HomeMy WebLinkAboutSWP27 - B060342-S- �-� �) a-:�
Letter of Transmittal
Transmitted By... Date: September 29, 2006 Project No
❑ Mail Project: Barbee Mill BrUla TNOcoo 341Z
■ Courier To: Juliana Fries
❑ Will Call Address: City of Renton
❑ 1055 South Grady Way, 6' Floor
Renton, WA 98055
We Are Sending You...
Transmitted...
im
❑ Drawings ❑ Prints
■ For Approval
❑ Specifications ■ Plans
❑ As Requested
10230 NE Points Drive
Suite 400
❑ Copy of Letter ❑ Samples
❑ For Your Use
Kirkland, WA 98033
❑ Change Order ❑ Other
❑ For Comment
Phone (425) 8224446
Fax (425) 827-9577
Copies Page No. Description
1 Each Barbee Mill May Creek Hydraulic Study
Items Are...
Attached ❑ Under Separate Cover via
30788
Remarks
Attached is the a set of mylar plans of the Barbee Mill TESC and Grading
Construction Plans dated September 18, 2006 for review and reissuance.
From Ray Smalling, PE
cc Steve Lee (1), Janet Conklin - Building Department (2), Gary Upper —
Conner Homes
Architects Engineers Landscape Architects
Planners Surveyors & Mappers Urban Designers
K:\project\30700\30788\Admin\Coaesp\FriesO92906T.dOc
Technical Information Report for
Barbee Mill
Grading and TESC
Construction Plans
and
May Creek Bridge
Prepared for:
Connor Homes
846 108th Avenue NE
Bellevue, WA 98004
Prepared by:
Otak, Inc.
Ray Smalling, PE
10230 NE Points Drive, Suite 400
Kirkland,WA 98033
Otak Project No. 30788
July 28, 2006
Revised: September 29, 2006
Table of Contents
Barbee Mill
Preliminary Technical Information Report
Revised: September 29, 2006
Section I —Water Quality and Detention Design
Section 2 Conveyance Design
Section 3— Special Reports and Studies
Appendices:
Appendix A.1—Water Quality Pond 1 Calculations
Appendix A.2—Water Quality Pond 2 Calculations
Appendix B Revised Hydraulic Analysis of Barbee Mill Development
Project
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Section I —Water Quality and Detention Design
Detention ponds are not required for this project because the site qualifies for the Direct
Discharge Exemption in the 1998 King County Storm Water Drainage Manual (KCSWDM).
The site discharges to Lake Washington, a major receiving water listed on page 1-29, Table
1.2.3.b.
Water Quality Pond I
Water Quality Pond 1, located within Tract "F", has a total basin area of 13.58 acres. 2.02
acres of this basin are impervious roof drainage that is bypassed to Lake Washington with no
treatment. Of the remaining 11.56 acres that are directed to Water Quality Pond 1, 7.13
acres are impervious and 4.43 acres are pervious.
Based on this area and land cover, Water Quality Pond 1 has a minimum required volume of
38,514 cubic feet and a minimum length to width ratio of 3:1. Approximately 51,635 cubic
feet of water quality treatment volume has been provided in this pond.
The calculated post -development 100-year 24-hour peak flow for the pond is 9.35 cfs
calculated by the SBUH method. Based on this flow rate, an outlet pipe from the pond sized
at 18 inches would require 1.21 feet of head to discharge the peak storm. Additionally, a 12-
inch-tall, 88-degree-wide jailhouse installed on a 48-inch manhole would provide overflow
capacity to convey the 100-year peak flow. Finally, an emergency overflow spillway 20 feet
wide and 0.26 feet high would provide sufficient capacity to convey the 100-year flow out of
the pond. Because of the pond's location across Street A from Lake Washington, backsloped
driveway pans located on both sides of the street at the low point on Street A would serve as
an overflow spillway.
Calculations for Water Quality Pond 1 are included in Appendix A. 1.
Water Quality Pond 2
Water Quality Pond 2, located within Tract "G", has a total basin area of 2.18 acres.
0.86 acres of this basin are impervious roof drainage that is bypassed to Lake Washington
with no treatment. Of the remaining 1.32 acres that are directed to Water Quality Pond 2,
0.92 acres are impervious and 0.39 acres are pervious.
Based on this area and land cover, Water Quality Pond 2 has a minimum required volume of
4,760 cubic feet and a minimum length to width ratio of 3:1. Approximately 11,431 cubic
feet of water quality treatment volume has been provided in this pond.
Barbee Mill
otak
K:\project\30700\30788\Reports\Revised TIR_092906\Textl.doc
Section I —Water Quality and Detention Design
Continued
The calculated post -development 100-year 24-hour peak flow for the pond is 1.10 cfs
calculated by the SBUH method. Based on this flow rate, an outlet pipe from the pond sized
at 12 inches would require 0.08 feet of head to discharge the peak storm. Additionally, a 6-
inch-tall, 30-degree-wide jailhouse installed on a 48-inch manhole would provide overflow
capacity to convey the 100-year peak flow. Finally, an emergency overflow spillway 6 feet
wide and 0.4 feet high would provide sufficient capacity to convey the 100-year flow out of
the pond.
Calculations for Water Quality Pond 2 are included in Appendix A.2.
Barbee Mill
otak
K:\project\30700\30788\Reports\Revised TIR_092906\Text1.doc
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Section 2—Conveyance Design
Conveyance calculations for the Barbee NO project will be included with future submittals.
Barbee Mill
otak
K:\project\30700\30788\Reports\Revised TIR_092906\Textl.doc
Section 3—Special Reports and Studies
The following special reports and/or studies have been prepared for the Barbee Mill project:
• Hydraulic Analysis of Barbee Mill Development Project, dated September 29, 2006
(Appendix B)
Barbee Mill
otak
K:\project\30700\30788\Reports\Revised TIR_092906\Textl.doc
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Appendix A.I —Water Quality Pond I
Calculations
NORTH BASIN CALCULATIONS
'Negative areas indicate "islands" within a larger area subtracted to obtain a correct area.
