HomeMy WebLinkAbout1994.04.29 - Stormwater Site Plan StandpipePort Townsend
Standpipe
Stormwater Site Plan
Prepared for
Ttre City of Port Townsend
Prepared by
CH2M HILL, INC.
April 29, t994
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This plan has been developed under the direction of a professional engineer.
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Stormwater Site Plan
I Project Overview
This project will construct a water supply standpipe to serve the City of Port Townsend,
Washington. The standpipe will provide increased water pressure and fire flows to the
water supply system customers above elevation 200. Construction of the standpipe will
require disturbance of approximately 0.8 acre of land with the addition of approximately
9,000 square feet of impervious surface. Impervious surface additions will be from the
installatibn to the standpipe roof and foundation, a lO-foot-wide gravel access drive around
the perimeter at the facility, and a treatment station with associated gravel driveway.
As designed, the standpipe will be 85 feet tall with a diameter of 47 feet. It will be sup-
ported by a concrete foundation 5 feet thick placed on a compacted backfill. Additional
iand-disturbing construction at the site includes the installation of water supply pipes for the
standpipe and existing resenroir, two overflow drains, a footing drain, and a roadway
culvert.
To address construction impacts,. an erosion and sedimentation control (ESC) plan has been
developed and included in this report. This plan will address site controls to limit the
construction impacts from the 0.8-acre disturbed parcel on the surrounding property and
the downstream water resources. The ESC plan will propose the use of site controls such
as silt fencing and straw bales to prevent the transport of sediment from the site, along with
other primary erosion control techniques.
As a result of the limited extent of impervious surface additions, the site setting, and the
existing soil characteristics, limited surface water runoff controls are proposed for this site
development. Runoff from impervious surfaces proposed for this project, which consists
primarily of the standpipe roof, will be relatively clean and not pose a detriment to surface
*atet quality. Similady, the peak rate and quantity of runoff from the development are
small compared to the runoff produced by the entire parcel under existing conditions. Run-
off from the existing reservoir appears to infiltrate currently into the near-surface soils as
no indications of erosion or runoff channels are evident at the site. Based on these obser-
vations, runoff control would provide only limited benefit to the surface water resources.
Minimum Requirements
The minimum requirements for controlling stormwater runoff for this project have been
determined using the flow chart in Figure I-2.1 on pagel-2-7 of the Stormwater Manage-
ment Manual foi the Puget Sound Basin (Stormwater Manual)', shown below. As identified
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SIOR}II|ATER I,IANAGEI.IENT ll{Al{UAL FOR IHE PUGET SOUND BASIN
FLgure I-2.1 Flowchart Denonstratlng Minimum Regui'rementa
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earlier, there will be greater than 5,000 square feet of impervious surface added and less
than 1 acre of land-disturbing activity. According to Figure l-2.L, the Large Parcel Mini-
mum Requirements No. 2 through 11 apply to this project in addition to a Small Parcel
Erosion and Sediment Control Plan.
The following sections explain how the minimum requirements will be met for this project.
Small Parcel Erosion and Sediment Control
A Small Parcel Erosion and Sediment Control Plan has been prepared and is presented in
Section IX of this report.
Large Parcel Minimum Requirement No. 2: Preservation of Natural Drain-
age Systems
To the extent practicable, all stormwater runoff from the developed site will flow offsite at
the current locations. Runoff from the standpipe site will be diverted to an existing man-
made dqxession adjacent to the site. The depression discharges through an existing culvert
and flows down an existing channel flowing to the north.
I-arge Parcel Minimum Requirement No. 3: Source Control of Pollution
The discharge of chlorinated water to the local stream system has been identified as having
the greatest potential to adversely affect surface water resources.
A full description of source Control strategies to control these impacts is provided in
Section V, Permanent Stormwater Quality Control Plan.
Large Parcel Minimum Requirement No. 4: Runoff Treatment BMPs
Runoff treatment for this site will be provided by filtration of site runoff through natural
vegetation located in the proposed detention facility. Runoff from the site is not expected
to contain measurable amounts of significant pollutants as the majority of the runoff will be
from roof areas and other impervious areas that receive little contaminant loading.
The proposed design will divert runoff from the standpipe structure to a detention basin
located in an existing man-made vegetated depression. Minor storm events will filter
across the natural -vegetation and likely infiltrate into the near-surface soils and continue to
flow laterally through the uppef soil profile.
Large Parcel Minimum Requirement No. 5: Streambank Erosion Control
Streambank erosion control will be provided through the use of a detention system. Runoff
from the site will be routed approximately 150 feet to the north to a depression created by
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Pott Townsend Standpipe
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Stormwater Site Plan
the existing roadway fill. The roadway fill will be reinforced, and a flow-control structurewill be installed to create a detention basin. The basin will serve to attenuate discharges of
stormwater runoff and overflows from the standpipe or existing reservoirs. The attenuationprovided by the flow-control structure will serve to reduce streambank erosion in the ex-isting drainage course flowing north from the site.
Large Parcel Minimum Requirement No. 6: Wetlands
Not applicable. A soil survey of the site has not identified any wetland areas within theproject area or as a receiving water for site runoff.
Large Parcel Minimum Requirement No. 7: Water Quality Sensitive Areas
f9 w-ater quality sensitive areas have been identified as receiving stormwater runoff fromthis site.
I-arge Parcel Minimurn Requirement No. 8: offsite Analysis
Offsite drainage impacts shall be controlled through installation of a flow-control structure.
Installation of the flow-control structure will create approximately 0.9 acre-feet of runoffdetention. The runoff release from the 100-year, 24-hour event will be restricted to less
than the existing condition 2-ye,ar,24-hour discharge rate. Since the amount of flow atten-uation will be four to five times the Ecology requirements, a detailed offsite analysis hasnot been prepared.
I-arge Parcel Minimum Requirement No. 9: Basin pranning
No overall basin plan has been developed for the drainage basin where the site is located.
Additional information is included in Section VII, Basin and Community planning.
Large Parcel Minimum Requirement No. I0: Operation and Maintenance
No stormwater facilities that will need ongding maintenance activities are proposed.
I-arge Parcel Minimurn Requirement No. rr: Financial Liabitity
The City of Port Townsend, being a municipality in the state of Washington, is not re-quiled to post a performance bond for the construction of public utilities. Financing for theproject is provided through utility billings and has been set aside for this project.
Port Townsend Standpipe
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U Site Plan
A site plan has been developed for the Port Townsend standpipe project. A copy of the
site plan is attached in Appendix A. The site plan outlines the erosion controls to be used
during construction of the project.
UI Preliminary Conditions Summary
The site of the proposed standpipe is located adjacent to an existing S-million-gallon water
supply reservoir owned and operated by the City of Port Townsend. The site is located
near the western city limits in the north quarter of Section 9, Township 30 N, Range I
West. Topographically, the site is located at the crest of a hill at approximately eleva-
tion 290. The hill slopes off generally to the north and south from the proposed site, with
surface water flows split between two drainages.
The majority of the proposed site is cleared and covered with unmaintained grass and
brush. Construction of the standpipe will require clearing approximately U3 to Il2 acre of
young fir,and alder trees with an average diameter of 12 to 18 inches. Access to the site is
provided by an existing gravel surface road that currently serves the existing reservoir. No
improvements or widening is proposed for the existing road.
Mffsite Analysis
Itrd use surounding the standpipe site is currently limited to timber growth, pasture, and
a few isolated single-family residences. Two residential developments are planned in the
immediate vicinity of the site-one directly to the west and another just northeast of the
standpipe location.
V Permanent Stormwater Quality Control Plan
The Permanent Stormwater Quality Control Plan (PSQCP) describes the water quality
objectives that will be achieved through implementation of the permanent stormwater
*nttot BMPs. The PSQC Plan also OescriUeJthe BMPs that have been selected and gives
important details of how they will be designed and installed. Engineering drawings are
included in Appendix A.
The BMPs have been selected based on the Stormwater Manual's selection process illus-
trated by Figure I-4.3 and explained on pages I-4-7 through I-4-19 of the Stormwater Man-
ual. This BMP selection process has been followed to develop the specific BMPs for the
Port Townsend standpiPe site.
Port Townsend Standpipe
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Stormwater Control Scenario
Section I-4.3.1 of the Stormwater Manual provides guidance and requirements for imple-mentation of permanent stormwater quality controls. These requiremints are based on thesize of the site and characteristics of the development. Based on Table I-4.2 of theStormwater Manual, the stormwater control scenario identified for this site is Scenario 1,which includes:
r Source controlo Runoff treatment for conventional pollutants
Source control and runoff treatment are required of all projects with greater than5,000 square feet of impervious surface or 1 aCre of disturbed arla. Streambank erosioncontrol can also be required when the site will discharge to a stream system. This projectwill not include streambank erosion control, as discusJed below.
The following three sections describe how these BMP objectives will be addressed by the
standpipe project.
Source Control
The primary source of potential contaminants from this site will be from the disposal ofchlorinated drinking water. Chlorination levels in potable water are in excess of dischargelimitations to stream networks and require dechlorination prior to release. potable water
discharges from normal maintenance activity, the testing station, and infrequent overflowsshall discharge to the detention facility. Chlorine level reduction will o..ut through air
contact, vegetative filtration, and soil infiltration.
During construction the standpipe will be sterilized with highly chlorinated water. Aftersterilization this water shall be neutralized by the addition oi soOium thiosulfate. prior torelease, the water will be tested to assure chlorine levels have been lowered to a minimum
of drinking water standards. If testing shows the chlorine levels do not meet these stand-ards' additional measures shall be taken to reduce the levels, and the water shall be retested
before discharge.
Runoff Treatment
Runoff treatment for this project will be provided through the use of sheet flow through
natural vegetation. The vegetation will provide treatment of any flow leaving the sitethrough filtration of any sediments and partial nutrient uptake through biological-activity.
The presence of glacial till at depths of 20 to 60 inches precludes the use of subsurfaceinfiltration on this site. The shallow depth to till prevents the installation of an under-
ground percolation system as an infiltration trench could easily be located in impermeable
material.
Port Townsend Standpipe
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Streambank Erosion Control
Streambank erosion control for this site will be provided through the use of a detention
basin with a controlled release. The detention volume will be provided in the existing
onsite closed depression created by the roadway fiIl. The detention basin will provide
temporary storage for site stormwater runoff and overflows from the standpipe structure.
The volume of the proposed basin will be much larger than the site runoff from the
100-year, 24-hour event. With the detention basin overflow set at elevation273.5, the
basin will have a volume of 39,000 cubic feet compared to a 100-year, 24-hour runoff
volume of 1,600 cubic feet. The total volume of this 100-year event could be contained
without discharge in less than 4 percent of the existing basin volume.
Design of the detention basin outlet control has considered both stormwater discharges and
standprpe releases. To provide control of both of these sources, the control structure has
been sized to provide a peak release rate equivalent to the existing condition 100-year
runoff rate. With 6.4 feet of total head, a l-inch-diameter orifice is required at the bottom
of the structure to provide this control. Use of several staged orifices of smaller diameters
has not been recommended because of their potential for clogging. Calculations showing
the anticipated runoff rates and detention volumes are included in Appendix B.
As noted above, the site soils are not conducive to infiltration facilities. The Type C soils
in the project area tend to have a moderately high runoff rate and low permeability rate
through the glacial till layer. Historically, infiltration facilities in the City of Port
Townsend have a history of failure or insufficient capacity. After consideration of this
information, subsurface disposal BMPs has not been selected for this site.
VI Special Reports and Studies
No special reports or studies have been required or prepared for this project.
VII Basin and Community Planning
The 1986 Comprehensive Stormwater Drainage Plan for the City of Port Townsend does
not indicate any particular conditions or objectives for stormwater control for this basin
area. In the 1993 Port Townsend Stormwater Management Plan (Draft), this site is located
within Basin 18. The 1993 plan does not document specific problems within this basin or
identify specific controls or regional facilities for this basin area. Land use for the area is
currently under residential zoning, and construction of the standpipe will require a condi-
tional use permit from the City of Port Townsend.
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VIII Permits
Applications for the following permits and approvals have been submitted to the City of
Port Townsend.
Building Variance
Conditional Use Permit
Building Permit
Clearing and Grading Permit
IX Erosion and Sediment Control Plan
Construction Activities
The proposed Port Townsend standpipe facility will include construction of an 8s-foot-tall
water supply standpipe adjacent to an existing water supply reservoir. Construction activi-
ties will include clearing approximately lt3 to lt2 acre of forested land, grubbing a total
site area of approximately 0.8 acre, excavating for a concrete foundation, *d installing the
steel standpipe structure.
