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� :�: DEWITT 4 LOT SHORT PLAT
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� TECHNICAL INFORMATION REPORT
� 210 DUVALL AVENUE. RENTON, WA 98058
COR Short Plat Construction Permit# (U13001062)
AUGUST 19, 2013 �
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Mark&Tanya DeWitt
26379 SE 276TH ST
RAVENSDALE, WA 98051
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BY:
PREFERRED ENGINEERING, LLC
11627 SE 58T" STREET
BELLEVUE, WA 98006
(206) 501-5708
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Table of Contents �
TASK 1 THROUGH 5 IS THE PROJECT OVERVIEW AND LEVEL 1 OFF-SITE ANALYSIS
Tableof Contents..........................................................................................................................................2 �
TASK 1: DEFINING & MAPPING STUDY AREA:..............................................................................................3
OFFSITEANALYSIS: ................................................................................................................................5
TASK 2 : RESOURCE RFs1/IF�N........�:...............................................................................................................7
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T�SK�3: FIEID�IVSPE�TIOfV..!.......'.'..............................................................................................................13
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fASK 4: DRqINAGE SY�Y�IIIM�CRIPTION & PROBLEM DESCRIPTIONS....................................................14
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`D��stream Analysis:.........................................................................................................................21
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TASK 5: MITI�ATION OF EXISTING OR POTENTIAL PROBLEMS..................................................................25
APPENDIX .................................�-��---�-��---..................--�--....................._......--��----......---.................................26
CORE AND SPECIAL REQUIREMENTS ANALYSIS ..................................................................................27
HYDROLOGICAL KCRTS RESULTS.........................................................................................................35
CONVEYANCE ANALY515 BACKUP MODELING PRINTOUT and BACKGROUND INFORMATION ..........40
TIR Worksheet
Existing and Proposed Site Conditions Analysis Results Using KCRTS
Water Quality BMP—Bioswale Calculation
CONVEYANCE CALCULATIONS
AS-BUILTS
BASIN DELINEATION MAPPING
DOWNSTREAM ANALY515 MAPPING
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The following report provides the Level 1 Downstream Analysis and TIR report(hereafter also referred
to as the drainage report) required for final engineering design approval, as well as discussions
pertaining to the City of Renton Core and Special Requirements. The following report shall comply with
the City of Renton Amendment to the King County Surface Water Design Manual pub�ished February
2010. This project proposes more than 2,000 square feet of new impervious surface and will result in
more than 7,000 square feet or more of land disturbing activity. Therefore is subject to the Full
Drainage Review criteria and requires discussion of the eight core requirements in Section 1.2 and the
six special requirements in Section 1.3. In addition, the following Tasks 1 through Task 5 are required to
be discussed within the Level 1 Drainage Analysis.
TASK 1 : DEFINING & MAPPING STUDYAREA:
The proposed Dewitt 4 lot short plat development is located generally northeast of the intersection of
SE 2"d Place and Duvall Avenue SE in parcel#1523059021. More specifically the project is located at 210
Duvall Avenue SE in the City of Renton. (See Figure 1 map) The existing use of the 1.09 acre lot is as a
single family residence with mostly grass cover and blackberries. There is currently 0.057 acres present
of impervious area including an existing house and gravel driveway. The proposed plat is developing 4
single family lots within the 4 du/acre allowable land use area with the City requirement to construct
the frontage sidewalk,grass landscape strip with trees, and approximately 8+/-feet of asphalt
grind/overlay for installing the water main trenching area. All of the surrounding land uses surrounding
the proposed project lot are currently single family residential to the north,west and east. Along the
south frontage is SE 2"d Place, a guardrail, a roadside ditch on the south side of SE 2"d Place,
approximately 8 feet to 10 feet of berm and a steep slope that drains eventually into Maplewood Creek.
This creek eventually drains much further downstream into the Cedar River. The proposed development
will allow access from SE 2"d Place via a private access road that will end at a hammerhead. Frontage
improvements along SE 2"d Place is proposed to include landscaping, water main construction and
curb/gutter improvements. This drainage report will comply with the 2010 City of Renton Surface Water
Design Manual that amends the 2009 King County Surface Water Design Manual and the project will
submit a Covenant for the proposed drainage facilities.
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Figure 1;Vicinity Map
Project Site
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Figure 2:Aerial Map
Called SE 2nd
PL. in Renton
_4 _ Project Site '
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OFFSITE ANALYSIS:
Upstream Discussion: An upstream and downstream analysis is provided in the following sections.
Upstream areas are primarily from vegetated backyard grass runoff from the east to northeast. The
slopes of the upstream areas are generally flat to slightly sloped (less than 2%). Most of the potential
offsite runoff is from the east which is grassed or treed areas with roof runoff directed eastward to their
own street drainage system. A ditch currently exists fronting SE 2"d Place and conveys runoff from an
east to west direction toward the intersection of SE 2"d Place and Duvall Avenue SE. The basin divide for
this runoff is at the 144th Avenue SE and SE 2"d Place intersection which also has a portion of the 144`n
Avenue SE runoff. All upstream runoff is from streets, single family homes and
treed/landscaped/grassed areas with about half of the upstream area also directed to the south of SE
2"d place via culverts in order to enter the ditch system to the south of SE 2"d. The immediate
development to the east consists of 9 single family homes with a cul-de-sac on 139t'' Place SE. Their
drainage is tight lined to the SE 2"d Place which discharges into the existing frontage ditch located along
the proposed short plat SE 2"d Place frontage. (There does not appear to be any above ground existing
runoff treatment or flow control facilities upstream of this proposed plat.) In addition, there does not
appear to be any indications of past or present erosive processes on the existing site frontage or
upstream of the site. The ditch system taking runoff from the 9 homes is in very good, grassed condition
and mowed frequently without any indicatioiis of sediments deposited.
Little to no runoff from the northern property line is directed to the project site due to an existing single
family development draining towards Duvall Avenue SE and northwards to an existing storm pond
fronting NE 15t Street.
Downstreom Discussion:The downstream analysis is provided in more detail later in a table format and
shall extend approximately more than 1/4 mile downstream of the project site. This analysis includes a
qualitative evaluation of fish habitat, groundwater levels,groundwater quality, or other environmental
features that may potentially be impacted by the proposed project due to iYs proximity and project size.
A Level 1 analysis is provided for this project site that includes defining and mapping the study area
(Task 1), reviewing resources(Task 2), inspecting the study area (Task 3), describing the drainage system
and problems (Task 4) and proposing mitigation measures (Task 5}.
The study area aerial map (see Figure 2) is provided on page 4. A downstream analysis flow direction
and basin boundary limits figure is provided. Data was primarily collected from the City of Renton 6`n
floor Development Services library, Rentonwa.gov website, USDA(soils) maps and data, from the geo-
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technical engineering report,from field investigations, talking to neighbors and from the King County
IMAP database.
The following sections(Core Requirement#3 and #8)will be further evaluated and analyzed within this
report. The conveyance system was analyzed using the 25 year event Rational Method without any
runoff surcharging above the rim elevation. This plat, according to the 2010 City of Renton Surface
Water Design Manual Amendment, shall treat for the new PGIS along the access tract, infiltrate using
trench infiltration and MH infiltration as recommended by the geotechnical report provided for this
report.
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TASK 2 : RESOURCE REVIEW
Resources reviewed include use of Renton existing and potential flooding and erosion data, as builts and
discussions with one neighboring property owner. The following resource review includes any basin
plans(basin reconnaissance summary reports), FEMA maps, sensitive areas folios, USDA sols reports,
King County Soils Survey,wetland inventory maps, Renton erosion maps, Renton landslide maps, and
any Washington State Department of Ecology's latest Clean Water Act Section 303d list of polluted
waters.
• Basin Reconnaissance Summary Reports: There exists a downstream creek system that
empties into the Maplewood Creek and ultimately to the Cedar River. The downstream
system has a sediment pond located in the Maplewood Creek area that appears to receive
eroded sediments from the upstream sub-basin and creek.
• FEMA Maps: There are floodway or floodplain areas on the project site according to IMAP
or FEMA Maps.
• Renton Flow Control Application Map: The project site is within the Pre-deve�opment
Forested Conditions Flow Control area (for matching Proposed to Existing Conditions). The
runoff flows into Cedar River via the Maplewood Creek.
• Sensitive Areas Folios:
o Groundwater Protection Areas: The project area is within the City of Renton stream
flow source area.
o City of Renton Soils Survey Map: The City of Renton soils in the project area is
mostly AgD soils which is Alderwood gravelly sandy loam, 6 to 15 percent slopes.
The USDA textural type sc ' ' ' ' .' '
classification of type C soil
c Coal Mine Hazard: The project is not within the City of Renton Coal Mine Hazard
Area.
o Steep Slope Areas: The project site is not within any steep slope protection areas.
Steeps slopes are close by to the south and west of NE 2"d Street frontage road.
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o Landslide Flooding Areas: There exists a landslide flooding area to the south of NE
2"d Street and west of Duvall Avenue SE.
c Seismic Hazard Areas: There exists no seismic hazard area on the site, but there is a
seismic hazard area to the south of NE 2�d Street and west of Duvall Avenue SE.
o Erosion Hazard Area: There exists no erosion hazard area on the project site, but
there is an erosion hazard area to the south of NE 2"d Street and west of Duvall
Avenue SE on the site.
o Wetland Areas: There is no SAO wetland in the project area.
o Liquidification Area: See Geotechnical report.
o Drainage Complaints: There have been drainage complaints upstream of the project
area or within the project area. Runoff primarily drains into Maplewood Creek.
