STORM DRAINAGE

January 2019 3 - 1

C H A P T E R 3

3.000 STORM DRAINAGE 3.010 Public Storm Drainage System Alterations, Extensions and

Connections

To allow the City to provide timely assistance and advice, anyone who wishes to alter, extend or connect to the City’s storm water drainage system must conform to the requirements specified in Section 13.02.130 of the Shelton Municipal Code, and the current edition of the City Comprehensive Plan. All proposed alterations, extensions or connections to the public storm drainage system must be reviewed and approved by the City of Shelton. The standards established by this Chapter are intended to represent the minimum standards for storm drainage and erosion control facilities.

3.020 Design Standards

The design of storm drainage and/or retention/detention systems shall depend on their type and local site conditions. The design elements of storm drainage systems shall conform to City standards as set forth herein, and follow current design practice. The currently adopted version of the Washington State Department of Ecology Storm Water Management Manual for Western Washington, and Chapter 13 of the Shelton Municipal Code are referenced as a part of these Standards. A. Swales Swales will only be allowed where approved by the City. If approved, swales shall be protected by curbing and maintained by the abutting property owner(s). Also, in residential developments

a homeowners association with covenants shall be formed to ensure enforcement of the maintenance requirements. Swales designed for transporting, storing and/or infiltrating stormwater from public roadways shall not be located on a lot designated for single-family occupancy. Easements proposed for such swales will not be allowed. This is necessary due to the complexity of operating and maintaining the integrity of such facilities within fenced and landscaped private property.

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B. Catch Basins Catch basins shall be located on the upstream side of every intersection. Where there are no intersections, maximum catch basin spacing shall be 300-feet on arterials and collectors and 500-feet on local streets. All storm drainage pipes shall be constructed in a straight line between catch basins and other drainage structures. C. Retention/Detention Ponds

The maximum depth of a retention or detention pond shall be 4.5-feet from the pond bottom to the top of the pond slope (not the water elevation). Deeper ponds may be allowed by the City if minimum 6-foot wide benches are provided at no more than 4.5 vertical foot intervals.

D. Fencing

Fencing for public safety shall be provided. Surface ponds and infiltration basins with a maximum depth of 3.0 feet or less do not require fencing, provided the maximum associated interior side slope of the pond or basin does not exceed 4H:1V (including baffle side slopes). All ponds and basins with a maximum depth of water greater than 3 feet will require a 6-foot high perimeter fence unless the following condition is met: 1. The facility is designed and constructed with a 10-foot wide

safety bench for every three feet of depth, and the interior side slopes are no greater than 4H;1V (including baffle side slopes); or

2. When fencing is required around a facility to be dedicated to

and/or maintained by the City, the fence shall be chain link. The chain link fence fabric shall be galvanized steel core wire and coated with bonded polyvinyl. The polyvinyl coating shall not be subject to fading, cracking, peeling, or shrinkage and shall be brown, black, or some shade of natural green (such as pine, forest, or olive). The fence manufacturer shall provide a 10-year (minimum) warranty on the polyvinyl coating. All fence/gate posts and top/brace rails shall be powder-coated the same color as the chain link fence fabric. The chain link fence shall meet all other applicable specifications for Type 3 chain link fence as set forth in the WSDOT/APWA Standard Specifications for Road, Bridge, and

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January 2019 3 - 3

Municipal Construction except that the line posts for Type 3 fence shall be set in concrete.

E. Driveway Culverts

Where roadside ditches are approved, all driveway culvert pipes shall be corrugated metal pipe (CMP), high-density polyethylene (HDPE), concrete or ductile iron with a minimum diameter of 12-inches, and of sufficient length to provide a minimum 3:1 slope from the edge of the driveway to the bottom of the ditch. Culverts shall have beveled end sections to match the side slope.

F. Release to Public System

All on-site storm drainage shall be infiltrated to the highest degree allowed by site conditions. If drainage outlets (stub-outs) are approved by the City to be provided for each individual lot, the stub-outs shall conform to the following: 1. The receiving drainage system shall have sufficient capacity

for the onsite release. The developer shall provide an engineered drainage analysis to verify the capacity.

2. Each drainage outlet shall be suitably located at the lowest

elevation on the lot, so as to service all future roof downspouts and footing drains, driveways, yard drains, and any other surface or subsurface drains necessary to render the lots suitable for their intended use. Each outlet shall have free-flowing, positive drainage to an approved storm conveyance system or to an approved outfall location.

3. Drainage outlets on each lot shall be located with a 5-foot

long steel reinforcing bar painted fluorescent green and driven into the ground. The stub-out shall visibly extend above the surface of the ground and be secured to the reinforcing bar.

