOUS
A CN
1.6 98.0
VOL(CU-FT)
TC(MINUTES)
7.1 '
I))FF, LV_SSTHAO
P'S_c- r-- s.
ENTER [d:][path]filename[.ext] FOR STORAGE OF COMPUTED HYDRO8RAPH:
1D100YR
SPECIFY: C - CONTINUE, N - NEWSTORM, P - PRINT, S - STOP
_�_
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DETENTION CALCULATIONS
8o I
CONCLUSION
The difference between the pre -developed and post -developed
runoffs during a 100-year storm is less than 0.50 cfs. In
accordance with Core Requirements #3, Rentention/Detention
facilities are not required.
V. CONVEYANCE SYSTEMS ANALYSIS AND DESIGN
The conveyance system will be composed of six catch basins, 12
inch and 15 inch storm drain pipe. The bio-filtration swale will
be regraded, with the pipe to the storm system being reinstalled
at a slightly higher grade. The calculations that follow
Indicate that this configuration is more than adequate to handle
the 100 year storm. A map is enclosed which shows the areas and
the drainage patterns.
1C)/'26/93 Enclenicus Systems, Inc_ page ].
Vo l_I.-EY MELD I i- r*)L [--:ENTER
Sf]U-fl-f ' AMF'US LOT
CONVEYANCE F' I F'E. SYSTEM
F:E0C- A SUMMO RY
F:Out i. nq based c:-n Seattle family @ 'X-:,5 yr f r eq
- �•t�ly Foe pt=Sl �aN
Net wr- Ir- k. 1 in e*2" J_ F'--/4G/G
Pipe Reach Basin Area --c- --c*A- --Sum- ---Tc- --i-- --AAct Dia -Man -Slope -AFull Vfull -Vact -Length --tt--
---------- Id ac --c*A- - min in/hr cfs in --n - ft/ft cfs fps fps ft min
p6 a6 0.11 0.94 0.09 0.09 6.30 2.70 0.25 12 0.014 0.0100 3.32 4.22 2.48 60.00 0.40
p5 a5 0.28 0.75 0.21 0.30 6.70 2.62 0.79 12 0.014 0.0138 3.90 4.96 3.89 150.00 0.64
Net w-_-rk: 1 ineI
Pipe Reach Basin Area --c- --cfA- --Sum- ---Tc- --i-- --AAct Dia -Mann -Slope -DFull Vfull -Vact -Length --tt--
---------- Id ac --cfA- - min in/hr cfs in --n-- ft/ft cfs fps fps ft min
pl al 0.45 0.79 0.36 0.36 6.30 2.70 0.96 12 0.014 0.0297 5.72 7.28 5.41 34.00 0.10
p2 a2 0.25 0.90 0.23 0.58 6.40 2.6B 1.56 12 0.014 0.0050 2.35 2.99 3.19 127.00 0.66
p3 a3 0.31 0.79 0.24 0.83 7.07 2.55 2.11 12 0.014 0.0050 2.35 2.99 3.38 60.00 0.30
p4 a4 0.51 0.86 0.44 1.57 7.36 2.50 3.91 15 0.014 0.0100 6.01 4.90 5.22 10.00 0.03
SEE TI-I c (3ASIN M Y1 P l4-T T/-1E I�AC.le 1) 7"rl /�.r -7
riclF'ri i. c:-r_i5.� �iit: F?fn�. � T r-i I_) cICIF? 1
vt._I.._EY MEU T i :F1I- i_::I -N T F=T
5 0 U H I I'_:FaMP1.Jf:, F'AF-'k:: T N".-i I_OT
F' r..rtJ.ncj bE),I > ri t;t;1.F' farn:i.Iy @ 1yY. fY'(-.cC1
Nc:t,...-,)'I: 1 inc
Pipe Reach Basin Area --c- --c*A- --Sum- ---Tc- --i-- --QAct Dia -Mann -Slope -OFull Vfull -Vast -Length --tt--