General5oils lnformation:
The project site is primarily AgC or Alderwood gravelly sandy loam with up to 6 to 15 percent slopes
according to the USDA—NRCS soils report. AgC soils typically have very low water capacities that are
moderately well drained (about 2.5 inches) with very low to moderate►y low capacity of iYs most limiting
layer to trasmit water. Typically a gravelly ashy sandy loam layer is present from 0 to 1z inches. Then
from 12 to 60 inches a very gravelly sandy loam is present. A soils report was conducted by Dr. U Shin a
geotechnical engineer from SSEE, Inc. Dr. Shin determined that the infiltration rate is 1.4 inches per
hour that includes within the rate a factor of safety of S. Therefore individual lot BMPs can employ
infiltration trenches for roof runoff on lots 1 and 2. The soils report is provided as part of the
preliminary plat submittal package. Also the site is located in Renton's stream flow resource area
according to the Renton Groundwater Protection Map so infiltration or rain-gardens are allowed for
clean roof runoff purposes. Runoff from the driveway and proposed private road shall be collected and
routed to the proposed bio-swale.
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Green = Forested Conditions as it's matching pre-development land-use
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City of Renton GIS: Groundwater Protection Map: Part of Stream-flow Source A a
Project Site
- 12 -
TASK 3: FIELD INSPECTION
A field visit was conducted on July 13, 2012 at 3:00 pm and again on August 6, 2012. The weather was in
the high 50s to low 60s and cloudy on July 13th. Rain occurred earlier in the day with thunderstorms
overnight and a downpour occurring in the evening. Soils onsite were moist, but no runoff was present
in the ditch system. The downstream CB at Duvall Avenue SE and SE 2"d Place had some trickle of flow
entering the catch basin and most likely was discharging to the bluff or down to the creek bottom. The
downstream runoff pathway was attempted to be walked but a large amount of blackberries and brush
as well as very steep slope on the bluff prevented safe traverse through the thick brush. It is not known
if runoff discharges on top of the slope or to the bottom of the creek since the slope is not accessible. It
is assumed by researched via City records that no discharge pipe exists downstream to the creek, but a
top of bluff discharge most likely occurs from the City system. Downstream of the creek are two ponds
that appear to collect gravels, sands and silts.
- 13 -
TASK 4: DRAINAGE SYSTEM DESCRIPTION & PROBLEM
DESCRIPTIONS
Existin� Draina�e System Description:
The existing drainage from the Dewitt site currently sheet flows southward to the SE 2"d Place frontage
ditch. The ditch is currently grass lined and in good condition without any indications of sediments
deposited or oil leaked into the grassy swale. Most of the existing Dewitt landuse is from existing tall
prairie grasses, weeds/blackberries and a single family house. There exists no existing treatment facility
on the current Dewitt site. The upstream basin boundary is approximately 100 feet east of the 139tn
Place SE and SE 2"d Place intersection. The street runoff to the east of this basin divide appears to drain
eastward towards the water quality pond on SE 2"d Place. A mixture of trees,grass and single family
homes from the 139th Place SE cul de sac currently discharges into this ditch system. The ditch drains
through a culvert and ends up into two existing catch basins located at the northeast corner of Duvall
Avenue and SE 2"d Place.
Proposed Drainage Svstem Description:
The proposed drainage system from the site shall not affect any offsite system. Any offsite system's
drainage shall maintain it's current flowpath and will not be diverted by this proposed development.
The on-site storm management system proposes to infiltrate the clean roof, porch, sidewalk and
driveway runoff using individual lot trench infiltration systems for lots 1, 2 and 3 in the backyard. Lot 4
shall utilize the infiltration MH option. The runoff from each lot's driveway(PGIS) and the new street
runoff shall discharge to a proposed tight lined storm pipe system along the new private access road
that will route flows towards the eastern end of the bio-swale. The bio-swale shall be privately
maintained and be a wet bio swale type due to the flat grades along SE 2"d Place at this location and the
high receiving pipe invert elevation downstream.
- 14-
Upstream Analvsis:
The upstream drainage basin area is presently draining past the project site's frontage from the SE 2"a
Place roadway and the 139'h Place SE cul-de-sac area which is a small development (81ots)to the east
along with trees (called the, grass and roadway runoff. There is not a significant upstream drainage
basin draining towards SE 2"d Place and the ditch fronting the DeWitt property. There is potentially a
drainage outfall intercepting part of SE 2"d Place runoff and conveying towards the south side of the
road. The south side of SE 2"d Place discharges directly into the south grassed ditch. (See pictures in the
following figures.)
There does not appear to be much or any indications of erosion or heavy runoff coming from upstream
to the onsite ditch system. It is a shallow,grassy ditch system that is frequently mowed and maintained
as shown in the following figures. The SE 2"d Place centerline is delineated as a basin boundary line. The
eastern border basin line is approximately 100 feet east of the SE 2"d Place and 139th Place SE
intersection.
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- 15-
FIGURE 1: AT DUVALL AVENUE SE &SE 2ND PLACE BEND
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FIGURE 2: LOOKING NORTH FROM SE 2N0 PLACE TO PROJECT SITE.
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- 16-
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- 18-
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- 19 -
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Downstream Analysis:
A downstream walk was conducted from the project site, from the natural drainage discharge point
westward towards the bend at the intersection of SE 2"d Place and Duvall Avenue SE. Two inlet catch
basins (both type 1s) are present at this intersection and it appears to discharge over the bluff or to the
toe of the steep slope (or to the creek). It is unknown if the runoff on the steep slope is piped or if it is
overland flow. There appears to be a recent slide/scarring west of Duvall Avenue SE that is eroding the
top of the slope. This runoff is channelized within a creek system called the Maplewood Creek. There
are two creek sediment ponds prior to the system entering the Maplewood Golf Course area next to the
Maplewood Treatment Plant.
A% mile detailed downstream analysis is provided in the following page along with the corresponding
map that is provided in the Appendix. This qualitative analysis pr�vides condition assessments
downstream as well as structure details, downstream conditions/assessments and distances. The
downstream analysis walk was examined from the top of the hillside and at the bottom by walking the
creek side via accessing the lower Creek through Maplewood.
- 21 -
% Mile Downstream Qualitati�e Analysis
ID STRUCTURE TYPE CONDITION NOTES, Slopes, Sizes Distance
D.S.
1 Grass roadside ditch on the north side OK structurally, Good condition. No signs of 0 ft.
of SE 2"d Place needs cleaning. erosion in the ditch. I
Approximately less than
1.0%slope.
2 Two type 1 CBs with inlet grates in OK The type 1 inlet sump area 130 feet DS
asphalt. 12"CMP pipes are directed has sediment filled to the
into the CBs. These rivo CBs are im-ert of the inlet pipes.
�vithin 10 feet of each other. (At Outlet pipe is not��sible.
intersection of SE 2"d Place and Inspection is impossible due
Duvall Avenue SE) to filled sumps full of
organic and silty debris
mostly. Pipe slopes into the
structure,as measured using
a grade scope, is less than
1%to 1%.
3 Base of steep slope. Top of slope is OK Stream in this area appears 300 feet DS
100 feet high and is very steep. to be in okay condition,but
there are signs of past
erosion on the slopes and a
scarp is apparent west of
' Duvall Avenue SE. Slope of
creek is approximately 5.3°�0.
4 Stream continues for approximately Full of sediment. Slope upstream of the 1630 feet DS
1320 feet downstream to the next structure is 5%or greater in of discharge
main structure which is a sediment the creek. Erosion upstream point.
pond. Sediment pond is`full', is occurring and evident in
this sediment pond structure.
Downstream of the 1,630 feet is another sediment pond located next to Renton's Maplewood Golf
Course. The lower sediment pond has sediment in the pond also and is partially full. This sediment
pond also has a fish ladder present. The project site area is less than 15%of the overall basin area at the
% mile downstream discharge point,therefore there is no reason for a more detailed analysis of Tasks 3,
4 and 5 per Section 2-10 of the City of Renton Surface Water Design Manual.
The existing drainage system from the single family site currently infiltrates into the ground or surface
discharges into the SE 2"d Place grass ditch. Runoff from the site is not significant and will not cause
- 22 -
additional problems downstream of the discharge point. It is recommended by the geotechnical
engineer to utilize infiltration outside of 200 feet of the top of steep bluff located to the south of SE 2nd
Place.
- 23 -
f
Existing Conditions:
The existing site conditions within the project site boundary is presently grassed, has a single family
home on it or used by blackberries. Most of the site (approximately 85%or more) is grassed or
blackberried. The perimeter of the site is vegetated with mostly blackberries. The project site slopes
are approximately 0 to 4�a without any drastic grade breaks present. The site may have in the past been
used as a dirt bike area. The frontage roadside ditch is small and appears to convey some upstream
areas with mostly residential and street runoff, but not too much upstream area is present since it is less
than 2.6 acres. The type 1 CBs located at the intersection of Duvall Avenue SE and SE 2"d Place to the
southwest of the project site collects runoff from Duvall and SE 2"d Street's north side of road ditch. The
southern half street of SE 2"d Place flows into it's own road side ditch.
Proposed Conditions:
The project site proposes to develop 4 single family residences. The existing residence will be
demolished and the land will be regraded except near the infiltration areas closest to the east property
line. The project proposes to improve the SE 2"d Place frontage with curb& gutter, sidewalk and a
landscaping strip. A new private access roadway will allow the 4 lots to enter from SE 2"d Place and
terminate as a hammerhead. It is anticipated that runoff will be intercepted from the upstream areas of
SE 2"d Place and will be conveyed separately around the proposed 4 lot short plat's wet bio-swale that is
used to treat on-site PGIS runoff. The project proposes to utilize infiltration trenches for the three north
lots and infiltration MHs for the south lot#4 that will place the structures to the north east area of the
lot. Driveways will first be routed to raingardens for water quality treatment prior to discharging to
each lots' individual infiltration facility.
The proposed drainage system models the fully forested existing peak rate runoff(with forested
conditions applied) and demonstrates that the proposed on-site areas do not exceed more than 0.1 cfs
of runoff increase for the 100 year probability of return by using trench infiltration or infiltration MHs
for each lot.
