HomeMy WebLinkAboutRS_Approved_TIR_210129_v1SURFACE WATER UTILITYrstraka 07/23/2018DEVELOPMENT ENGINEERINGrnair 07/30/2018
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I. Project Overview
The proposed project will develop 6 single-family lots. The site is located at the southwest
corner of the intersection of 156th Avenue SE and SE 2nd Place in the Renton Highlands
north of the Cedar River. The address of the site is 13609 156 th Avenue SE. The site
area is 1.69 acres before Right of way dedication and 1.67 acres after Right of way
dedication along 156th Avenue SE. The site consists of two existing parcels that form an
overall rectangular piece of property that is approximately 484’ x 152’ with frontage on its
eastern short side along 156th Avenue SE and frontage on its northern long side along
SE 2nd Place. The project site includes both on-site development area and off-site
improvements along 156th Ave SE and SE 2nd Place. The site is located in the City of
Renton R-4 zone. The surrounding parcels are all single-family residential also zoned R-
4. The site is located in the Lower Cedar River drainage basin. The site is located in the
Flood Problem Flow Control area (with Forested conditions) and Basic water quality
control area.
There are two single-family residences and various outbuildings on the two existing
parcels. All existing buildings will be demolished and removed for the proposed
development. The remainder of the property is covered with grass and trees. The site is
moderate sloped with average slope of 8% slopes southwesterly toward adjacent
properties. There is no sensitive area on the site.
Difficult conditions for the proposed development are listed as follows:
1. The site slopes southwesterly and there is no storm drainage connection point to
the public storm drainage system near the southwest corner of the site or along
the south property line of the site.
2. There are existing downstream drainage problems along Toledo Avenue SE.
3. The downstream drainage ditch between SE 2nd Place and the Highland Estates
combined detention/wet pond has maintenance problems.
For the onsite improvement, Restricted footprint and Basic dispersion for downspouts are
used for each lot as On-site BMPs. New plus replaced impervious area is approximately
0.49 acres before applying On-site BMP credits, new pervious area is approximately 1.18
acres. A detention vault is proposed to provide the required Flood Problem Flow Control
standard (forested site conditions).
The offsite frontage improvements along SE 2nd Place and 156th Avenue SE remove
approximately 5,395 square feet of existing impervious area and create approximately
6,801 square feet of new / replaced impervious area (1,620 square feet of it is pollution
generating impervious area). For flow control, the new impervious area created by the
SE 2nd Place offsite improvement is routed to the onsite detention vault. Due to the
topography of the site, new impervious area created by the 156 th Ave SE offsite
improvement can’t be routed to the onsite detention vault and is counted as bypassed
target area Per RSWDM Section 1.2.3.2.E. To mitigate the bypassed target areas in
156th Avenue SE and in the north side of SE 2nd Place, the existing asphalt pavement
form the center line of SE 2nd Place to the new south curb line of the street along the
frontage of the site is also routed to the onsite detention vault for flow control treatment
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as a mitigation trade per RSWDM Section 1.2.3.2.G. See section 4 for more detail
calculations. The onsite detention vault is sized to provide required Flood Problem Flow
Control standard (forested site conditions) at the point of compliance (Near the
intersection of 149th Place SE and SE 142nd Street).
For water quality treatment, total new and replace pollution generating area (onsite plus
offsite) is only 4,620 square feet (less than 5,000 square feet), no water quality treatment
facility is required per RSWDM 1.2.8 Surface Area Exemption.
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II. Conditions and Requirements Summary
CORE REQUIREMENTS – SECTION 1.2 OF RSWDM
1.2.1 CORE REQUIREMENT #1: Discharge at the Natural Location
Overall topography throughout the drainage basin generally conveys flows from
northeast-to-southwest and north-to-south. Streets and manmade conveyance systems
within the vicinity of the site have broken up these flows, directing them in various
directions that eventually flow to the same, original natural discharge point of the overall
basin, which is a series of wooded ravines located on the south side of SE 142 nd Street
approximately 2,600 feet south of the project site. These ravines convey flows south off
the Maplewood Heights / Renton Highlands to the valley below and connect to the
Cedar River.
Existing micro-topography on the project site generally slopes northeast to southwest in
the general overall pattern of the drainage basin, directing surface flows from the site
across neighboring downstream residential parcels toward 154 th Ave SE. Surface flows
in this direction are eventually collected by manmade conveyance systems in 154 th Ave
SE and directed south.