---------- Id aC --c*A- - min in/hr cfs in --n-- ft/ft cfs fps fps ft min
p6 36 0.11 0.84 0.09 0.09 6.30 3.40 0.31 12 0.014 0.0100 3.32 4.22 2.65 60.00 0.38
p5 a5 0.28 0.75 0.21 0.30 6.60 3.32 1.00 12 0.014 0.0130 3.90 4.96 4.16 150.00 0.60
Ner tw---- i-1:: 1 inc--1
Pipe Reach Basin Area --c- --c*A- --Sum- ---Tc- --i-- --9Act Dia -Mann -Slope -AFull Vfull -Vact -Lenqth --tt--
----------
Id
ac
--c*A-
- min in/hr
cis in
--------------
--n--
ft/ft
cfs
fps
fps
ft
min
pl
at
0.45
0.79 0.36
0.36
6.30 3.40
1.21 12
0.014
0.0297
5.72
7.28
5.79
34.00
0.10
p2
a2
0.25
0.90 0.23
0.59
6.40 3.39
1.96 12
0.014
0.0050
2.35
2.99
3.34
127.00
0.63
p3
a3
0.31
0.79 0.24
0.03
7.03 3.24
2.67 12
0.014
0.0050
2.35
2.93
3.41
60.00
0.29
p4
a4
0.51
0.86 0.44
1.57
7.32 3.10
4.97 15
0.014
0.0100
6.01
4.90
5.40
10.00
0.03
MIND12
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(� V
VI. SPECIAL REPORTS AND STUDIES
Bio-filtration calculations are included in this section of the
report. The 2 year devoloped peak runoff will be used to
determine the required width of the bottom of the swale. The
actual slope and roughness will be used to determine the actual
depth of flow in the swale for the 2 year runoff and to show that
the flow velocity is less than 1.5 fps. Next a one foot
freeboard will be added and the 100 year flow will be checked to
see that there will be no overtopping of the swale.
Trapezoidal Channel Analysis & Design
Open Channel - Uniform flow
Worksheet Name: VMC SO. CAMPUS
Comment: BIO-FILTRATION ALONG WEST BOUNDARY
Solve For Bottom Width
Given Input Data:
Left Side Slope..
Right Side Slope.
Manning's n......
Channel Slope....
Depth............
Discharge........
Computed Results:
Bottom Width....
Velocity.........
Flow Area........
Flow Top Width...
Wetted Perimeter.
Critical Depth...
Critical Slope.'.
Froude Number....
3.00:1 (H:V)
3.00:1 (H:V)
0.350 --
0.0200 ft/ft
0.50 ft
0.93 cfs
F0 Q I-) MI-Y
4.31
ft
0.32
fps
2.91
sf
7.31
ft
7.48
ft
0.11
ft
3.8502 ft/ft
0.09
(flow is Subcritical)
V.S' m C V-+L Uj}x[[F
s
Open Channel Flow Module, Version 3.4 (c) 1991
Haestad Methods' Tnc * 37 9rnnksiHe PH * W=+p~h'- Of 06700
Trapezoidal Channel Analysis & Design
Open Channel - Uniform flow
Worksheet Name: VMC SO. CAMPUS
Comment: BIO-FILTRATION ALONG WEST BOUNDARY
Solve For Depth
Given Input Data:
Bottom Width.....
Left Side Slope..
Right Side Slope.
Manning's n......
Channel Slope'...
Discharge........
Computed Results:
Depth............
Velocity...'.....
Flow Area........
Flow Top Width...
Wetted Perimeter.
Critical Depth...
Critical Slope...
Froude Number....