DUPLEX LOTS
4-PLEX LOTS
DUPLEX LOTS
4-PLEX LOTS
ROADWAY
OPEN SPACE
WQ
TO POND
TO POND
TO LAKE WASH.
TO LAKE WASH.
r £r_111,Z sf228$
401 7; sf
sf
�7�14"7� sf
r $4
sf
268324 sf
w ,
20t�0 sf
18,948 sf
sf
143625 sf
28 sf
sf
.3
1922, sf81'
sf
sf
�445.8sf
8761 sf
T sf
r
2246 sf
4736 sf
ER
TOTAL
230900 sf
12288 sf
135331 sf
0 sf
131079 sf
63095 sf
18948 sf
5.30 ac
0.28 ac
3.11 ac
0.00 ac
3.01 ac
1.45 ac
0.43 ac
65% imperv.
85% imperv.
65% imperv.
85% imperv.
100% imperv.
0% imperv.
100% imperv.
IMPERVIOUS
AREA
3.45 ac
0.24 ac
2.02 ac
0.00 ac
3.01 ac
0.00 ac
0.43 ac
PERVIOUS
AREA
1.86 ac
0.04 ac
1.09 ac
0.00 ac
0.00 ac
1.45 ac
0.00 ac
IMPERVIOUS
AREA TO
POND
3.45 ac
0.24 ac
0.00 ac
0.00 ac
3.01 ac
0.00 ac
0.43 ac
PERVIOUS
AREA TO
POND
1.86 ac
0.04 ac
1.09 ac
0.00 ac
0.00 ac
1.45 ac
0.00 ac
IMPERVIOUS
AREA TO
LAKE WASH.
0.00 ac
0.00 ac
2.02 ac
0.00 ac
0.00 ac
0.00 ac
0.00 ac
PERVIOUS
AREA TO
LAKE WASH.
0.00 ac
0.00 ac
0.00 ac
0.00 ac
0.00 ac
0.00 ac
0.00 ac
TOTAL IMPERVIOUS AREA TO PONDS: 7.13 AC TOTAL PERVIOUS AREA TO PONDS: 4.43 AC
TOTAL IMPERVIOUS AREA TO LAKE WASH.: 2.02 AC TOTAL BASIN AREA: 13.58 AC
FOR DOCUMENTATION SEE CADD FILE: K:/project/30700/30788/xref/C788H300.dwg
Barbee Mill
K:\project\30700\30788\WaterRes\WQ\WQ1.xls Otak
Assumptions Printed: 7/27/2006
Step 1: Wetpond volume factor, f:
f = 3.0 Based on the Nationwide Urban Runoff Program (NURP).
Step 2: Rainfall for the mean annual storm, R:
R = 0.47 1998 KCSWDM Fig 6.4.1A (p. 6-69)
Step 3: Runoff volume of the mean annual storm, V,:
Vr = (0.9A; + 0.25At9 + 0.10Atf + 0.01Ao) x (R/12) x (43560)
where: A; = area of impervious surface including pond, ac
At9 = area of till soil covered with grass, ac
Ar = area of till soil covered with forest, ac
Ao = area of outwash soil covered with grass or forest, ac
Atot = Ai + At9 + Att + A. =
Vr = 12838 (sf)
Step 4: Wetpond volume, Vb:
Vb = f Vr
Vb = 38514 (cu ft)
11.56
A,=. 7.13
At9 4.43
Att 0.00
A. = 0.00
Barbee Mill
K:\project\30700\30788\WaterRes\WQ\WQ1.xis Otak
WQVolumel Printed: 7/27/2006
CELL
ELEV
AREA
VOLUME
CHANGE
VOLUME
TOTAL
FT
SQ FT
CU FT
CU FT
Bottom
20.00
14,404 r
Bottom
TOP SED
21.00
15,505
0
0
22.00
16,630
16,068
16,068
23.00
17,778
17,204
33,272
24.00
18,948
18,363
51,635
MAX WSE
25.00
20,427
38,205
71,477
Barbee Mill
K:\project\30700\30788\WaterReskWQ\WQ1.xls
DesignStorage
Target Water Quality, cu ft = 38,514
Design Water Quality Volume, cu ft = 51,635
Otak
Printed: 7/27/2006
SBUH Peak Flow Calculation
SCS, Type la, 24-hr
SBUH Input
Total Area (ac.)
11.56
Pervious Area (ac.)
4.43
Impervious Area (ac.)
7.13
Pervious CN
86
Impervious CN
98
Sheet Flow: Tt=(.42*(ns*L)^.8)/(P2A.5*So^.4)
............
ns
0.15
T,(min)
9.3
T, (min)
9.3
Time step (min) 1 10
6-mo(72% of 2yr)
2-yr
5-yr
10-yr
25-yr
50-yr
100-yr
Peak
Precipitation Discharge
(in) (cfs)
1.4
2.64
2.0
4.10
2.5
5.45
2.9
6.55
3.4
7.95
3.5
8.23
3.9
9.35
Barbee Mill
K:\project\30700\30788\WaterRes\W Q\W Q 1.xis
PeakFlow
Otak
Printed: 7/28/2006
Outlet Pipe - WQ Pond 1
Design Diameter:
D, inches
X'i 18
D, feet
1.5
Orifice:
Q.,jf = C.,if x D 2 x 1-11/2
Corif 3.782
H
Q0rif
QTotal
[ft]
[cfs]
[cfs]
0.00
0
0.0
0.20
3.8
3.8
0.40
5.4
5.4
0.60
6.6
6.6
0.80
7.61
7.6
1.00
8.51
8.5
1.20
9.31
9.3
1.40
10.1
10.1
1.60
10.8
10.8
1.80
11.4.