-24-
TASK 5: MITIGATION OF EXISTING OR POTENTIAL
PROBLEMS
The proposed development will have little or no long term impact to the basin or downstream
drainage system. The proposed infiltration facilities to mitigate to fully forested conditions will
actually decrease the amount of runoff from the existing site. The use of the onsite BMPs for
flow control exemption compliance, per the 2010 Renton Surface Water Design Manual, is
complied with for flow control.
Since the project proposes to increase PGIS by more than 5,000 sq-ft, then a wet bio-swale shall
treat runoff prior to discharge into the existing discharge location to minimize water quality
impacts.
Potential temporary problems may occur if the site is left opened up during heavy storm
events, so erosion and sediment control BMPs must be used during construction if continuous
or high precipitations are expected. A temporary erosion and sedimentation control plan will
be created during the final engineering design phase to minimize transport of sediment laden
runoff to the downstream system. During construction the use of stabilized entrances, CB
inserts to protect downstream inlets and slope/soils erosion BMPs (silt fence, seeding, straw
waddles, check dams, plastic covering on stockpiles, etc.) will be utilized to reduce impacts to
the downstream storm system and adjacent properties.
- 25-
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CORE AND SPECIAL REQUIREMENTS ANALYSIS
Core Requirement#1: Discharge at the Natural Location
This project proposes to discharge to the existing discharge location to the southwest of the parcel. The
existing runoff drains south to southwest and along the SE 2"d Place roadside ditch prior to entering the
two CBs at SE 2"d Place and Duvall Avenue SE. All proposed runoff pathways shall be the same as the
existing runoff pathways. No adverse impacts are anticipated from this development since no diversion
of flows is being proposed and flow increases from the lot is expected to be minimal (runoff will not
exceed 0.1 cfs of increase for the 100 year peak flowrate using Renton's Peak Flow Control Standard for
this project area).
Core Requirement#2: Offsite Analysis
An offsite analysis is provided in this report that contains the offsite, upstream and downstream
analyses(See Task 1 page 5 and Task#4 page 14). This report pro�ides a Level 1 downstream analysis as
required by the Renton Storm-water Manual Section 1.2.2.1 and is contained within Task 1 through Task
5.
Core Requirement#3: Flo�� Control
The project site is proposing over 2,000 square feet of new or replaced impervious surface and is subject
to the area specific flow control facility requirement. The project area is within the Forested Conditions
Flow Control Standard that mimics forested site conditions as directed by the City of Renton Flow
Control Application Map contained in the February 2010 Renton Surface Water Design Manual
Amendment Reference 11 Maps.
Using KCRTS continuous modeling software,this project was mimic'd to match the forested site
conditions in order to extract the 100 year return events from the proposed development. The 100 year
peak rates for the proposed development would be compared against the 100 year existing `forested'
conditions runoff rate. Per the Forested Flow Control Standard with matching existing conditions per
Renton Surface Water Design Manual Section 1.2, the project proposes to also utilize full infiltration
trenches for lots 1, 2 and 3. Infiltration is possible according to the soils report provided with this plat by
SSEE, Inc. for the sandy loam soils. Lot 4 proposes to utilize the infiltration MHs or 48-inch diameter
type infiltration in order to remain outside the 200 feet steep slope buffer as recommended by the geo-
technical engineer.
The modeling of the impervious areas was credited for lots 1, 2, 3 and 4. Rooftops, driveways and
sidewalks are maximized for each lot with 55%allowable impervious area for each lot in this zoning.
Preliminary soils information from the soils engineer specifies that the sandy material has a 1.4 in/hr
infiltration rate after applying a very conservative safety factor on the infiltration capacity of the site
soils of 5.0(or S.F. = 5), the rate used for any modeling should be 1.4in/hour.
- 27-
Final design of each individual trench BMP shall follow the 2009 King County Stormwater Design Manual
Section C.2.2.5. In general,either infiltration trenches or ground surface depressions with full
infiltration shall be designed during final engineering with at least 60 cubic feet of storm-water per
1,000 square feet of impervious surface served. For example, if 3,000 square feet of house is proposed
as the footprint,then 180 cubic feet of volume will be provided.
-28-
The following is the existing and proposed land-use conditions and it's areas used in the KCRTS
modeling:
De`'�riti Renton 4 Lot
Upstream Contributing Ditch Area to be routed thru bio-swale
Total Area = 64,469.00 sq-ft 1.479 ac
Impervious Area= 22,564.20 sq-ft 0.518 ac
Treed Areas= 20,952.00 sq-ft 0.480 ac
Grass Areas= 20,952.00 sq ft 0.480 ac
EXISTING PROIECT BASIN:
Onsite Area(assume all forested)= 47,480.40 sq-ft 1.089 ac
Offsite ROW(assume all forested)= 1960.3 sq-ft 0.045 ac
PROPOSED PROIECT BASIN(without Onsite BMPs):
Impervious(Onsite Roads)= 5,772.80 sq-ft 0.132 ac �Requires WQ Treatment)
Impervious(Onsite House/dwy"/sw�= 18,223.00 sq-ft 0.418 ac
Pervious(Onsite Grass)= 23,484.60 sq-ft 0.539 ac
Impervious{Offsite new dwy ramp)= 302 sq-ft 0.007 ac
Impervious(Offsite new s-w) 690 sq-ft 0.016 ac
Pervious(Offsite Grass)= 968 sq-ft 0.022 ac
*(Note 1 New dwy has reduction in sq-ft due to reduction in driveway configuration)
*(Note2 Offsite water trenching area not required to be included into overall project area.)
CREllI1'S C.aI.Ct?LATIONS:
', MINUS INFILTRATION for LOTS(#i,#2,#3 and q4):
j TOTAL IMPERVIOUS DEDUCTED= 18,223.00 sq-ft 0.418 ac
----- —�__.,� ----- _ . __----------------
_.._. _____._ __ .
�
NOTE: Max.permissible lot SF of 55%allowable,but project is proposing less impervious for each onsite lot.
onsite bmps include routing all driveway runoff towards rain-garden in backyard,collecting roof runoff and s/w towards infiltration BMPs.
PROPOSED(MITIGATED USING ONSITE BMPS)BASIN SUMMARY:
IMPERVIOUS(Onsite&Offsite) 6,764.80 sq-ft 0.155 a:
PERVIOUS(GRASS) 24,452.90 sq-ft 0561 a.
- 29 -
EXISTING CONDITIONS PEAK FLOW RATE RESULTS
RETURN PERIOD PEAKS(CFS)
1Q0 0.092
• Note: The existing site area landuse was modeled as fully forested per page 29.
DEVELOPED CONDITIONS PEAK FLOW RESULTS
RETURN PER/0D PEAKS(CFS)
100 0.192
• Note: Offsite areas including proposed sidewalk and driveway areas were included in the
impervious areas and grass/tree planter area was included in the pervious area calculations to
determine post BMP flow rates.
Difference in Existing 100 year to Developed 100 year is 0.1 cfs of increased flow after utilizing BMPs
for the 4 houses that includes 3 infiltration trenches and one infiltration MH type drywell. The drywell
type structure is used for lot 4 based upon keeping any full infiltration facility more than 200 feet
away from the steep slope on the south side of SE 2"d Place as recommended by the geotechnical
Iengineer. Rain gardens are used for all four IoYs driveway treatment prior to discharge into the
infiltration facilities per the COR aquifer protection plan requirements.
- 30-
Since the project discharge area will not generate more than 0.1 cfs of flow increase from the existing
site conditions,the project is exempt from a flow control facility as allowed by the City of Renton storm
water design manual. (See 2010 Renton Surface Water Design Manual Section 1.2.A.) As a matter of
fact the project will decrease the 100 year return flow rate since the runoff being mimic'd is the fully
forested condition, which is not today's exi5ting conditions for the property(since there is mostly grass
and weeds). This runoff will not cause additional adverse impact to any critical area, any flooding
problem or exacerbate any severe erosion problems downstream.
Core Requirement#4: Conveyance System
This project will safely convey runoff from the site using 12-inch or 18-inch cpep and/or DI pipe which is
an acceptable storm pipe by the City of Renton. The pipe system will be on SE 2"d Place and connect
into the existing grassed ditch to the west. From the proposed bio-swale, a discharge pipe will connect
to the existing CB located on SE 2"d Place and Duvall Avenue SE. From there,the system flows
southward downhill to Maplewood Creek and ultimately to the Cedar River.
The modeled system will be refined in this section of the Core Requirements with the proposed invert
elevations tor the designed catch basin and pipe system. It is anticipated that normal 12-inch and 18-
inch storm pipe systems will work well for this small site since minimal upstream areas enter or pass
through the site. The project analyzed the 25 year storm event using the Rational Method, a
conservative runoff method,to check for any potential pipe surcharges and if the spec'd out pipe is
adequately sized. The project is adequately sized for the 25 year storm events. The 100 year does
surcharge, but the downhill conveyance will be to the bioswale so no properties will be adversely
affected. The analyses results are provided in the Appendix.
Core Requirement#5: Erosion and Sediment Control
The project proposes to practically utilize erosion and sediment control BMPs to the extent that the site
can contain it's own erosion and sediments from discharging downstream/offsite. The site is more than
1 acres so will require a Department of Ecology storm-water discharge permit with a SWPPP and
monitoring during construction. The SWPPP and monitoring is developed by a Certified Erosion and
Sediment Control Lead/ESC supervisor.
The erosion control BMPs that will be utilized include use of silt fencing, downstream catch basin
inserts/protection, straw mats, straw bales, a construction entrance, debris pile coverings, and water
trucks. ESC BMPS that will be used during final engineering design include clearing limits,cover
measures, perimeter protection,traffic stabilization, sediment retention, surface water collection,
dewatering control and dust control using water tanks.