4.31 ft
3.00:1 (H:V)
3.00:1 (H:V)
0.027-------
0.0050 ft/ft
0.93 cfs _
0.17 ft
Gronss KontwNr/aw
f)LJQNL-S L, 0Fz��
__�
�l
/~
1.12 fps T/yM/4 >-�SF"`
0.83
sf
5.34
ft
5.40
ft
0.11
ft
0.0229 ft/ft
0.50
(flow is Subcritical)
�
FeFF- 7300,60 h0 0
--
/ PT-Pl L_ --- , | � '-7 1
Open Channel Flow Module, Version 3.4 (c) 1991
Trapezoidal Channel Analysis & Design
Open Channel - Uniform flow
Worksheet Name: VMC SO. CAMPUS
Comment: BIO-FILTRATION ALONG WEST BOUNDARY
Solve For Depth
Given Input Data:
Bottom Width..... 4.31 ft
Left Side Slope.. 3.00:1 (H:V)
Right Side Slope. 3.00:1 (H:V)
Manning's n...... 0.027
Channel Slope.... 0.0050 ft/ft
Discharge........ 2.02 cfs
Computed Results:
Depth..........'. 0.27 ft puDu/ L>[n PTyl
Velocity......... 1.46 fps -----------LE�s�S, -[-TV-1y) 1-4
Flow Area..''.... 1.38 sf
Flow Top Width... 5.93 ft
Wetted Perimeter. 6.02 ft
Critical Depth... 0.18 ft
Critical Slope... 0.0197 ft/ft
Froude Number.... 0.53 (flow is Subcritical)
130VIP-1�, tqT 0/00
T-0TA L- /-7
�L���
0 '`7D
00 N\LL -6 F:�- C- 0 1--1T0/t-1 G��
Open Channel Flow Module, Version 3'4 (c) 1991
KING COUNTY, W ASHINGTON, SURFACE WATER DESIGN MANUAL
c "Q1 V
N
2-YEAR 24-HOUR PRECIPITATION
3.4 -'" ISOPLUVIALS OF 2-YEAR 24-HOUR
TOTAL PRECIPITATION IN INCHES
0 1 2 3 4 5 6 7 8 Mlles
1: 300.000
3.5.1-8
IV
' - 1 /90
VII. BASIN AND COMMUNITY PLANNING AREAS
No community plans are included for this project.
VIII. OTHER PERMITS
The other permits that are a part of this submittal are:
Building Permit
Landscaping Permit
Filling and Grading Permit
IX. EROSION/SEDIMENTATION CONTROL DESIGN
The Temporary Erosion calculations are included in this section
of the report.
TEMPORARY EROSION
The total area of this project is 2.28 with .82 acres of existing
asphalt to remain intact. The gravel areas and the landscape
area have 1.46 acres which could be disturbed, and subject to
erosion runoff. The soils per the King County Soil Survey are
AgC which have a medium to high runoff potential. With less than
3 acres of tributary exposed soils subject to runoff a sediment
trap will be employed.
The sedimaent trap required volume is based on the volume of
sediment plus the volume resulting from providing a 2 foot deep
settlement zone above the sediment storage.
From chapter 5.4.4.1-2 of the KIng County Surface Water Design
Manual use equation:
A..,, = (R) (K) (LS) (CV) (PR)
P2 = 2.0 inches
R = 2.22(P2)2.2 = 3.04
K = 0.15
LS = L = 2201, S = 5%
LS = 0.80
CV = 1.0
PR = 1.3
A..d = (3.04)(0.15)(0.80)(1.0)(1.3) = 0.474
Cleared = 1.46(0.474) = 0.692 tons
Vol = 0.692/.05 T/ft3 = 13.85 ft3
Determine the configuration dimensions. Try to have about a 3:1
length to width ratio.
I oV6eT=- Zvi
-QE Prr-4
3
2 SEMI-ING ZDFIF 1.2' 5r--bI F_r�7 `T01-A r-
Try a 2' x 6' bottom = 12sq ft
13.85/12 = 1.15' deep
bottom 2' x 6' = 12 sq ft
1.2' deep 9.2' x 13.2' = 121 sq ft
Vol = (12 = 121)/2 x 1.2' = 80 cu ft OK
13.85 cu ft regd.
dimensions at 3.2' deep
top 21.2' x 25.2'
overflow 4.2' deep
27.2' x 31.2'
The overflow will be directed to the realigned and regraded bio-
filtration swale.