11.4
2.00
12.01
12.0
2.20
12.6
12.6
2.40
13.2
13.2
2.60
13.7
13.7
2.80
14.2
14.2
3.00
14.7
14.7
3.20
15.2
15.2
3.40
15.7
15.7
3.60F
16-1r
16.1
Reference: 1998 King County Storm Water Drainage Manual, Figure 5.3.4.1-1
Riser Inflow Curves
By:
Checked:
Barbee Mill
K\project\30700\30788\WaterRes\WQ\WQI.xls
Riser
Design Flow Rate
Q100 ": 9.35
,Otak
Printed: 7/28/2006
Jailhouse Inlet for Water Quality Pond 1
Reference: 1998 KCSWDM, Page 5-46, Rectangular Sharp -Crested Weir
Design Flowrate = 100-year Developed Flow
Developed 100-year Runoff Rate is 7.10 cfs. We are using two weirs of equal size, so:
Design 100-year Runoff Rate,
Design overflow depth,
Weir Coefficient,
Weir Length,
Riser Diameter,
Angle forjailhouse inlet,
Q100= 9.35 cfs
H feet
H = 12 inches
C = 3.27 (unitless)
L = QH0siz + 0.2 H
L = 3.06 feet
L = 36.7 inches
D
48 inches
6 = 87.66 °
Barbee Mill
K:\project\30700\30788\WaterRes\WQ\WQ1.xls Otak
Jailhouse Printed: 7/28/2006
Water Quality Pond 1 Emergency Spillway Design
Equations:
SECONDARY EMERGENCY SPILLWAY DESIGN
Per KCSWDM Section 5.3.1.2
Weir shall be designed to pass 100-year, undetained flow
Based on Figure 5.3.1.E, Spillway is a rip rap weir with 3:1 side slopes
Use KCRTS, 100-year, 15-min flow rate, Q100= E 9.35 cfs
Adjust Length until weir will carry Q,00
Emergency Weir
Q = C*(2g)1/2*[(2/3)L*H3/2 + (8/15)*TAN(T)*H512]
where: C= 0.6 and Tan(T) = 12 (for 12:1 slopes)
Therefore, Q = 3.21*[L*H3/2 + 9.60*H5/21
L = length of contracted weir 20 ft. (6 feet is minimum)
H = depth of flow (assume 0.4 feet minimum) 0.26 1 ft.
Q = total peak discharge in cfs 9.57 cfs (equal or greater
than 100-year flow)
By:
Checked:
Barbee Mill
K:\project\30700\30788\WaterRes\WQ\WQ1.xls Otak
Spillway Printed: 7/28/2006
Appendix A.2— Water Quality Pond 2
Calculations
SOUTH BASIN CALCULATIONS
DUPLEX LOTS
TO POND
4-PLEX LOTS
TO POND
DUPLEX LOTS
TO LAKE WASH.
4-PLEX LOTS
TO LAKE WASH.
ROADWAY
OPEN SPACE
WQ
% �4295 sf
32140_sf
a 615'sf
,',36668`sf
1`3141;sf
-3,572 sf
3,572 sf
TOTAL
0 sf
0 sf
4295 sf
40755 sf
36668 sf
9569 sf
3572 sf
0.00 ac
0.00 ac
0.10 ac
0.94 ac
0.84 ac
0.22 ac
0.08 ac
65% imperv.
85% imperv.
65% imperv.
85% imperv.
100% imperv.
0% imperv.
100% imperv.
IMPERVIOUS
AREA
0.00 ac
0.00 ac
0.06 ac
0.80 ac
0.84 ac
0.00 ac
0.08 ac
PERVIOUS
AREA
0.00 ac
0.00 ac
0.03 ac
0.14 ac
0.00 ac
0.22 ac
0.00 ac
IMPERVIOUS
AREA TO
POND
0.00 ac
0.00 ac
0.00 ac
0.00 ac
0.84 ac
0.00 ac
0.08 ac
PERVIOUS
AREA TO
POND
0.00 ac
0.00 ac
0.03 ac
0.14 ac
0.00 ac
0.22 ac
0.00 ac
IMPERVIOUS
AREA TO
LAKE WASH.
0.00 ac
0.00 ac
0.06 ac
0.80 ac
0.00 ac
0.00 ac
0.00 ac
PERVIOUS
AREA TO
LAKE WASH.
0.00 ac
0.00 ac
0.00 ac
0.00 ac
0.00 ac
0.00 ac
0.00 ac
TOTAL IMPERVIOUS AREA TO PONDS: 0.92 AC TOTAL PERVIOUS AREA TO PONDS: 0.39 AC
TOTAL IMPERVIOUS AREA TO LAKE WASH.: 0.86 AC TOTAL BASIN AREA: 2.18 AC
FOR DOCUMENTATION SEE CADD FILE: K:/projectt30700/30788/xref/C788H30O.dwg
Barbee Mill
Otak
K:\project\30700\30788\WaterRes\WQ\WQ2.xls Printed: 7/28/2006
Step 1: Wetpond volume factor, f:
f = .3.10Based on the Nationwide Urban Runoff Program (NURP)
Step 2: Rainfall for the mean annual storm, R:
R = 0.47 1998 KCSWDM Fig 6.4.1A (p. 6-69)
Step 3: Runoff volume of the mean annual storm, Vr:
V, = (0.9A; + 0.25At9 + 0.10Atf + 0.01k) x (R/12) x (43560)
where: A; = area of impervious surface including pond, ac
At9 = area of till soil covered with grass, ac
Atf = area of till soil covered with forest, ac
Ao = area of outwash soil covered with grass or forest, ac
Atot = Ai + At9 + Atf + A. =
Vr = 1587 (sf)
Step 4: Wetpond volume, Vb:
Vb= fVr
Vb = 4760 (cu ft)
1.32
A; = 0.92
At9 = 0.39
Atf = 0.00
Ao = 0.00
Barbee Mill Otak
K:\project\30700\30788\WaterRes\WQ\WQ2.xls Printed: 7/28/2006
Barbee Mill Pond 2
PERMANENT DESIGN STORAGE TABLE
CELL 1
ELEV
AREA
VOLUME
CHANGE
VOLUME
TOTAL
FT
SQ FT
CU FT
CU FT
Bottom
17.25
2,255
Bottom
18.00
2,454
0
0
TOP SED
18.25
2,535
0
0
19.00
2,739
1,978
1,978
20.00
3,010
2,875
4,852
21.00
3,288
3,149
8,001
WQ LEVEL
22.00
3,572
3,430
11,431
Barbee Mill
K \project\30700\30788\W aterRes\W Q\WQ2.xls
Measured by: A. Braun, 07/26/2006
Calculations: A. Braun. 07/26/2006
Target Water Quality, cu ft = 4,760
Design Water Quality Volume, cu ft = 11,431
Barbee Mill Pond 2 - South Pond
SBUH Peak Flow Calculation
SCS, Type la, 24-hr
SBUH Input
Total Area (ac.)