4. Drainage easements are required for drainage systems

designed to convey flows through individual lots.

5. The Engineer is responsible for coordinating the locations of all stub-out drainage conveyance lines with respect to utilities (e.g., water, sewer, electrical power, gas, telephone, and television).

6. All individual stub-outs to the main or catch basin shall be

privately owned and maintained by the lot owner.

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January 2019 3 - 4

3.030 Storm Water System Rainfall Design Criteria

Where single-event modeling is applicable, the following values are to be used as design criteria for stormwater facilities: 100 Year – 24 Hour Design Event 8.50 inches 50 Year – 24 Hour Design Event 7.80 inches 25 Year – 24 Hour Design Event 7.05 inches 10 Year – 24 Hour Design Event 5.50 inches 5 year – 24 Hour Design Event 4.75 inches

2 Year – 24 Hour Design Event 4.00 inches 6 Month – 24 Hour Design Event 2.56 inches 100 Year – 7 Day design Event 16.60 inches

The applicable design storm event shall be used in all calculations submitted to the City for review. All stormwater facilities shall be designed to meet all requirements of the currently adopted Department of Ecology Stormwater Management Manual for Western Washington as referenced in Shelton Municipal Code Title 13, and all Best Management Practices. All stormwater detention, infiltration and conveyance systems shall be sized to accommodate the modeling requirements of the currently adopted stormwater management manual. Additionally, whenever an overflow system is proposed, a complete downstream analysis will be required to ensure that downstream properties or stormwater conveyance systems are not compromised.

A. Infiltration Rate Guidelines

Obtaining a design infiltration rate utilizing a soils evaluation and infiltration test is highly desirable for all projects utilizing storm water infiltration systems within the City. The largest infiltration rate allowed for design without a soils investigation and infiltration test is 6-inches per hour (or ten minutes per inch). This rate may be allowed only in locations where the City has sufficient knowledge of existing soils in the vicinity of the project, and where infiltration systems in that location have been performing as designed with this design infiltration rate.

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An adequate soils investigation for designing infiltration systems includes a soils exploration and an infiltration test at the depth of the bottom of the proposed infiltration system. The exploration shall be a minimum of three feet below the elevation of the bottom of the proposed infiltration system to determine if high groundwater or impermeable soil layers will impede vertical movement of the stormwater unless otherwise approved by the City. The largest infiltration rate allowed for design with a soils investigation and infiltration test is ten-inches per hour (or six-minutes per inch).

In all cases, an adequate factor of safety shall be utilized when determining a design infiltration rate to compensate for soil clogging and cementation, high groundwater levels, and vertical separation between the bottom of the infiltration system and impermeable soil layers. Additionally, all infiltration rates utilized in the design shall be reviewed and approved by the City. It is recommended that the infiltration rate proposed for the design of infiltration systems be approved by the City prior to the start of design to avoid unnecessary revisions that could prove costly for the applicant and cause delays in the progress of the project.

Storm drain pipe within a public right-of-way or easement shall be sized to carry the maximum anticipated runoff for a 100-Year 24-Hour Storm Event from the contributing area. The minimum size for mains and laterals shall be eight inches in diameter, or as otherwise approved by the City. Nothing shall preclude the City from requiring the installation of a larger-sized storm drain if the City determines a larger size is needed to serve adequate areas or for future service. When the property discharges to the public storm drainage system, installation of appropriately sized storm drains across the face of the property may be required by the City where applicable. Storm drain pipe shall meet the requirements of Section 7-04.2 of the WSDOT Standard Specifications.

All storm drainage systems are required to be air testable in conformance with Section 7-04.3(1) of the WSDOT Standard Specifications. Special structures, oil/water separators and outlet controls shall be installed and tested per the approved plans and manufacturer’s recommendations.

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The minimum cover for storm drain pipe shall be two feet, or as otherwise approved by the City. Where the minimum depth includes the roadway section, structural calculations or manufacturer’s specifications for the appropriate H-loading shall be submitted along with the plans. All drain pipe specified where the cover is two feet or less shall be HDPE, concrete or ductile iron of a class determined by the structural calculations or manufacturer’s specifications. Where connections require field verifications, connection points will be exposed by the contractor and fittings verified

two business days prior to beginning work. 3.040 Staking All surveying and staking shall be performed by a Professional

Land Surveyor, licensed within the State of Washington. A preconstruction meeting shall be held with the City prior to commencing staking. All construction staking shall be inspected by the City prior to construction.