- 31 -
Core Requirement#6: Maintenance and Operation
Any future BMPs will be designed in accordance with current City of Renton standards and/or KCSWDM
criteria. The O&M of the property will be the responsibility of the property/developer as stipulated
within the Renton Storm-water Manual 1.2.6. Maintenance responsibilities will be clearly defined
during final engineering design for the Final TIR and will coordinate what facilities and who will be
responsible for the built system and for how long. Typically the developer will be responsible for
maintaining the system until the City takes over the facility after 2 years of performance. It is
understood that the private facility may have inspections by the City and deficiencies must be fixed by
whoever is responsible for maintenance.
Core Requirement#7: Financial Guarantees and Liabilities
The project will post a bond during/after final engineering in accordance with RMC 4-6-030J via an
assignment of funds or certified check. In addition, the applicant shall maintain liability insurance prior
to a permit issuance for construction to the amounts of$1,000,000 for commercial general liability
insurance with a $2,000,000 aggregate. Copies of this insurance policy shall be provided to the City
during/after final engineering. In addition, the applicant will furnish a Construction Maintenance Bond
for any new public improvements to be deeded to the City for 2 years. The bond calculation worksheet
will be furnished during final engineering submittal.
The owner of the plat has initiated and will finalize the development of the stormwater facilities
covenant document. This covenant will be recorded prior to the plat being approved.
Core Requirement#8: Water Qualit��
Per the 2010 City of Renton Surface Water Design Manual 1.2.8, the project proposes to add more than
5,000 square feet of new PGIS and is proposing to install a bio-swale fronting SE 2"d Place. (2009 Renton
Surface Water Design Manual, 1.2.8, page 1-61)
The total amount of new pollution generating vehicular surface is slightly over 6,075 square feet with
runoff to be treated for basic water quality by utilizing the wet bio-swale design with a high flow bypass
structure routing the full 2 year, 24 hr flows to the bioswale and high flows are bypassed to the existing
grassy ditch. A 4.1-feet bottom width is provided with the bioswale,with a slope equal to 1.O�o that is
allowed per the 2009 King County Surface Water Design Manual for a wet bioswale type has been
designed. The 100 year upstream runoff of 0.38 cfs is also accommodated within the bioswale with the
swale upsized. The water quality calculation is provided in the Appendix. The wet bioswale is designed
as a continuous inflow bioswale due to the lack of available vertical elevation from the low elevation on
the proposed roadway and the high elevation �f the receiving ditch to the southwest. Therefore no
room exists to install a bypass MH at the low elevation so the bioswale is a continous inflow bioswale
with hardy wet plants. The bioswale allows the 100 year event to pass through without approaching the
3.0 fps velocity threshold for the 100 year event.
- 32 -
Bioswale calculations are provided within the Appendix.
The driveways for each lot will be treated thru designed bottom rain gardens as dictated by the use of
WWHMv3. The rain gardens are located behind the lots in existing ground areas not subject to
compaction during construction. The required bottom areas for each lot is provided for in the Appendix.
- 33 -
Special Requirement#1: Other Adopted Area Specific Requirements
The proposed project's drainage basin is within the Lake Washington WRIA 8—Cedar Sammamish
Watershed that contains Lake Washington also. The City of Renton has adopted the WRIA 8 within it's
Ordinance for protection Salmon and other wildlife draining to Lake Washington. Any and all
endangered species must comply with the WRIA 8 plan for this basin,which this project is within.
' The project is located upstream of the two Maplewood Creek sediment ponds. There does not exist any
in City basin plans beyond the Cedar River WRIA 8 Watershed plan that was de�eloped by the County.
Special Requirement#2: Flood Hazard Area Delineation
There exists no flood hazards within the project area or immediately downstream of this discharge
location.
Special Requirement#3: Flood Protection Facilities
There exists no known flood protection facilities in this area, upstream, or downstream.
Special Requirement#4: Source Control
This project shall not contain any stored materials which may contaminate the land and runoff that may
infiltrate into the aquifer. No short or long term gasing trucks,containers, or other flammable or toxic
chemicals will be stored on-site without proper containment methodologies.
Special Requirement#5: Oil Control
Oil controt is not necessary for this development since traffic through the intersection of SE 2"d Place
and Duvall Avenue SE does not exceed 1,000 ADT or more.
Special Requirement#6: Aquifer Protection Area
The proposed project is located in Renton's Resource Stream Flow per the City of Renton Aquifer
Protection Mapping. Since the project is within the City's Zone 2 APA, per RMC 4-6-030E,the drainage
plan submittals and methods of analysis for drainage into, out and through the property has it's final
engineering TIR prepared and stamped by a professional civil engineer registered in the state of
Washington. The drainage plans conform to Ordinance 4367 and Ordinance 4851.
-34-
HYDROLOGICAL KCRTS RESULTS
The following KCRTS output files are provided as backup information that supports the conclusion
reached in Core Requirement#3:
KCRTS Program...File Directory:
C:\KC_SWDM\KC_DATA\dewitt8.exc
[C] CREATE a new Time Series
ST
1.13 0.00 0.000000 Till Forest
0.00 0.00 0.000000 Till Pasture
0.00 0.00 0.000000 Till Grass
0.00 0.00 0.000000 Outwash Forest
0.00 0.00 0.000000 Outwash Pasture
0.00 0.00 0.000000 Outwash Grass
0.00 0.00 0.000000 Wetland
0.00 0.00 0.000000 Impervious
dewex8.tsf
T
1.00000
T
[T] Enter the Analysis TOOLS ModulE
[P] Compute PEAKS and Flow Freque�����e;
dewex8.tsf
dewex8.out
(R] RETURN to Previous Menu
[C] CREATE a new Time Series
ST
0.00 0.00 0.000000 Till Forest
0.00 0.00 0.000000 Till Pasture
0.56 0.00 0.000000 Till Grass
0.00 0.00 0.000000 Outwash Forest
0.00 0.00 0.000000 Outwash Pasture
0.00 0.00 0.000000 Outwash Grass
0.00 0.00 0.000000 Wetland
0.16 0.00 0.000000 Impervious
dewpr8.tsf
T
1.00000
T
[T] Enter the Analysis TOOLS Module
[P� Compute PEAKS and Flow Frequencies
dewpr8.tsf
dewpr8.out
[R] RETURN to Previous Menu
[X] eXit KCRTS Program
-35-
FROM: DEWITT8.OUT FILE
KCRTS Command
� CREATE a new Time Series
------------------------
Production of Runoff Time Series
Project Location : Sea-Tac
Computing Series : dewex8.tsf
Regional Scale Factor: 1.00
Data Type : Reduced
Creating Hourly Time Series File
Loading Time Series File:C:\KC_SWDM\KC_DATA\STTF60R.rnf :
Till Forest 1.13 acres
--------------
Total Area : 1.13 acres
Peak Discharge: 0.091 CFS at 9:00 on Jan 9 in Year 8
Storing Time Series File:dewex8.tsf :
Time Series Computed
KCRTS Command
Enter the Analysis TOOLS Module
-------------------------------
Analysis Tools Command
----------------------
Compute PEAKS and Flow Frequencies
----------------------------------
Loading Stage/Discharge curve:dewex8.tsf :
Flow Frequency Analysis
--------------------------------------------------------
Time Series File:dewex8.tsf
Project Location:Sea-Tac
Frequencies & Peaks saved t� File:dewex8.out :
Analysis Tools Command
----------------------
RETURN to Previous Menu
-----------------------
KCRTS Command
CREATE a new Time Series
------------------------
Production of Runoff Time Series
Project Location : Sea-Tac
- 36-
Computing Series : dewpr8.tsf
Regional Scale Factor : 1.00
Data Type : Reduced
Creating Hourly Time Series File
Loading Time Series File:C:\KC_SWDM\KC_DATA\STTG60R.rnf :
Till Grass 0.56 acres
Loading Time Series File:C:\KC_SWDM\KC_DATA\STEl60R.rnf :
Impervious 0.16 acres
--------------
Total Area : 0.72 acres
Peak Discharge: 0.192 CFS at 6:00 on Jan 9 in Year 8
Storing Time Series File:dewpr8.tsf :
Time Series Computed
KCRTS Command
Enter the Analysis TOOLS Module
-------------------------------
Analysis Tools Command
----------------------
Compute PEAKS and Flow Frequencies
----------------------------------
Loading Stage/Discharge curve:dewpr8.tsf :
Flow Frequency Analysis
--------------------------------------------------------
Time Series File:dewpr8.tsf
Project Location:Sea-Tac
Frequencies & Peaks saved to File:dewpr8.out :
Analysis Tools Command
----------------------
RETURN to Previous Menu
-----------------------
KCRTS Command
eXit KCRTS Program
------------------
- 37 -
COMPARISON BETWEEN EXISTING AND DEVELOPED(Entire Proiect Area After Usin�BMPs)
Flow Frequency Analysis '
Time Series File:dewex8.tsf
Project Location:Sea-Tac
---Annual Peak Flow Rates--- -----Flow FrequencyAnalysis-------
Flow Rate Rank Time of Peak -- Peaks-- Rank Return Prob
(CFS) (CFS) Period �,
0.071 2 2/09/01 18:00 0.092 1 100.00 0.990
0.019 7 1/06/02 3:00 0.071 2 25.00 0.960
0.053 4 2/28/03 3:00 0.055 3 10.00 0.900
0.002 8 3/24/04 20:00 0.053 4 5.00 0.800
0.032 6 1/05/OS 8:00 0.046 5 3.00 0.667
0.055 3 1/18/06 20:00 0.032 6 2.00 0.500
0.046 5 11/24/06 4:00 0.019 7 1.30 0.231
0.092 1 1/09/08 9:00 0.002 8 1.10 0.091
Computed Peaks 0.085 50.00 0.980
Flow Frequency Analysis
Time Series File:dewpr8.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
0.088 4 2/09/O1 2:00 0.192 1 100.00 0.990
0.059 7 1/05/0216:00 0.108 2 25.00 0.960
0.108 2 2/27/03 7:00 0.092 3 10.00 0.900
0.049 8 8/26/04 2:00 0.088 4 5.00 0.800
0.063 6 10/28/0416:00 0.084 5 3.00 0.667
0.092 3 1/18/0616:00 0.063 6 2.00 0.500
0.084 S 11/24/06 3:00 0.059 7 1.30 0.231
0.192 1 1/09/08 6:00 0.049 8 1.10 0.091
Computed Peaks 0.164 50.00 0.980
-38-
KCRTS FLOW FREQUENCY ANALY515 OUTPUT FOR PROPOSED CONDITIONS WITH 15 MINUTE TIME
STEP FOR USE WITH BYPASS FLOW CALCS.
