HomeMy WebLinkAboutWTR2703531CITY OF RENTON
Lake Washi --& on 9a,levara.
Hawks Landing Storm and Water
System Im x ent
in
Hydrologic/Hydraulic Analysis
APRIL 2010
Gray & Osbome #09583
Grail 8z Osborne, Iivc.
CONSULTING
Lake Washington Blvd Hawks Landing
Hydrologic/Hydraulic Analysis
Table of Contents
Introduction.......................................................................................................1
HydrologicModeling.........................................................................................1
Hydrologic Modeling Components..............................................................1
BasinDelineation..................................................................................1
Hydrologic Modeling Assumptions.......................................................2
Hydrologic Modeling Results.......................................................................4
Detention Requirements..............................................................................5
HydraulicModeling...........................................................................................6
Hydraulic Modeling Components................................................................6
Hydraulic Modeling Scenarios.....................................................................7
Hydraulic Modeling Results.........................................................................8
WaterQuality..................................................................................................10
Water Quality Modeling Components.......................................................10
Water Quality Treatment Facility Alternatives...........................................11
Biofiltration Swale................................................................................11
Wetva u I t...............................................................................................12
StormFilter...........................................................................................12
Filterra..................................................................................................13
RainGarden........................................................................................13
Additional Water Quality Treatment Facilities....................................14
Treatment Facility Costs............................................................................14
GRAY & OSBORNE, INC 1
APRIL 13, 2010
Recommendations.........................................................................................15
GRAY & OSBORNE, INC. 11 APRIL 13, 2010
Lake Washington Blvd Hawks Landing
Hydrologic/Hydraulic Analysis
List of Tables
Table 1 — Basin Land Use Coverages..........................................3
Table 2 — Model Area Inputs Based Upon Land Use Coverage.3
Table 3 — Peak Flows for the 2 through 100-Year Storms ..........5
Table 4 — Threshold Discharge Area Inputs Based Upon
Land Use Coverage................................................................5
Table 5 — Peak Flows for the 2 through 100-Year Storms
for the Threshold Discharge Area..........................................6
Table 6 — Modeling Results for Existing Conditions .....................9
Table 7 — Modeling Results under Future Conditions..................9
Table 8 — Freeboard Results.......................................................10
Table 9 — Water Quality Related Impervious Area.....................11
Table 10 —Rain Garden Plants...................................................14
Table 11 — Water Quality Treatment Facility Costs ...................15
List of Figures
After Page
Figure1 — Vicinity Map................................................................................2
Figure 2 — Basin Map and Existing Land Use............................................2
Figure 3 — Future Land Use........................................................................2
Figure 4 - Model Input Map.........................................................................4
Figure 5 — Recommended Treatment Alternative....................................15
GRAY & OSBORNE, INC. III APRIL 13, 2010
Lake Washington Blvd Hawks Landing
Hydrologic/Hydraulic Analysis
List of Appendices
Appendix A — Basin Figure from the Environmental Assessment for the I-405/NE 44!' St.
Interchange Project
Appendix B - Soil Map from USDA
Appendix C —1995 FEMA King County Flood Insurance Study Information
Appendix D — KCRTS Input and Output Files
Appendix E — Digital XP-SWMM Modeling Files
GRAY & OSBORNE, INC. IV APRIL 13, 2010
Lake Washington Blvd Hawks Landing storm
and Water Improvement Project
Hydrologic/Hydraulic Analysis
The project is located along Lake Washington Blvd. North, west of 1-405 near the
vicinity of Exit 7 (see Figure 1). The major storm drainage system in this area
consists of a depression located just north of the proposed Hawk's Landing
development site which collects runoff from 1-405. From this depression, a 24"
pipe conveys stormwater to a ditch along the east side of Lake Washington Blvd
North. The ditch continues for approximately 500 LF to an existing 24-inch pipe
that discharges directly into May Creek, approximately 1,100 feet upstream of the
creek's discharge into Lake Washington.
The City of Renton has been provided funding to complete the curb, gutter, and
sidewalk along the east side of Lake Washington Blvd. North in this vicinity. The
following analysis of the drainage system within this area includes the hydrologic
and hydraulic modeling of both the existing and future land use scenarios. It also
includes the preliminary design of the pipe alignment which will accommodate
both revisions to the road and future development within the area. An analysis of
water quality treatment alternatives is presented as well.
Hydrologic Modeling Components
Basin Delineation
The first step in hydrologic modeling involves delineation of the drainage basins
for the project area. The Hawk's Landing area was partially delineated in the
January 2001 Draft Environmental Assessment Discipline Reports for the I-
405/NE 44th Street Interchange Project. (Associated Earth Sciences, January
2001, See Appendix A). This figure was used to assist with delineating the
"Eastern 1-405 Basin". This basin collects runoff from the northbound lanes of I-
405 and NE 44t' St. The "Western 1-405 Basin" encompasses runoff from the
proposed Hawk's Landing development and runoff from Lake Wa. Blvd. N. Land
use for the basins was obtained from an existing Bush Roed Hitchings survey
and the proposed development plans for Hawk's Landing as provided by Sound
Development Group.
APRIL 13, 2010
Project
Loc
CITY OF RENTON
Lake Wa. Blvd. Hawk's Landing
Storm and Water Improvements Project
Figure 1
Vicinity Map
tzray ISLOsbOI'ne, jnc7.
CONSULTING ENGNEERS
The Eastern 1-405 drainage basin encompasses approximately 7.6 acres
whereas the Western 1-405 drainage basin encompasses approximately 7.6
acres as well. Figures 2 and 3 depict the location of these basins.
Hydrologic Modeling Assumptions
The King County Runoff Time Series (KCRTS) model was used to determine
peak flows in the basin for existing and future land use conditions. The input
parameters used in the KCRTS model include soil information, a rainfall scale
factor based upon project location, and the amount of pervious and impervious
area located within the basin. The KCRTS software program then takes these
parameters and combines them with over 40 years of rainfall data to produce
hydrographs displaying flow rates represented for a number of storm events
ranging from the 6-month storm to the 100-year storm event for each particular
basin.