Pervious Area (ac.)
Impervious Area (ac.)
Pervious CN
Impervious CN
Sheet Flow: Tt=(42*(nS*L)^.8)/(
L(ft)
so
ns
Tt(min)
T, (min)
1.32
0.39
0.92
86
98
.:......::
0.15
9.3
9.3
Time step (min) 1 10
6-mo(72% of 2yr,
2-yr
5-yi
10-yr
25-yi
50-yi
100-yr
5*So^. 4)
Peak
Precipitation Discharge
(in) (cfs)
1.4
0.33
2.0
0.50
2.5
0.65
2.9
0.78
3.4
0.94
3.5
0.97
3.9
1.10
Barbee Mill
K:\project\30700\30788\WaterRes\W Q\W Q2.xls
PeakFlow
Otak
Printed: 7/28/2006
Outlet Pipe - WQ Pond 2
Design Diameter:
D, inchesD,
Fzi
feet
Orifice:
Qorif = Corif x D2 x 1-11/2
Corif 3.782
H
Qorif
QTotal
[ft]
[cfs]
[cfs]
0.00
0
0.0
0.02
0.5
0.5
0.04
0.8
0.8
0``.066xy
0.9
0.'r9�.
0.10
1.2
1.2
0.12
1.3
1.3
0.14
1.4
1.4
0.16
1.51
1.5
0.18
1.61
1.6
0.20
1.71
1.7
0.22
1.8
1.8
0.24
1.9
1.9
0.26
1.9
1.9
0.28
2.0
2.0
0.30
2.11
2.1
0.32
2.1
2.1
0.34
2.2
2.2
0.36
2.3
2.3
0.38
2.3
2.3
Reference: 1998 King County Storm Water Drainage Manual, Figure 5.3.4.1-1
Riser Inflow Curves
By:
Checked:
Barbee Mill
K:\project\30700\30788\WaterRes\WQ\WQ2.xls
Riser
Design Flow Rate
Q100 = 1.10
Otak
Printed: 7/28/2006
Jailhouse Inlet for Water Quality Pond 2
Reference: 1998 KCSWDM, Page 5-46, Rectangular Sharp -Crested Weir
Design Flowrate = 100-year Developed Flow
Developed 100-year Runoff Rate is 7.10 cfs. We are using two weirs of equal size, so:
Design 100-year Runoff Rate,
Design overflow depth,
Weir Coefficient,
Weir Length,
Riser Diameter,
Angle for jailhouse inlet,
Q, 00 = 1.10 cfs
H = `; S feet
H = 6 inches
C = 3.27 (unitless)
L= QIOO +0.2H
L = 1.05 feet
L = 12.6 inches
D > 4 feet
48 inches
O = 30.10 °
Barbee Mill
K:\project\30700\3O788kWaterRes\WQ\WQ2.xls Otak
Jailhouse Printed: 7/28/2006
Barbee Mill Pond 2 Emergency Spillway Design
Equations:
SECONDARY EMERGENCY SPILLWAY DESIGN
Per KCSWDM Section 5.3.1.2
Weir shall be designed to pass 100-year, undetained flow
Based on Figure 5.3.1.E, Spillway is a rip rap weir with 3:1 side slopes
Use KCRTS, 100-year, 15-min flow rate, Q100 = LF---1.10 jcfs
Adjust Length until weir will carry Q100
Emergency Weir
Q = C*(2g)112*[(2/3)L*H312 + (8/15)*TAN(T)*H112]
where: C= 0.6 and Tan(T) = 12 (for 12:1 slopes)
Therefore, Q = 3.21 *[L*H3/2 + 9.60*H5/21
L = length of contracted weir i6—] ft. (6 feet is minimum)
H = depth of flow (assume 0.4 feet minimum) 0.40 1ft.
Q = total peak discharge in cfs 7.99 cfs (equal or greater
than 100-year flow)
RESULTS:
Set Minimum Spillway width at 6 feet
Set Minimum Spillway depth to 0.70 feet to carry 100-year flow with 0.3 feet of freeboard
By:
Checked:
Barbee Mill
K:\project\30700\30788\WaterRes\WQ\WQ2.xls Otak
Spillway Printed: 7/28/2006
Appendix B—Revised Hydraulic Analysis
of Barbee Mill Development Project
Technical Memorandum
To:
From:
10230 NE Points Drive
Copies:
Suite 400
Kirkland, WA 98033
Phone (425) 8224446
Date:
Fax (425) 827-9577
Subject:
Project No.:
Introduction
City of Renton
Carolyn Butchart
Ray Smalling
September 29, 2006
Hydraulic Analysis of Barbee Mill Development
Project
30788
The objective of this memorandum is to identify the existing and proposed hydraulic conditions of
May Creek in the vicinity of the Barbee Mill Development Project, approximate reach length of
1,125 feet, to ensure no adverse flood impacts will occur as a result of the Barbee Mill Development
Project.