Flow Frequency Analysis
Time Series File:dew15pr4.tsf
Project Location:5ea-Tac
---Annual Peak Flow Rates--- -----Flow Frequency Analysis-------
Flow Rate Rank Time of Peak -- Peaks-- Rank Return Prob
(CFS) (CFS) Period
0.108 5 2/09/0112:45 0.459 1 100.00 0.990
0.073 7 1/06/02 1:00 0.253 2 25.00 0.960
0.253 2 12/08/0217:15 0.241 3 10.00 0.900
0.060 8 8/26/04 0:45 0.112 4 5.00 0.800
0.241 3 11/17/04 5:00 0.108 5 3.00 0.667
0.112 4 10/27/0510:45 0.108 6 2.00 0.500
0.108 6 10/25/06 22:45 0.073 7 1.30 0.231
0.459 1 1/09/08 6:30 0.060 8 1.10 0.091
Computed Peaks 0.390 50.00 0.980
-39 -
�
CONVEYANCE ANALYSIS BACKUP MODELING PRINTOUT and
BACKGROUND INFORMATION
-ao- I
. .
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 1 PROJECT OWNER AND Part 2 PROJECT LOCATION AND
PROJECT ENGINEER DESCRIPTION
Project Owner M�e�C � TAn�. baw,�+- Project Name 1��„O;.N 4�..o-r Sl�,t Plafi
Phone (�oc�� Z7�-B13�} gDE� Permit# �vA � i7-[�PS Si1R-
Address 2L319 SE ?�r�+"` St Location Township �.31�.' �
(�a���s.�210 WA 9 Ro5� Range 5�
Project Engineer R;��,..,ti�. �la��r �c Section ��
Company �,relp,r��� �„�r �t,C Site Address 2�o D�Ua�t A�.2 SE ,
Phone r���15 + -S�aB 2P�. �k Bo5 �
Part 3 TYPE OF PERMIT APPLICATION Part 4 OTHER REVIEWS AND PERMITS
0 Landuse Services ❑ DFW HPA ❑ Shoreline
Subdivison / Short Subd. / UPD Management
❑ COE 404
❑ Building Services ❑ DOE Dam Safety � Structural
M/F/Commerical / SFR RockeryNaulU '
� Clearing and Grading ❑ FEMA Floodplain � ESA Section 7
� Right-of-Way Use ❑ COE Wetlands
❑ Other ❑ Other
Part 5 PLAN AND REPORT INFORMATION
Technical Information Report Site Improvement Plan (Engr. Plans)
Type of Drainage Review Ful�/ Targeted / Type(circle one): Full ! Modified /
(circle): �ta ge Site Small Site
Date (include revision Z � � � 20�- Date(include revision z % � �Zoi3
dates): � dates): '
Date of Final: Date of Final:
Part 6 ADJUSTMENT APPROVALS
Type(circle one): Standard / Complex / Preapplication / Experimental/ Blanket
Description: (include conditions in TIR Section 2)
Date of A roval:
2009 Surface Vr'ater Desi�n�lanual 1/9,'2009
1
, .
. "
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET '
Part 7 MONITORING REQUIREMENTS
Descnbe: /�l o,,,-�..,,.d ���e!, �;':� ��«+�,.lf
Monitoring Required: Ye ! No 1 Q
Sl D�vw\ W�w e 21A�-1�L 1 �)-���:"'!) ZO �
Start Date: 7��3} Zot3 ;.;�„�1 r ��Q � �.�:.+„-.o:.f-,�,-, .
Completion Date: Q;f I . 2oi3
,
Part 8 SITE COMMUNITY AND DRAINAGE BASIN '
Community Plan : �n JQ I'
Special District Overlays: — '
Drainage Basin: Lo�.,oJ,_, (�t.a„� t2,,� &,oN. .
Stormwater Requirements: (',�„ T ..-�-,r,. �+ ' res+ FN ;�,. ��
Part 9 ONSITE AND ADJACENT SENSITIVE AREAS
❑ River/Stream ❑ Steep Slope
❑ Lake ❑ Erosion Hazard
❑ Wetlands � Landslide Hazard c , =-�. �� �= '`�� �L
❑ Closed Depression ❑ Coal Mine Hazard
Co�.-�s,"t�
❑ Floodplain ❑ Seismic Hazard
❑ Other ❑ Habitat Protection
❑ �
Part 10 SOILS I
Soil Type Slopes Erosion Potential
.r-
,..r �, •1 �-C :i,/r I-��„l,L_._-..C..
_ I
�
I �
I �
❑ High Groundwater Table (within 5 feet) ❑ Sole Source Aquifer �
� Other (�-,4.� "�a';�`,� (.n �` o � «� i p 5 ❑ SeepslSprings
❑ Additional Sheets Attached
2009 Surface Water Design Manual 1;'S;'�009
2
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 11 DRAINAGE DESIGN LIMITATIONS
REFERENCE LIMITATION/SITE CONSTRAINT
❑ Core 2—Offsite Analysis n 1�
❑ Sensitive/Critical Areas h�Cs� �. �►J4,+ O..�yi.�. �,-,� 1W�,r.1
❑ SEPA ^I 50 0�
❑ Othe� _ ro�/Q'
� � J�CG)
❑ Additional Sheets Attached '
Part 12 TIR SUMMARY SHEET rovide one TIR Summa Sheet r Threshold Dischar e Area �!
Threshold Discharge Area: ,
name or descri tion '�
Core Requirements(all 8 apply) �,,
Dischar e at Natural Location Number of Natural Dischar e Locations:
Offsite Analysis LeveL / 2 / 3 dated: Nov 20�2.
Flow Control Level: 1 I 2 I 3 or Exemption Number
incl. facili summa sheet Small Site BMPs V�s - 4..�':1�� Po=:��'oEr ���'
Conveyance System Spill containment located at: � a
I
Erosion and Sediment Control ESC Site Supervisor: �',��. �.-���1 C c�.=r..�-~:. `F+ . �
�
Contact Phone: —
After Hours Phone: —
Maintenance and Operation Responsibility: n te Public
If Private, Maintenance Lo Re uired: Ye /No
Financial Guarantees and Provided: es / No
Liabilit `� I
Water Quality Type: i Basic / Sens. Lake J Enhanced Basicm / Bog �
(include facility summary sheet) or Exemptio���. i
I Landsca e Mana ement Plan� Yes / No1
S ecial Re uirements as a licabfe
Area Specific Drainage Type: CDA/SDO/MDP/BP/LMP/Shared Fac. !None !
Re uirements �' `" Name: �
Floodplain/Floodway Delineation Type: Major / Minor / Exemption / None
,��� 100-year Base Flood Elevation (or range): I
Datum:
Flood Protection Facilities � Describe:
�
Source Control Describe landuse:
(comm./industrial landuse) !
N/q- Describe any structural controls: !
2009 Surface Water Design A4anua1 1:9!2009
3
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET I
Oil Control High-use Site: Yes / o I�I
Treatment BMP: '
Maintenance Agreement: Yes /� ,
with whom? �
Other Draina e Structures
Describe: �S� 1„L,1.},ak.�m BMPS ��— ��- lof ,
Part 13 EROSION AND SEDIMENT CONTROL REQUIREMENTS
MINIMUM ESC REQUIREMENTS MINIMUM ESC REQUIREMENTS
,�,/ DURING CONSTRUCTION AFTER CONSTRUCTION
LJ learing Limits �Stabilize Exposed Surfaces '
�J Cover Measures ❑ Remove and Restore Temporary ESC Facilities ,
ly Perimeter Protection �Clean and Remove All Silt and Debris, Ensure '
�TrafFc Area Stabilization Operation of Permanent Facilities '
❑ Sediment Retention ❑ Flag Limits of SAO and open space '
preservation areas
❑ S rface Water Collection ❑ Other
I� Dewatering Control ,
�Dust Control
❑ Flow Control
Part 14 STORMWATER FACILITY DESCRIPTIONS Note: Include Facili Summa and Sketch
Flow Control T e/Descri tion Water Quali T e/Descri tion
1 �{i��i- r:..:"�::�J��
❑ Detention i Biofiltration t.
.�� ,
�Infiltration ��- +g� ❑ Wetpool
� ,
❑ Regional Facility ❑ Media Filtration
❑ Shared Facility � ❑ Oil Control !
❑ Flow Control � ❑ Spill Control '
BMPs � ' '
❑ Flow Control BMPs '�,
❑ Other I
❑ Other
I
,
2009 Surface Water Design Manual 1!9�2Q09
4
KING COUNTY, WASHINGTON, SURFACE WATER DESIGN MANUAL
TECHNICAL INFORMATION REPORT (TIR) WORKSHEET
Part 15 EASEMENTS/TRACTS Part 16 STRUCTURAL ANALYSIS
❑ Drainage Easement ❑ Cast in Piace Vault
�Covenant ❑ Retaining Wall
❑ Native Growth Protection Covenant ❑ Rockery>4' High
❑ Tract ❑ Structural on Steep Slope
❑ Other ❑ Other
Part 17 SIGNATURE OF PROFESSIONAL ENGINEER
I, or a civil engineer under my supervision, have visited the site. Actual site conditions as observed were
incorporated into this worksheet and the attached Technical Information Report. To the best of my
knowledge the information provided�re is accurate.