There are several issues associated with releasing flows at the southwest corner of the
site as a developed project:
This project will require installation of a detention vault to provide Flood Problem
Flow Control.
There is no existing conveyance system located at the southwest corner of the
site.
There is not adequate distance on-site to disperse flows from the detention vault
to the surface toward the southwest corner of the site.
Parcels south and west of this site prohibit our ability to convey flows via pipe or
swale in that direction without easements across those parcels.
Emerging groundwater is already an existing problem on parcels immediately
south of us along 156th Ave SE (see downstream analysis).
Conveyance systems in 154th Ave SE further south (outside city of Renton) are
documented by homeowners in the area as overwhelmed in heavy and
prolonged rain events. The overall topography in this area is virtually flat.
Downstream conveyance pipe system along the south side of SE 2nd Place has
good capacity.
Maintenance problems at the ditch between SE 2nd Place and the Highland
Estates pond can be solved by replacing the ditch with a piped conveyance
system.
The drainage systems downstream of the two outfalls of the Highland Estates
pond are well defined and have good capacities.
For these reasons, we propose connecting our storm drainage system (post detention) to
the piped conveyance system that runs along the south side of SE 2nd Place which flows
west to a ditch that drains to the combined detention/wet pond for the Highland Estates.
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The new conveyance system is designed to convey and contain the 25-year peak flow
with 6 inches of free board and the 100-year peak flow and thus meets the requirements
listed above. KCBW is used for Back water analysis following the requirements of City of
Renton 2017 SWDM 4.2.1.2 and designed for the 100-year peak flow.
1.2.5 CORE REQUIREMENT #5: Erosion and Sediment Control
Erosion control will be installed as necessary for the frontage improvements and the on-
site improvements.
1.2.6 CORE REQUIREMENT #6: Maintenance and Operations
Any necessary maintenance of the onsite drainage system will be the responsibility of the
property owner and manager. The detention vault will be maintained by City of Renton
after a 2-year maintenance warranty.
1.2.7 CORE REQUIREMENT #7: Bonds and Liability
Necessary bonds will be provided at the time the building permit plans are approved
and the construction started.
1.2.8 CORE REQUIREMENT #8: Water Quality
Total pollution generating area is 4,620 square feet (onsite plus offsite), no water quality
treatment facility is required per RSWDM 1.2.8 Surface Area Exemption.
1.2.9 CORE REQUIREMENT #9: On-site BMPs
On-site BMPs such as restricted foot print and basic dispersion are used in this project to
meet the Small lot BMP requirements per Section 1.2.9.2.1 and the Small subdivision
project BMP requirements per Section 1.2.9.3.1 of the RSWDM. BMPs need to be
applied in the order of preference per Section 1.2.9.2.1 to the maximum extent feasible.
After all the BMPs are applied to the maximum extent feasible, then BMPs need to be
implemented as described in number 5 in Section 1.2.9.2.2 of the 2017 RSWDM. For
frontage improvement, BMPs need to be implemented as described in Section 1.2.9.3 of
the 2017 RSWDM.
SPECIAL REQUIREMENTS – SECTION 1.3 OF RSWDM
1.3.1 Special Requirement #1: Other Adopted Area Specific Requirements
No other area specific requirements are applicable. The site is not within a CDA, MDP,
BP, SCP, SWCP, LMP, FHRPU or SFDP.
1.3.2 Special Requirement #2: Flood Plain / Floodway Delineation
Not applicable to this site. There is no flood hazard area in the site. The site is not
within a floodplain or floodway. The site is not subject to inundation by the base flood or
channel migration.
1.3.3 Special Requirement #3: Flood Protection Facilities
Not applicable to this site. There is no flood hazard area in the site. The site does not
rely on any flood protection measures.
1.3.4 Special Requirement #4: Source Controls
This project is a single family short plat project. Source Controls are not required.
1.3.5 Special Requirement #5: Oil Control
This project is a single family short plat project in R-4 zone and this site is not a high
used site. Oil Control is not required.
City of Renton Special Requirement #6: Aquifer Protection Area
Not applicable to this site. The site is not located in the Aquifer Protection Areas
(zone1, zone 1 modified and zone 2) shown on the City of Renton Aquifer Protection
Zones Map.
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Task 5 Mitigation of Existing or Potential Problems
See Task 4 for existing and potential drainage problems within 1 miles downstream of
the site.