Excavation volumes will be in the range of 2,700 cubic yards of native material. The con-struction contractor shall identify the disposal sites for the material and submit this infor-
mation to the City prior to the start of construction. Material disposed of onsite shall be
compacted in place and permanently stabilized (see Small Parcel Minimum Requirement
No. 2). Excavations for the foundation and associated piping will be kept neat and con-
fined to the minimum required working area. Trench excavation spoils shall be stockpiled
on the uphill side of the trench. Waste material stockpiled on the site prior to final dis-posal will be covered during inactive periods to prevent wind and water erosion. Delivery
of aggregate materials for roadway and foundation construction will be timed to minimizl
stockpiling prior to installation. Stockpiling of construction materials will be confined to
the area identified on the site plans.
Existing Site Conditions
The majority of the proposed site is cleared and covered with unmaintained grass and
brush. Construction of the standpipe will require clearing approximately Lt3 rc Ll2 acre of
young fir and alder trees with an average diameter of 12 to 18 inches. Access to the site is
provided by an existing gravel surface road that currently serves the existing reservoir. No
improvements or widening is proposed for the existing road beyond replacement of the top
course at the close of construction.
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Adjacent Area Impacts
Potential for erosion and sediment impacts to adjacent areas exists along the downstream
property line. The drainage from the majority of this site exits along the south and north-
east edges of the construction site. These downstream areas shall be protected from sedi-
mentation damage by the installation of silt fences and straw bale barriers. The temporary
erosion and sediment control plan included in Appendix A provides details of these
controls.
Onsite Soil Description
A soil investigation and review of the Soil Conservation Service (SCS) soil survey for the
area found that the site soils are classified as a Clallam series gravelly sandy loam. These
soils are expected to have a relatively free-draining surface layer approximately 20 to
40 inches thick, underlain by a weakly cemented glacial till with very low permeability
rates.
Soil borings and test pits in the project area confirm the presence of till at shallow depths.
Analyses of soil samples indicate that the surface soil layer in this vicinity is composed of
approximately 60 percent silt, which conflicts with the general SCS characteristics of the
site soils. This soil is not expected to have a particularly free-draining surface layer and
would not be suiable for subsurface infiltration facilities.
The Clallam soils are classified in hydrologic soils group Type C. This soil type char-
acteristically has a moderately high potential for runoff. Seasonal runoff is expected to
run subsurface across the top of the till layer and emerge in low-lying areas and at drainage
courses.
Critical Areas r
The proposed site is located on a relatively flat area on top of a ridge with cross slopes in
the range of 5 percent. There are no steep slope areas within the construction area or in
the near vicinity that could be classified as critical areas. A site survey concluded that no
jurisdictional wetlands are located in the project area.
The Port Townsend critical area maps were also reviewed for the subject site. The only
map that highlighted areas on the site was the critical aquifer recharge area map. Sites that
are designated as critical aquifer recharge areas have restrictions on developments that have
a higher-than-average probability of groundwater pollution. These restrictions will not im'
pact the proposed standpipe construction significantly.
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Erosion and Sediment Control Measures
Minimum Requirements
Minimum requirements for erosion and sediment control for this project site have beenidentified in Section I, Project Overview. In summary, the mini*ur t"quirements forerosion and sediment control for this project will be provided by the development of aSmall Parcel Erosion and Sediment Controi Plan (SPES-P;. rnese minimum requirements
are defined in Chapter I-2.3 of the Stormwater Manual and repeated below. The con-tractual requirement for erosion and sediment control is established in the construction
specifications Section 3.3, Environmental Controls.
The temporary erosion and sediment control plan included in Appendix A identifies thelayout of BMPs to control erosion and sediment. Appendix C includes details for construc-tion of the various individual BMps for erosion conirol.
Small Parcel Requirement No. 1: Construction Access Routes. Prior to the start ofgeneral construction, the construction vehicle entrances to the site shall be stabilized with arock pad system to reduce the transport of disturbed soils off the site. Design for stabilized
construction entrances shall follow the guidelines from Chapter II-5.6.1 of the StormwaterManual. Construction roads shall also be stabilized as outlined in BMp E2.L5 with theapplication of aggregate to the road surfaces. Dust control (BMP Fjz.ZO) shall be imple-mented during dry weather. The contractor shall be responsible for maintenance and re-placement of the rock access pad and other construction controls.
As identified on the sitg plan, a temporary construction material stockpiling area will be
established at project initiation. Temporary fencing will be placed around ihat portion of
the area that does not directly abut the construction acg:ss road. The size and shape of the
area can be modified by the contractor to suit operational needs of the site. Runoff con-trols such as silt fencing (BMP E3.10), straw bale barriers (BMP E3.15), and runoff con-trol dikes (BMP E2.55) shall be installed along the downsrream perimeter of the site to
prevent the discharge of sediment laden runoff.
Small?arcel Requirement No. 2: Stabilization of Denuded Areas. Immediate protec-
tion of exposed soils shalt be provided during construction delays or over winter months.All areas left exposed more than 7 days in the summer arrrd2 days in the winter shall be
stabilized with mulching @MP E1.15) and seeding (BMP E1.10). Shredded srraw mulchshall be applied to a minimum thickness of 2 inches over the ground surface. Other
mulches may be used when approved by the engineer.
Small Parcel Requirement No. 3: Protection of Adjacent Properties. Following the
delineation of the clearing limits, a filter fabric fence (BMp E3.10) shall be installed
around the lower end of the site. Preliminary location of the fence is shown in the attachedtempogry sediment control plan. The fence shall be located such that any runoff from thesite will be filtered prior to offsite discharge. Design standards foi the filter fence
Port Townsend Standpipe
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construction and materials shall follow the requirements of Chapter II-5.8.1 of the
Stormwater Manual. Alternatively, the contractor may use a series of straw bale barriers
(BMP E3.15) or brush barriers (BMP E3.20) to control offsite runoff with approval from
the Engineer.
Small Parcel Requirement No. 4: Maintenance. Erosion and sediment BMPs shall be
inspected at regular intervals for damage and sediment accumulation. At a minimum, the
facilities shall be inspected weekly and after any runoff-producing rain event. Weekly
inspections shall take place at the end of the work week and any needed repairs completed
before the job is shut down for the weekend. BMP inspections shall continue at these
intervals during periods of work stoppages or until permanent cover has been established.
Specific inspection schedules for the various BMPs shall follow the recommendations in
Chapter tr-5 of the Stormwater Manual. A copy of this section shall be kept at the job site
for reference by the contractor during the construction period.
Permanent Stabilization
As soon as possible after final grades are established, all disturbed soils shall be stabilized
with permanent ground cover to prevent wind and water erosion. Stabilization shall, at a
minimum, follow the guidelines established for BMP E1.35, "Permanent Seeding and
Planting," in Chapter II-5.4.3 of the Stormwater Manual.
Maintenance
Maintenance of the erosion and sedimentation BMPs has been set forth above under Small
Parcel Requirement No. 4.
X Bond Quantity Worksheets, Detention Facility
Summary Sheet and Sketch, Declaration of Covenant
The City of Port Townsend is not required to post bonds for municipal contracts; detention
facilities will not be installed with this project; and no covenants will be necessary for
operation of stormwater facilities. Therefore, this section is not applicable to this project.
XI Maintenance and Operation
Maintenance activities for the permanent stormwater facilities will involve regular inspec-
tion of the vegetated strip around the standpipe. A vegetated filter strip 25 feet in width
will be maintained around the perimeter of the standpipe facility. If the surrounding area
becomes denuded or sparsely vegetated, maintenance crews will reestablish a stand of thick
grass by seeding the area and watering as required until the new grass is established.
Port Towwend Standpipe
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IMaintenance activities for the temporary erosion and sediment control. measures have beencovered above in the SPESCP. Filter fabric fences and other temporary erosion controlsshall be removed as directed by the Engineer, after permanent er-osion control plantings
have become established.
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Vertical 8ar Gratefor Pond Overflow
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2 .5
Std. Galv. Handholds
Steps or Ladder
B
Elbow Restrictor
5161 Reluired
IZ'ICMP
Shear Gate w/
Control Rod For
Cleanout/Drain
(Rod Bent as Req.d
for Vertical Alignment
w/ Cover)
Elbow RestriNal Re1u
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DoT c4<h,Bagn lF"v./ Flovt Kesfrra*or
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Stormwater ControlsDetention Rout,j-ng
======== ======================================== =====================
BASIN SUMMARY
BASIN ID: lOO
SBUH METHODOLOGY
TOTAL 4R84.......:
RAINFALL TYPE....:
PRECIPITATION....:
TIME INTERVAL....:
TIME OF CONC.....:
ABSTRACTION COEFF:
NAME: 100-yr existing
0.20 Acres
TYPElA2.50 inches
10.00 min
5.00 rnin
0.20
BASEFLOWS: 0.00 cfs
PERVIOUS AREAAREA..: 0.20 AcresCN....: 90.00
IMPERVIOUS AREAAREA..: 0.00 AcresCN....: 98.00Ac-ft TIMEz 480 minPEAK RATE: O.O7 CfS VOL: O 03
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BASIN ID: 108
SBUH METHODOLOGY
TOTAL 4R84.......:
RAINFALL TYPE....:
PRECIPITATION....:
TIME INTERVAL....:
TIME OF CONC.....:
ABSTRACTION COEFF:
PEAK RATE: O.O5 CfS
NAME: 2-year future
0.20 Acres
TYPElAL.20 inches
10.00 min5.00 nin
0.20
VOL: 0.02
BASEFLOWS: O. OO CfS
PERVIOUS AREAAREA..: 0.00 Acres
CN. . . . : 90.00
IMPERVIOUS AREAAREA..: 0.20 AcresCN....: 98.00Ac-ft TIME: 480 min
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BASIN ID: 109
SBUH METHODOLOGY
TOTAL AREA.......:
RAINFALL TYPE....:
PRECIPITATION....:
TIME INTERVAL....:
TIME OF CONC.....:
ABSTRACTION COEFF:
PEAK RATE: 0.07 cfs
NAME: lO-year future
0.20 Acres
TYPElA
7 .7 5 inches
10.00 min
5.00 min
0.20
VOL: 0.03
BASEFLOWS: O. OO CfS
PERVIOUS AREAAREA..: 0.00 AcresCN....: 90.00
IMPERVIOUS AREAAREA..: 0.20 AcresCN....: 98.00Ac-ftr 'TIME: 480 minl
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================================ =====================================
BASIN SUMMARY
BASIN ID: 110
SBUH METHODOLOGY
NAME:100-year future
TOTAL AREA
RAINFALL TYPE....:
PRECIPTTATION....:
TIME INTERVAL....:
TIME OF CONC.....:
ABSTRACTTON COEFF:
PEAK RATE: 0.10 cfs
0.20 Acres
TYPElA2.50 inches
10.00 min5.00 min
0.20
VOL: 0.04
BASEFLOWS: 0.00 cfsPERVIOUS AREAAREA..: 0.00 AcresCN....: 90.00
TMPERVIOUS AREAAREA..: 0.20 AcresCN....: 98.00Ac-ft TIME: 480 min
BASIN ID: 98
SBUH METHODOLOGY
TOTAL AREA
RAINFALL TYPE....:PRECIPITATION....:
TIME INTERVAL....:TIME OF CONC.....:
ABSTRACTION COEFF:
PEAK RATE: 0.02 cfs
NAME: 2 year existj-ng
0.20 Acres
TYPElAL.20 inches10.00 min5.00 min
0 .20
VOL: 0.01
BASEFLOWS: O. OO cfs
PERVIOUS AREAAREA..: 0.20 AcresCN....: 90.00
IMPERVIOUS AREAAREA..: 0.00 AcresCN....: 98.00Ac-ft, TIME: 480 min
BASIN ID: 99
SBUH METHODOLOGY
TOTAL AREA.