''�.:�'��.✓ �`7l,:.-� r Z-G�-,��i 3
' � Si ned/Date
I
i
�
k
�:r
�'`
� '
• I
I I�
2009 Surface Water Design Manual 1/9;'20G9
5
Site Improvement Bond Quantity Worksheet
Uriginal bond computations prepared by:
Name: �"`i ir l-l�,�.�� (:,-(,�i . Date: `.'.l 1 � � 20�j
PE Registration Number: =?(,�' '�-% Tel.#: �Zo(p� 501 -$�o$
Firm Name: � �-f. ��r..` �,: ,� ! '��
Address: 1 1��L� �., r , '�'. _ k- t'„��'�. ;,, ,�L�. •.� �r�7 Project No: N�A
ROAD IMPROVEMENTS 8 DRAINAGE FACILITIES FINANCIAL GUARANTEE REQUIREMENTS
PERFORMANCE BOND" PUBLIC ROAD 8 DRAINAGE
AMOUNT BOND"AMOUNT MAINTENANCE/DEFECT 80ND"
REQUIRED AT RECORDING OR
Stabilization/Erosion Sediment Control (ESC) (A) $ ���{S� - `"�'� TEMPORARY OCCUPANCY'"*
L=•xisting Right-of-Way Improvements (B) $ �p �I ZF, _ '��
�
Future Public Road Improvements & Drainage Facilitie (C) $ — c� - c�a
I'rivate Improvements (D) $ ��t ��� �� - ��
Calculated Quantity Completed (E) $ — 0 - �
Total Right-of Way and/or 5ite Restoration Bond"/'" (q+g) $ -�,r'!�-lr.� _ �c�
(First$7,500 of bond`shall be cash.
Performance Bond'Amount (A+B+C+D) = TOT/�L (T) $ ��,�_'�(�O - j�j T x 0.30 $ � _`,, 1OE -2� OR
Tviirnmum on amoun is `
Reduced Performance Bond"Total '*" (T-E) $ -
Use larger o x o or - (g+C)x
Maintenance/Defect Bond*Total 0.25= $ ��32 - I�
NnME OF PERSON PRGPARING BOND"REDUCTION. Date: i
'NOTE: The word"bond"as used in this document means any financial guarantee acceptable to King County.
*`NOTE: KCC 27A authorizes right o(way and site restoration bonds to be combined when both are required.
The restoration requirement shall include ll,e total cost for all TESC as a minimum,not a maximum. In addition,corrective work,both on-and off-site needs to be included.
Quantities shall reflect worse case scenarios not just minimum requirements. For example,if a salmonid stream may be damaged,some estimated costs for restoration
needs to be reflected in this amount. The 30"/a continyency and mobilization costs are computed in this quantity.
"«"NOTE: per KCC 27A,total bond amounts rernaining aiter reduction shall not be less than 30%of the original amount(T)or as revised by major design changes.
SURETY 80ND RIDER NOTE: I(a bond rider is used,minimum additional performance bond shall be $ - (C+D)-E
REQUIRED BOND'AMOUNTS ARE SUBJECT TO kEVIEW AND MODIFICATION BY DDES
Page 9 of 9 Unit prices updated: 02/12/02 I
Vers'ion: 4/22/02
REFBH BOND QUANTITY WORKSHEET Check out the DDES Web site Rannrt nata• �/11/�flflq
DEWIT25YRRESULTS-CIA.prn
Drainage Area Id: BSN1
Description.....: ONSITE BASIN TO PRIV. CB SYSTEM
<---Description--> SubArea SubC L (ft) Slope -Kr-- (min)
IMPERV 0.25 0.98 222.00 0.0184 20.00 1.36
PERV,GRA55 0.36 0.62 71.00 0.0236 4.70 1.64
Composite "c" value........0.77 Time of conc (min).. 3.00
orainage area zd: ssr�c
Description.... .: OFFSITE UPSTREAM BASIN TO EAST
<---�escription--> subArea subC � (ft) slope -Kr-- (min)
IMPERV 0.51 0.98 455.00 0.0150 20.00 3.10
PERV,GrtAss 0.48 0.62 125.00 0.0125 4.70 3.96
PERV,TREE 0.48 0.45 60.00 0.0100 2.50 4.00
Composite "c" value........0.69 Time of Conc (min)..11.06
Drainage Area Id: BSNX1
Description. ... .: OFFSITE FRONTAGE NE 2ND STREET
<---�escription--> SubArea SubC � (ft) Slope -Kr-- (min)
IMPERV 0.05 0.98 89.00 0.0055 20.00 1.00
Composite "c" value........0.98 Time of Conc (min). . 1.00
2/4/13 1:57:36 am page 1
DEWITT 4 LOT SHORT PLAT
25 YEAR RESULTS
------------------------------------------------------------------
------------------------------------------------------------------
REACH SUMMARY
Hydraulic Gradeline for rteach HYDPRIV
<-FROM-> <--TO--> <FLOW> f1055 Ent_HGL EntL055 EXtL055 OutLet Inlet AppHedd BndHedd JUnHedd
Headwtr -cb/mh-
-------- -------- cfs -loss- -Elev-- --loss- --loss- --elev- --elev- --loss- --loss- --loss-
--El ev- -rti m--
---------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------
OUTLET2
387.44
CB1 oUTLET2 1.26 0.05 387.49 0.01 0.04 387.54 0.00 0.04 0.05 0.00
387.55 390.57
Ca2 CB1 1.26 0.39 388.09 0.01 0.04 388.13 0.00 0.20 0.09 0.00
388.02 390.57
c63 Ce2 1.26 0.15 tw & dn <dc: inlet Ctrl Assumed 388.79 0.00 0.00 0.00
388.79 388.87
Hydraulic Gradeline for Reach HYDX1
<-FROM-> <--TO--> <FLOW> floss Ent_HGL EntLoss ExtLoss OutLet Inlet AppHead BndHead JunHead
Headwtr -cb/mh-
-------- -------- cfis -loss- -Elev-- --loss- --loss- --Elev- --Elev- --loss- --loss- --loss-
--Elev- --Rim--
___________________________________________________________________________________________________________
OUTLETI
387.50
Ca2nd2 oUT�ETl 1.79 0.30 387.80 a.OG fl.02 387.82 0.00 0.02 0.03 -0.00
387.82 39G.00
Ca2nd1 CB2nd2 2.03 0.49 388.35 0.00 0.02 388.38 Q.00 0.02 0.00 0.00
388.36 391.10
INLETl C62nd1 1.94 0.02 tw & dn <dc: Inlet Ctrl a,ssumed 390.66 0.00 0.00 0.00
39Q.66 393.00
NetwOr'k RedCh NE2ND
REACH <-AREA> <-DIA> LENGTH SLOPE < tl > DSGN Q °�6 PIPE Ndepth %Depth VdCt VfUll C�,rea
zo (ac) (ft) (ft) ft/ft ----- (cfs) ------ (ft) ----- (fps) (fps)
Pxl 1 47 1 50 15 43 0 1886 0 0120 1.94 3 64 0 20 13 51 13 59 30 95 BSNx
P2nd1 1.5Z 1.50 396.55 0.0012 0.0120 2.03 47.12 0.76 50.41 2.28 2.51 BSNxl
P2nd2 1.52 1.50 240.60 0.0012 0.0120 1.79 41.22 0.70 46.63 2.21 2.52
Network Reach PRIV
REACH <-AREA> <-DICu LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %oepth VdCt VfUll C�rea
i� (a,c) (ft) (ft) ft/tt ------ (cfs) ------ (ft) ------ (fps) (fps)
_________________________________________________________________________________________________
P3 0.61 0.67 15.70 0.0248 0.0120 1.26 56.80 0.38 56.46 6.22 6.54 BSN1
P2 0.61 1.00 119.07 0.0050 0.0120 1.26 42.78 0.48 47.64 3.43 3.86
P1 0.61 1.00 10.22 0.0049 0.0120 1.26 43.42 0.48 48.05 3.�9 3.80
2/4/13 1:57:36 am page 2
DEWITT 4 LOT SHORT PLAT
Page 1
DEWI725YRRESULTS-CIA.prn
25 YEAR RESULTS
-------------------------------------
STRUCTURE REPORT
PROPOSED STRUCTURE REACH ID NO. CB1
LOCdtIOn : FRONTAGE CONV CALC NO�th . 178402.1000
Str Type : East . 1313572.8000
str Cat : Catch aasin ttim elev : 390.5700
Area/sump: 0.00 sf/1.50 ft aottom El: 385.5100
Cont area: Hgrade E1: 387.5521 ft
aend.. ...: No special shape
Ent type.: Area/sump:
Ent Loss: 0.008 Exit: 0.040 App Vel: 0.040 7unct: 0.000 eend: 0.054
rteach <inverb <Diam> < n > <End>
P1 387.010 12.00 0.012 upper
P2 387.010 12.00 0.012 Lower
PROPOSED STRUCTURE REACH ID NO. CB2
Location : FRONTAGE CONV CALC North . 178405.7000
Str Type : East . 1313453.7800
Str Cat : Catch easin Rim Elev : 390.5700
Area/sump: 0.00 sf/1.50 ft Bottom E1: 386.1100
cont Area: Hgrade E1: 388.0227 ft
aend.. ...: No special shape
Ent type.: Area/sump:
Ent Loss: 0.008 Exit: 0.040 App vel: 0.204 7unct: 0.000 aend: 0.092
Reach <invert> <oiam> < n > <End>
P2 387.610 12.00 0.012 Upper
P3 387.290 8.00 0.012 �ower
PROPOSED STRUCTURE REACH ID No. C62nd1
Location : FRONTAGE CONV CALC North . 178365.8100
Str Type : East . 1313575.3200
str Cat : Catch Basin rtim elev : 391.1000