For the onsite improvement, Restricted footprint and Basic dispersion for downspouts are
used for each lot as On-site BMPs. New plus replaced impervious area is approximately
0.49 acres before applying On-site BMP credits, new pervious area is approximately 1.18
acres. A detention vault is proposed to provide the required Flood Problem Flow Control
standard with forested site conditions.
The offsite frontage improvements along SE 2nd Place and 156th Avenue SE remove
approximately 5,395 square feet of existing impervious area and create approximately
6,801 square feet of new / replaced impervious area (1,620 square feet of it is pollution
generating impervious area). For flow control, the new impervious area created by the
SE 2nd Place offsite improvement is routed to the onsite detention vault. Due to the
topography of the site, new impervious area created by the 156 th Ave SE offsite
improvement can’t be routed to the onsite detention vault and is counted as bypassed
target area Per RSWDM Section 1.2.3.2.E. To mitigate the bypassed target areas in
156th Avenue SE and in the north side of SE 2nd Place, the existing asphalt pavement
form the center line of SE 2nd Place to the new south curb line of the street along the
frontage of the site is also routed to the onsite detention vault for flow control treatment
as a mitigation trade per RSWDM Section 1.2.3.2.G. The onsite detention vault is sized
to provide required Flood Problem Flow Control standard (forested site conditions) at the
point of compliance (Near the intersection of 149 th Place SE and SE 142nd Street).
For water quality treatment, total new and replace pollution generating area (onsite plus
offsite) is only 4,620 square feet (less than 5,000 square feet) and is counted as untreated
discharge per 2017 Renton SWDM Section 1.2.8.2.D. No water quality treatment facility
is required.
With connection to the piped conveyance system in SE 2nd Place, the proposed
development will not create any adverse impact on the downstream drainage system in
either direction between the site and the wooded ravine south of SE 142 nd Street where
the two downstream systems re-converge. To mitigate existing maintenance problem at
the drainage ditch between SE 2nd Place and the Highland Estate pond, ditch
improvement is required for the Storm drainage adjustment application.
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Part B Developed Site Hydrology
Offsite frontage improvement along 156th Avenue SE
This is an existing developed street Right of way.
Total disturbed area = 0.059 acres (this area will be collected and conveyed to the
existing storm drainage system that runs along the east side of 156th Avenue SE and
bypass the onsite detention vault)
Total new and replaced impervious area = 0.029 acres
Total pervious area = 0.03 acres (till grass, group C)
Offsite frontage improvement along SE 2nd Place
This is an existing developed street Right of way.
Total disturbed area = 0.234 acres
Total new and replaced impervious area = 0.145 acres
Total pervious area = 0.089 acres (till grass, group C)
Total bypassed area in SE 2nd Place R.O.W. = 0.040 acres (include 0.031 acres of
impervious area and 0.009 acres of pervious area, till grass)
Total bypassed area in 156th Avenue SE = 0.059 acres
Total offsite bypassed area = 0.099 acres
Traded non-target impervious area in SE 2nd Place collected and treated by the onsite
detention vault = 0.110 acres. > 0.099 acres, o.k. (See Part A)
Total drainage area from SE 2nd Place to onsite detention vault = 0.304 acres
Total offsite impervious area to onsite detention vault = 0.224 acres
Total offsite pervious area to onsite detention vault = 0.08 acres
Onsite improvement
Under developed condition, onsite runoffs will be collected and conveyed to the onsite
detention vault. See Part D for sizing of On-site BMPs and detention vault.
Onsite impervious area calculation (before applying On-site BMP credits):
Roofs of lot 1 through lot 5 = 3,000 sf per lot.
Roofs of lot 6 = 2,400 sf.
Private, driveway for 6 lots = 500 * 6 = 3,000 sf. (PGIS)
Private walkways for 6 lots = 100 * 6 = 600 sf.
Driveway to detention vault = 1,553 sf.
Total onsite impervious area = 22,553 sf. = 0.518 acres
Total onsite area = 1.666 acres
Total onsite impervious area = 0.518 acres
Total onsite pervious area = 1.666 – 0.518 = 1.148 acres (till grass, group C soil)
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Flow Frequency Return Periods for Developed condition. POC #1 (No detention
and no On-site BMPs)
Return Period Flow(cfs)
2 year 0.533121
5 year 0.737113
10 year 0.882546
25 year 1.078263
50 year 1.232864
100 year 1.395111
Q100y dev – Q100y pre = 1.3951 – 0.3644 = 1.0307 cfs > 0.15 cfs
Flow control mitigation is required.