RAINFALL TYPE....:PRECIPITATION....:
TIME INTERVAL....:
TIME OF CONC.....:
ABSTRACTTON COEFF:
PEAK RATE: O.O4 cfs
NAI{E : 10 -year existing
0.20 Acres
TYPElA1.75 inches10.00 min5.00 min
0 .20
VOL: 0.01
BASEFLOWS: O. OO cfsPERVIOUS AREAAREA..: 0.20 Acres
CN. . . . : 90.00
IMPERVIOUS AREAAREA..: 0.00 AcresCN....: 98.00Ac-ft TIME: 480 min
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Port Townsend Standpj-Pe
Stormwater Controls
Detention Routing
== == ===== = ==== == == == = = == = = ===== = = = = = == ==== = = = === === == === === == = = === ===
STAGE STORAGE TABLE
CUSTOM STORAGE ID NO. S1OO
Description: existl-ng depression
STAGE <----STORAGE--.->
(ft) ---cf--- --Ac-Ft-
STAGE <----SToMGE----)
(ft) ---cf--- --Ac-Ft-
STAGE <----SToMGE----)
(ft) ---cf--- --Ac-Ft-
STAGE <----SToMGE---- )
(ft) ---cf--- --Ac-Ft-
,l
267.10
267.20
267.30
267.40
267,50
?67.60
267.70
?67,80
267.90
268.00
268.10
268.20
268.30
268.10
268.50
268.60
268.70
268.80
0.0000
83.333
166.67
250.00
333.33
116,67
500.00
583.33
666.67
750.00
1075
1400
1725
2050
2375
2700
3025
3350
0.0000
0.001 9
0.0038
0.0057
0.0077
0.0096
0.01 1 5
0.01 34
0.01 53
0.0172
0.0217
0.0321
0.0396
0.0171
0.0545
0.0620
0.0691
0,0769
268.90
?69.00
269,10
269.20
?69.30
269,40
269,50
269.60
269.70
269.80
269.90
270.00
270.10
270.20
270.30
270,40
270.50
?70.60
3675
4000
4325
1650
1975
5500
5625
5950
6275
6600
69?5
7250
7890
8530
9170
981 0
't0450
1 1090
0.0844
0.0918
0.0993
0.1067
0.1112
0.1217
0.1291
0.1366
0.1441
0.1515
0.1 590
0.1661
0.181 1
0. 1 958
0.21 05
0.2252
0.2399
0,2546
270.70
270.80
270-90
271,00
271,10
271,20
271.30
271.10
272,00
272.10
272.?0
?72.30
272.40
11730
12370
13010
13650
11290
11930
15570
16210
1 6850
17490
181 30
18770
19I',t0
20050
21 000
21950
22900
23850
0.?693
0.2840
0.2987
0.3134
0.3281
0.3127
0.3574
0.3721
0.3868
0.401 5
0.4't62
0.4309
0,1456
0,4603
0.4821
0. 5039
0.5257
0.5475
272.50
272.60
272.70
272.80
272.90
271,00
273.10
273.20
273.30
273.40
273.50
273.60
273,70
273.80
273.90
271.00
24800
25750
7.6700
27650
28600
29550
30500
31450
32400
33350
34300
35250
36200
37150
581 00
59050
0,5693
0. 591 1
0.6129
0.6348
0.6566
0.6784
0.7002
0,7220
0.7138
0.7656
0.7874
0.8092
0.83 1 0
0.8528
0.8747
0.8965
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271.50
271.60
271.70
271.80
271.90
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===== = ====== ======= ====== ==== = === ========================= == = = == =====DISCHARGE STRUCTURE LIST
DISCHARGE LIST ID No. dlOoDescriptlon: 1 inch orifice I
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Port Townsend StandpiPe
SLormwater ControlsDetention Routj-ng
======================== =============================================
STAGE DISCHARGE TABLE
DISCHARGE LIST
Descriptlon:1
ID No. d100inch orifice
STAGE
( ft)
<--DI SCHARGE.--)
---cfs--
< --DISCHARGE--.)
---cfs --
(--DI SCHARG E- -- >
---cfs--
< --DI SCHARGE--- >
---cfs--
STAGE
( ft)
STAGE
( ft)
STAGE
( ft)
267,10
267.20
267,30
?67,40
267.50
267.60
267.70
267.80
267.90
268.00
268,10
268.?0
268.30
268.10
268.50
268.60
268.70
268.80
0.0000
0.0028
0.0056
0.0083
0.01 1 1
0.01 39
0,0167
0.0't9_4
0.0222
0.0250
0.0261
0.0271
0.0282
0,0292
0.0503
0.031 3
0,0324
0.0334
268.90
269.00
?69.10
?69.20
269.30
269.10
269.50
?69.60
269,70
269.80
269.90
270.00
270.10
270.20
0.0345
0.0555
0.0566
0.0376
0.0387
0.0397
0.0/'08
0.0/r18
0.0429
0.0439
0.0450
0.0460
0,0167
0.0173
0.0/'80
0.0486
0. 0/'93
0.0199
270.70
?70.80
271.90
27?.00
27?.10
272.20
?72.30
272.10
0.0506
0.051 2
0. 051 9
0. 0525
0.0552
0.0538
0.0545
0.0551
0.0558
0.0564
0.0571
0.0577
0.0584
0.0590
0.0596
0.0602
0.0608
0. 06't /i
272,50
272,60
272,70
272.80
272.90
273,00
273.10
273.20
273.30
273.40
273.50
271.60
273,70
?73.80
?73.90
274.00
0.0620
0.0626
0.0632
0.0638
0.0644
0. 0650
0.0656
0.0662
0.0668
0.0674
0.0680
0.0686
0.0692
0.0698
0.0704
0. 071 0
270.90
271.00
271.10
?71.20
271.30
271.40
271.50
271.60
271.70
271.80
?70.30
270.40
270.50
270.60
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stormwater controls Port rownsend standpipe
Detention Routing
= =============== ====== ====== === === ===== == ==== = ==== = ===== = =========== =LEVEL POOL TABLE SUMMARY
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<--------DESCRI pTI 0N---------)
MATCH INFLG' -STO- -DIS- (-PEAK-) STOMGE(cfs) (cfs) --id- --id- (-STAGE> id VOL (cf)1
ilZ-year future
1O-year future
1O0-year future
0.00
0.00
0.00
s1 00
s 100
s1 00
d1 00
d1 00
d1 00
10
11
12
0.05
0.07
0.10
267.43
267.61
?67.87
273.54
4.27.78
640.34
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STORMVTATER I.TANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
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rI-5.3 IrEMPORARY CO\TER PRACTICES
II-5.3.1 BMP E1.10: Temporarv Seedinq of Stripped Areae
Code:symbol: -+-
.J
Definition The eetabllehment of a temporary vegetative cover on disturbed areas by
,"edi"g ,ith appropriate rapidly growing annual plants'
ffir."e temporary aoil etabillzation by planting grasBea and legumes to areas
which would remain bare for more than Z dly! where permanent cover ig not necesaary
or appropriate.
conditiong Where PractLce Applieg
r permanent etructurea are to be inetalled or extensive re-grading of.
the area ,iif-".J"r prior to the eetablishment of Permanent vegetation.
r Areae which wiII not be eubjected to heavy wear by conetruction
traffic.
r Areaa eloping uP to 1Ot for lOO feet or legg (where temPorary eeeding is the
only BMP uEed.
AdvantaqeE
o Thie ia a relatively inexpeneive form of eroeion control but should only be
used on eiiee awaiting p"-"."n"trt planttng or grading. -.Those giteg ehould have
permanent-;;;d;;-""6a- (Eee BMp ir.gs, iermanent seedlng and Planting).
r vegetatlon wLll not only prevent eroeion. from occurring, but will also trap
eediment in runoff from other parts of the gite'
. Temporary eeeding offere fairly rapid protection to expoeed areag.
D isadvantaqe g / Prob leme
. Temporary eeeding ie only viable when there ie a eufficient window in time for
planta to grow aid estaUii"h "otr"r. During the eatablishnent period the bare
soil ehoufi Ue protected with mulch (aee BMP El.15) and/or clear plaetic
covering. (see BMP 81.20).
r If solrn on eubeoil, growth will be poor unlege heavily fertilized and limed'
Because over-fertiliiation carr cauge pollution of gtormwater
. runoff, otn-r practicee euch ag mulching (BMP 81.15) alone may be more" appropriate. the potential for over-fertilization is an even worEe
problem in or near aquatic systems'
. once seeded, areaa cannot be used for heavy traffic.
r May require regular irrigation to flourish. Regular,irrigation is not
encouraged beciuee of the expense and the potential for erogion in areas
that are "oi i"g"farly inepeitea. The use of low maintenance native
speciee should be encouragla, and planting ehould be timed to minimize
the need for irrigation-
P 7 annino Considerat ions
sheet erosion, caused by the impact of tain on bate soil, is the soutce of most fine
p"tii"t"t in sediment. To redu}e this sediment l-oad in tunoff, the soiT sutface
rr-5-2 FEBRUARY,L992
STORM9IATER I{ANAGEI.iENT ITANUAI, FOR THE PUGET SOUND BASIN
itseLt shou-ld be protected. The most efficient and economical me'ans of controrringsheet and ri77 etosion js to establish vegetative cover. Annual plants nniii-ZproutrapidLy and sutviu-e for only one groving leason are suitable tor Zstatrlishing !
temPotary vegetative covet. Temporary seeding is ettective vhen conbined wiihconsxtuct'ion phasing so bare areae of the site are minimized ax al_L times.
Tempotaty seeding may ptevent costly maintenance operations on other erosion controLsystems. For example, sediment.basjn clean-outs wiLL be teduced if the arainigeatea ot the basin is seeded where grading and consxruction are not taking iliiZ.Petimeter dikes wiLl be more eftective i7 not choked r'itll sediment.
Temporaty -see ,i4g is essent ial to preserve the integrity of earthen structu:re.s usedto conttol sedimenx, such as dikes, diversions, and the banks and, dams of sed,imentbasing.
Ptopet see.dbed pre,paration and tlre use of quality seed are important in thispractice just as in pexmanent seeding. FaiTure 7o caretully ?orlon "oini igrononictecommendations vi77 otten tesult in an inadequate stand of vegetation thax'providesTittLe or no erosion eontrol.
Desiqn Criteria
' Time of Planting - Planting ehould preferab).y be done between April 1 andJune 30, and_september 1 through oclober 31. If planting is done in the.months of .ruly and August, irrigation may be required. ir ptantitrt -ir---orr"
bet$teen November 1 and March 31, mulchin! ehall be required immediitery iit"tplanting- If eeeding ie done during the gummer monthe, irrigation of 'eomeeort erill probably be neceeeary.
a Site Preparation - Before eeeding,meaauree euch ae gradient terraces,and eediment babins.
install needed gurface runoff controlinterceptor dike/swales, Ievel spreaders,
'iu!F'a
Name
a
seedbed Preparation - The eeedbed ehould be firm with a fairly fine eurface.Perform all cultural operatione across or at right angles io fn" elope. seeBMP 81.-45,- Topsoiling, and BMP 82.35, surface noughening for."r" i.i"rtn.iioton eeedbed preparation. A minimum of 2-4 inchee 5r tiriea toletir isrequired.
Fertilization - aa per suppliers and/or soil coneervation servicerecommendatione. Developmente adjacent to water bodiee must use non-phoephorue fertilizer.
seeding - seeding mixturee will vary depending on the exact location, soiltype, elope, etc. Information on_mixee-may b6 obt,ained from 1ocal suppliere,the t{aehington state Department of Tranepoitation, or the Soil coneervationService. Hohtever, approval to uEe any plrticular mix must be obtained fromthe rocal government. The following leea mix is supplied as guidance.
Redtop (AqroEtis alba)Annual Rye (Lolium multiflorum)Chewings Fescue(Festuca rubra commutata)White Dutch Clover (Trifolium repens)
"Hydro-eeeding,'also be used.
applicatione with approved seed-mulch-fertilizer mixtures may
Proportions
Bv Weioht
PercentPurity PercentGermination
90
LOr40r
40r
10r 95
92
98
9'1
90
90
80
a
I I-5-J FEBRUARY, 1992
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STORMWATER I.IANAGEMENT !,I,ANUAL FOR THE PUGET SOUND BASIN
Maintenance
r Seeding ahould be eupplied with adequate moisture. Supply water as needed,eapecially in abnormally hot or dry weather or on adveree sites. Waterapplication ratee ehould be controlled to Prevent runoff.
e Re-seeding - AreaE which fail to eetablieh vegetative cover adequate to prevent
erosion ehall be re-eeeded ae aoon aE euch areas are identified.
All temporary erosion and eediment control measures ehould be removed within
30 daye after final site etabilization is achieved or after the temporary BMPsare no longer needed. Trapped sediment muet be removed or etabilized on eite.Dieturbed soil areas reeulting from removal ehould be permanently etabilized.
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STORMWATER I.IANAGE}.IENT I'{ANUAL FOR THE PUGET SOUND BASIN
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If-5.3.2 BMP 81.15: Mulchinq and Mattinq
Code:symbol, *-
Definition Application of plant residueg or other suitable materiale to the eoil
srurf ace.
Purpose
To provide immediate protection to exposed Eoilg during the period of ehort
conitruction delaye, 6r over winter monthg through the application of plant
residues, or othei Euitable materiale, to expoaed eoil areag.