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
o The temporary sediment trap volume is the volume of sediment storage computed (not to
exceed 1.5' in depth) plus the volume resulting from providing a 2' deep settlement zone above
the sediment storage, while not exceeding trap side slopes of 3:1.
o Computing the sediment storage volume - The sediment storage volume required is the volume
required to contain the annual sediment yield to the trap and can be estimated by using the
Universal Soil Loss Equation (USLE) developed by the United States Department of Agriculture.
ABED = R*K*LS*CV*PR
Where ASED = annual sediment yield in tons per acre
R =
rainfall erosion Index; use R'=2.22(P2)2.2; where P2 is the
2 year/24 hour precipitation in Inches (See 2 year - 24
hour Isopluvial Map In Figure 3.5.1 C)
K =
soil erodibility factor, from Table 5.4.4A or -as determined
by field and laboratory testing by a geologist, soil
scientist, or geotechnical engineer.
LS =
length -slope factor; from Table 5.4.46 (note, lengths
measured are horizontal distance from a plan view)
CV =
cover factor, use 1.0 which represents no ground cover
during the construction process.
PR =
erosion control practice factor; use 1.3 which represents
compacted and smooth slopes.
Note, the USLE rainfall erosion index equation for the SCS Type 1 A storm region is R =10.2
(P2)2,2, where P2 is the total precipitation for the 2 year, 6 hour duration design storm. Since the
total precipitation for the 2 year, 6 hour duration design storm is equal to exactly one-half of the
total precipitation for the 2 year, 24 hour duration design storm, the equation can be rearranged
as shown.
o Annual sediment yield calculation, step-by-step procedure:
a. Compute the R value by obtaining the P2 value from the 2-year/24-hour Isopluvial Map in
Figure 3.5.1 C.
b. Divide the site into areas of homogeneous SCS. soil type and of uniform slope and
length.
C. Note the K value from the SCS soils chart (Table 5.4.4A) for each soil type.
d. Determine the LS value for each uniform area (See Table 5.4.46).
e. Compute the annual sediment yield (A4ed) In tons per acre for each
homogeneous/uniform area by multiplying R times the K and LS values for each area.
Multiply the annual sediment yield (ASed) for each area by the acreage to be exposed
(only that area to be cleared) of each area. Sum the results to compute the total annual
sediment load (in tons) to the trap (Lsed).
o The sediment storage volume 1"sed) is then determined by dividing the total annual sediment load
In tons (L3ed) by an average density for the sediment deposited (�eV9). UsePv9= 0.05 ton per
cubic foot. Vsed = Lsed/Pavg•
5.4.4.1-2 1/90
Slope
IS values for following slope lengths 1, ft (m)
1S values for following slope lengths 1, ft (m)
Slope
gnuiienl
10
20
30
.10
50
60
70
80
90
100
150 200 250 300 350 400 450 500
600
700
800
900
1000
ratio
(3.0)
(6.1)
(9.1)
(12.2)
(15.2)
(18.3)
(21.3)
(24.4)
(27.4)
(30.5)
(.Ifi) (61) (76) (91) (107) (122) (137) (152)
(183)
(213)
(214)
(274)
(305)
0.5
0.01;
0.07
0.07
0.08
0.08
0.09
0.09
0.09
0.09
0.10
0.10 0.11 0.11 0.12 0.12 0.13 0.13 0.13
0.14
0.14
0.14
0.15
0.15
IIN):I
1
0.08
0.09
0.10
0.10
0.11
().11
0.12
0.12
0.12
0.1?
0,1.1 0.1.1 0.1.5 O.lfi 0.16 0.16 0.17 0.17
0.18
0.18
0.19
0.19
0.20
2
O.10
n.12
0.11
0.15
0.16
0.17
0.18
0.19
0.19
0.20.