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Part C Performance Standards
The site is located in Conservation Flow Control Area (Forest existing condition). Since
there are some drainage problems within 0.25 miles downstream from the site, Flood
Problem Flow Control standard (forest existing condition) is required.
Per RSWDM section 1.2.9, On-site BMPs are required for the onsite development. On-
site BMP’s for more than 10% of each lot area is required for lots 1 through 5 and On-site
BMP’s for more than 20% of the lot area is required for lot 6.
BMPs need to be applied in the order of preference per Section 1.2.9.2.1 to the maximum
Extent feasible. After all the BMPs are applied to the Maximum extent feasible per
numbers 1 – 4 then BMPs need to be implemented as described in number 5 in Section
1.2.9.2.1 of the 2017 RSWDM.
Final signed On-site BMP Covenant is required prior permit is issued and will be recorded
with the Final Short Plat map.
On-site BMPs are required to the maximum extent feasible for infrastructure in the
frontage improvements such as sidewalks and road widening per Section 1.2.9.3.
Onsite flow control facility is provided by a detention vault to provide the required Flood
Problem Flow Control (Forest existing condition) for onsite area and offsite improvement
along SE 2nd Place. The offsite frontage improvement along 156 th Avenue SE and some
uncollectable bypassed areas in SE 2nd Place, as discussed in Section 1 of this report,
are counted as bypassed target areas Per RSWDM Section 1.2.3.2.E. To mitigate the
bypassed target areas, the existing asphalt pavement form the center line of SE 2 nd Place
to the new south curb line of the SE 2 nd Place along the frontage of the site is also routed
to the onsite detention vault for flow control treatment as a mitigation trade per RSWDM
Section 1.2.3.2.G.
Since total new plus replaced pollution generating impervious area is less than 5,000
square feet, water quality treatment facility is not required per the Surface area
Exemption in Section 1.2.8 of the 2017 RSWDM. The proposed detention vault
provides 1’ dead storage and 0.5’ sediment storage which provides enough sediment
control.
See Section 2 of this report regarding special requirements, the only special
requirement applicable to this site is special requirement 1.3.4 for source control.
Dumpsters and recycle bins will be stored in the garages of each houses. Since the site
is not a high use site, oil control is not required.
The new onsite conveyance system is designed per chapter 4 of the 2017 Renton
SWDM to convey the 25-year peak with 6 inches of free board and the 100-year peak
flows.
Soil amendment as per rswdm C 2.13 shall be done
with the single family building permits.
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Part D Flow Control System
Apply the Flood Problem Flow Control Standard which matches the flow duration of
predeveloped rates for forested (historical) site conditions over the range of flows
extending from 50% of 2-year up to the full 50-year flow AND matches peaks for the 2,
10, and 100-year return periods.
Offsite frontage improvement along 156th Avenue SE
This is an existing developed street Right of way.
Total disturbed area = 0.059 acres (this area will be collected and conveyed to the
existing storm drainage system that runs along the east side of 156th Avenue SE and
bypass the onsite detention vault)
Total new and replaced impervious area = 0.029 acres
Total pervious area = 0.03 acres (till grass, group C)
Offsite frontage improvement along SE 2nd Place
On-site BMP feasibility study per Section 1.2.9.3:
Full dispersion is not feasible because the Right of way of SE 2 nd Place is a developed
street and no native growth forest flow path is available. According to the Geotechnical
report prepared by Cobalt Geosciences, updated April 24, 2017, ground water seepage
was observed at a depth of 2.5 feet below grade in the two Pilot infiltration test pits and
infiltration rates were less than 0.1 inch/hour. Full infiltration, limited infiltration,
Bioretention and permeable pavement are not feasible for this project.
Basic dispersion for the 5’ wide sidewalk along the frontage of the site is feasible by
using the 8’ wide landscape strip between the sidewalk and the curb and gutter.
Longitudinal slope along the curb and gutter is approximately 6%, cross slope of the
sidewalk is 2%, slope along the flow direction is approximately 6.3% (less than 15%).
Length of the 5’ wide sidewalk (less than 10’) along flow direction is approximately 16’
(less than 20’) and length of vegetated flow path in the 8’ wide landscape strip along
flow direction is approximately 25’ (longer than 10’). Requirements for use of sheet flow
dispersion for Basic dispersion per C2.4.5 can be met.