Mulchea aleo enhance plant eetabllehment by conserving moisture and moderating eoil
temperaturee. t{ulch lretpe ho]d fertilizer, eeed, and topaoil in place- in the
pre-eence of wind, rainr. lnd runoff and maintaina moieture near the eoil surface.
Conditl-ong Where Practice Appliee .
o In areaa whicn have been geeded either for temporary or permanent cover,
mulching should immediately follow seeding.
. Areae which cannot be eeeded because of the season, or are otherwiee
unfavorable for Plant growth.
o Areae which have been eeeded ae epecified in TemPorary Seeding (BMP El-fQl.
o In an area of greater than 2:1 elope, mulching should immediately follow
seeding.
Advantaqes
o Mulching offers .instant protection to exposed areas.
r Mulchee coneerve moisture and reduce the need for J.rrigation.
r Neither mulching nor matting require removal; seede can grow through them
unlike plaetic coveringe.
D i s advantaqee /Prob lema
. Care muet be taken to apply mulch at the specified.thicknegs, and on steeP
elopeg mulch muet be eupplemented with netting.
o Thick mulchee can reduce the eoil temperature, delaying eeed germination.
o Mu1cheE euch as straw, which are often applied to areag after grading must then
be removed and either compoeted or landfilled. Straw ie hollow, so it can
actually draw water into lhe ground below it if the etraw ie at an angle.
P lanning Considerations
Ilulches are applied to the soiT surface to consetve a desjtable soiT propert-y ot to
promote plant- gtovth. A surface mulch js one of the most effective means of'controlting tul.off and erosion on disturbed Tand (see Eigure rr-5.7 tor a comparison
of pollutant loading reductions for vatious nulches).
Mulches can increase the infiTtration rate of the soi7, reduce soiT moistute
Ioss by evaporafion, ptevent crustjng and se.aling of the soiL s_urtace, modify
soil tbnpeiatures, an? ptovide a sui'table microclimate tor seed germination.
Organic mulch matetials, such as strantt urood chips, batk, and. vrood fiber, have been
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STORM9IATER UANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
found to be the most eftective
A variety of nets and mats have been deveToped, for erosion controL in recent yeats,
and thesL are aJ,so used as mulches, patticuJarly in ctitical areas sucll as
watenays. They may be used to hoTd other muTches to the soil sutface.
11he choice of materials for mulching wi77 be based on the type of soiT to be
protected, site conditions, seasor?, and economics. It is especiaTTy inp_ortant to'nulch libetalTy in mid-summer and prior to winter, and on cut sTopes and southetn
slope exposurel. TAbTe II-5.1 gives a comparison of costs based on 1988 figutes.
Oroanic Mulchee
Straw - Straw ie the mulch most commonly ueed in conjunction_with seeding. Ite use
Is recornnended where immediate protection ie desired and preferably where the need
for protection vrill be lees than 3 monthe. The straw ehould come from wheat or
oatsl and may be spread by hand or machine. If the etraw is not clean, weed growth
can occur. Straw can be windblown and muet be anchored down. common anchoring
methodg are:
1. Crimping, disking, rolling or punching into the soili
2. Covering wlth netting;
3. Spraying with a chemical or fiber binder (tackifier); and
4. Keeping moist. Natural precipitation can often provide sufficient moisture. (21
Corn Stalkg - TheEe should be ghredded into 4 to 5-inch lengths. Stalke decompose
alowly and are resietant to wlndblow.
Wood Chlpe'- Suitable for areaE that wLll not be closely mowed, and around
ornameltal plantings. Chips decompoee slowly and do not reguire tacling. -They must
be treated;ith 12 pounda nitrogen-per ton to prevent nutrient deficiency in planta.
Chlpe can be a very inexpeneJ.ve mulih if they are obtained from treea cleared on the
ette. Ho!,rever, bolh wood and bark chipa tend to wash down slopes of more than
6 percent and create problems by clogging inlet grates etc. and are therefore not
preferred for uee in thoee areas.
Bark Chipg, Shredded Bark - By-products of timber processing. Used in landscaped
@-isalsoaguitabIemu1chforareasp1antedto9raseesandnot-cloaely-mowed; may be applied by hand or mechanically; Bark is not usually toxic to
grassee or legumel, and additional nitrogen fertilizer is not required.
Wood Fiber - Used in hydro-aeeding operations, applied as part.of the slurry. These
short celfuloge fiberE-do not reguire tacking, although a tacking agent or soil
binderg are sometimes used with wood fiber. The longer the fiber length, the better
the wood fiber will work in eroeion control. This form of mulch doeE not provide
eufficient protection to erodible soils to be uged alone during the eevere heat of
summer or for tate fall seedings. tfood fiber hydro-seed slurries may be uged to
tack gtraw mulch. This combinition treatment ie well suited for steep slopee and
critical areas' and gevere climate conditions.
There are other organic materials which make excellent mulches but are olly
available locally 6r seasonally. Creative use of these materials can reduce cosLs-
Manure l.lulchee - tlanure mulches should be well-aged and.are not recommended for use
near waterbodiee
Chemical Mulches and Soil Binders
The use of eynthetic, Epray-on materialg (except tacking agents used with hydro-
seeding) ie ;lot recommeirded. A major problem with their use is the creation of
impervi6us sffF"ces and, possibly,=adverse effects on water quality. Research has
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STORMWATER I.IANAGEI.iENT I,IANUAL FOR THE PUGET SOUND BASIN
shown that they can cause more eroeion when used than doee bare exposed goil.
-l Nets and Hate - Ueed alone. netting does not retain eoil moisture or
I l?iE_ffi- rt etabirizee the eoil surface whire grasaea are being
' ;il-i"-"=.f"I in graeeed waterwaye and on elopea- Light netting may
hold other mulchei in place. Ite relatively high coat makes it most
small eiteg.
The moet critical aepect of installing nets and matE ie obtaining firm' continuoue
contact between the iraterial and the eoil. Without guch contact' the material ie
ugeleee and eroeion occur6. It ie important to use an adequate number of etaplee
and to roll the material after laying it to ensure that the EoiI ie protected.
Table II-5.1 Summary of Eetimated Service Livee and Cogte
1998 Baee - Horner' ,JanuarY, 1990
Tbc crtimrrcd colt of tedilg whcrc it wu urcd il brr€!
oo bydrotccdiag (rpprorinrrcly 3500rcrc)'
modify soil
eetabliehed,also be used toeuitable for
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BtinradScrvica
Lifc(nmtls) -
f,3rirumdQ6l
O(segwd)
(6 nrmths rcwicc)Tcc{rniruce
3.200Sraw (4 T/ac)
3 2.500tr"w (..2STtacl
z4a06Straw (4 T/r)
nallltr-mdclE4
fcrtilird. lc&d
3.?006furc met
irccls 3.600r
{.1006
vndret 3.300c fiber blar*ct
6 1,300Wodfibcrmulch(t25T/r) fcnilizc4
rF{d
1,9006W@d frbcrrulch
(125 T/rc) with
tactificr (50 gaUac),
fatilizcd !ce&d
11006Wodfibcrmulch
(125 T/rc) with
r-abifis1(90 grllac),
fenilirld.serd
2,3006Wodfibcrmulch
(125 T/r) with
trcLificr (120 gaUrc),
fatilizcd. s&rded
2.1006Chemicd aqent
23006Plastic sheetine,
< {r00>6D6igrtod
rcdimmutim mnd
< ?.500>(Nsr-dcsimedpmd
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STORMWATER I.TANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
Figure If-5.1 l{ean TSS and Overall Pollutant Loading Reductions
of Slope Treatmente Relative to Controlsfrom Horner, January, 1990
TSS Reduclion
Overall pollulant
loading reduclion
100
80
60
40Go\;
€20fE(l,
cr
0
-20
-40
-60
Straw Slraw Straw Slraw(4 (1.2s (4 12.7sT/ac) T/ac) T/ac) T/ac)
M,F,S M,F,S
Jute Excel- Woven Syn-sior Slraw lhetic
Fiber
Wood Wood Wood
Fiber Fiber Fiber(1 (r (r
T/ac) Tlacl T/ac)
F,S T,F,S T,F.S
(1e87- (t988 -. 88) 8e)
Wood Chemic- FilterFiber al Fabric
(1.s
T/ac)
T,F.S
Fence
ffi
Slope Treatment
Figurc 3. Mean TSS and Overall Pollutant Loading Reductions
of Slope Treatments Relative to Controls
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STORMWATER I.TANAGEI.{ENT MANUAL FOR THE PUGET SOUND BASIN
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Deeion Criteria
o Site Preparation - same as Temporary Seeding.
i Mulch Materiale, Application Ratee, and Specifications - See Table II-5.2.
. EroEion blankete (nete and mata) may be ueed on level areag' on elopea !P to
50 percent, and in eraterwaya. Where eoil ie highly erodible, netg ghall only
be ireed in connection with an organic mulch euch aE Etraw and wood fiber. Jute
nets ehall be heavy, uniform cloih woven of eingle jute yarn, which if 35 to 48
inchee wide ehall weigh an average of 1.2 lbe./linear yald: It must be so
applied that it is in complete c6ntact wlth the goil. If it ig not, erosion
will occur beneath it. lletting shall be gecurely anchored to the soil with No.
11 gauge wire ataples at leaet 5 incheg long, with an overlap of three inches.
o Exceleior blanketg are congidered protective mulcheg and may be ueed alone on
erodible goile and during all times of year.
o S€€ Ftgure II-5.2 for orientatlon of netting and matting'
llaintenance
o Mulched areas should be checked periodically, eepecially following severe
stormE, when damaged areae of mu-Ich or tie-down material ehould be repaired.
o AII temporary erogion and eediment control meagures ehall be removed within
30 days aftei final eite etabllizatlon ie achieved or after the temporary BMPe
are n6 longer needed. Trapped sediment shall be removed or stabilized on eite.
Dieturbed ioLl areae reEulting from removal ehall be permanently etabilized'
Referencee
Horner,RichardR.'JunoGuedryandl{l.chaeIH.Kortenhof,@pffectiveness of tti-qhwav constiuction Site ErosigB=a9d Eollutlon,ggEtrolr, WA-RD 20O'1' JanuarY' 1990'
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STORMWATER I.{ANAGETIENT I.IANUAL FOR TIIE PUGET SOUND BASIN
Table II-5.2 Guide to l{ulch Materials, Ratee and Usee
MuIchMaterial QualityStandarde
Applicat,ion Ratee
/1000 ft2 facre
Depth ofApplication Remarksl
GraveI,alag or
crushedgtone
Waehed,t-1L"eize
9 yds3 3 inchee Excellent mulchfor ehort elopee
and around woodyplant8 &ornamentala. Use
where subject tofoot traffic.Approx. 200O lbe/yd'
Hay orgtra$t Air dried,free from
unwantedseedg &
coarEematerial
7s-100lbg. or2-3 baleg
Ltr-2t,tonsor
90-120
baleg
Minimum of2 inches
Uee where the
mulching effect ieto be maintainedfor >3 monthg. Iseubject to windblowing unleeekept moiet ortacked down. MoEt
common & widelyuaed mulchingmaterial. Can be
ueed in criticaleroeion areab.
l{oodfibercelluloee(partially
digeeted
woodfibere )
Dyed greenghould notcontaingrowthinhibitingfactore.
2s-30lbe.1000-
1500lbs.
If ueed oncritical areas,double the normalapplication rate.
Apptyw/hydromulcher. Notie-down reguired.
Packaged in 1O0lb. bags.
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rAll mulchcr will providc somc dcgrcc of (l) crorion control, €) moirorc
conscwrtion, @) wccd control, end (4) rcduction of roil cnrrting.
r r-s-10 FEBRUARY, L992
STORMT{ATER MANAGEI{ENT I{ANUAI, FOR THE PUGET SOUND BASIN
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Figure II-5.2 orientation of Netting and Matting
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llhere there.is a berm at the top of the slope'
Oring the netting over the berm and anchor it
behind the berm.
Shal I ow
Si ope
Steep ..,
Di tch
0n shallow slopes' striPs
of netting may be apPlied
across the slope.
(Slopes up to l:1)
Berm
rtl
z4
In ditches, aPPIY netting
parallel to the direction
of flow. Use check slots
every 15 feet. Do notjoin striPs 'in the center
of the ditch.
0n steep sloPes, aPPIY-- -strips bf netting Parallelto the direction of flow
and anchor securelY.
(Slopes grealer han 1 :l )
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terminating the installation. Turn the
end under 6" and staple at 12" intervals.