The Barbee Mill Preliminary Plat Final Environmental Impact Statement (EIS) was prepared for the
City of Renton in May 2004. Appendix F of the EIS includes the Floodplain Analysis Technical
Report outlining the hydrology and hydraulic floodplain analysis. At this point in the project,
different scenarios were reviewed with the assumption that the proposed Barbee Mill project would
include changes to the existing bridges and associated cross sections, construction of a new bridge,
and benching of the creek throughout the vicinity of the project.
Otak met with Larry Fisher of the Washington State Department of Fish and Wildlife on May 23,
June 6, and June 13, 2006, and learned that recent mitigation measures had taken place in May Creek
by Barbee Forest Products, and no changes were permitted in May Creek at the proposed project
site. Subsequently, the HEC-RAS model was revised in September 2006 to evaluate the following
conditions:
• Removal of the three existing bridges and preserving the associated natural cross -sections (no
modifications of the associated channel cross -sections);
• Proposed bridge at Section 3 designed with a span of 80 feet and bottom deck height
approximately 5 feet above the FEMA 100-year flow (FEMA 1996) water surface elevation.
• An embankment offset 50 feet from the right bank (looking downstream) to elevations above
the FEMA 1996 flow; and
• Constant creek bed elevation set at 16.9 feet from the mouth of May Creek to approximately
800 feet upstream to represent the discontinuation of dredging.
K:\project\30700\30788\Reports\Revised TIR_092906\Revised HydraukTechMeMo092906.doc
City of Renton Page 2
Hydraulic Anay1 is of Barbee Mill Development Pri� ject September 29, 2006
The analyses presented in this memorandum supplements the Floodplain Analysis provided in the
2004 EIS with updates to the HEC-RAS model to incorporate the above design parameters.
Hydraulic Analysis
The HEC-RAS model was previously used to evaluate potential impacts associated with six
development and mitigation scenarios, which are outlined in the 2004 EIS. At the time the EIS was
prepared, Scenario 6 was the selected mitigation measure, which included all of the existing bridges
be removed, the middle and lower bridges replaced with bridges that do not influence the
floodplain, the existing channel cross sections modified to create a floodplain bench, and
discontinuing of the dredging operations. Figure 1 represents the reach of May Creek at the
proposed project site and the location of the cross sections in the HEC-RAS model.
The objective of the updated model was to evaluate the new design parameters at the FEMA 1996
flow of 870 cfs (provided in the 2004 EIS). The updated model includes the original existing
conditions model without any modifications to cross sections, removal of the three existing bridges,
addition of the proposed bridge, an embankment placed 50 feet from the right bank (looking
downstream) to elevations above the FEMA flow, and downstream aggradation of sediment
represented by a set elevation of 16.9 feet for Sections 1 through 5. The updated model for
proposed conditions is referred to as Plan 45.
Hydraulic parameters in the updated model (including the Manning's roughness coefficient, entrance
and exit loss coefficients, and discharge rates for specific frequency events) are consistent with those
provided in the EIS.
Figure 2 shows the water surface profile of existing conditions, referred to as Plan 18 in the 2004
EIS. Figure 3 shows the water surface profile of the proposed conditions, referred to as Plan 45.
The downstream water surface elevation for Plan 18 and Plan 45 was set at 17.5 feet, which is the
winter average Lake Washington water level. Figure 4 shows the profiles for Plan 18 and Plan 45 �--
overlaid to provide a comparison of the surface water elevations.
The proposed project includes the placement of a new bridge, approximately 245 feet upstream of
the mouth of May Creek (Section 3). The proposed bridge is designed with an 80 foot span between
the inside abutment walls and vertical clearance of the FEMA 1996 flow of approximately 5 feet.
The proposed bridge was modeled in Plan 45 to evaluate the elevation and top width of the channel
for the FEMA 1996 storm event at Section 3 to determine if the proposed bridge would project into
the channel.
Figure 5 shows the extent of the water surface for the FEMA 1996 storm event at Section 3 to be
approximately 54.8 feet wide. This provides approximately a 25-foot buffer (12.5 feet on each side)
K:\project\30700\30788\Reports\Rexised TIR_092906\Revised HydraubcTechMemo092906.doc
City ofRenton
Hydraulic Analysis of Barbee Mill Development Project
Page 3
September 29, 2006
between the FEMA 1996 storm event water surface elevation and the proposed bridge abutment
walls.
The updated model was also run for the 100-year future mitigation flows of 1,059 cfs (King County
1995) to provide a profile of the water elevation at this storm event, refer to Figure 6.
The FEMA 1996 flow water surface elevations derived from the HEC-RAS model were used to
delineate the FEMA 1996 flood plain, shown on Figure 1. The proposed project is designed such
that any development will be outside of the 100-year mitigation flood event.
Also included in the back of this memorandum is the HEC-RAS output for Plan 18 and Plan 45.
In summary, Figures 1 through 6 provide a comparison of existing conditions, assuming dredging
occurring in the downstream reach of May Creek (Plan 18), and of proposed conditions, assuming
no dredging taking place (Plan 45). The removal of the existing three bridges offsets the higher
stream bed elevations downstream due to no dredging, resulting in no net increase in water surface
elevations for the proposed conditions. The water surface profiles of Plan 18 and Plan 45 converge
at Section 11, which is the upstream boundary of the project. The proposed levees on the right bank
(looking downstream) will be designed at an elevation to safely clear the 100-year future mitigation
flow event and accordingly no water will overtop the levee. The proposed bridge is designed with an
80 foot span and approximately 5 foot clearance to the bottom deck of the FEMA 1996 flow
elevation, and accordingly will not have an adverse flood impact. Assuming no dredging will occur,
the bed elevation set at 16.9 feet for approximately 800 feet upstream of the mouth of May Creek
does not raise the water surface elevations above existing conditions.