,4rea/sump: 0.00 sf/1.50 ft aottom el: 386.0900
Cont Area: a5Nx1 Hgrade E1: 388.3610 ft
aend.....: No special shape
Ent type.: Area/sump:
Ent �oss: 0.004 Exit: 0.021 App vel: 0.019 ]unct: 0.001 Bend: 0.003
Reach <Inverb <Diam> < n > <End>
P2nd1 387.590 18.00 0.012 Upper
PX1 387.590 18.00 0.012 Lower
2/4/13 1:57:36 am page 3
DEWITT 4 LOT SHORT PLAT
25 YEAR RESULTS
--------------------------------------------------------------------
--------------------------------------------------------------------
STRUCTURE REPORT
PROPOSED STRUCTURE REACH ID N0. CB2�d2
Location : FRONTAGE CONV CALC North . 178368.2500
Str Type : East . 1313178.i300
Str Cat : Cauh aasin Rim Ele� : 390.0000
Areaisurnp: O.GO sf.%1.50 ft sottom E1: 385.6000
Cont Area: Hgrade El: 387.8230 fL
Bend. . . . . : No spec=,a1 shaoe
Ent type. : Area/sump:
Ent �oss: 0.003 Exit: O.C16 a.pp vel: 0.021 7unct: -0.002 Bend: 0.027
RedCh <Invert> <Diam> < n > <End>
P2nd2 387.100 18.00 0.012 Upper
P2nd1 387.100 18.00 0.012 �ower
PROPOSED STRUCTURE REACH ID N0. CB3 II
LOCatiOn : PRIV. CB SYSTEM North . 178394.1000
str Type : East . 1313443.2000
Str Cat : Catch Basin Rim Elev : 388.8700
Area/sump: 0.00 sf/1.50 ft Bottom El: 386.1800
Cont Area: BSN1 Hgrade El : 388.7924 ft
Bend... ..: No special shape
Ent type.: Area/sump:
Ent �oss: 0.041 Exit: 0.204 App vel: 0.000 7unct: 0.000 Bend: 0.000
rteach <invert> <�iam> < n > <end>
Page 2
DEWIT25YRRESULTS-CIA.prn
P3 387.680 8.00 0.012 upper
PROPOSED STRUCTURE REACH ID NO. INLETI
Location : FRONTAGE CONV CALC North . 178371.9000
str Type : East . 1313589.5000
Str cat : Catch Basin Rim Elev : 393.0000
Area/sump: 0.00 sf/1.50 ft Bottom E1: 389.0000
Cont area: eSNx Hgrade E1: 390.6622 ft
aend.....: No special shape
Ent type.: area/sump:
Ent �oss: 0.004 Exit: 0.019 App vel: 0.000 7unct: 0.000 Bend: 0.000
Reach <=nverv <�iam> < n > <end>
Pxl 390.500 18.00 0.012 upper
2/4/13 1:57:36 am page 4
DEWITT 4 LOT SHORT PLAT
2� YEAR RESULTS
---------------------- --------------------------------------
STRUCTURE REPORT
PROPOSED STRUCTURE REACH ID No. OUTLETI
LOCdtiOn : FRONTAGE CONV CALC North . 178378.5600
str Type : East . 1313419.1600
str Cat : Dummy Structure Rim Elev : 390.0000
str Diam : 0.00 in Bottom E1: 386.8000
cont Area: Hgrade E1: 387.4994 ft
aend.....: No special shape
Ent type.: Str Diam :
Ent Loss: 0.000 Exit: 0.000 App vel: 0.000 ]unct: 0.000 Bend: 0.000
Reach <Invert> <Diam> < n > <End>
P2nd2 386.800 18.00 0.012 Lower
PROPOSED STRUCTURE REACH ID NO. OUTLET2
LOCdtiOn : PRIV. CB SYSTEM North . 178391.9000
str Type : East . 1313572.1000
5tr Cat : Dummy Structure Rim Elev : 390.0000
Str Diam : 0.00 in Bottom E1: 386.9600
Cont Area: Hgrade E1: 387.4405 ft
Bend.....: No special shape
Ent type.: Str Diam :
Ent Loss: 0.004 Exit: 0.021 app vel: 0.019 7unct: 0.001 eend: 0.003
Reach <Inverb <Diam> < n > <End>
P1 386.960 12.00 0.012 Lower
€
Page 3
DEWIT100YRRESULTS-CIA.p��
D�dindge A�Ed Id: BSN1
DeSCription.....: ONSITE BASIN TO PRIV. CB SYSTEM
<---�escription--> subArea subC � (ft) slope -Kr-- (min)
IMPERV 0.25 0.98 222.00 0.0184 20.00 1.36 .
PERv,GrtA55 0.36 0.62 71.00 0.0236 4.70 1.64
Composite "c" value........0.77 Time of Conc (min).. 3.00
Drainage Area id: BSNX
D25CriptiOn.....: OFFSITE UPSTREAM BASIN TO EAST �
<---�escription--> subarea SubC � (ft) slope -Kr-- (min)
IMPERV 0.51 0.98 455.00 0.0150 20.00 3.10
PERV,GRASS 0.48 0.62 125.00 0.0125 4.70 3.96
PERV,TREE 0.48 0.45 60.00 0.0100 2.50 4.00
Composite "c" value........0.69 Time of Conc (min). .11.06
orainage area Id: asNxl
DeSC�iptiOn.....: OFFSITE FRONTAGE NE 2ND STREET
<---oescription--> SubArea SubC � (ft) Slope -Kr-- (min)
IMPERV 0.05 0.98 89.00 0.0055 20.00 1.00
Composite "c" value.. ......0.98 Time of Conc (min).. 1.00
2/4/13 2:0:39 am page 1
DEWITT 4 LOT SHORT PLAT
100 YEAR RESULTS
--------------------------------------------------------------------
------------------------------------------------------------------
REACH SUMMARY
Hydraulic Gradeline for Reach HYDPRIV
<-FROM-> <--TO--> <FLOW> fl O55 Er1t_HGL E11tL055 ExtLOSS OUtL2t I�let AppHead BndH2dd JUnH2dd
Headwtr -cb/mh-
-------- -------- cfs -loss- -elev-- --loss- --loss- --Elev- --elev- --loss- --loss- --loss-
--Elev- --Rim--
__________________________________=_____________=_=________________
-__________________-------------___
OUTLET2
387.51
Csl OUTLET2 1.59 0.05 387.56 0.01 0.06 387.64 0.00 0.06 0.08 0.00 '
387.66 390.57 �
C62 CB1 1.59 0.35 .388.16 0.01 0.06 388.23 0.00 0.32 0.15 0.00
388.06 390.57
Cs3 CB2 1.59 0.23 tw & dn <dc: Inlet Ctrl ,4ssumed 389.16 0.00 0.00 0.00
388.97= 388.87
Hydraulic �radeline for Reach HYDX1
<-FROM-> <--TO--> <FLOW> floss Ent_HGL EntLoss ExtLoss OutLet Inlet AppHead BndHead JunHead
Headwtr -cb/mh-
-------- -------- cfs -loss- -Elev-- --loss- --loss- --Elev- --elev- --loss- --loss- --loss-
--Elev- --Rim--
_________________________________________________
___________________
_________________________________________=___'
OUTLETI
387.62
CB2nd2 OUTLETI 2.32 0.30 387.92 0.01 0.43 387.9: 0.00 0.03 0.05 -0.00
387.96 390.00
Cg2nd1 CB2nd2 2.64 0.49 3$8.48 0.01 0.03 388.52 0.00 0.03 0.00 0.00
388.50 391.10
INLETI Ca2nd1 2.52 0.02 tw & dn <dc: inlet Ctrl Assumed 390.71 0.00 0.00 0.00
390.71 393.00
Network R2dCh NE2ND
REACH <-AREA> r DIN LENGTH SLOPE < n > DSGti Q % PIPE Ndepth %�epth VdCt Vfu�� C�area
ID (Ac) (f:) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps)
________________________________________________________________________________________
Pxl 1.47 1.50 15.43 0.1886 0.0120 2.52 4.72 0.23 15.32 14.68 30.95 asNx i
P2nd1 1.52 1.50 396.55 0.0012 0.0120 2.64 61.10 0.89 59.15 2.42 2.51 BSNxl
P2nd2 1.52 1.50 240.60 0.0012 0.0120 2.32 53.47 0.82 54.39 2.36 2.52
Network Reach PRIV
REACH <-AREA> <-DI/U LENGTH SLOPE < n > DSGN Q % PIPE Ndepth %Depth Vact Vfull C�+rea
ID (Ac) (ft) (ft) ft/ft ------ (cfs) ------ (ft) ------ (fps) (fps)
_________________________________________________________________________________________________
P3 0.61 0.67 15.70 0.0248 0.0120 1.59 71.53 0.44 65.79 6.54 6.54 B5N1
P2 0.61 1.00 119.07 0.0050 0.0120 1.59 53.87 0.55 54.64 3.63 3.86
P1 0.61 1.00 10.22 0.0049 0.0120 1.59 54.68 0.55 55.15 3.58 3.80
Page 1
WET BIOSWALE VELOCITY CHECK(a�WQ STORM:
Width = 2 feet
Length = 100 feet
Sideslope= 3 : 1
b (width) = 2 feet
n= 0.2 I
Qwq= 0.108 cfs ,
1. Bioswale Design Depth =4 inches
Q = (1.49!n)*A` R^(0.67)"s^0.5
b=Qwq ' nwq/[1.49'y^(1.67)*s^(0.5]
y= (Qwq"nwq/(1.49*s^.5*b)^�.6
V= 0.058 fps <----OKAY
(Using 15 minute time step with proposed conditions.)
WET BIOSWALE VELOCITY CHECK(a� 100YR STORM:
Width = 2 feet
Length = 100 feet
Sideslope= 3 : 1
b(width) = 2 feet
n= 0.2
Qwq = 0.459 cfs
1. Bioswale Design Depth=4 inches
Q = (1.49/n) `A" R^{0.67)*s^0.5
b=Qwq * nwq I[1.49"y^(1.67)*s^(0.5]
y= (Qwq'nwq/(1.49's^.5'b)^0.6
V= 0.459 fps <---OKAY
(Using 15 minute time step with proposed conditions.)