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STORMWATER I.T,ANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
CPC
fI-5.3.3 BMP El.20: Clear Plastic Coverinq
Code:Syrmbol r -@-*
Definition The covering with clear plaetic eheeting of bare areas which needimmediate protection from eroeion.
Purpose
To provide immediate temporary erosion protection to slopee and disturbed areae thatcannot be covered by mulching, in particular during the apeclfied aeedlng periods orae otherwiee required by the local goverrunent. Clear plaetic is algo uged toprotect digturbed areaa which muet be covered during ehort periode of inactivity tomeet November l-l,larch 31 cover requ!,rements. Because of many dieadvantagee clearplaatic covering ig the least preferred covering BMp.
Conditiong l{here Practice Applies
o Dleturbed areas which requLre immediate erosion protection.
. Areas eeeded during the time period from November 1 to March l.(Note! Plantings at thiE time require clear plastic covering for germinationand protection from heavy rains.
Advantaqeg
r Clear plaatJ.c covering ia a good method of protecting bare areaa which needimmediate cover and for winter plantings.
. May be quickly and eaeily placed.
D I gadvantaoe g /Prob lema
e There can be probleme with vandals and maintenance.
o The eheeting will result in rapid, 1O0t runoff which may cauEe gerioue erogionproblema and/or floodlng at the baee of elopes unleea the runoff ie properlyintercepted and safely conveyed by a colleclJ.ng drain. Thie ie strictly atemporary mea8ure' Eo permanent stabilization ie etill required.
o It ie relatively expenaive.
r The plaetic may blow away if it ts not adequately overlapped and anchored.
Ultraviolet and poaaibty vigible light can cauae some types of plastic tobecome brittle and eaeily torn.
Plaetic mugt be diepoeed of at a landfill;environment.it is not easily degradable in the
T
a
o If plaatic ig left on too long during the epring it can severely burn anyvegetation that hae grown under it during coolei periods.
Design Criteria
Clear plastic eheeting ghall have a minimum thicknese of 6 mil and meet therequirementg of WSDOT/APWA Section 9-14.5.
a Covering shall be installed and maintained tightly !.nor tiree on ropes with a maximum 10 foot grid spa-ingaeamE ehall be taped or weighted down fuII length and1 to 2 foot overlap of all seams. Seams should then
place by uaing eandbagsin all directione. Atlthere ghall be at leagt abe rolled and etaked or
rr-5-12 FEBRUARY, L992
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STORI.{WATER MANAGEI.{ENT I.iANUAL FOR THE PUGET SOUND BASIN
a
tied.
Covering ehall be installed imrnediately on areas eeeded between November 1 to
March 1, and remain until vegetation ie firmly eatablighed.
When the covering ie used on uneeeded elopee, it shall be left in place until
the next eeeding period.
Sheeting ehould be toed in at the top of the elope to prevent eurface flow
beneath the plaetic.
Sheeting ehould be removed ae soon ae ig poaeible once vegetation ie well grown
to prevent burning the vegetation through the plaetic eheeting, which acts aa a
greenhouse.
Maintenance
o Check regularty for ripe and placea where the plaatic may be dialodged.
Contact between the plaetic and the ground ehould alwaye be maintained. Any
air bubblee found ehould be removed tmmediately or the plaetJ.c may rip during
the next windy period. Re-anchor or replace the plaetic as neceasary.
AII temporary eroaion and sediment control meaaures ehall be removed within
30 days after final site etabilization ig achieved or after the temporary BMPeare no.longer needed. Trapped eediment ehall be removed or gtabilized on site.
DiEturbed eoil areae resulting from removal ehall be permanently etabilized.
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STORMWATER I.iANAGEMENT I'{ANUAI, FoR THE PUGET SoUND BASIN
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II-5.4.3 BMP 81.35: Permanent Seedino and P1antlnq
Code:Symbol:
Definition The eetabliEhment of perennial vegetative cover on dieturbed areae'
PurDoee
To eetabllsh Permanent vegetation (such as grasses, Iegumee and trees and ghrubs) aE
;;pi;it is poieiule to prevent- eoii erogion by wind or water, and to improve
witatite nabitat and eite aeethetice'
To provtde pollutant filtration (biofiltration) in vegetation-lined channels and to
eetablieh congtructed wetlande ai reguired (gee BMP Rw.10 in Chapter III-4 and RV'05
in Chapter III-5).
Condl,tione Where Practice Apoliee
r Graded, final graded or cleared areaE where Permanent vegetative cover ig
needed to stabilize the soil.
. Areaa which will not be brought to final grade for a year or more.
o Vegetation-lined channelg-
o Retentlon or detention ponds as required'
AdvantaqeE
o !{ell eetabllehed graae and ground covere can give an aesthetically p}easing,
finished look to a develoPment.
. Once eEtablished, the vegetation will Eerve to prevent erosion and retard the
velocity of runoff.
D ieadvantaqeE /Prob leme
. vegetation and mulch cannot prevent soil elippage and erosion if eoil ie not
inherentlY stable.
. coarge, high graageg that are not mowed can create a fire hazard in gome
localee. ri"ri "nott mowed graEg, however, provides lesg etability and Eediment
filtering caPacitY.
. Graaa planted to the edge of a watercourse may encourage fertilizing and mowing
near the water,a edge aid increaee nutrient and pesticide contamination'
o l{ay require regular irrigation to eEtab}ish and maintain.
P lannino Considerations
vegetation controTs erosion by teducing the ueT.ocity and the volume of overland ffow
ani protecting the bare soiT surtace from raindrop impact.
Areas uhich must be stabiTized aftet the Tand has been disturbed tequite.vegetative
covet. The most common and economical means of establishing this cover is by
seeding grasses and Tegumes-
Advantages of seeding over other means of establishing plan-ts- inelude the smaLl
initial estaDl,jsiment cosx, the iide uariety of grassls-,and legumes available' 7ow
latror tequirement, and ease of esXabl.ishment in difficuft areas.
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STORI.{WATER UANAGEIT{ENT MANUAL FoR THE PUGET soUND BASIN
consider the microclimate(s) within,the deveTopment area. Low areas may be frostpockets and requi.e, hardier vegetaxion since cold air tends to sink ,nd tlow towardslow spots. soutfi-facing sJopes may be more difticult to re-vegetate because they l.tend to be sunnier and drier. '
i
Disaduantages vhich must be deaLt with are the potential. for erosion during theest'ablishment, st'age, a ieed to reseed areas tha| faiT to establish, Jimii"T piri"a" ,duri-ng .the yeat euit,able f or seeding, and a need f or water and appropriate cliniljZ ,conditions during germination.
Thete are so many variables in plant growth xhat an end. product cannot be iguaranteed. I'luch can be done in the planning stages to lncrease the chances for jsuccessful seeding. SeJ,ection o-f the right plant- naterials for the site, gooa-seedbed prepatat_ion, tining, and conscientjous maintenance are important'.'whenevet possibTe,, n1tive species of plants should be used tor laidscaping. ?leseplants are altead.y adapted to the LocaLe and survivabiTity should re highZr tianwith exotic species.
Native species ate also Less -ljkely to require irrigation, which can be a largemaintenance burden and is neither cost-efiective no? e"oibgicaTly sound. t,
If non-natiu-e. pTant species are u.sed, they should be tolerant of a large range otgrowing conditions and as low-maintenance as possibJ.e. - ----v-
:
_lDeeion Criteria
' vegetation cannot, be expected. to supply an eroeion control cover and preventslippage on a soil that ie not stable aue to its texture, structure, iatermovement, or exceEaJ-ve elope
' seeqing ehould be done immediately after final shaping, except during thepelio$ of November 1 through March 1, when the gitl sf,ould bi protecied bymulching or plastic coveriig untir tire next seeding p"tioa.
o Permanent vegetatiol may be in the form of graes-type growth by aeeding orsodding' or it may be treeE or shrubs, or a combinalion of theee. Est;blishingthis cover may require the uge of supplemental materialE, such as mulch or jut6netting (Eee BMp 81.15).
o Site.Preparation: Inatall needed surface runoff control measureE such asgradient terracesr berms, dikes, level spreaders, waterways, and sedimentbaEine prior to seeding or planting.
r Feedino-GraFeeg, and Lequmee: Seedbed Preparation -- If infertile or coaraetextured subeoil will be exposed lrrrring lind shaping, it is best to etoctlifetopsoil and respread it over the finished slope it i-minimum 2 to G-inch depthand roll it to provide a firm seedbed. If construction fills have left soilexposed with a loose, rough, or irregular surface, smooth with blade and roll.If cutE or conetruction equipment have left a tightfy compacted surface, breakwith chisel plow or other-su-itabte implement. perfoim all cuLtural operationsacroaa or at right angles to the slope (contoured), such as with cat Lracks onthe final PaEs. The seedbed should be firm with a fairly fine Eurface.
o Soil Amendments: Rates will depend on site characteristics and soil, but as aguide, apply lime at the rate_of 1o0 pounds per 1,ooo square feet., ippryactual nitrogen at the rate of-1-2_pounds pei 1,Ooo sq. feet, phosphoiic'acidat the rate of 1.5 pounds per IrOOO-sg. feet, and potissium at the rate of 1.5pounde per 1,00O eg. feet. l{ork in lime and other nutrients to a depth of aminimum of 4 inches with suitable eguipment. scatter amendmerits uniiormly andwork into the soil during seedbed preparation.
r $peginc: Apply an aPproPriate mixture to the prepared Eeedbed at a rate of L2Olbs/acre. (s9ed mixture may be varied by the focaf government to take accountof local conditions).
I I-5-2 1 FEBRUARY, 1992
STORMWATER MANAGEMENT MANUAL FOR TTIE PUGET SOUND BASIN
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Name
Kentucky Bluegraee
Creeping Red FeecuePerennial Rye
Rural Application:
Kentucky Bluegrase (Poa 159prateneigl
Tall Feecue (Festuca 4Ot
arundlncea)Perennial Rye (Lolium perenne) 30t
Chewinge Fescue 15t
Name
Urban ApplLcation:
Red Top (Aqrogtis alba)Birdgfoot Trefoil(Lotus corniculatug)Creeping Red Feecue
30*
40r
30s
85
98
9s
Portions
bv'?leiqht
30r
30r
40r
PercentPuritv Germination
Germination
80
80
90
80
90
90
80
90
90
90
Cover the seed with topsoil or mulch no deeper than t inch. It ls better to work
topsoil into the upper soil layer rather than spread a layer of it directly onto the
top of the native eoil
.Hydro-seeding,, applicatione with approved geed-mulch-fertilizer mixtures may also
be uEed.
Wetlandg Seed Mixturee: For newly created wetlands, a wetlands epeclallst should
@providethebestchanceofsuccess.AsaguideappIythefollowing mixture at a rate of 6O lbs/acre, and/or additional tuberg for cattail,
bulrueh, slough eedge, ae reguired by the local government. See Chapter III-4,
Volume fII for more infotmation on constructed wetlands.
Do not uadar any circunstances use introduced, invasive plants like reed cauarygrass
(Phalerie arundLnacea) or purple loosestrife (Lvthrun salicaria). Using plants such
ag tbeee will cause Darry nore probleue tban they will ever solve.
85
9s
9s
9s
Proportions Percentbv Weiqht Puritv
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-14;/
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92
90
98
Tree and Shrub Plantinq
Besides their erogion and Eediment control values, trees and shrubs alEo provide
natural beauty and wildlife benefits. When used for the J-atter, they are usually
more effective when planted in clumps or blocke. These procedures should be
followed:
1. TreeE and shrubs will do best in topsoil. If no topsoil ie available,
they can be egtabliEhed in subsoil with proPer amendment. If trees and
ehrilbs are to be planted in subsoil, particular attention ghould be paid
to amending the soit witn generous amounts of organic matter. Mulchesghould also be used.
2. Good quality planting stock should be used. Normally one or two-year old
deciduous eeedlings, and three or four-year old coniferous transplants,
when properly produced and handled are adequate. Stock should be kept
cool ind-moiet-from time of receipt and planted ast aoon as possible.