K:\project\30700\30788\Reports\Reidsed TIR_092906\Revised Hydrau1icTechMemo092906.doc
I
Figu r e s
Figure I
Figure 2: Plan 18 - Existing Conditions
w
Mav Creekat Barbee Mill Plan_ Plan 18 9/9R/90AA
u 200 400 BDO 800 1000 1200
Main Charnel Distance (ft)
Legend
M FEMAIM
Ground
Figure 3: I'Lm 45 - Proposed Conditions
May Creekat Barbee Mill Plan: Plan 45 9/28/2006
30
28
25
24
22
�i
w
20
18
16
Legend
WS FEMA 1996
Sed.t Fill
Ground
14
0 200 400 600 800 1000 1200
Main Charnel Distance (ft)
Figure 4: Plan 18 & Plan 45 — Overlay of Existing and Proposed Conditions
May Creekat Barbee Mill Plan: 1) Plan 45 9/28/2006 2) Plan 18 9/28/2006
Legend
WS F EMA 1996 - R an 45
WS FEMA 1996 - Ran 18
Ground
U 'LUU 400 600 800 1000 1200
Main Channel Distance (it)
Figure 5: Cross Section 3 Water Surface Elevation for the FEMA 1996 100-year Flow Event
U1
CU
25
aD
w
!l
May Creekat Barbee Mill Plan: Plan 45 9/28/2006
RiNer = MayCreek Reach = 1 RS = 3
07 - .026 .07
0 50 100 150
Station (ft)
Legend
WS FEMA 1996
Sediment Fil I
Ground
Le\,ee
Bank Sha
Figure 6: Plan 45 — Proposed Conditions with Future Land Use Condition Hydrology (100-year future mitigation flow provided by King
County 1995)
May Creekat Barbee Mill Plan: Plan 45 9/28/2006
cm
0
a?i
w
MayCreekl
h�
14
i
lri
16
LO
N ao N v r- m 0
N N N N v V 7 Ln cD c0 c0 0o m r
1A
0 200 400 600 800 1000 1200
Main Charm] Distance (ft)
Legend
■
Ground
A
H EC-RAS Output
HEC-RAS Plan: Plan 18 River. May Creek Reach: 1
Reach
River Sla Profile
0 Total
Min Ch El
W.S. Elev
Crit W.S.
E.G. Elev
E.G. Slope
Val Chnl
Flow Area
Top Width
Froude # CM
(cfs)
(ft)
A .
(ft)
(ft)
(fttft)
(ft/s)
(sq ft)
(ft)
1
11 100-yr Future Mi
1059
21.99
29.03 ,
27.54
29.84
0.012124
7.26
152.43
42.66
0.58
1
11 FEMA 1996
870
21.99
28.5T
27.06
29.25
0.011557
6.66
134.29
36.36
0.56
1
10 100-yr Future Mi
1059
21.37
28.1
29.04
0.015244
7.8
140.16
37.69
0.64
1
10 FEMA 19%
870
21.37
27.81
28.54
0.012787
6.88
129.35
35.53
0.59
1
9 100-yr Future Mi
1059
20.27
27.87
28.34
0.006514
5.62
216.62
105.05
0.42
1
9 FEMA 1996
870
20.27
27.61
27.98
0.005239
4.91
193.48
77.41
0.38
1
8.65384' 100-yr Future Mi
1059
20.12
27.42
27.66
0.00419
4.52
410.07
349.82
0.35
1
8.65384` FEMA 1996
B70
20.12
26.99
27.33
0.005447
4.93
258.59
323.57
0.39
1
8 100-yr Future Mi
1059
20.03
27.2
27.4
0.003359
4.12
340.27
117.07
0.32
1
8 FEMA 1996
870
20.03
26.82
27.01
0.003258
3.87
297.04
111.81
0.31
1
7.95
Let Struct
1
7.66666' 100-yr Future Mi
997.12
19.47
27.1
27.29
0.002769
4.1
346.94
123.18
0.3
1
7.66666' FEMA 1996
847.78
19.47
26.7
26.9
0.002913
4.02
298.38
121.3
0.3
1
7.33333' 100-yr Future Mi
901.22
18.9
27.02
23.98
27.2
0.00217
3.98
353.31
129.37
0.27
1
7.33333' FEMA 1996
798.69
18.9
26.61
23.68
26.8
0.002447
4.05
300.76
122.78
0.28
1
7 100-yr Future Mi
775.54
18.34
26.79
23.4
27.1
0.002895
4.95
235.62
99.5
0.32
1
7 FEMA 1996
719.29
18.34
26.43
23.24
26.7
0.002756
4.67
211.81
58.41
0.31
1
6.9 100-yr Future Mi
729.83
18.34
26.73
23.69
27.05
0.00323
5.16
199.15
54.01
0.33
1
6.9 FEMA 19%
689.45
18.34
26.32
23.56
26.65
0.003458
5.14
175.93
49.34
0.34
1
6.8
Bridge
1
6.75 100-yr Future Mi
729.83
18.42
24.42
22.5
24.98
0.007055
6.19
131.73
42.96
0.48
1
6.75 FEMA 19%
689.45
18.42
24.29
22.39
24.82
0.006831
5.99
127.39
40.84
0.47
1
6.7 100-yr Future Mi
729.83
18.42
24.5
22.06
24.81
0.003934
4.68
182.13
51.29