This is an existing developed street Right of way.
Total disturbed area = 0.234 acres
Total new and replaced impervious area = 0.145 acres
Total pervious area = 0.089 acres (till grass, group C)
Total bypassed area in SE 2nd Place R.O.W. = 0.040 acres (include 0.031 acres of
impervious area and 0.009 acres of pervious area, till grass)
Total bypassed area in 156th Avenue SE = 0.059 acres
Total offsite bypassed area = 0.099 acres
Traded non-target impervious area in SE 2nd Place collected and treated by the onsite
detention vault = 0.110 acres. > 0.099 acres, o.k. (See Part A)
Before applying On-site BMP credits:
Total drainage area from SE 2nd Place to onsite detention vault = 0.304 acres
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Total offsite impervious area to onsite detention vault = 0.224 acres
Total offsite pervious area to onsite detention vault = 0.08 acres
Total sidewalk treated by basic dispersion = 0.05 acres
Credited as 90% impervious area, 10% grass. Counted as 0.045 acres of impervious
area and 0.005 acres of grass.
After applying On-site BMP credits:
Total drainage area from SE 2nd Place to onsite detention vault = 0.304 acres
Total offsite impervious area to onsite detention vault = 0.224 – 0.005 = 0.219
acres
Total offsite pervious area to onsite detention vault = 0.08 + 0.005 = 0.085 acres
Onsite improvement
On-site BMPs:
Average lot size of this project is approximately 10,900 square feet, Small lot BMP
requirements per 2017 Renton SWDM Section 1.2.9.2.1 apply to this project. BMPs must
be implemented, at minimum, for an impervious area equal to at least 10% of the site/lot
for site/lot size up to 11,000 square feet and at least 20% of the site/lot for site/lot size
between 11,000 and 22,000 square feet.
The feasibility and applicability of full dispersion is studied first, the study found full
dispersion is not suitable for this site to fully disperse the new impervious areas and new
non-native pervious areas because long native flow path is not available. Full infiltration
is also not suitable for this site because onsite soil is till soil (Alderwood gravelly sandy
loam, 6 to 15% slopes, AgC) according to City of Renton Soils Map. According to the
Geotechnical report prepared by Cobalt Geosciences, updated April 24, 2017, ground
water seepage was observed at a depth of 2.5 feet below grade in the two Pilot infiltration
test pits and infiltration rates were less than 0.1 inch/hour. That means all infiltration
related BMPs (Full infiltration, limited infiltration, pervious pavement, perforated pipe
connection etc.) are not feasible for this project. Bioretention BMPs and rain gardens are
also not suitable for this project due to not enough vertical separation to ground water
level.
The following On-site BMPs are used:
1. Restricted footprint. Impervious area coverage in each lot will be restricted to
maximum 34% of their lot sizes for lots 1 through 5 and maximum 25% for lot 6.
2. Tree retention. 4 trees along the south property lines are preserved.
3. Basic dispersion for downspouts. Downspouts of the southeast corners of the
houses on lots 1 through 5 up to 700 square feet per house are treated by Basic
dispersion using splash blocks. Downspouts from the south half of the house on
lot 6 up to 1,400 square feet total are treated by Basic dispersion (20 linear feet of
gravel dispersal trench are used). Other downspouts are connected to onsite catch
basins and directly routed to the onsite detention vault.
For lots 1 through 5:
Average lot size 10,655 sf.
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10% of the lot size = 1,066 sf.
Total impervious area in each lot is restricted to 3,600 sf.
Total impervious area treated by Restricted foot print = 4,000 – 3,600 = 400 sf.
Total impervious area treated by Basic dispersion for downspouts = 700 sf.
Total impervious area treated by On-site BMPs = 1,100 sf. > 1,066 sf., o.k.
For lot 6:
Lot size = 12,019 sf.
20% of the lot size = 2,404 sf.
Total impervious area in this lot is restricted to 2,996 sf.
Total impervious area treated by Restricted foot print = 4,000 – 2,996 = 1,004 sf.
Total impervious area treated by Basic dispersion for downspouts = 1,400 sf.
Total impervious area treated by On-site BMPs = 2,404 sf., o.k.