Ir-5-22 , 1992
STORI.iWATER I.iANAGET{ENT I{ANUAL FOR THE PUGET SOUND BASIN
3. Competing vegetation, if eignificant, ehould be pulled out of the areawhere the plant or plante are to be placed
Maintenance
rnspect eeeded areas for failure and make neceasary repaire and regeed immediately.Conduct or follow-uP aurvey after one year and replace failed plante wherenecessary.
t If vegetative cover ie inadequate to prevent rill eroeion, overseed andfertilize in accordance with eoil teel reguLte.
o If a etand hae lese than 40t cover, reevaluate choice of plant materialg andguantitiee of lime and fertilizer. Re-eetablish the gtani foltowing eeeaUeapreparation and eeeding recommendatione, omitting lime and fertiliz6r in theabeence of eoil teet reeulte. rf the seaaon preventE reaowing, mulch "r j"t"netting ig an effective temporary cover.
r t-5-23 FEBRUARy, L992
STORMWATER I.IANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
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II-5.6 STRUC,:IURIL EROSIOI{ coNlRoL BMP8.
f I-5.6.1 Bl.tP E2. 10! Stabilized Construction Entrance and Tire Wash
Code:Symbol !I
Definition A temporary atone-etabilized pad located at pointe of vehicular ingress
and egreaa on q conatruction eite.
PurDoge
To reduce the amount of mud, dirt, rocke, etc. transported onto public roads by
motor vehlclee or runoff by constructJ.ng a etabilized pad of rock epalla at
entrancea to conotructl-on eitee and waehing of tires during egreEa.
conditlone Where Practice Aopliee
a Whenever traffic will be leaving a conetruction glte and moving directly onto a
public road or other paved areas.
Advantaqeg
o Mud on vehicle tiree is stgnificantly reduced which avoids hazarde caused by
depoeiting mud on the public roadway.
Sediment, which ie otherwlee contained on the construction site, does not enter
atormwater runoff eleewhere.
P lannino Considefaxions
Construction enttancea ptovide an atea vthere mud can be temoved from vehicle tites
betote they enter a public road. It the action of the vehicle travelistg ouet the
gravel pad is not sutficient to remove the majority of the mud, then xhe tires must
be wash-ed betore the vehicle enters a public road. If traehing is used, provisions
must be made to intercept the wash water and trap Xhe sediment befote jt js catried
off-site. Construcxion entrances slould be used in conjunction with the
stabiTization of conatruction toads to teduce the amount of mud picked up by
vehiclee.
It is important to note that this BIIP ttiTl only be effective it sediment conttol is
used throughout the regt of the construction site.
Desion Criteria
o l{aterlal Ehould be quarry spalls (where feaeible), 4 inches to 8 inchee size.
o The rock pad ehall be at least 12 inches thick and 100 feet in length for eites
more than I acre; and may be reduced to 50 feet in length for giteg lees than
1 acre.
r A filter fabric fence (Eee BMP 83.10) ehould be inEtalled down-gradient from
the conetruction entrance in order to contain any eediment-Iaden runoff from
the entrance.
r Vll-dth shall be the full width of the vehicle ingreea and egrees area (minimum
20 feet).
o Addttional rock ehould be added periodically to maintain proPer functlon of the
pad.
o S€€ Figure II:5.4 for details.
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rr-5-30 FE I L992
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STORI,II{ATER }I,AI\IACEMENT I,TANUAL FOR THE PUGET SOUND BASIN
Tire waghlng ahould be done before the vehicle entere a paved Etreet. Washingshould be done on an area covered with cruehed rock and the waeh vrater ehouldbe dralned to a eediment retention facility guch ag a sediment trap or baein.
The volume of waeh water produced by tire waehing ehould be included whencalculatlng the eediment trap or basin eLze.
Maintenance
r The entrance ghall be maintained in a condition which will prevent tracking orflow of mud onto public righte-of-way. Thie may reguire periodic top dreeeingwith 2-inch stone, ae conditiona demand, and repair and/or cleanout of anyatructuree ueed to trap sediment. AII materlalg sptlled, dropped, eraahed, ortracked from vehiclea onto roadwaya or into Etorm drains must be removedimmediately.
Al1 temporary eroaion and eediment control meaEureE ehall be removed within30 daya after final site stabilization is achieved or after the temporary BMPeare no longer needed. Trapped eediment ehall be removed or etabilized on site.Dieturbed eol,l areae resulting from removal ghall be permanently etabilized.
Figure II-5.4 Stabilized Congtruction Entrance
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R = 25'min.
12" min.
4' to 8' quarry spalls
6e
ad
provide full width of
ingress/egress area
rr-5-31 FEBRUARY, L992
SIORMI{ATER I.TANAGEMENT }ANUAL FOR THE PUGET SOUND BASIN
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II-5.6.2 BMP 82.15: Construction Road Stabilization
Code:symbol:
Definition The temporary etabilization with etone of accese roade, eubdivieion
r"adr, parking area-e, and other on-eite vehicle tranaportation routes immediateJ-y
after grading.
Purpose
r To reduce eroeion of temporary road bede by construction traffic during wet
weather.
o To reduce the eroeion and therefore regrading of permanent road bedg between
the time of initial grading and final etabllization.
conditione l{here Practlce Appliee
o Wherever rock-baee roadg or parking areas are conetructed, whether permanent or
temporary, for uae by conatruction traffic.
o Note: Exceptione may be granted in areas with gravelly soile, such as the
Everett eerieg, as approved by the local goverrunent.
Advantaoes
o Efficiently conetructed road etabilization not only reducea on-Eite eroeion but
can elgnificantly epeed on-eite work, avoid ingtanceg of immobil.ized machinery
and delivery vehiclea, and generally improve eite efficiency and working
conditione during adverae weather.
D isadvantaoee /Probleme
o Meagurea on temporary roada muet te cheap not only to inetall but algo to
demolieh if they intLrfere with the eventual surface treatment of the area.
o Application of aggregate to construction roads may need to be made more than
once during a conatruction perlod.
P lannino Consideraxions
Areas vhich are gtaded for construction vehicle ttansporx and parking. put_p_oses ate
especiaTTy susceptible to erosion. The exposed soif surface is continuaLTy
di'stutbed-, Teavi-ng no oppottunity for vegetative stabilization. Such areas also
tend to coJ,lect and tta-nbport ruhoff vaters aTong theit surfaces. During wet .veather, they often becomle muddy quagmires which generate significant quantities of
sedinent that may poTTute neatb-y itrearrs or be trAnsported otf-site on the trheeTs of
consttuction vehicles. Oitt roAds can become so unstable duting vtex weathet that
they are vittualTy unusable.
Innediate stabiTization of such areas vith stone may cost money at the outset, but'
it nay actuaTTy save money in the Tong run by incre'asing the uiefu-lness of the toad
duting tret veather.
pemanent toads and patking ateas should be paved as .soon as possible after grading.
As an alternative, t-he eatly application of ltone may solve potential erosion and
stabiTity ptobTems and elininatb Tater regrading costs. some of the stone vill aTso
probably remain in place tor use as part it tne final base course of the toad-
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sroRl'{wATER MANAGEI'IENT MANUAL FoR THE pucET souND BAsrN
Desiqn Criteria
I | 6-inch course of 2 Eo 4-inch cruehed rock, gravel base, or cruehed eurfacingbaee couree shall.be apptied immediately after grading or the compretion-otutirity inetallation within the right-oi-way. i a-in6rr courEe ot-asprratt--treated baee (ATB) may be ueed in lieu of tlre crushed rock, or as advieed bythe local government.
r where feaeible, alternative routea ehould be made for congtruction traffici onefor use in dry condition, the other for wet conditions which incorpoiia;-t;"meaaures lieted below.
' Temporary roade ehould follow the contour of the natural terrain to the maximumextent poesible. sloPe ehould not exceed 15 percent. Roadwaye ghould becarefurly graded to drain tranevereely. Provide drainage ewares on each sideof the roadway in the case of a crownid eection, or one side in the cage of asuper-elevated eection. Drainage gwalee shall be deeign"a-in accorainc" ,itnthe etandarde given in Chapter itt-2.
Installed inlete ehall be protectedthe drain Eeerer syEtem lseE SectionBMP E3.30).
prevent eediment-laden water entering-5.8.5 on Storm Drain Inlet protectioi
a toII
' simPle gravel berme without a trench can be used for lese travered roads.
o undisturbed buffer areaE should be maintained at aII stream croeeings.
' Areas adjacent to culvert crosginge and ateep slopee ehould be geeded andmulched and/or covered.
' Dust contror shourd be ueed when necesaary (see BMp 82.2o,t.
Maintenance
' rnsPect stabilized areaE regularly, eepecialty after large storm events.cruehed rock if necessary and reelabtlize any areas founi to be eroding.
AII -temporary erosion and gediment control meaaures ghall be removed within30 daya after final eite etabilization ie achieved or after the temporary Bl,tpeare no- longer needed. Trapped eediment shall be removed or stabilized on site.Disturbed soil areag reeull-ing from removal shalr u" peimin";al; etabilized.
Add
II .5-J J FEBRUARY, I9g2
STORI.TWATER }TANAGEMENT UANUAL FOR THE PUGET SOUND BASIN
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fI-5.6.3 BMP 82.20: Dust control
Code:symbol: .-O-
Reducing eurfaie and air movement of duet during land dieturbing,and conetruction activitiee.
@
Definitiondemolition,
PurDose
To prevent eurface and air movement of dugt from expoeed eoiL eurfacea.
Conditiong llhere Practice Appliee
In areag (including roadways) eubject to eurface and air movement of duet whereon-gite and off-gite damage ig likely to occur if preventive meaeures are nottaken.
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Advantaqes
o A decrease in the amount of dust in the air will decreaee the potentl-al foraccidente and reepiratory problems.
D isadvantaoee /Problemg
o UEe of water on-site to control dust emissionE, particularly in areaE where thesoil ig already compacted, can cause a runoff problem vrhere there r.raEn't one.
P Tannina Cons iderations
construction activ.itjes inevitabl.y result in the exposure and. disturbance of soil.Fugitive dust is emitted both during the activities (i.e., excavaxion, demolition,vehicle traftic, human activity) and as a resul,t of wind erosion over the exposedeatth surfaces. Latge guantjtjes of .dust are typicaTTy generated in "h:eavy,coistruction activities, suci as road and stteet consttuction and subdivision,commercial and industrial development, which involve disturbance of signiticantateas of soil guttace. Research at construction sjtes }ras established an averagedust emission rate of 1.2 tons/acre/month for active construction. Earthmovingactivities comptise the major source of construction 'dust emjssjons, but traffic andgeneraT disturbance of the soil also generate significant dust emissjons.
In planning fot dust .control, remembet that tle Less sojJ, is exposed at any one
ptoject and utiTizing temporary stabilization practjses upon the completion ofgrading can significantTy reduce dust emjssjons.
Desiqn Criteria
Minimize the period of eoil exposure through uee of temporary ground cover andother temPorary etabilization practices (see Seeding and Mulching, BMPe 81.10and 81.15 ) .
Sprinkle the eite with water until surface ie wet. Repeat as needed. Toprevent carryout of mud onto street, refer to Stabilized Construction Entrance(BMP 82.10).
SPray expoeed eoil areag with approved dust palliative. Oil should not be usedfor dust, suppreseion. Check with the local government to see which other dustpalliativea may be used in the area.
Maintenance
Respray area ag neceasary to keep dust to a minimum.
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STORI.{?TATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
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Definition A ridge
the toP or baae of a
ofeI
Advantaqes
o Thig BMP Provideg a Practlcal,situations.
Code:Symbol:
compacted soll or a swale with vegetative lining Iocated at
oping dist'urbed area'
PurDoge
To intercePt 6torm runoff from drainage areag above unProtected slopea and direct it
to a etabilized outlet'
o i{here the volume and verocity of runoff from exposed.or. digturbed slopee muet
be reduced. when an irrr""!!it;; eil;7;r.r" i" itacea above a dleturbed erope'
it reduces the volume "r t"I5i-;";;r;; [n" ai"l"rbed area bv intercepting
runoff from above (Flgure"-ii-s.is.rut]. wnen I't is placed horizontally across
a digturbed elope, it reauce" it" vetocity oi runoet-flowing down the slope by
reducing tne-ai-etlnce that irre runoff can flow directly downhill'
inexpensive method to divert runoff from erosive
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P Tannino Considetations
A temporaty divetsion dlke ot swaTe is intende-d. to diverx overland sheet flot' to a
stabirized outret ot a se4ineft Z:r;61"i. tiiitixv- aii_ing estabrishment of pezmanent
stabilizaxion on a sloping aisxutlZT'i,rZ"' wnei'"iia "i xhe xop ot a sloPe' the
structure protects expbsed t;',pZJiy X"Zgt.l "pi"ia tunoft away-' tlhen used at the
base of a slope, Xhe structute pto,tL.t" aai|cent and downstteam areas by divetting
sediment-Iaden ,"iitt-iz a sedi'ment xrapping facility.