0.23 0.25 0.26 0.28 0.29 0.30 0.32 0.33 -
0.34
0.36
0.37
0.39
0.40
3
0.11
0.18
0.20
0.22
0.23
025
0.26
0.27
0.28
0.29
0.32 0.35 0.38 0.40 0.42 0.43 0.45 0.46
0.49
0.51
0.54
0.55
0.57
4
0.16
0.21
0.25
0.28
010
0.33
0.35
0.37
0.38
OAO
0.47 0.53 0.58 0.62 0.66 0.70 0.73 0.76
0.82
0.87
0.92
0.96
1.00
20:1
5
0.17
0.24
0.29
0.34
0.38
0.41
0.45
0.48
0.51
0.53
0.66 0.76 0.85 0.93 1,00• 1.07 1.13 1.20
1,31
1.42
1.51
1.60
1.69
6
0.21
0.30
0.37
0.43
0.48
0.52
0.56
0.60
0.64
0.67
0.82 0.95 1.06 1.16 1.26 1.34 1.43 1.50
1.65
1.78
1.90
2.02
2.13
7
0.26
0.37
0.45
0.52
0.58
O.G4
0.69
0.7.1
0.78
0.82
1.01 1.17 1.30 1.43 1.54 1.65 1.75 1.84 -
2.02
2.18
2.33
2.47
2.61
12'!,:1
8
0.31
0.44
0.54
0,63
0.70
0.77
0.83
0.89
0.9.1
0.99
1.21 1.40 1.57 1.72 1.85 1.98 2.10 2.22
2.43
2.62
2,80
2.97
3.13
9
0.37
0.52
0.64
0.74
0.83
0.91
0.98
1.05
1.11
1.17
1.44 1.66 1.85 2.03 2.19 2.35 2.49 2.62
2.87•
3.10
3.32
3.52
3.71
111:1
10
0.43
0.61
0.75
0.87
0.97
1.06
1.15
122
1.30
1.37
1.68 1.94 2.16 .2.37 2.56 2.74 2.90 3.06
3.35
3.62
3.87
4.11
4.33
11
0.50
0.71
0.86
1.00
1.12
1.22
1.32
1.41
1.50
1.58
1.93 2.23 2.50 2.74 2.95 3.16 3.35 3.53
3.87
4.18
4.47
4.74
4.99
8:1
12.5
0.61
0.86
1.05
1.22
1.36
1.49
1.61
1.72
1.82
1.92
2.35 2.72 3.04 3.33 3.59 3.84 4.08 4.30
4.71
5.08
5.43
5.76
6.08
1.5
0.81
1.14
1.40
1.62
1.81
1.98
2.14
2.29
2.43
2.56
3.13 3.62 4.05 4.43 4.79 5.12 5.43 5.72
6.27
6.77
7.24
7.68
8.09
6:1
16.7
0.96
1.36
1.67
1.92
2.15
2.:16
2.54
2.72
2.88
3.04
3.72 4.30 4.81 5.27 5.69 6.08 6.45 6.80
7.45
8.04
8.60
9.12
9.62
5:1
20
1.29
1.82
2.23
2.58
2.88
3.16
3.41
3.65
3.87
4.08
5.00 5.77 6.45 7.06 7.63 8.16 8.65 9.12
9.99
10.79
11.54
12.24
12.90
1a
4h:1
22
1.51
2.13
2.61
3.02
3.37
3.69
3.99
4.27
4.53
4.77
5.84 6.75 7.54 8.26 8.92 9.54 10.12 10.67
11.68
12.62
13.49
14.31
15.08
A
4:1
25
1.86
2.63
3.23
3.73
4.16
4.56
4.93
5.27
5.59
5.89
7.21 8.33 9.31 10.20 11.02 11.78 12.49 13.17
14.43
15.58
16.66
17.67
18.63
A
30
2.51
3.56
4.36
5.03
5.62
6.16
6.65
7.11
7.54
7.95
9.74 11.25 12.57 13.77 14.88 15.91 16.87 17.78
19.48
21.04
22.49
23.86
25.15
3:1
33.3
2.98
4.22
5.17
5.96
6.67
7.30
7.89
8.43
8.95
9.43
11.55 13.34 14.91 16.33 17.64 18.86 20.00 21.09
23.10
24.95
26.67
28.29
29.82
35
3.23
4.57
5.60
6.46
7.23
7.92
8.55
9.14
9.70
10.22
12.52 1.1.46 16.16 17.70 19.12 20.44 21.68 22.86
25.04
27.04
28.91
30.67
32.32
2%:1
40
4.00
5.66
6.93
8.00
8.95
9.80
10.59
11.32
12.00
12.65