0.36
1
6.7 FEMA 1996
689.45
18.42
24.37
21.96
24.66
0.003841
4.54
175.49
48.67
0.35
1
6.65
Let Struct
1
6.466W 100-yr Future Mi
729.83
18.41
24.37
24.69
0.004822
4.01
183.61
62.91
0.39
1
6.46666' FEMA 1996
689.45
18.41
24.24
24.54
0.004737
4.68
175.74
57.07
0.38
1
6.23333' 100-yr Future Mi
729.83
18.41
24.17
22.67
24.53
0.006573
5.18
169.05
64.06
0.43
1
6.23333• FEMA 1996
689.45
18.41
24.02
22.55
24.38
0.006719
5.12
160.01
61.81
0.44
1
6 100-yr Future Mi
729.83
18.4
23.86
24.31
0.009247
5.76
149.65
52.98
0.49
1
6 FEMA 1996
689.45
18.4
23.7
24.15
0.00957
5.75
141.31
52.36
0.5
1
5 100-yr Future Mi
729.83
17.54
23.19
23.51
0.005073
4.77
174.79
50.96
0.39
1
5 FEMA 1996
689.45
17.54
23.01
23.32
0.005286
4.74
165.41
50.26
0.39
1
4.4 100-yr Future Mi
729.83
15.31
22.68
23.07
0.005651
5.63
171.82
52.52
0.41
1
4A FEMA 1996
689.45
15.31
22.46
22.86
0.006051
5.68
160.1
51.56
0.42
1
4.35 100-yr Future Mi
729.83
15.31
22.55
21.11
23.01
0.006576
5.98
151.72
52.64
Q44
1
4.35 FEMA 1996
689.45
15.31
22.32
20.99
22.79
0.00702
6.02
142.51
51.58
0.45
1
4.3
Bridge
1
4.25 100-yr Future Mi
729.83
16.66
22.48
21.03
22.94
0.007
5.81
144.71
48.4
0.46
1
4.25 FEMA 1996
689.45
16.66
22.25
20.89
22.73
0.007566
5.85
135.37
47.55
0.47
1
4.2 100-yr Future Mi
729.83
16.66
22.47
20.93
22.88
0.006401
5.55
159.42
48.38
0.44
1
4.2 FEMA 1996
689.45
16.66
22.24
20.74
22.66
0.006946
5.6
148.27
47.51
0.45
1
4 100-yr Future Mi
729.83
17.46
22.24
20.6
22.65
0,007114
5.18
150.08
48.02
0.45
1
4 FEMA 1996
689.45
17.46
21.99
20.5
22.41
0.007947
5.25
138.24
44.64
0.47
1
3.66666' 100-yr Future Mi
729.83
17.07
21.98
20.46
22.44
0.005705
5.54
139.81
44.24
0.49
1
3.66666' FEMA 1996
689.45
17.07
21.67
20.35
22.17
0.006696
5.7
126.78
41.86
0.52
1
3.33333' 100-yr Future Mi
729.83
16.67
21.83
20.21
22.31
0.003328
5.62
143.39
46.7
0.49
1
3.33333' FEMA 1996
689.45
W67
21.49
20.1
22.01
0.003915
5.84
128.1
43.71
0.53
1
3 100-yr Future Mi
729.83
16.28
21.81
19.91
22.23
0.00135
5.34
168.34
53.95
0.44
1
3 FEMA 1996
689.45
16.28
21.46
19.79
21.92
0.001575
5.54
149.95
52.55
0.47
1
2.3 100-yr Future Mi
729.83
14.86
21.67
19.08
22.16
0.000935
5.72
155.16
32.49
0.41
1
2.3 FEMA 1996
689.45
14.86
21.36
18.96
21.84
0.001006
6.72
145.03
31.79
0.42
1
2.25 100-yr Future Mi
729.83
14.86
21.69
19.07
22.14
0.002063
5.53
155.08
32.53
0.4
1
2.25 FEMA 1996
689.45
14.86
21.37
18.95
21.82
0.002232
5.55
145.23
31.83
0.41
1
2.2
Mutt Open
1
2.15 100-yr Future Mi
729.83
15.47
19.87
19.21
20.79
0.007898
7.89
101.93
31.21
0.72
1
2.15 FEMA 19%
689.45
15.47
19.72
19.1
20.62
0.008151
7.8
97.29
30.95
0.73
1
2.1 100-yr Future Mi
729.83
15.47
19.33
19.19
20.63
0.01354
9.32
85.82
30.3
0.92
1
2.1 FEMA 1996
689.45
15.47
19.29
19.08
20.48
0.012693
8.93
84.44
30.22
0.89
1 2.05' 100-yr Future Mi
729.83
15.73
19.28
19.18
20.31
0.016647
8.13
89.77
39.05
0.94
1 2.05' FEMA 1996
689.45
15.73
19.21
19.08
20.19
0.016112
7.91
87.18
38.57
0.93
1
2 100-yr Future Mi
729.83
15.98
18.97
18.97
20.02
0.019583
8.2
88.97
42.79
1
1
2 FEMA 1996
689.45
15.98
18.9
18.9
19.9
0.019719
8.05
86.62
42.61
1
1
1 100-yr Future Mi
729.83
14.73
1T5
16.99
17.85
0.007726
4.73
154.31
179.05
0.62
1
1 FEMA 1996
689.45
14.73
17.5
16.96
17.81
0.006895
4.47
154.31
179.05
0.59
HEC-RAS Plan: Plan 45 River: May Creek Reach: 1
Reach
River Sta Profile
Q Total
Min Ch El
W.S. Elev
Crit W.S.