The minimum staking of stormwater lines shall be as follows,

unless otherwise directed by the City. A. Stake centerline alignment every 50 feet with cut or fill to

invert of pipe. B. Stake location of all catch basins, manholes and other

structures for grade and alignment with cut or fill to rim and invert of all pipes. Two offsets to the centerline of the structures shall be provided.

C. Grade stake, or slope stake as appropriate, at intervals

sufficient to control the location, size and depth of retention/detention facilities.

D. Stake finished grade of all stormwater features, including, but

not limited to catch basin/manhole rim elevations, overflow structures, weirs and invert elevations of all pipes in catch basins, manholes, and those pipes that daylight.

3.050 Trench Excavation

See Chapter Two, Section 2.200 for requirements regarding trench excavation.

3.060 Backfilling

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January 2019 3 - 7

See Chapter Two, Section 2.200 for requirements regarding

backfilling. 3.070 Street Patching and Restoration

See Chapter Two, Sections 2.190 and 2.200 for requirements regarding street patching and trench restoration.

3.080 Maintenance

The City shall maintain all stormwater drainage elements such as catch basins, oil water separators, and conveyance systems located within the public rights-of-way. All private stormwater systems are required to have an Operations and Maintenance Manual per Department of Ecology’s requirements. The manual must be submitted to the City for review prior to construction authorization. The development's owners’ association shall be responsible for maintaining the on-site stormwater facilities including, but not limited to, on-site retention/detention ponds, catch basins, oil-water separators and conveyance system(s). Each property shall also submit a Stormwater Maintenance Agreement for City approval that addresses the long-term maintenance of its system. Property owners are responsible for conducting inspections and maintenance of their system each year.

3.090 Storm Drainage Construction General Notes

In addition to the General Construction Notes in Chapter One, the Engineer shall include the following notes on any plans dealing with the construction, alterations, extensions or connections to the storm drainage system A. All storm mains, structures, conveyance systems and

retention/detention areas shall be staked for grade and alignment prior to the start of construction.

B. All storm drainage systems are required to be air tested in

conformance with Section 7-04.3(1) of the WSDOT Standard Specifications. Special structures, oil/water separators and outlet controls shall be installed and tested per the approved plans and manufacturer’s recommendations.

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L I S T O F D R A W I N G S

C H A P T E R 3 S T O R M D R A I N A G E Title Drawing Inlet Structure ..................................................................................... SD-01 Catch Basin Type 1L ............................................................................ SD-02 Catch Basin Type 1 .............................................................................. SD-03 Sheet 1 of 2 ~ Combination Inlet (CB Type 1 Shown) ………………… ..... SD-04 Sheet 2 of 2 ~ Combination Inlet Notes) .……………………………………… SD-04

Catch Basin Type 2, 48" & 54" ............................................................. SD-05 Catch Basin Type 2, 72" & 96" ............................................................. SD-06 Flow Restrictor Catch Basin ................................................................. SD-07 Floatable Material Separator ................................................................ SD-08 Typical Restrictor Installation .............................................................. SD-09 East Jordan Hinged CB Type 2 Cover & Frame for Paved Areas ............ SD-10 Manhole Ring and Cover for Unpaved Areas………………………………….. SD-10A Overflow Structure Detail .................................................................... SD-11 Square Beehive Drain Grate ................................................................ SD-12 CB Type 2 w/Bird Cage Trash Rack ..................................................... SD-13 Debris Barrier Detail ……………………………………………………………… SD-14 Frame for Grate or Solid Cover ............................................................ SD-15 Recessed Gutter Detail ........................................................................ SD-16 Lift Gate Assembly & Secondary Orifice Details ................................... SD-17 Biofilter Swale Detail ............................................................................ SD-18 Manhole Surface Restoration within Right-of-Way ............................... SD-19 Infiltration Gallery .............................................................................. SD-20 Alternate 1 ~ Roof Drain Drywell .......................................................... SD-21 Alternate 2 ~ Roof Drain Drywell .......................................................... SD-22 This Page Intentionally Left Blank ........................................................ SD-23 This Page Intentionally Left Blank ........................................................ SD-24

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INLET STRUCTURE

CATCH BASIN TYPE 1L

CATCH BASIN TYPE 1

CATCH BASIN TYPE 2 (48" & 54")

CATCH BASIN TYPE 2 (72" & 96")