The input parameters used in the KCRTS modeling analysis are as follows:
Soils
Outwash
(as determined from the USDA's National Resource Conservation Service
website; see Appendix B)
Rainfall
Sea-Tac Region with scale factor = 1.0
(2009 King County Surface Water Design Manual)
Pervious/Impervious Areas
The pervious and impervious areas for the Eastern 1-405 and Western 1-405
basins were derived from survey information and proposed development
plans as indicated earlier. Table 1 presents the land use coverage used for
each basin. Figures 2 and 3 represent these areas graphically. The Eastern
1-405 basin is expected to be unchanged between existing and future
conditions.
GRAY & OSBORNE, INC. 2 APRIL 13, 2010
Legend
• CB Structures
Stormwater Conveyance
May Creek
Eastern 1-405 Basin
Western 1-405 Basin
Pervious Forest Areas
Pervious Grass areas N
Parcel
0 75 150 300
Feet
Western 1-405 Basin
Total Acres: 7.6
Impervious Acres: 6.5
Pervious Grass Acres: 0.5
Pervious Forest Acres: 0.6
Outwash Soil
a
Eastern 1-405 Basin
Total Acres: 7.6
Impervious Acres:3.3 �t
Pervious Grass Acres:4.3 ,y
Outwash Soil
CITY OF RENTON
Lake Washington Blvd. Hawk's Landing
Storm and Water Improvements Project
Figure 2
Basins and Existing Land Use
CCNSMTNO ENGINEERS
Lucilu
Pervious Grass Areas
QEastern 1-405 Basin
Western 1-405 Basin
Western ts:7. Basin
Total Acres: 6
Future Building/Curb Line
Impervious Acres:6.83
Pervious Grass Acres: 0.77
N
Outwash Soil
0 75 150 300
Feet
Note: Proposed development plans y r - - I r
p P Y. P P �� ♦"V �' I y A rovided 6 Sound Development Group
mbA—
II
II
1f
r. •
� V
� 7
Eastern 1-405 Basin -
Total Acres: 7.6
Impervious Acres: 3.3
Pervious Grass Acres: 4.3
Outwash Soil
CITY OF RENTON
Lake Wa. Blvd. Hawk's Landing
Storm and Water Improvements Project
1 Figure 3
Future Land Use
G■+r 8c Odaorre, Imo.
Table 1 - Basin
Current Land Use
Land Use Coverages
Effective
Impervious
Outwash
Forest•
Outwash
Basin
.
East 1-405
3.3
4.3
7.6
West 1-405
6.5
0.6
0.5
7.6
Land Use Total:
9.8
0.6
4.8
15.2
Future Land Use
East 1-405
3.3
4.3
7.6
West 1-405
6.83
0.77
7.6
Land Use Total:
10.13
0.0
5.07
15.2
The nodes selected for hydrologic and hydraulic modeling are shown in Figure 4.
Table 2 shows the drainage basins flowing to each node, and summarizes the land
use and areas for each node. Node N1 represents the Eastern 1-405 basin and
Node N2 represents the Western 1-405 basin.
Table..Upon Land Use Coverage
Effective Outwash Outwash Basin
Impervious ForestTotal
Current Land Use
Node N1
3.3
4.3
7.6
(East 1-405
Node N2
6.5
0.6
0.5
7.6
West 1-405
Land Use Total:
9.8
0.6
4.8
15.2
Future Land Use
Node N1
3.3
4.3
7.6
East 1-405
Node N2
6.83
0.77
7.6
West 1-405
Land Use Total:
10.13
0.0
5.07
15.2
Downstream Backwater Condition:
All hydraulic scenarios were modeled using the backwater conditions in May
Creek which discharges to Lake Washington approximately 1,100 feet from the
project's discharge site. This creek collects runoff from a large basin within the
north portion of the city limits.
Backwater elevations for the hydraulic modeling were obtained from the August
2002 Otak Technical Information Report entitled "Barbee Mill Preliminary Plat", as
provided by the City. Cross section "D" was the backwater location selected from
the May 1995 FEMA King County Flood Insurance Study located at the
GRAY & OSBORNE, INC. 3 APRIL 13, 2010
M
30,G2
--30. 5R
3► ��
Zq,y3
�8 5
F"rk ( cs
K-, -
4 4.5v
3K-. aD
31.66
32.0-0
Jl ISo
21.50
} us-fo
�.50
C"V� lztq 33.05
$a4 —G,v' Qftkw JVS7 A N C
Legend Eastern 1-405 Basin
Modeled 24" Stormwater Line Input Node
Modeled 12" Stormwater Line
Modeled Node/Manhole Western 1-405 Basin
j Input Node
QEastern 1-405 Basin N
Western 1-405 Basin
N
0 50 100 200
Feet i
N3
3
N4 U1
N5
N6
f
N7
Discharge
Location
CITY OF RENTON
Lake Wa. Blvd. Hawk's Landing
Storm and Water Improvements Project
Figure 4
Model Input
Gray &C Oaborne1�
CONSULTING ENGINEERS
intersection of May Creek and Lake Washington Blvd. North (see appendix C).
The 100-year flood elevation obtained from this Study resulted in an elevation of
25.7 (NGVD 29 datum). Converting this into the NAVD 88 datum, the backwater
elevation used for the 25-year and 100-year hydraulic models was 29.26 feet.
Conservatively, since the 25-year flood elevation was not available, the 100-year
flood elevation was used for the 25-year storm event. According to the Study, the
10-year flood elevation is approximately 25 (NGVD 29 datum) which converts to
28.56 with the NAVD 88 datum. Therefore, a backwater condition of 28.56
elevation was used for the 2-year and 10-year modeling scenarios since the 2-
year flood elevation was not available.
It should be noted that the elevation of Lake Washington fluctuates between
winter and summer. The Army Corps of Engineers have documented summer
elevation of the lake to be 18.8 feet NAVD88 and the winter elevation to be 16.8
feet NAVD88. It is presumed that the Flood Insurance Study took these varying
elevations into consideration when obtaining the flood elevations of May Creek.
Therefore, for the purpose of this hydraulic model, the 10-year flood elevation of
28.56 was used to set the backwater condition for the 2-year and 10-year storms
and the 100-year flood elevation of 29.26 feet was used to set the backwater
condition for the 25-year and 100-year modeling scenarios.