15.50 17.89 20.01 21.91 23.67 25.30 20.84 28.29
30.99
33.48
35.79
37.96
40.01
45
4.81
6.80
8.33
9.61
10.75
11.77
12.72
13.60
14.42
15.20
18.62 21.50 24.03 26.33 28.44 30.40 32.24 33.99
37.23
40.22
42.99
45.60
48.07
2:1
50
5.64
7.97
9.76
11.27
12.60
13.81
14.91
15.94
16.91
17.82
21.83 2521 28.18 30.87 33.34 35.65 37.81 39.85
43.66
47.16
50.41
53.47
56.36
55
6.48
9.16
11.22
12.96
14.48
15.87
17.14
18.32
19.43
20.48
25.09 28.97 32.39 35.48 38.32 40.97 43.45 45.80
50.18
54.20
57.94
61.45
64.78
1Y:1
57
6.82
9.64
11.80
13.63
15.24
16.69
18.03
19.28
20.45
21.55
26.40 30.48 34.08 37.33 40.32 43.10 45.72 48.19
52.79
57.02
60.96
64.66
68.15
60
7.32
10.35
12.68
14.64
16.37
17.93
19.37
20.71
21.96
23.15
28.35 32.74 36.60 40.10 43.31 46.30 49.11 51.77
56.71
61.25
65.48
69.45
73.21
114:1
66.7
8.44
11.93
14.61
16.88
18.87
20.67
22.32
23.87
25.31
26.68
32.68 37.74 42.19 46.22 49.92 53.37 56.60 59.66
65.36
70.60
75.47
80.05
84.38
70
8.98
12.70
15.55
17.96
20.08
21.99
2:1.75
25.39
26.93
28.39
34.77 40.15 44.89 49.17 53.11 56.78 60.23 63.48
69.54
75.12
80.30
85.17
89.78
75
9.78
13.83
16.94
19.56
21.87
23.95
25.87
27.66
29.34
30.92
37.87 43.73 48.89 53.56 57.85 61.85 65.60 69.15
75.75
81.82
87.46
92.77
97.79
1 %: 1
8O
10.55
14.93
18.28
21.11
2:1.60
25.85
27.93
29.85
31.66
33.38
40.88 47.20 52.77 57.81 62.44 66.75 70.80 74.63
81.76
88.31
94.41
100.13 105.55
85
11.30
15.98
19.58
22.61
25.27
27.69
29.90
:11.97
33.91
35.74
43.78 50.55 56.51 61.91 66.87 71.48 75.82 79.92
87.55
94.57 101.09
107.23
113.03
90
12.02
17.00
20.82
24.04
26.88
29.44
31_80
34.00
36.06
38.01
46.55 53.76 GO. 10 65.84 71.11 76.02 80.63 84.99
93.11
100.57 107.51
114.03
120.20
95
12.71
17.97
22.01
25.41
28.41
31.12
3:1.62
35.94
38.12
40.18
4921 56.82 63.53 69.59 75.17 80.36 85.23 89.84
98.42
106.30 113.64
120.54
127.06
1:1
100
13.36
18.89
23.14
26.72
29.87
32.72
35.34
37.78
40.08
42.24
51.74 59.74 66.79 73.17 79.03 84.49 89.61 94.46 103.48
111.77 11.9.48
126.73
133.59
'Calculated
from
'.
(65.41 X s
1.ti
4.56Xa
+
+ 0.()fi5
` l 1
I (72.5/
I - factor
\at + 10,000
x
+ 10.000
/
1 slope ltopogrength,
1 � slope length, ft Im X 0.30481
s - slope steepness,
m a exponent dependent upon slope steepness
(0.2 for slopes < I %. 0.3 for slopes I to 3%.
0.4 for slopes 3.5 to 4.5 i,, and
0.5 for slopes > 5'S )
m
XI. MAINTENANCE AND OPERATIONS MANUAL
No Maintenance and operations instructions or manual are included
with this report.