Total onsite area = 1.666 acres
Total impervious area = 22,553 sf. = 0.518 acres (before applying On-site BMP credits)
Total impervious area treated by Basic dispersion of downspouts = 7* 700
= 4,900 sf. (credited as 90% impervious area, 10% grass)
For lots 3 through 6, dispersed flow from the downspouts (southeast down spouts of lots
3 through 5 and two south downspouts of lot 6) and runoff from the back yards of these
lots are collected by a yard drain located at the southwest corner of lot 3 and be routed
to the onsite detention vault. For lots 1 and 2, dispersed flows from their southeast
downspouts and runoff from their back yards sheet flow to the Storm Drain Tract and
are collected by a catch basin located near the southwest corner of the onsite detention
vault and then be directly routed to a new catch basin located at the SE 2 nd Place
bypassing the onsite detention vault.
After applying the On-site BMP credits, onsite drainage area draining to the
detention vault = 1.408 acres
Impervious area = 22,553 – 4,900 + (5 * 700) * 0.9 = 20,803 sf. = 0.478 acres
Pervious area = 1.408 – 0.478 = 0.93 acres (till grass, group C soil)
Onsite bypassed area = 0.258 acres
Impervious area = 2 * 700 * 0.9 = 1,260 sf. = 0.029 acres
Pervious area = 0.258 – 0.029 = 0.229 acres (till grass, group C soil)
Flow control facility:
A detention vault is used to provide the required Flood Problem Flow Control standard
(forest existing condition). 2012 WWHM method with 15-minute time step is used to
size the detention vault.
The proposed detention vault (87’ long x 36’ wide x 7’ live storage) meets all the
requirements for Flood Problem Flow Control standard (Forest existing site condition).
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Offsite 156TH Avenue SE network #4 to existing catch basin:
Network #4 collects and conveys runoff from west half of 156th Avenue SE to the existing
12” storm system that runs along the east side of the street.
Total drainage area = 0.160 acres.
Total impervious area = 0.134acres (C = 0.9)
Total pervious area = 0.026 acres (till grass, C = 0.25)
Q25y = C * IR * A = (0.90 * 0.134 + 0.25 * 0.026) * 2.734 = 0.35 cfs
Q100y = C * IR * A = (0.90 * 0.134 + 0.25 * 0.026) * 3.194 = 0.41 cfs
BACKWATER COMPUTER PROGRAM FOR PIPES
Pipe data from file:N4.bwp
Surcharge condition at intermediate junctions
Tailwater Elevation:455.28 feet
Discharge Range:0.35 to 0.41 Step of 0.06 [cfs]
Overflow Elevation:457.2 feet
Weir:NONE
Upstream Velocity:1. feet/sec
PIPE NO. 1: 36 LF - 12"CP @ 2.00% OUTLET: 454.18 INLET: 454.89 INTYP: 5
Q(CFS) HW(FT) HW ELEV. * N-FAC DC DN TW DO DE HWO HWI
*******************************************************************************
0.35 0.35 455.25 * 0.012 0.25 0.18 1.00 1.00 0.28 0.35 0.31
0.41 0.39 455.29 * 0.012 0.27 0.19 1.00 1.00 0.28 0.39 0.34
The offsite storm 156TH Avenue SE network #4 has the capacity to contain the 25-year
peak flow with minimum 6” of free board at all structures and has the capacity to convey
the 100-year peak flow without overtopping at any structures.
Onsite Bypass network #5 to CB#1 at SE 2nd Place:
Network #5 collects and conveys runoff from the back yards of lot 1 and 2 to the CB#1 at
SE 2nd Place.
Total drainage area = 0.258 acres.
Total impervious area = 0.029acres (C = 0.9)
Total pervious area = 0.229 acres (till grass, C = 0.25)
Q25y = C * IR * A = (0.90 * 0.029 + 0.25 * 0.229) * 2.734 = 0.23 cfs
Q100y = C * IR * A = (0.90 * 0.029 + 0.25 * 0.229) * 3.194 = 0.27 cfs
BACKWATER COMPUTER PROGRAM FOR PIPES
Pipe data from file:N5.bwp
Surcharge condition at intermediate junctions
Tailwater Elevation:433.5 feet
Discharge Range:0.23 to 0.27 Step of 0.04 [cfs]
Overflow Elevation:437. feet
Weir:NONE
Upstream Velocity:1. feet/sec
PIPE NO. 1: 37 LF - 8"CP @ 1.00% OUTLET: 432.83 INLET: 433.20 INTYP: 5
JUNC NO. 1: OVERFLOW-EL: 444.50 BEND: 90 DEG DIA/WIDTH: 1.0 Q-RATIO: 0.00