Hydrologic Modeling Results
The KCRTS model was run with 15-minute timesteps for each of the 2 input
nodes under both existing and future land use conditions based upon input
parameters stated earlier. From these modeling runs, hydrographs were
extracted for a minimum 24-hour time period surrounding the peak flow for each
basin corresponding to the 2-year, 10-year, 25-year and 100-year storm events.
Table 3 shows the peak flows for each of these storm events under both the
existing and future land use conditions. The data from these hydrographs were
inserted as "gauged inflow" tables within designated nodes in the XP-SWMM
hydraulic modeling program.
GRAY & OSBORNE, INC. 4 APRIL 13, 2010
Table 3 — Peak Flows for the 2 through I 00-Year Storms
1 11
._ak ._ak ._ak ._ ak
Flow Flow• •
••-
Current Land Use
Node N1
1.57
2.13
3.03
4.21
East 1-405
Node N2
3.10
4.20
5.86
7.71
West 1-405
Total:
4.67
6.33
8.89
11.92
Future Land Use
Node N1
1.57
2.13
3.03
4.21
East 1-405
Node N2
3.25
4.42
6.16
8.12
West 1-405
Total:
4.82
6.55
9.19
12.33
Detention Requirements
A threshold discharge area represents the area of runoff collected and treated
within a project. A threshold discharge area was delineated to assist with
detention calculations. Table 4 depicts the land use within the site's threshold
discharge area which encompasses the east half of Lake Washington Blvd. to
the east side of the proposed sidewalk.
Table 5 displays the results of the KCRTS derived flows for the threshold
discharge area during the existing and developed conditions. Per the City's
current standards, the site is located within a "Basic Flow Control Area" and
requires a flow control duration standard. This standard allows the existing flows
to match current land use conditions instead of forested conditions.
GRAY & OSBORNE, INC. 5 APRIL 13, 2010
As seen in Table 5, the difference between the existing land use condition during
a 100-year storm event (0.212 cfs) and the future land use condition during the
same storm (0.305 cfs) is less than 0.1 cfs. Per the exceptions listed in Section
1.2.3.1.A of the manual, this project site is exempt from flow control restrictions
due an increase of less than 0.1 cfs between the existing and developed 100-
year storm events.
Hydraulic Modeling Components
Once the hydrologic flows were determined, the flows were routed through a
hydraulic model. The hydraulic model provides flow and water elevation at
representative nodes, and is used to determine when the storm flows are
contained in the pipe system and when overflow occurs.
The existing Bush Roed Hitchings survey was utilized to determine the storm
system in the Hawk's landing area to obtain elevation and location information to
use in the hydraulic model. The survey information was then input into the
hydraulic routing software program known as XP-SWMM, which uses the EPA
SWMM engine for modeling. The surveyed information includes pipe lengths,
pipe diameter, rim elevations and invert elevations and is shown in Tables 6 and
7.
With pipe information placed into the modeling program, XP-SWMM was then
used to route the current and future storm flows obtained from the KCRTS model
shown in Table 6. Figure 4 depicts a schematic of the hydraulic model for the
existing system. Each "node" represents a manhole. Only 2 of the manholes
were chosen as "input nodes." These nodes are depicted in Figure 4 as "N1" and
"N2." Hydrographs were extracted from the KCRTS program, converted to a
recognizable file format, and were then attached to each input node in XP-
SWMM.
GRAY & OSBORNE, INC. 6 APRIL 13, 2010
Hydraulic Modeling Scenarios
With extracted KCRTS hydrographs attached to the designated input nodes, the
XP-SWMM program routed the flows from the hydrographs through the surveyed
pipe information to help determine where pipes surcharge under various storm
events. The model was prepared under both existing and future conditions as
described below.
The existing upstream and downstream pipe system and a new 24" pipe
replacing the existing ditch was modeled using existing land use conditions in
the two basins. This scenario was modeled with the 2-year, 10-year, 25-year
and 100-year storm events using flows generated in KCRTS.
The existing upstream and downstream pipe system and a new 24" pipe
replacing the existing ditch were modeled using future land use conditions.
This run was done for the 2-year, 10-year, 25-year and 100-year storm
events using flows generated in KCRTS.
The 100-year storm event was modeled for the future land use scenario to ensure
that flooding would not occur on the surface.
GRAY & OSBORNE, INC. 7 APRIL 13, 2010
Hydraulic Modeling Results
Modeling results for Scenarios 1 and 2 (existing upstream and downstream pipes
with a new 24" pipe under existing and future land use) can be found in the
summaries provided in Tables 6 and 7.
GRAY & OSBORNE, INC. 8 APRIL 13, 2010
Table 6 - Modeling Results for Existing Conditions
Upstream
Node
Upstream
Rim Elev
ft
Downstream
Node
Downstream
Rim Elev.
ft
Conduit
Name
Pipe
Diameter
in.
Pipe
Length
ft
Upstream
IE
Downstream
IE
Sloe
Pipe
Design
Capacity
cfs
2-Year
Existing
Flow cfs
10-Year
Existing
Flow cfs
25-Year
Existing
Flow cfs
100-Year
Existing
Flow cfs
U1
32.0
U2
35.64
U1-U2
12
37
29.64
29.24
1.080%
3.70
0.00
0.00
0.12
0.11
U2
35.64
N1
34.27
U2-N1
12
151
29.24
26.77
1.640%
4.56
0.00
0.00
0.23
0.22
N1
34.27
N2
44.50
N1-N2
24
1 132
26.77
1 26.75
0.016%
2.86
4.62
2.13
3.12
4.28
N2
44.50
N3
38.00
N2-N3
24
150
26.75
26.72
0.020%
3.19
4.66
5.74
8.76
11.76
N3
38.00
N4
31.6
N3-N4
24
186
26.72
26.68
0.020%
3.19
4.64
5.75
8.80
11.79
N4
31.6
N5
31.5
N4-N5
24
145
26.68
26.65
0.020%
3.19
4.71
5.71
8.78
11.78
N5
31.5
N6
32.56
N5-N6
24
255
26.65
26.63
0.009%
2.13
4.71
5.77
8.81
11.80
N6
32.56
N7
32.56
N6-N7
24
50
26.63
26.50
0.260%
10.7
4.71
5.78
8.82
11.80
1 Source: Tables E1, E9, E10 and E16 of XP-SWMM output files "Hawks Landing Existing 2.out, Hawks Landing Existing 10.out, etc. located in digital files in the appendices.