FLOW RESTRICTOR CATCH BASIN

FLOATABLE MATERIAL SEPARATOR

TYPICAL RESTRICTOR INSTALLATIONSD-09

SD-10

SD-11

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SD-16

EAST JORDAN HINGED CB TYPE 2 COVER & FRAME FOR PAVED AREAS

OVERFLOW STRUCTURE DETAIL

SQUARE BEEHIVE DRAIN GRATE

CATCH BASIN TYPE 2 W/ BIRD CAGE TRASH RACK

DEBRIS BARRIER DETAIL

FRAME FOR GRATE OR SOLID COVER

RECESSED GUTTER DETAIL

SD-17

BIOFILTER SWALE

STORM DRAINAGE DETAILS

TABLE OF CONTENTS

SD-18

SD-19

ALT. #2 ~ ROOF DRAIN DRYWELL

SD-20 INFILTRATION GALLERY

SD-21

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ALT. #1 ~ ROOF DRAIN DRYWELL

Sht. 1 of 2 ~ COMBINATION INLET (CB TYPE 1 SHOWN)

MANHOLE SURFACE RESTORATION WITHIN THE RIGHT-OF-WAY

Sht. 2 of 2 ~ COMBINATION INLET NOTES

LIFT GATE ASSEMBLY & SECONDARY ORIFICE DETAILS

(r.4)

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SD-24

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SD-10A MANHOLE RING AND COVER for UNPAVED AREAS

ADJUSTMENT SECTION GRADE RING

NOTES:

12" ADJUSTMENT SECTION

GRADE RINGS

REQUIRED:

INLET

STRUCTURE

SD-01

PRECAST BASE SECTION

FRAME AND GRATE

NOTES:

REQUIRED:

2"-6" ADJUSTMENT SECTION

GRADE RINGS

12" ADJUSTMENT SECTION

GRADE RINGS

CATCH BASIN

TYPE 1L

SD-02

PRECAST BASE SECTION

FRAME AND GRATE

NOTES:

REQUIRED:

12" ADJUSTMENT SECTION GRADE RING

4"-6" ADJUSTMENT SECTION GRADE RING

CATCH BASIN

TYPE 1

SD-03

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NOTES:

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SD-05

CATCH BASIN: TYPE 2

DESIGN ASSUMPTIONS

NOTES:

PRECAST BASE JOINT

SPECIAL NOTES:

72" & 96"

SD-06

CATCH BASIN: TYPE 2

NOTES:

SPECIAL NOTES:

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SD-07

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NOTES:

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SEPARATOR

SD-08

FLOATABLE MATERIAL

TYPICAL RESTRICTOR

INSTALLATION

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* FOR TYPE 1 CATCH BASIN

SQUARE BEEHIVE

DRAIN GRATE*

SD-12

AA

PLAN VIEW

SECTION A-A

HOOK CLAMP DETAIL

NOTES:

ALTERNATE RACK CONNECTION DETAIL

CI ON

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TYof SHELT

CI ON

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OTGNIHS

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TYof SHELT

CATCH BASIN, TYPE 2

w/ BIRD CAGE

TRASH RACK

SD-13

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A A

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TOP VIEW

SECTION A-A

NOTES:

SPECIAL NOTE:

CATCH BASINS AND GRATES TO CONFORM

TO WSDOT STANDARD PLANS. VERIFY

TYPE W/ CITY ENGINEER.

FRAME FOR GRATE

OR SOLID COVER

SD-15

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SECONDARY ORIFICE DETAIL

LIFT GATE ASSEMBLY

LIFT GATE DETAIL

NOTES:

LIFT GATE ASSEMBLY

& SECONDARY ORIFICE

DETAILS

SD-17

BIO

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A A

SECTION A-A

INSTALLATION NOTES

CATCH BASIN TYPE 2 RING &

COVER W/ CONCRETE COLLAR

STORM

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WITHIN RIGHT OF WAY

SD-19

SURFACE RESTORATION

SECTION A-A

PLAN VIEW

PROFILE VIEW

A

A

*SUMP NOTE

*

*

SCHEMATIC

INFILTRATION GALLERY

SD-20

SECTION A-A

PLAN VIEW

A

A

ALTERNATE #1

ROOF DRAIN

DRYWELL

SD-21

NOTE:

FOR USAGE ONLY WHEN AUTHORIZED BY THE

CITY ENGINEER AND IF SIZE OF ROOF AREA IS

LESS THAN 1,000 SF.

NOTE:

FOR USAGE ONLY WHEN AUTHORIZED BY THE

CITY ENGINEER AND IF SIZE OF ROOF AREA IS

LESS THAN 1,000 SF.

ALTERNATE #2

ROOF DRAIN

DRYWELL

SD-22

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TITLE

SD-23

DETAIL

TITLE

SD-24

DETAIL

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