If the dike or suale is going to temain in ptace fot longer than 75 days' jt sha-l'l
be stabiTized with temporary ot- pZr^tnent vegettti"i' f-he slope behind the dike or
svale is atso an import"nX "on"{d.iii,ion. The aii" "t su,.ale 7ust have a positive
grade to assure'd;;i;;;a)- gu.t-i}-tltr-"r,ope i-2 too gteat' Ptecautions must be taken
to prevenx ercsiii due-to high veTocity of tTow'
This ptactice is consideted an econonical one because jt uses material avaiTable on
the site and can usuaTTy ne contliu.ttd nith .q"lpiZit needed fot site grading' The
usefur rife ot the practice can-iZ- "*t"na"a ay-ll-a-iiiiring the dike or sware vith
D isadvantaoee /Probleme
o None
vegetation.
DeEion Criteria
o Interceptor dikes ehall meet the followinq criteria:
Top Width
Height
2 feet minimum.
18 inches minimum. Measured.from
"p"i"p" toe and at a comPaction of
Sb p.it.ttt ASTM D698 etandard proctor'
2zL or flatter.Side SloPee
r r-5-54 992F,I
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STORMWATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
Grade
Horizontal. Spacing offnterceptor Dikee
Slopee
Slopee
Slopea
Topography dependent, except thatdike ehall be limited to giadesbetween 0.5 and 1.0 percent.
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300 feet200 feet
1O0 feet
Stabilization
Slopee <5t
Slopea
Outlet
Stabilization
Swale Spacing
Slope of dieturbed area:
Seed and mulch appliedwithin 5 daye of dikeconEtruction (see BMp 81.10).
Dependent on runoff velocitieeand dike materiale. Stabilizationehould be done immediately using eithereod or riprap to avoid er6eion. -
5-40$
1 foot minimum.
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5-10r
10-40r
30O feet
2O0 feet
10O feet
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The.upslope side of the dike shall provide positivedrainage to the dike outlet. No erogion shall occur atthe outlet. provide_energy dieeipatio" ,"ir"r"" "" necessary.sediment-raden runoff mue€-be rellaeed th;;;;h i eedirnenttrapping facility.
tq:
Other
Minimize conetruction traffic over temporary dikes.
Bottom Width 2 feet minimum; the bottomehall be level.
Depth
Side Slope
Grade
2zI or flatter.
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Maximum 5 percent, withpoeitive drainage to aeuitable outlet (such as asedlment trap).
Seed ae per BMp E1.10Temporary Seeding, or 82.75Riprap 12 inches thick preesedinto the bank and extendingat leagt 8 incheg verticalfrom the bottom.
Outlet Level Spreader or Riprap to etabilizedoutlet/eedimentation pond.
STORMWATER MANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
Maintenance
rThemeaSureehouldbeinepectedaftereverymajneceEsary. o"a"g" cauaed-by conatruction-traff
repaired-before the end of each worlcing day'
AII temporary erosion and eediment control meagureE ehalI be removed within
30 daye after ri""r-"iie eiabirization ig achieved or after the temporary BMPg
are no longer needed. Trapped ""aito"ttt ehall be removed or etabilized on eite'
Dieturbed eoir areae reeultlng from removal shall be permanentty stabilized'
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:or etorm and rePairg made ae
ic or other activitY muet be
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STORT,TWATER I.{ANAGEMENT MANUAL FOR THE PUCET SOUND BASIN
Figure II-5.13(a) Temporary Interceptor Dikes
Dike Material compacled
907" Standard Proctor
'i,l ', ..
2 mtn.
l ttmin.
27
8 mrn.
lF min
intercepror dike spacrng - 100'. 2O0'0r
3O0'dcpcndrng on grada
Level Eonom
1-r.*
I ftmin.
Grass or Rod<ROW or Other
Expose<i Slope (
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2
2 h min.Spacing - 100'. 200'. or 300'
depending on Slops
Figure II-5.13(b) Interceptor Swale
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STORT{WATER I.TANAGEI{ENT MANUAI FOR THE PUGET SOUND BASIN DRAFT
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II-5 .8 SEDII{E*T REIE}IIIOI|
ff-S.8.1 BMP 83.10: Filter Fence
Code:symbol: df-l\4
Definition A temporary eediment barrier coneisting of a filter fabric etretchedacrose and attached to eupporting poats and entrenched. The filter fence isconetructed of stakeg and eynthetic filter fabric with a rigid wire fence backing
where necesEary for support.
Purpoge
1 To intercept and detain emall amounte of eediment under eheet flow conditionefrom dieturbed areas during conatruction operati,one in order to prevent
Eediment from leaving the eLte.
2. To decreaee the velocity of eheet flowe.
Conditions Where Practice Applies
Filter fenceg muEt be provided juet upatream of the point(e) of discharge ofrunoff from a site, before the flow becomeg concentrated. They may aleo berequired:
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1. Below dieturbed areas rrrhere runoff may occur in the form of sheet and rilleroeion; wherever runoff has the potential. to impact downstream resourceE.
Perpendicular to minor awales or dLtch lineg for contributing drainage
areas up to one acre in size.
Advantaqee
o Downstreali riparian areas will not be darnaged by sediment deposits originatingfrom the development.
r Sediment will not'cauee damage to fish habitat.
D isadvantaqee / Problemg
Filter fences are ry.1! practical where large flowe of water are involved, hencethe need to reetrict their uee to drainage areaa of one acre of lese, and flowratea of leee than 0.5 cfe. This flow ehould not be concentrated; it ghould beapread out over many linear feet of filter fabric fence.
Probleme may arise from incorrect eelection of pore size and/or improperingtallation.
Filter fencee ehould not be conetructed in streatne or uged in V-shaped ditches.
They are not an adequate method of runoff control for anything deeper thanEheet or overland flow.
P 7 annina Considerdtions
Laboratory work at the Virginia Highway and Transportation Research Council has
can sttav baJ,es. silt, tences are ptetetahle to straw battiers in many cases.Howevet, while the failure rate of silt fences is Tourer than that of straw barriers,thete ate many jnstances locally in which siTt fences have been improperly
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STORI.II{ATER I.TANAGEMENT I.(ANUAI, FOR THE PUGET SOUND BASIN DRAFT
instaTTed. ?he instaTTaxion methods outlined here can lnprove pettormance.
Fabric Typest
There are four xyPes of material uged tor tiTter fabric fences; woven slit-filnfabric, toven monotilament fabrics, voven composites (ot diftering materials) andnon-vroven heat'tteat'ed or needle punched fabrics. Slit-tiLn tabrlcs are made tromhroven sheets of nonpotous polymers. The sleets are very thin but are cut or elit invidet bands to fozm the thieads vhich are xhen etoven i-nto the tabric. Since sJ,it-tiTm veaves use atrands that are quite thin, the resulxing woven tabric has Ljtt-terigidity, and pore stpacest are not uniform. ltire fencing nust.be used as a backingtor this typ,e ot tiTter fabric fence. t{hile this type ot tauric is generallycheapeat and. the most widely used, xhe additional cbits ot the wire Tencejnsta.l-lation mugt be tigured in.
woven monotiTament fabrics are made trom uniform spun or extruded tilaments urhichate then eroven to form the tabtic. They are usuallly thicker and thus more rigidthan slit-filn fabr_ircs. -T-he pores in ionofilanent Tabrics are regularly spac-ea anathe incteased rigidity otfers more resistance to pore distortion. The -natlerial hasa very Low flow-thtough rate. lloven composites ale simiTat in structure but usemore than one fiber type.
Non-|'oven tabric-s.-ate made by using either continuous fiTaments or short staplefibers- ?hese fibers are then bonded togethet by various proceases that can includea ne-edling procesa that inxertwines the Tibers p-hysicatly) or a thezmal or chemicalbond_ing operation that tuses adjacent tibere xogelher. -fhe resulting fabric has atandom fiber orientation and may have a thicknels that ranges from tlhick felt xo arelatively thin tabric.
K,ing County conservation Distriet reeently eompleted tests on 18 ditferent types oftiTtet fabrics. ?.heit resul,ts have been lncoiporated inxo xhe design critei!'a.
Degiqn Criteria
o DraLnage irea of 1 acre or lege or in combination with eedLmdnt basin in alarger eite.
. Maximum slope steepness lnormal (perpendicular) to fence line) 1:1.
Maximum eheet or overland flow path length to the fence 100 feet.
r No concentrated flowe greater than 0.5 cfs.
o Selection of a filter fabric ia baeed on eoil conditione at the conetructloneite (which affect the apparent opening size (Aos) fabric epecification) andcharacteriEticg of the Eupport fence (thich affect the choile of teneil6strength). The deeigner ehall epecify a filter fabric that retains the soilfound on the congtruction eite yet will have openinge large enough to permitdrainage and prevent clogging. The larger the AoS number, tne sialler-the Aossize of the opening in the fabric.
o The material used in a filter fabric fence muet have gufficient strength towithatand varioug atreEs conditiong and it also muEt have the ability to allow
PaEsage of water while retaining eoil particleE. The ability to paa- flowthrough must be balanced with the material,e ability to trap-gedimentg.
The folrowing criteria are recommended for serection of the Aos:
1. BecauEe of the propertlee of eoils in the Puget Sound basin, field workmuEt be done to determlne the optimum AOS for filter fence ingtallations.Because of glaciation, many soils in this area contain both cobbleg and
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I I-5-75 FEBRUARY, L992
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STORMWATER MANAGEI.{ENT }.IANUAI, FOR THE PUGET SOUND BASIN DRAFT
fineE. If an sCs etandard eoil description is ueed, (e.9. Alderwoodgravelly eandy loam) the AOS epecified will not be sufficient to trap thefiner particlee of eoil. Including gravels and larger gizee ekewg theregults towards an AoS which ie too emall to capture euepended eettleablegolide and reduce TSS. Monofilament and non-woven geotextilee mugt have a
minirnum AoS of 70 when uged in glacial goile. compoEitee and elit filmfabrice muet be extra-etrength to perform eimilarly; in their caEe the Aosrange may be from 40-60. In areaE where llazana aeh ig plentiful in theeoil profile, a larger AoS will be neceeeary, or' fabric with an AOS of ?0
ehould be ueed for outwash eoile.
For aII other aoil typee, the AOS should be determined by first paeeing
eoil through a #10 eieve (2.0 mm). Baeed on the amount of the remainingsoil, by weight, which paEEeE through a U.s. standard sieve No. 200,Eelect the AOs to retain 85 percent of the eoil. Where direct diachargeto a etreann, lake, or wetland will occur, then the AoS ehall be no largerthan Standard Sieve No. 100.
. Non-woven and regular strength elit film fabrice shall be eupported with wire
. mesh. Filter fabric material ghall contain ultraviolet ray inhibitorE andstabitizerE to provide a minimum of eix months of expected ueable conetructionlife at a temperature range of OoF. to 12O"F.
Standard Notes
In additlon to the Technical Information Report (Eee Chapten I-3) required by thelocal government when preparing an eroaion and eedinent control plan, add thefollowing notea to the Filter Fabric Fence Detail (Figure II-5.18):
a. The filter fabric shall be purchaeed in a continuouE roll cut to the length of
,,,',,,the barrLer to avoid use of jotnts. When jointe are neceEsary, filter clothshall be epliced together only at a support post, with a minimum 6 inch
. overlap, and both ende securely faetened to the post.
b. Poeta shall be spaced a maximum of 5 feet apart and driven eecurely into theground a minimum of 30 inches (where physically poeeible).
c. A trench ghall be excavated approximately 8 incheE wide and 12 inches deep
along the line of poets and upslope from the barrier. The trench ehall be
constructed to follow the contour.
d l{hen Ellt film filter fabric ia used, a wire meeh aupport fence ehall befaetened aecurely to the upelope eide of the poete using heavy-duty wirestaples at leaet 1 inch long, tie wireg or hog rings. The wire ehall extendinto the trench a minimum of 4 incheg and ehall not extend more than 35 inches
above the original ground surface.
SIit fLlm filter fabric ghall be wired to the fence, and 20 inches of thefabric ahall extend into the trench. The fabric ehall not extend more than
36 incheg above the original ground surface. Filter fabric shall not beetapled to existing treea. Other types of fabric may be stapled to the fence.
When extra-etrength or monofLlament fabric and closer post epacing are uaed'the wire meeh eupport fence may be eliminated. In such a case, the filterfabric ie stapled or wired directly to the poEta with all other provieions of
Standard Note "e" applying. Extra care should be used when joining oroverlapping theee etiffer fabrice.