Table 7 - Modeling Results under Future Conditions
Upstream
Node
Upstream
Rim Elev
ft
Downstream
Node
Downstream
Rim Elev. ft
Conduit
Name
Pipe
Diameter
in.
Pipe
Length
ft
Upstream
IE
Downstream
IE
Sloe
Pipe
Design
Capacity
cfs
2-Year
Existing
Flow cfs
10-Year
Existing
Flow cfs
25-Year
Existing
Flow cfs
100-Year
Existing
Flow cfs
U1
32.0
U2
35.64
U1-U2
12
37
29.64
29.24
1.080%
3.70
0.00
0.00
0.12
0.10
U2
35.64
N1
34.27
U2-N1
12
151
29.24
26.77
1.640%
4.56
0.00
0.00
0.22
0.21
N1
34.27
N2
44.50
N1-N2
24
132
1 26.77
26.75
0.016%
2.86
1 1.56
2.13
3.12
4.27
N2
44.50
N3
38.00
N2-N3
24
150
26.75
26.72
0.020%
3.19
4.77
5.96
9.06
12.16
N3
38.00
N4
31.6
N3-N4
24
186
26.72
26.68
0.020%
3.19
4.81
5.96
9.10
12.19
N4
31.6
N5
31.5
N4-N5
24
145
26.68
26.65
0.020%
3.19
4.78
5.96
9.08
12.17
N5
31.5
N6
32.56
N5-N6
24
255
26.65
26.63
0.009%
2.13
4.86
5.99
9.12
12.22
N6
32.56
N7
32.56
N6-N7
24
50
26.63
26.50
0.260%
10.7
4.86
5.99
9.12
12.22
1 Source: Tables E1, E9, E10 and E16 of XP-SWMM output files "Hawks Landing Future 2.out, Hawks Landing Future 10.out, etc. located in digital files in the appendices.
GRAY & OSBORNE, INC. 9 APRIL 13, 2010
Peak modeled flows seen in the pipes under the existing land use condition for
the 100-year storm varied between 0.1 cubic feet per second (cfs) on the
upstream 12-inch pipes (Nodes U1 and U2) to 11.8 cfs in the 24-inch pipe at the
downstream end near May Creek (Node N7). Likewise, peak future flows varied
between 0.1 cfs near the upstream nodes (Nodes U1 and 1.12) to 12.2 cfs in the
24-inch pipe downstream. Minimal flows were shown in the upstream nodes due
to the fact that the flow for the Eastern 1-405 Basin was input downstream into
Node N1. The upstream pipes were placed in the model to monitor the effect on
the hydraulic grade line upstream of the project.
As shown in Tables 6 and 7, a slight increase in flow occurred between the
existing and future land use scenarios. This is due to a slight increase in effective
impervious area from 64.4% (9.8 ac/15.2 ac) under current conditions to 66.6%
(10.13 ac/15.2 ac) underfuture conditions.
As depicted in Tables 6 and 7, most of the pipes experience flow beyond their
capacity. However, due to the depth of the pipe and storage available within the
manholes, no surcharging was experienced between the existing and future
model scenarios. Table 8 displays the amount of freeboard available under each
scenario.
Table 8
— Freeboard
Results
_Node
Freeboard Available
Existing Conditions
2- 10-
Year Year
until Flooding
25-
Year
Occurs
100-
Year
(ft)
Future Conditions
2-
Year
10-
Year
25-
Year
100-
Year
The elevations of nodes N2 through N5 should be verified with actual design
plans to ensure flooding is not experienced during the 25-year and 100-year
storm events.
Water Quality Modeling Components
To assist in determining water quality alternatives available for this project, the
water quality flow was calculated using the KCRTS modeling software based on
the impervious surfaces shown in Table 9.
GRAY & OSBORNE, INC. 10 APRIL 13, 2010
Pollution Generating 18,470 19,950 1,480"
Impervious Surfaces (i.e.
road):
Non -Pollution Generating 0 7,450 7,450
Impervious Surfaces (i.e.
sidewalk
Total New Impervious Surface 8,930
1. Area used to determine the water quality treatment flow rate.
Based on the Surface Water Design Manual, the project qualifies for the Basic
Water Quality Menu however, the Manual states that the threshold to treat new
and replaced impervious pollution generating impervious surfaces is 5,000 sf.
Based upon page 1-4 and Chapter 1.2.8 of the City's Amendments to the
Manual, utility trenches and overlay projects are not included in the "replaced
impervious surfaces" definition. Therefore, the overlay and trench areas for this
project do not need to be treated. With this exemption and since this project is
creating 1,480 sf of new impervious surface which is below the water quality
requirement threshold, the project does not need to incorporate water quality
treatment. However, the City is interested in utilizing the 10' x 160' planter strip
area north of the bridge to incorporate a water quality facility. Based upon the
availability of this area, a number of alternatives were evaluated.
Water Quality Treatment Facility Alternatives
Biofiltration Swale
A biofiltration swale is one alternative to treating water quality for the project area.
The project site is bound by the minimal slope available between the existing
conveyance systems (0.008% slope). Since the slope is less than one percent
and the groundwater is high (S&EE, January 2010), the Design Manual states
that only a "wet biofiltration Swale" should be considered. A wet biofiltration swale
includes a ditch with vegetation appropriate for saturated conditions.
The biofiltration Swale would be located just south of the southern entrance to
Hawk's Landing (Node 5 in Figure 4) and would extend to the north end of the
existing 24" culvert that discharges to May Creek (Node 6 in Figure 4). This is a
distance of approximately 160 lineal feet which meets the minimum required
length of 100 feet needed for a bioswale. The biofiltration swale would need to
have a minimum bottom width of 2 feet and side slopes of 3:1 for the water quality
depth of 4". Above 4", the bioswale can have slopes of 2:1. Since the swale
would be a "wet biofiltration" swale with an allowable maximum depth of 4", a
bypass would be necessary for high flows so a flow splitter manhole would be
installed at Node 5 so that only the water quality flow to be treated would flow
through the Swale while the remaining flow would be conveyed through a 24" pipe
GRAY & OSBORNE, INC. 11 APRIL 13, 2010
elsewhere. The two conveyance systems would connect at a new manhole
installed at Node 6 (north end of the existing 24" culvert).