E.G. Elev
E.G. Slope
Val ChM
Flow Area
Top Width Froude # Chi
(cfs)
(ft)
(ft)
(ft)
(ft)
(ft/ft)
(ft/s)
(sq ft)
(ft)
1
11 100-yr Future Mi
1059
21.99
29.01
27.55
29.82
0.012288
7.29
151.65
42.36
0.58
1
11 FEMA 1996
870
21.99
28.52
27.06
29.22
0,011933
6.73
132.7
36.1
0.57
1
10 100-yr Future Mi
1059
21.37
28.03
26.92
29
0,016163
7.95
137.22
36.85
0.66
1
10 FEMA 19%
870
21.37
27.68
26.44
28A6
0.014064
7.1
124.91
34.76
0.61
1
9 100-yr Future Mi
1059
20.27
27.77
25.25
28.27
0.006782
5.74
206.86
82.73
0.43
1
9 FEMA 1996
870
20.27
27.44
24.79
27.84
0.005836
5.11
181.48
69.2
0.4
1
8 100-yr Future Mi
1059
20.03
26.9
24.91
27.07
0.005117
3.41
326.92
162.23
0.36
1
8 FEMA 1996
870
20.03
26.48
24.55
26.65
0.006159
3.36
258.87
160.96
0.39
1
7 100-yr Future Mi
1059
18.34
25.71
23.92
26.29
0.010615
6.17
188.49
90.4
0.53
1
7 FEMA 1996
870
18.34
25.25
23.48
25.78
0.010885
5.85
149.25
47.39
0.53
1
6.9 100-yr Future Mi
1059
18.34
25.36
23.92
26.1
0.014333
6.91
156.43
89.95
0.62
1
6.9 FEMA 1996
870
18.34
25
23.8
25.61
0.012658
6.26
138.89
37.76
0.57
1
6.75 100-yr Future Mi
1059
18.42
25.8
22.74
25.83
0.000983
1.98
948.5
590.33
0.17
1
6.75 FEMA 1996
870
18.42
25.3
22.34
25.36
0.001687
2.39
656.36
589.71
0.22
1
6.7 100-yr Future Mi
1059
18.42
25.55
22.73
25.8
0.004489
4.11
289.62
111.02
0.36
1
6.7 FEMA 19%
870
18.42
25.08
22.34
25.32
0.004871
3.96
238.4
110.44
0.37
1
6 100-yr Future Mi
1059
18.4
24.87
23.3
25.27
0.008197
5.07
223.03
106.48
0.47
1
6 FEMA 1996
870
18.4
24.38
22.99
24.75
0.00887
4.88
178.1
55.03
0.48
1
5 100-yr Future Mi
1059
17.54
24.09
22.01
24.43
0.006406
4.66
241
109.21
0.42
1
5 FEMA 1996
870
17.54
23.61
21.68
23.92
0.005924
4.43
196.61
52.54
0.4
1
4.4 100-yr Future Mi
1059
17.31
23.47
21.87
23.86
0.007737
5.03
230.74
104.32
0.46
1
4.4 FEMA 1996
870
17.31
22.94
21.55
23.32
0.009248
4.97
175.39
59.78
0.49
1
4.35 100-yr Future Mi
1059
17.29
23.36
21.87
23.78
0.008654
5.22
219.54
104.25
0.48
1
4.35 FEMA 1996
870
17.29
22.82
21.55
2323
0.010445
5.16
168.77
53.9
0.51
1
4.25 100-yr Future Mi
1059
17.27
23.31
21.58
23.73
0.008571
5.22
212.17
104.98
0.48
1
4.25 FEMA 1996
870
17.27
22.77
21.24
23.16
0.008841
5.04
172.45
50.71
0.48
1
4.2 100-yr Future Mi
1059
17.26
23.24
21.58
23.69
0.008365
5.39
203.97
99.69
0.48
1
42 FEMA 1996
870
17.26
22.71
21.24
23.12
0.008978
5.13
169.56
49.98
0.49
1
4 100-yr Future Mi
1059
17.46
22.78
21.35
23.33
0.013041
5.97
177.53
55.07
0.59
1
4 FEMA 1996
870
17.46
22.21
20.96
22.75
0.013213
5.86
148.57
47.6
0.58
1
3 100-yr Future Mi
1059
16.9
22.51
21.03
22.95
0.001717
5.28
200.56
56.8
0.49
1
3 FEMA 19%
870
16.9
21.89
20.71
22.32
0.002039
5.24
166.1
54.28
0.53
1
2.8 Bridge
1
2.3 100-yr Future Mi
1059
16.9
21.41
20.92
22.68
0.004985
9.04
117.09
31.6
0.83
1
2.3 FEMA 1996
870
16.9
20.94
20.46
22.06
0.004959
8.5
102.36
30.41
0.82
1
2.25 100-yr Future Mi
1059
16.9
20.92
20.92
22.6
0.007449
10.39
101.88
30.37
1
1
2.25 FEMA 1996
870
16.9
20.46
20.46
21.97
0.007652
9.86
88.19
29.22
1
1
2.15 100-yr Future Mi
1059
16.9
19.89
20.51
22.34
0.014254
12.57
84.23
31.08
1.35
- 1
2.15 FEMA 1996
870
16.9
19.53
20.08
21.72
0.014733
11.87
73.27
30.45
1.35
1
2.1 100-yr Future Mi
1059
16.9
20.12
20.51
22.2
0.011126
11.59
91.39
31.48
12
1
2.1 FEMA 1996
870
16.9
19.75
20.08
21.59
0.011225
10.86
80.08
30.84
1.19
1
2 100-yr Future Mi
1059
16.9
18.93
19.74
21.64
0.023676
13.2
00.2
42.02
1.68
1
2 FEMA 1996
870
16.9
18.71
19.41
21.04
0.023338
12.23
71.13
41.5
1.65
1
1 100-yr Future Mi
1059
16.9
18.57
18.57
19.4
0.008659
7.31
144.89
183.35
1.01
1
1 FEMA 1996
870
16.9
18.37
18.37
%1
0.008914
6.83
127.33
182.55
1