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Local governrnents may specify the use of properly compacted native material.In many inetancee, this may be the preferred alternative becauge the eoil formsa more continuouE contact with the trench below, and use of native materials
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STORUWATER I{ANACE}IENT MANUAL FOR TTIE PUGET SOUND BASIN DRAFT
cutE down on the number of tripE that muet be made on and off-eite. If gravelie ueed inetead, the trench ehall be backfilled with l-inch minimum diameter
waghed gravel. Care muet be taken when ueing gravel to eneure good contactbetween the fabric and the trench bottom to prevent undercutting.
Filter fabric fencee ehall be removed when they have eerved their usefulpurPose, but not before the upelope area hag been permanently etabilized.Retained eediment muet be removed and properly dispoeed of, or mulched andgeeded.
Maintenance
InaPect inmediately after each rainfall, and at leaet daily during prolongedrainfall. Repair as neceEaary.
Sediment muet be removed when it reaches approximately one third the height ofthe fence, eepecially if heavy raine are expected.
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Any eediment depoeite remaining in place after the filter fence ie no 1reguired ghall be dregeed to conform with the exietj-ng grade, prepared
seeded.
onger
and -l,]
''q*r-
AII temporary erosion and gediment control measureE ghall be removed within30 daye after final eite etabilization is achieved or after the temporary BMPeare no longer needed. Trapped gediment ehall be removed or etabilized on eite.Digturbed soil areae reeulting from removal shall be permanently Etabilized.
Referenceg;
(1) Kulzer, Louiee, Coneideratlone for Ueino Geotextilee in Silt FenceAooligationg, Metro Technology Tranafer Publication, Nov., 1988.
(21 Varney, Dick, An Evaluation of Geotextilee ae Filter Fabric Fence UeinoLocal Soils for Planninq and Enqineerinq, King County ConservationDiatrict, Sept., 1991.
(3) Varney, Dick, pereonal communication, March 4, 1992.
STORMWATER I.IANAGEI.TENT MANUAL FOR THE PUGET SOUND BASIN DF.AFT
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Figure II-5.18 Filter Fabric Fence Detail
Filtrr labric matrrial in conlinuour rolb;
Ur rtaplor or wirr ringr to attach fabric
lo wirc Wirc mcrh.upport trncc
lor rlit lilm labricr
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Filtrr labrlc
mrtrrirl
Provido warhrd grrvol
brcllill or comprctrd
by local gov.mm.nl
Bury bonom ol lilt.r mlt rill +
in 8' bv 12'tronch
6'M.ax.
2'bV 2'wood poltr, rtrndard or b.tt.r
or rqulvalcnt
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STORI.{WATER I.IANAGEI.TENT MANUAL FOR THE PUGET SOUND BASIN
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If-S.8.2 BMP E3.15 Straw Bale Barrier
Code:Symbol: r'.-
Definition A temporary aediment barrier consisting of a row of entrenched andanchored gtraw baleg.
Purpoge
To intercept and detain emall amounts of eediment from diaturbed areas ofl-imited extent to prevent gediment from leaving the site.
To decrease the velocity of eheet flows and low-to-moderate leveL channelflowe
Conditione Where Practl-ce Aoplies
Below dieturbed areaa aubject to sheet and rill eroeion.
Where the gize of the drainage aiea is no grdater than L/4 acre per 1OO feet ofbarrier length; the maximum elope length behind the barrier ig 1OO feet; andthe maximum elope gradient behind the barrier ig 50 percent (2:1).
In minor Er.tales or ditch lines where the maximum contributing drainage area isno greater than 2 acres.
Where effectiveneeE ia required for less than 3 months.
Under no circumEtanceE should Etrar., bale barriers be conEtructed in liveBtreams or in ewalee where there is the poseibility of a washout.
Advantaqee
a When properly ueed, straw bale barriers are an inexpeneive method of sedimentcontrol.
D isadvantaoee / Prob lemg
straw bale barrierE are eaEy to misuse and can become contributora to aeediment problem ingtead of a.solution.
a It ig difficult to tell if bales are securely seated and anug againet eachother.
P Tannino Considetations
Sased on obsetvations made 7oca77y and in Virginia, Pennsylvania, Hatyland, andother parts of the nation, straw bal,e barriers have not been as ettective as manyusers had hoped they vouTd be. fhere ate three major teasons tor suchineftectiveness.
Improper use of stranl' bale barrjers has been a majot problem. Strav balebartiete have been used in streams and drainageerays uhere high water veTocitiesand volumes trave desttoyed or impaired their effectiveness.
ImproPer placement and instaTTation of the barriets, suci as staking tlte Dafesditectly to the gtound vith no sojl seal or entrenchment, has aTTowedundercutting and end flow. fijs }las resul,ted in additions to, rather thanremoval of, sediment from tunotf paters.
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STOR$WATER I.{ANAGEMENT }IANUAL FOR lHE PUGET SOUND BASIN DRAFT
3. Inadequate maintenanee Lovers the etfecXiveness of these battiers. For
"xampie, trapping efticiencies of carefuTly instaTTed sXraw bale bartiers on
one project in Vlrginia dropped from 57 percent to 15 percent in one month due
to Tack of maintenance.
There are serious guestions about the continued use of straw bale barriers as they
are presently instillea and maintained. Averaging apploximatel,y 54.00 pet linear
foot', the thbusands of sXrav bale barrjers used annualTy tepresent'sutficient
expense that optimum instalTation procedures should be emphasized. If such
pricedures are carefulTy foL7owed, sttat, bale barriers can be quite etfective.'fherefore, continued designation of straw bale batrjerg as a BIIP wiLl" be contingent
upon signifieant improvemlent in xhe instalTation and maintenance procedutes applied
xo their use.
Deeion Criteria
o A formal deeign ie not required.
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1. Baleg shall be placed in a eingle row, lengthwiee q the contour, with
. .:. ende of adjacent bales tiqhtlv abutting one another.
'2. AII baleg Ehall be either wire-bound or gtring-tied. Straw balee ehall be
inetalled Eo that bindings are oriented around the eideg rather than along
the tope and bottoms of the baleg j.n order to prevent deterioration of the' bindinge (Figure II-5.19).
3. The barrier ghall be entrenched and backfilted. A trench ehall be. excavated the width of a bale and the length of the propoeed barrier to a
.. - ,. minimum depth of 4 incheg. The trench mugt be deep enough to remove all
grass and 6ther material whlch rnight allow underflow. After the bales are
itaked and chinked 1filled by wedging), the excavated eoil ehall be
backfilled againet the barrier. sacltitt eoil ahall conform to the ground
Ieve1 on the downhill glde and ahatl be built up to 4 incheE against the
uphill eide of the barrier (Figure II-5.19)-
4. Each bale ghall be securely anchored by at least 2 gtakes or re-barg
driven through the bale. ihe firet gtake in each bale shall be driven
toward the pieviouely laid bale to force the baleg together. - stakeE or
re-bars etrait be driien deep enough into the ground to eecurely anchor the
balea. Stakeg ghould not extend above the balee but inetead ghould be
driven in flush with the top of the bale for eafety reaaonE
5. The gape between the baleg ghall be chinked (filled by wedging) with Etraw
to pievent water from egcaping between the balee. LooEe straw Ecattered
over the area immediately uphitl from a straet bale barrier tendg to
increaae barrier efficiency. l{edging must be done carefully in order not
to eeparate the balee.
G. Inepection shall be frequent and repair or replacement ghall be made
promptly ag needed.
7. Straw bale barrierg ehall be removed when they have served their
ueefulneee, but not before the upelope areaa have been permanently
etabilized.
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1. Balee shall be placed in a single row, lengthwiee, oriented perpendigular
to the contour, with ende of adjacent baleg tightly abutting one another.
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STOR.I-IWATER I,IANAGEI.{ENT I'{ANUAI FOR THE PUGET SOUND BASIN
Flgure II-5.19 croaa-Section of a Properly Inetalled Straw Bal.e Barrier
Staked and Entrenched
Straw Bale
Einding llireor Twine ted Soil to
Prevent Piping
Fi 1 tered Runoff
Sediment Laden
Runo ff
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The remaining stepE for installing a straw bale barrier for Eheet flowapplications apply here, with the following addition.
The barrier ehall be extended to auch a length that the bottomg of the endbalee are higher ln elevation than the top of the loweet middle bale(Figrure II-5.20) to aeeure that eediment-Iaden runoff will flow eitherthrough or over the barrier but not around it.
Maintenance
Straw bale barriere Ehall be J-nspected l-mmediately after each runoff-producingrainfall and at leagt daily during prolonged rainfall.
Cloee attentl-on ghall be paid to the repair of damaged baleg, end rune, andundercutting beneath balee.
Neceaoary repaire to barriera or replacement of balee ehall be accompliehedpromptly.
Sediment depoeita should be removed after each runoff-producing rainfall. They
muet be removed when the level of deposition reachee approximately one-half theheight of the barrier.
Any eedirnent depoeite remaining in place after the etraw bale barrier ie nolonger required shall be dressed to conform to the exieting grade, prepared and
seeded.
AII temporary and permanent erogion and eediment control practicee ehall be
maintained and repaired ae needed to aEEure contlnued performance of theirintended function. AII maintenance and repair shall be conducted in accordancewith an approved manual.
All temporary erosion and eediment controL measures ehalL be removed within
30 days after final gite stabilization ie achieved or after the temporary BMPeare no Ionger needed. Trapped sediment ehall be removed or etabilized on eite.Dieturbed eoil areaE resulting from removal shall be permanently gtabilized.
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STOR.I.{WATER T,TANAGEMENT MANUAL FOR THE PUGET SOUND BASIN
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Figure II-5.20 Proper Ingtallation of a straw BaIe Barrier
nld
riljtttildlf,
A
B
Poi nts A shou'ld be hi gher than poi nt I
PROPER PLACEMENT OF STRAI'I BALE BARRIER IN DRAINAGE I'IAY
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2. P'lace and stake straw bal es1. Excavate the trench
CONSTRUCTIOII OF A STRAI.I BALE BARRIER
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Backfi 1 I and comPact the
excavated soi'l .
Wedge loose straw betwee.n
bal es .
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STORJ'{WATER MANAGEI'iENT MANUAI FOR THE PUGET SOUND BASIN
rI-5.8.3 BMP 83.20: Brueh Barrier
Code:Symbol: W
Definition A temporary eediment barrier conatructed at the perimeter of adieturbed area from residue material.e available from cleaning and grubbing on-site.
Purpoge
To intercept and retaLn eediment from Iimited disturbed areae.
Conditiong llhere Practice Apoliee
o Below dieturbed areas of lees than one quarter acre that are aubJect to eheetand rill eroslon, where enough residue material ig avaLlable for conetructionof euch a barrier. Note: Thie doee not replace a gediment trap or pond.
Advantaqeg
o Brugh barrierg can often be constructed using materiale found on-eite.
Problems
o None
P l-annino Considerations
Organic Tittet and spoiT material trom site clearing operations js usually burned orhauled attay to be d.umped elsen}tere. Ifuch of this material can be used effectiveLyon the constructjon sjte iteelf. Duting clearing and grubbing operations, equipmentcan push or dump xhe mixture of Limbs, sma77 vegetation, and root mat along withminor amounta of soil and rock into utindtows aTong the toe of a slope where erosionand acceleraxed runotf are expected. Attchoring a fiTter tabric over the bermenhances the fiTxration abiTity of the batrier. Eecause brush barriers ate fairLystabTe and compoged of r2atura.l, materials, maintenance requirements are smaJ,I.Ilaterial containing Tatge amounts of trood chips shou-l,d not be used because of t}tepotential for Teaching from xhe chips
Deeiqn Criteria
o Height 3 feet (minimum) to 5 feet (maximum)
. l{idth 5 feet at bage (minimum) to 15 feet (maximum)
r Filter fence anchored over the berm will enhince ite filtration capacity.
a Further deaign details are illustrated in Figure II-5.21.
Maintenance
Brush barrierg generally require little maintenance, unlese there are veryheavy depoeits of eediment. Occasionally, tearing of the fabric may occur.
l{hen the barrier is no longer needed the fabric can be removed to allow natura}eetablishment of vegetation within the barrier. Over time the barrier wilIrot. AII temporary and permanent eroeion and eedl,ment control practicee shallbe malntained and repaired ag needed to assure cont,inued performance. A11maintenance and repair shall be conducted in accordance with an approvedmanual.
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STORMT{ATER MANAGEMENT I,IANUAL FOR THE PUGET SOUND BASIN
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Figure II-5.21 Brueh Barrier
filter fabric draped over
brush pilc and secured in
trench w/ compacted backtill
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anchor downhill cdgo of
brush barrier w/ twinc
fastened to tabric & stakes
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6' x 6" (min.l trench
along uphill sdge of
brush barrier
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vegetativc debris/brush piled
uniformly in row to form barrier
min.3'high
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