The advantage to a biofiltration swale is that it is relatively low maintenance and
provides an economic cost alternative in comparison to manufactured or cast -in -
place systems.
Wetvault
A wetvault is a concrete vault that treats runoff by removing harmful particulates
through settling. The wetvault can be combined with an oil water separator to
increase water quality treatment. Beginning with the available water quality
facility area to work with (i.e. 10' x 160' planter strip), per the Design Manual, the
area of runoff to be treated in a vault that is 10' wide by 160' long x 8' deep would
equate to approximately 10,000 square feet or 0.23 acres. This was calculated
using three times the runoff estimated for the mean annual storm of 0.47" as
determined from Figure 6.4.1.A in the Design Manual. Similar to the wet
biofiltration swale, only the water quality storm would be diverted to the vault while
the remaining runoff would be conveyed in a 24" pipe elsewhere. A flow splitter
manhole would be used to divert the flow.
The advantage to a wetvault is that access for maintenance is easily provided.
However, the wetvault consumes a large territory underground, is costly to install
as a pre -cast or cast -in -place vault, it tends to not be as effective with pollutant
removal rates and may need to be maintained more than other water quality
alternatives.
StormFilter
The StormFilter cartridge is a media based filter that removes polluted
particulates from runoff and is typically housed in a vault or catch basin. The
media within the cartridge may consist of leaf compost, perlite, zeolite, activated
carbon or a combination thereof.
StormFilter manufactures individual catchbasin filters that could discharge into the
trunk line. Each catchbasin would provide for both collection and treatment of
road runoff. The exact location of these catchbasins will be determined by the
final road design layout. If five StormFilter units were used, treating
approximately 0.02 cfs per unit, an area of approximately 0.6 acres of runoff could
be treated.
Maintenance associated with the StormFilter typically consists of inspecting the
cartridges once a year and replacing the media cartridge if necessary. This can
be costly however, the StormFilter is advantageous due to its efficient removal
rates which may exceed those presented by other water quality alternatives. It
also requires less space than a bioswale and wetvault.
GRAY & OSBORNE, INC. 12 APRIL 13, 2010
Filterra
The Filterra is a stormwater biofiltration system that filters polluted particulates
through a specially designed filter media mixture. The Filterra unit is installed
along the curbside and houses landscaping items such as a small tree. The tree
is installed within a 4' x 4' concrete box that contains the filter media which is used
to filter pollutants such as petroleum, heavy metals, TSS, bacteria, and
phosphorus. The clean, filtered water then flows through a drain at the bottom of
the concrete box and discharges to a stormwater conveyance system.
The Filterra unit has been given a General Use Level Designation by the
Washington State Department of Ecology with the provision that the Filterra unit
processes a minimum of 91 % of the influent runoff being collected. Using DOE's
WWHM3 modeling software, modeling results reveal that this project would
require five 4' x 4' Filterra units to treat the 19,950 square feet (0.46 acres) of
impervious surface flowing to the units. The Filterra unit would also need an
overflow catch basin just downstream from the Filterra unit so as to provide an
overflow bypass for large storm events.
Maintenance associated with the Filterra unit typically consists of inspecting the
units once to twice a year which may then lead to removal of trash and debris as
well as the upper layer of mulch. Approximately 3-4 bags of mulch would be
needed to maintain the unit. Like the StormFilter, the Filterra unit may be
advantageous due to its efficient removal rates which may exceed those
presented by other water quality alternatives. Likewise, it requires less space
than a bioswale and wetvault. However, it should be noted that the City has not
approved Filterra units within their 2009 Amendments to the King County Surface
Water Design Manual and would require a variance if used.
Rain Garden
The City has adopted rain garden standards in Section 6.7.1 of the Amendments
to the 2009 King County Surface Water Design Manual. In reviewing these
standards, the area available for a water quality treatment facility (i.e. 10' x 160'
just north of the bridge) can be utilized to treat approximately 2,700 sf which
equates to the road runoff area betweens Node 4 and 5 in Figure 4.
The rain garden would consist of 18" of amended soil which would consist of an
imported sand with compost mixed in. Above the amended soil, a six inch
ponding depth would be available for runoff diverted from the road. An overflow
riser would be located at the top of this ponding depth and connected into the 24"
conveyance system. A rain garden measuring 140' in length with a bottom width
was modeled in WWHM per City standards. Due to the available area's narrow
width, the pond was modeled using 1.5:1 side slopes to give it a top width of 9.5'.
Using the NRCS soils shown in Appendix B, a short term infiltration rate of 1 in/hr
was input into WWHM. Since the side slopes were greater than 2:1, the wetted
surface of the slopes could not be modeled for infiltration. With this input, the
WWHM model revealed that 100% of the runoff from the 2,700 square foot area
could be infiltrated through the bottom of the rain garden. The City's standards
state that a rain garden should have a minimum 3' separation between the
GRAY & OSBORNE, INC. 13 APRIL 13, 2010
groundwater table and the bottom of the pond unless there is less than 5,000
square feet of impervious surface flowing to the pond. If less than 5,000 square
feet is flowing to the area, a minimum separation of 1' is allowed. Based on the
groundwater elevations determined from the Geotechnical Report for this project,
it is recommended that the City diverts less than 5,000 square feet of impervious
area to the rain garden.
It is necessary that the rain garden be planted with plants that can sustain being
saturated while also tolerating drought conditions. Table 10 depicts which plants
may be utilized within the rain garden to meet these conditions.
Table i - Rain Garden Plants
Common Name Spacing(On Center)
Western mannagrass Seed
Velvetgrass
Seed
Shortawn foxtail
Seed
Water foxtail
Seed
Spike rush
4 inches
Slough sedge
6 inches or seed
Sawbeak sedge
6 inches
Sedge
6 inches
Slender rush
6 inches
Water parsley
6 inches
Hardstem bulrush
6 inches
Watercress
12 inches
Small -fruited bulrush
12 inches
Maintenance for rain gardens include checking them annually to ensure the
overflow is free of debris and in good working condition. Erosion channels or
bare spots within the garden shall be stabilized with soil, plants, or mulch. Any
dead vegetation should be replaced and noxious vegetation shall be removed
immediately.