Bypass Outfall Calculations
Water Quality(w/out flow control):
2 year, 24 hr Flowrate= 0.108 cfs from KCRTS 15 minute time step
Q= CA*(2`gh)^1/2
Q=flow
C = coeff. Of discharge= 0.62 for plate orifice
A=Area of orifice(s�
h = hydraulic head (ft)= 0.77
g = gravity(32.2 ft/sec^2)
overflow elevation = 388.45
invert elevation out= 387.68
Orifice diameter= 1.135 inches
Area = 0.0070 sf '
What is the flowrate out for the orifice diameter and overflow elevation provided?
Q= 0.108 cfs �
3.2.1 RATIONAL METHOD
TABLE 3.2.1.A RUNOFF COEFFICIENTS-"C"VALUES FOR TFIE RATIONAL METFIOD
Generat Land Covers Single Family Residential Areas�
Land Cover C Land Cover Density C
Dense forest 0.10 0.20 DU/GA(1 unit per 5 ac.) 0.17
Light forest 0.15 0.40 DU/GA(1 unit per 2.5 ac.) 0.20
Pasture 0.20 0.80 DU/GA(1 unit per 1.25 ac.) 0.27
Lawns 0.25 1.00 DUlGA 0.30
Playgrounds 0.30 1.50 DU/GA 0.33
Gravel areas 0.80 2.00 DU/GA 0.36
Pavement and roofs 0.90 2.50 DUlGA 0.39
Open water(pond, lakes, 1.00 3.00 DU/GA 0.42
wetlands) 3.50 DU/GA 0.45
4.00 DUIGA 0.48
4.50 DU/GA 0.51
5.00 DU/GA 0.54
5.50 QU/GA 0.57
6.00 DU/GA 0.60
�Based on average 2,500 square feet per lot of impervious coverage.
For combinations of land covers listed above,an area-weighted "C�:x A;'sum should be computed based on the
equation C�:x A,_(Ci x Ar)+(C2 x A2)+ ...+{C„x A„),where A,_(A�+,q2+..,+A„),the total drainage basin area. �
TABLE 3.2.1.B COEFF'ICIENTS FOR THE RATIONAL METH011"iR"EQUATION
Design Storm Return Frequency aR bR
2 years 1.58 0.58
5 years 2.33 0.63
10 years 2.44 0.64
25 years 2.66 0.65
50 years 2.75 0.65
100 years 2.61 0.63
TABLE 3.2.1.0 kR VALUES FOR T,USING THE RATIONAL METHOD
Land Cover Category � kR
Forest with heavy ground litter and meadow 2.5
Fallow or minimum tillage cultivation 4.7
Short grass pasture and lawns 7.0
Nearly bare ground 10.1
Grassed waterway 15.0
Paved area (sheet flow)and shallow gutter flow 20.0
2009 Surface Water Design Manual i/9/2004
3-13
3.2.1 RATIONAL METHOD
FIGURE 3.2.1.D 100-YEAR 24-I30UR ISOPLUVIALS
�
3���-1— _ o _ �o_.v1�
�� � H cOUATY
32 e^ --- ------ -- ---- ---� -- ,�
�� ,.1�, � r' . � ,..o . _
�
� .
36 � I � .-- -- '= � --
39 8 3s ,.., 1'� t �f., ..; --- - �
�p ,, � -' ° - �,,�
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7 _1 \. ..-
v� _ �, , ,
4 2 r � � �
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43 t '� - i � �°�U ` ' I �, \ ,p
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' vIE CE COUHTY
WESTERN a ^� � '�;_
KING COUNTY �o � .r, ..: s.5
s.o
�, D�• �, -- 5.5
100-Year 24-Hour ' °` �,'� �.� _ � f..�,
Precipitation °`��,� -� ��,, �
in Inches ° Z `""�es y� � _�- ���
,�_�.—�
h�
2009 Surface Water Design Manual i!9.�2009
3-17
SECTION 3.2 RUNOFF COMPUTATION AND ANALYSIS METHODS
FIGURE 3.21.0 25-YEAR 24-HOUR ISOPLiJVIALS
?S _ _ _
—' — — — 6H HOMISH COUNTY
� NIN6 COUNTY
26 � '� �'�ti,� - ---�,.{ - - ---J -- �-
?, ' - *�oo ' _
2g m � a �'�;'� h
3� , � � � ' ' �•
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.� ', _ _ 4 0 q
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llielt / .-' . F �
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^ � h �� � � �, � �--�` ��-.. , _
�• n> M, . � ; �., "'� � � S� Y_
A. �_�yqqy` _•"�/I(iNG COUM1TY� �
�7�� � _, _-,,
WESTERN ��,-.
KING COUNTY � �`. -- _ _ �- so
25-Year 24-Hour � � ` �', � 4.s
Precipitation �'� ^ �, .� J� �
��;
in lnches 0_�_�Miles ^�' �,•� o � � �.-
� �,.
' l/9/2009 2009 Surface Water Design Manual I!
3-16 I
� DeWitl Renton 4 Lot.
Upstream Contributing Ditch Area to be routed thru bio-swale
Total Area = 64,469.00 sq-it 1.479 ac
Imperv.Area= 22,564.20 sq-ft O.S1S ac
Treed Areas= 20,952.00 sq-ft. 0.480 ac
Grass Areas= 20,952.00 sq-ft 0.480 ac _
EXISTING PROIECT BASIN:
Onsite Area,assume all forested)= 47,48Q.40 sq-�t 1.089 ac
Offsite ROW(total area}= 1960.3 sq-ft 0.045 ac
PROPOSED PROJECT BASIN(without Onsite BMPs):
Impervious(Onsite Roads)= 5,772.80 sq-ft 0.132 ac (Requires WQTreatmen;l
Impervious(Onsite House/dwy`/sw}= 18,223.00 sq-ft 0.418 ac
Pervious(Onsite Grass)= 23,484.60 sq-ft 0.539 ac
Impervious(Offsite new dwy ramp)= 302 sq-ft 0.007 ac
Impervious(OfFsite new s-w) 690 sq-ft 0.016 ac
Pervious(Offsite Grass)= 968 sq-ft 0.022 ac
`f Note New dwy has reduttion in sq-ft due to reduction in driveway configuration)
CREDTTS CALCLZATIOVS:
MiNUS INFILTRATION for LOTS�#1,#2,#3 and#4): �
TOTALIMPERVIOUSDEDUCTED= 18,223.00 sq-ft 0.418 ac I
NOTE: Max.permissible lot SF of 55%allowable,but project is proposing less impervious. ��
; onsite bmps indude routing all driveway runoff towards rain-garden in backyard,mlle;ting roof runoff and s/w towards in'iltration BMPs. '
PROPOSED(MITIGATED USING ONSITE BMPS)BASIN SUMMARY:
IMPERVIOUS(Onsite&Offsite) 6,764.80 sq-ft 0.155 ac
PERVIOUS(GRASS) 24,452.90 sq-ft 0.561 ac
Raingarden Water Quality Bottom Area Determination:
(with 1 -foot depth and 6-inch pipe overflow)
(Converted to Grass)
Original Parking Area(SF) Reduced Parking Area(SF) Final Parking Area(Sf) Percentages �
Lot 1: 900 26.1 873.9 27.3
Lot 2: 900 120.1 779.9 24.4
Lot 3: 900 123 777 24.3 ',
Lot 4: 900 128.2 771.8 24.1 I
3600 397.4 3202.6 100.0
In acres= 0.083 0.009 0.074
From WWHMv3:
Water Quality Online Volume Required for all Driveways=0.0088 acre-ft 383.328 cu-ft
Bottom Area (sq-ft)
Required for each lot
Lot 1: 104.6
Lot 2: 93.3
Lot 3: 93.0
Lot 4: 92.4
recv�aioN3
,� „ N.E. 1 /4, S.W. 1 /4 SEC. 8 TWP. 25N., RGE. SE., W.M. �
II
- — — I SE 2ND ST _;x �:-;<
��
-Ag I'S•�_� .
SCALE: 1"=1 O� � �; .���.�f=-��.�3.;�j r:�
-�_ � __ . - = .
io s o to ao � � — — — . _ . . _
— — --� — — � —
\
I - . � -chaee ina�' -----� - ' _
1 I �e�r wao c� G ��
I - � �
(ra I LOT 1 �
Z , �
EXISTING �
� � --7� v ;,,,,� , ONSITE BASIN: ��
I ` .. , y.-L. 4 _ouna.
Q _ ��=.C:/;Y ( P� PERVIOUS (TREES) : 47.480.4 Sf(1.09/�CR6) � $
L 2c.
�' � ' � �
a ¢ � � ��
� (� TRACT -_.�1------------------- �$ � ��
I �e� #�
� '� PROPOSED �a � ��
� � �� �-'- '-•=�� / ONSITE BASIN_ �' E
A
I � aEav�oia c«+w� : o.s3e�c �� � �i �
I � I '''/ : �anous(aawos) : ai32�c
. � � ' " - j i�ERVqUS (HOUS�S.SM.PORCH) : 0.478 AC 6b
� r �I-- _�=�.� � LOT 2
I,;� � � �,r� ���
� r� � _�-� _
{ �'REx E�Yi�Y � �
( F__ "2'_CONG M=YF.-� � _'
•2•CONC 5�.7A \
_ ( . _ , �� � 3
� _ ,_ =I �� ; . __ I �---------------- Q
� _ v= _ ��= - - - � ; --� _ �
� � � i- �_
_ -���C#EA`.E�7r .�.,r.� 1.Y "__`_ .'L
� I
/
� I � i LOT 3 �
I ' � �
� I �
^- _ � ,f I ; � �
_ _ � � � I z �--
� _�_ � - - �.--------
_ � , , ---------- � o
�1'IC NTM. �
r. _ - - - - n�F ( I Q J
— � m
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