Additional Water Quality Treatment Facilities
Numerous other water quality treatment facilities exist but are not applicable to
this project. A sand filter is high in maintenance and is not recommended for this
area. Inadequate space is available for a filter strip, wetpond, or a wetland. So
based on particular site constraints, these water quality treatment alternatives
were not considered.
Treatment Facility Costs
The costs associated with the identified water quality alternatives are listed in
Table 11. The costs listed are approximate installation costs.
GRAY & OSBORNE, INC. 14 APRIL 13, 2010
QualityTable 11 - Water
Approximate Installation
maintenance
Cost
Cost
Wetvault
$60,000
Medium
Filterra
$65,000
Medium
StormFilter
$10,000 (1 cartridge)
High
$50,000 5 cartridges)
Wet Biofiltration Swale
$20,000
Low
Rain Garden
$10,000
Low
For hydraulics, a 24-inch pipe in front of the new Hawk's Landing Development
would meet the City's criteria of preventing flooding during either a 25-year storm
event or a 100-year storm event under future conditions.
For water quality treatment, using the preferred water quality facility area, it is
recommended that the City install a wet bioswale. The bioswale would treat the
road runoff collection area just north of the bioswale and would provide the City
an economical option both in terms of installation and future maintenance.
Likewise, if space becomes limited, it is recommended that the City use a single
StormFilter catch basin toward the south end of the project site (see Figure 5).
The StormFilter provides a relatively economic option while minimizing the
amount of property needed. It is also likely to provide a high efficiency removal
rate for pollutants coming from Lake Washington Blvd.
GRAY & OSBORNE, INC. 15 APRIL 13, 2010
0
PROPOSED 400p
24" STORM
PIPE
ys�.ic
r
,�� �•,-- • � /\i'�%/x^�,� ,try I
140'
WET
BIOSWALE
SINGLE / (Option 1) )^
STORMFILTER
(Option 2)
I
+m�
SCALE: 1"=80'
CITY OF RENTON
LAKE WASHINGTON BLVD
HAWKS LANDING
STORM AND WATER IMPROVEMENTS
PROJECT
�7ray �c �eliorne, Ir
CONOMTMO OR101MRs
APPENDIXA
BASIN FIGURE FROM THE ENVIRONMENTAL
ASSESSMENT FOR THE 1-405/NE 44T" ST.
INTERCHANGE PROJECT
GRAY & OSBORNE, INC. 1 FEBRUARY 26, 2010
II GYPSY SU8-BASIN
IDRAINAG� / '
� \�13� � � A _ IXISTING C RCUU,RtESIDENTUL 1
■ � rrr
•r:v
�� i Y�•Iq
APPROXIMATE EXTENT OF
FORMAL WETLAND
DELINEATION
LEGEND
EXISTING RESIDENTIAL LAND USE
Cx STING ROAD
® GTPSY SUBBASIN VIA 44TH ST12RNWATER POND
® GYPSY SUBBASIN
MAY CREEK SUBBASIN
DIRECTION OF FLOW
REFERENCE: HUGH G. GOLDSMITH & ASSOCIATES.
EXISTING DRAINAGE PATTERNS AND SENSITIVE AREAS FIGURE 33
1-405RJE 44TH STREET INTERCHANGE EA PROJECT NO.
RENTON, WASHINGTON KBOO270A
APPENDIX B
SOIL MAP FROM USDA
GRAY & OSBORNE, INC. 2 FEBRUARY 26, 2010
❑� tKtD_JlwebsoiH+reY.ncs. usda.govjapp�1Va66a15t.wy,tlpa V' IIX� L:+e Sean�r: -. - P
__..—.__------_-
File Edt View Favortm Tools flab
y Web Sd Suvey r' Page f Til
K, J-1J sl #1J.4J eJ J Scalc
W,
King County Area, Washington (WA633)
Map Unit
Map Unit Name
Acres in Percent
of
Symbol
AOI
AOI
aqr
Aldenvood gravelly
0.3
0.7-,,
sandy loam, 6 to
15 percent slopes
Bh
Bellingham sift
1.6
3.71,1e
loam
InC
Indianola loamy
0.3
0.7%
fine sand, 4 to 15
percent slopes
No
Norma sandy loam
42.8
95.0%
Totals for Area of Interest
45.1
100.0%
Appendix B — NRCS Website map showing locations of soils
WM
r, ® lnternet *, Ini-ir -
APPENDIXIC
1995 FEMA KING COUNTY FLOOD INSURANCE STUDY
INFORMATION
GRAY & OSBORNE, INC. 3 FEBRUARY 26, 2010
m
STREET To determine it flood insurance is available, contact an insurance agent or
call the National Flood Insurance Program at (800j 63&6620.
4
APPROXIMATE SCALE IN FEET
500 0 500
BEET
F-
CC
Z
w
Z
Q
J
CO
CAMAS
AVENU
NORTHEAST
STREET
. w
Q Q
w
L'J =
Z F-
g 0
In z
1 47030'00"
122011' 15"
NATIONAL FLOOD INSURANCE PROGRAM
FIRM
FLOOD INSURANCE RATE MAP
KING COUNTY,
WASHINGTON AND
INCORPORATED AREAS
PANEL 664 OF 1725
(SEE MAP INDEX FOR PANELS NOT PRINTED)
CONTAINS:
COMMUNITY
KING COUNTY.
UNINCORPORATED AREAS
RENTON. CITY OF
NUMBER PANEL SUFFIX
530071 0664 F
530089 0664 F
MAP NUMBER
53033CO664 F
MAP REVISED:
MAY 16,1995
Federal Emergency Management Agency
Appendix B
otak
G
122011' 15"
—� 47031'52"
to
f—
J
IW
Q
O
0-
CC
O
U
:X
Z)
O
f— f—
Z Z
W L)
ir O
LL
U
O C7
\ } Z
F- Y
U
I
l
"5
REET
-TY
�0 AREAS
MNTON
530088
ZONE X ti
A
4211 9
'o
N
O /
LEGEND
SPECIAL FLOOD HAZARD AREAS INUNDATED
WIN BY 100-YEAR FLOOD
ZONE A No base flood elevations determined.
ZONE AE Base flood elevations determined.
ZONE AH Flood depths of Ito 3 feet fusually areas
of ponding); base flood elevations
determined.
ZONE AO Flood depths of I to 3 feet (usually sheet
slow on sloping terrain); average depths
determined. For areas of alluvial fan flooding,
velocities also determined.
ZONE A99 To be protected from 100-year flood by
Federal (Mod protection system under
construction; no base elevations determined.
ZONE V Coastal flood with velocity hazard (wave
action); no base flood elevations determined.
ZONE VE Coastal flood with velocity hazard (wave
action); base flood elevations determined.
R FLOODWAY AREAS IN ZONE AE
OTHER FLOOD AREAS
ZONE X Areas of 500-year flood: areas of 100--year
flood with average depths of less than
I foot or with drainage areas less than
t square mile; and areas protected by
levees from 100-year flood.
OTHER AREAS
ZONE X Areas determined to be outside 500-year
floodplam.
ZONE D Areas in which flood hazards are
undetermined.
UNDEVELOPED COASTAL BARRIERS
Identified
Identified Otherwise
1983
1990 Protected Areas
Coastal barrier areas are normally
located within or adjacent to Special
Flood Hazard Areas.
Flood Boundary
FModway Boundary
Zone D Boundary
Boundary Dividing SpeciFlood
B
Hazard Zones, and Boundary
Dividing Areas of Different
Coastal Base Flood Elevations
Within Special Flood Hazard
Zones.
Base Flood Elevation Line;
513
Elevation in Feet. See Map Index
for Elevation Datum.
p
Cross Section Line
Base Flood Elevation in Feet
(EL 987)
Where Uniform Within Zone.
See Map Index for Elevation Datum.
RM7 X
Elevation Reference Mark
• M2
River Mile
Horizontal Coordinates Based on Nora
97007'30". 32022"30"
American Datum of I927 (NAD 27!
Projection.
NOTES
This map is for use in administering
the National Flood Insurance Program.
it does not nec—r,t., inontifv all areas sahiect to floodino. Darticularly from
local drainage
Special Flood
Coastal base f
the effects of
from those
o.,aroa+inn ntanmmn
Appendix B
otak
JOINS PANEL 0675
� ZONE X
<
a
NCr
LIMIT OF
O
I
DETAILED STUDY
N3N
ti�
ao5 Z
ZONE X
1
>
w
9
May Creek
ZONE AE
F
�
~
G
pO�
N 40TH STREET
RM210
ZONE X
R o
0
`
�
z
F
MEADOW
tNE NORTH
,
-r
OQ�j�P
O
w
47
NORTH 38TH STREET
Z
'
w
w
>
z
¢
w
z
2
NORTH
37TH STREET
w
52
z
NORTH
37TH STREET
0
a
0
z
W
�
J
W
>
NORTH 36TH STREET
32
�JQJ�
NORTH 36TH STREET
�1
z
_
KIN,
�0
NORTH 35TH STREET
w
a
UNINCORI
Q
6
3
0
a
Q
\ 64
C
NORTH 34TH STREET
B>
z
May
NORTH 33RD PLACE
w
Creek
m
z
72
ZONE X
NORTH
33RD STREET
a
w
ZONE X
?
M
M
NORTH 32ND STREET
77
ZONE
NORTH
32ND STREET
I
w
Z
>
NORTH ¢
31ST STREET
CV
`
ZONE A
Co
CO
ZONE X
NORTH
30TH STREET
NORTHEAST 30TH
STREET
=
m
ZF�y
NORT
Note: Datum
= 1929 NGVD
`2
Z
Appendix B
Scale: 1" = 500'
otak
FLOG
INSUi
STUD
KING COUNTY,
WASHINGTON
AND INCORPORATED AREAS
VOLUME 1 OF 3
COMMUNITY COMMUNITY
NAME NUMBER
AUBURN,CITY OF ...........
530073
BELLEVUE,CITY OF ..........
530074
BLACK DIAMOND,TOWN OF ....
530272
BURIEN,CITY OF ............
530321
CARNATION,TOWN OF .......
530076
DES MOINES,CITY OF ........
530077
DUVALJOWN OF ...........
530282
ENUMCLAW,CITY OF ........
530319
FEDERAL WAY,CITY OF.......
530322
ISSAOUAH,CITY OF .........
530079
KENT,CITY OF .............
530080
KING COUNTY,
UNINCORPORATED AREAS ..
530071
KIRKLAND,CITY OF ...........
530081
LAKE FOREST PARK,CIT'Y OF ...
530082
NORMANDY PARK,CITY OF ....
530084
NORTH BEND,CITY OF ........
530085
PACIFIC,CITY OF ...........
530086
REDMOND,CITY OF ..........
530087
RENTON,CITY OF ...........
530088
SEATLE,CITY OF ............
530089
SEATAC.CITY OF .
530320
SKYKOMISH,TOWN OF ........
530236
SNOQUALMIE,CITY OF .......
530090
TUKWILA,CITY OF ..........
530091
WOODINVILLE, CITY OF
530324
REVISED: MAY 16,1995
Federal Emergency Management Agency
o �
0
i
Appendix B
otak
tia
FLOODING SOURCE
FLOODWAY
BASE FLOOD
WATER SURFACE ELEVATION
DISTANCE
WIDTH
SECTION
AREA
MEAN
VELOCITY
REGULATORY
WITHOUT WITH
FLOODWAY FLOODWAY
INCREASE
CROSS SECTION
(FEET)
(SQUARE
FEET)
(FEET PER
SECOND)
(FEET NGVD)
May Creek
A
0.14
34
158
5.5
21.0
21.0
21.5
0.5
B
0.16
60
239
3.6
21.8
21.8
22.2
0.4
C
0.24
42
99
8.8
23.3
23.3
23.3
0.0
D
0.25
42
110
7.9
25.7
25.7
25.7
0.0
E
0.31
31
121
7.2
29.0
29.0
29.2
0.2
F
0.39
40
150
5.8
32.5
32.5
33.0
0.5
C
0.46
28
87
10.0
35.8
35.8
35.8
0.0
H
0.52
23
123
7.1
40.0
40.0
40.6
0.6
I
0.57
45
165
5.3
41.8
41.8
42.5
0.7
J
0.63
31
89
9.7
45.3
45.3
45.3
0.0
K
0.78
33
133
6.5
55.2
55.2
55.2
0.0
L
0.94
79
143
6.1
64.7
64.7
64.7
0.0
M
1.09
33
113
7.7
76.4
76.4
76.6
0.2
N
1.25
39
128
6.6
85.4
85.4
85.4
0.0
0
1.36
32
89
9.6
93.1
93.1
93.2
0.1
P
1.39
40
172
4.9
95.6
95.6
96.0
0.4
Q
1.41
33
90
9.5
95.8
95.8
95.8
0.0
R
1.42
33
ill
7.7
96.4
96.4
96.4
0.0
s
1.46
30
95
8.9
99.8
99.8
99.9
0.1
T
1.54
22
91
9.3
106.8
106.8
106.9
0.1
U
1.56
8
68
12.5
112.2
112.2
112.2
0.0
V
1.61
43
283
2.9
114.2
114.2
115.1
0.9
.W
1.74
27
81
9.9
120.9
120.9
120.9
0.0
X
1.83
38
170
4.8
125.0
125.0
125.7
0.7
Y
1.96
52
101
8.0
135.8
135.8
135.8
0.0
Z
2.02
42
130
6.3
140.4
140.4
140.5
0.1
iMiles Above Mouth
T I FEDERAL EMERGENCY MANAGEMENT AGENCY
B KING COUNTY, WA
E AND INCORPORATED AREAS
FLOODWAY DATA
MAY CREEK
100
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LEGEND+.
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APPENDIX D
KCRTS INPUT AND OUTPUT FILES
GRAY & OSBORNE, INC. 4 FEBRUARY 26, 2010
LWsdetl.out
KCRTS Command
-------------
CREATE a new Time Series
------------------------
Production of Runoff Time Series
Project Location Sea-Tac
Computing Series ex-detl.tsf
Regional Scale Factor 1.00
Data Type Reduced
Creating Hourly Time Series File
Loading Time Series File:C:\KC_SWDM\KC_DATA\STOF60R.rnf
outwash Forest 0.16 acres
Loading Time Series File:C:\KC_SWDM\KC_DATA\STOG60R.rnf
outwash Grass 0.16 acres
Loading Time Series File:C:\KC_SWDM\KC_DATA\STE160R.rnf
Impervious 0.42 acres
--------------
Total Area 0.74 acres
Peak Discharge: 0.212 CFS at 6:00 on Tan 9 in Year 8
storing Time series File:ex-detl.tsf
Time Series Computed
KCRTS Command
-------------
CREATE a new Time series
------------------------
Production of Runoff Time series
Project Location Sea-Tac
Computing Series pr-detl.tsf
Regional Scale Factor 1.00
Data Type Reduced
Creating Hourly Time series File
Loading Time Series File:C:\KC_SWDM\KC_DATA\STOG60R.rnf
outwash Grass 0.11 acres
Loading Time Series File:C:\KC_SWDM\KC_DATA\STE16OR.rnf
Impervious 0.63 acres
--------------
Total Area 0.74 acres
Peak Discharge: 0.305 CFS at 6:00 on Tan 9 in Year 8
storing Time series File:pr-detl.tsf
Time Series Computed
KCRTS Command
-------------
Enter the Analysis TOOLS Module
-------------------------------
Analysis Tools Command
----------------------
Compute PEAKS and Flow Frequencies
----------------------------------
Loading Stage/Discharge curve:pr-detl.tsf
Flow Frequency Analysis
--------------------------------------------------------
Time Series File:pr-detl.tsf
Project LOCatiOn:Sea-Tac
Frequencies & Peaks saved to File:pr-detl.out
Analysis Tools Command
----------------------
Compute PEAKS and Flow Frequencies
----------------------------------
Page 1
LWBdetl.out
Loading Time series File:ex-detl.tsf
Flow Frequency Analysis
--------------------------------------------------------
Time series File:ex-detl.tsf
Project Location:Sea-Tac
Frequencies & Peaks saved to File:ex-detl.out
Analysis Tools Command
----------------------
RETURN to Previous Menu
-----------------------
KCRTS Command
-------------
exit KCRTS Program
------------------
Page 2
ex-detl.out
Flow Frequency Analysis
Time Series
File:ex-detl.tsf
Project
Location:Sea-Tac
---Annual
Peak
Flow Rates---
-----Flow Frequency
Analysis -------
Flow Rate
Rank
Time of
Peak
- - Peaks - -
Rank
Return
Prob
(CFS)
(CFS)
Period
0.108
6
2/09/01
2:00
0.212
1
100.00
0.990
0.091
8
1/05/02
16:00
0.154
2
25.00
0.960
0.130
3
2/27/03
7:00
0.130
3
10.00
0.900
0.106
7
8/26/04
2:00
0.125
4
5.00
0.800
0.125
4
10/28/04
16:00
0.110
5
3.00
0.667
0.110
5
1/18/06
16:00
0.108
6
2.00
0.500
0.154
2
10/26/06
0:00
0.106
7
1.30
0.231
0.212
1
1/09/08
6:00
0.091
8
1.10
0.091
Computed
Peaks
0.192
50.00
0.980
Page 1
pr-detl.out
Flow Frequency Analysis
Timeddrie5
File:pr-detl.tsf
Project
Location:Sea-Tac
---Annual
Peak
Flow Rates---
-----Flow Frequency
Analysis -------
Flow Rate
Rank
Time of
Peak
- - Peaks - -
Rank
Return
Prob
(CFS)
(CFS)
Period
0.156
7
2/09/01
2:00
0.305
1
100.00
0.990
0.134
8
1/05/02
16:00
0.228
2
25.00
0.960
0.187
3
2/27/03
7:00
0.187
3
10.00
0.900
0.157
6
8/26/04
2:00
0.186
4
5.00
0.800
0.186
4
10/28/04
16:00
0.164
5
3.00
0.667
0.164
5
1/18/06
16:00
0.157
6
2.00
0.500
0.228
2
10/26/06
0:00
0.156
7
1.30
0.231
0.305
1
1/09/08
6:00
0.134
8
1.10
0.091
Computed
Peaks
0.279
50.00
0.980
Page 1