Module 5: Bioretention Design Specs Details - Melanie Mills

centralcoastlidi.org

Module 5: Bioretention Design Specs Details - Melanie Mills

Module 5: Bioretention Design Specs/Details

Melanie Mills, MLA

Central Coast LIDI


100

Standard Details

Specifications & Standard Details!

BIORETENTION DESIGN NOTES

1. Overflow structure required for in-line systems without overflow bypass, Detail

140.

2. Provide spot elevations on civil plans (TBSM, OE, GIE, IE). See Detail 120.

3. Edge condition will vary for new and retrofit projects. Curb details may be

modified for project by civil and geotechnical engineers.

4. If check dams are needed, see Concrete Check Dam Detail 131.

5. If Caltrans Class 2 Permeable is not available, substitute Class 3 Permeable with

an overlying 3" deep layer of 3/4" (No. 4) open-graded aggregate.

6. Bioretention Soil Media (BSM) specification per BASMAA Soils for Biotreatment

or Bioretention Facilities.

7. Plant Selection per LIDI Plant Guidance for Bioretention Areas Technical

Assistance Memo (TAM).

8. Mulch (optional) per LIDI Plant Guidance for Bioretention Areas TAM. Grading to

allow for specified soil and mulch depths while achieving finished elevations per

civil plans.

9. Locate energy dissipation cobble only as specified in inlet details - avoid

decorative use.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

Bioretention Area

Planter

CONSTRUCTION NOTES

1. Scarify subgrade before installing bioretention

area aggregate and BSM.

2. Compact each 6" lift of BSM with landscape

roller or by lightly wetting. If wetting, allow to

dry overnight before planting.

3. Never work within bioretention area limits

during rain or under wet conditions.

4. Keep all heavy machinery outside bioretention

area limits.

detail number

100

Design Specifica-ons

Low Impact Development Initiative (LIDI)

Bioretention Area Design Specifications (without underdrain)

Facility Design/Dimensions

� Bottom width – provide 2’ wide minimum flat bottom for facilities with side slopes and

longitudinal slope

� Allowable ponding duration – 72 hours.

– Allowable ponding time is typically associated with mosquito vector control, and

varies by location. Confirm with local vector control agency to confirm appropriate

drawdown time for facility.

� Energy dissipation – provide an aggregate or concrete splash pad at inlet per LIDI

details.

– For aggregate: 6” depth, 3" – 6" rounded, washed cobble (CalTrans Class 2 or 3

Permeable)

– For sloped sided facilities, extend a cobble flow path from pad 1’ into bioretention

area bottom.

� Planter minimum widths are typically associated with their application. Considerations

influencing minimum widths include:

– 3’ minimum for planters in ROW with trees

– 2’ minimum for planters without trees

� Planter depth – (from pedestrian surface to top of facility planting surface) is related to

planter width. Planters can be deeper as they get wider, and need to be shallower as

they narrow. This is a perception and safety issue. Recommended ratios are:

– TBD, table with width/depth guidelines.

� Ponding depth - Min. 6", max. 12"

� Slope/grades

– Side slope - 4:1 preferred

• Max. 3:1 allowed with min. 12" shoulder (2% slope) adjacent to pedestrian use

or curb

– Longitudinal slope – Max. 6% longitudinal slope of bottom.

• Erosion and movement of soil and mulch intensifies with increased longitudinal

slope, minimize longitudinal slope.

• Stair stepping planters on a slope to provide flat bottomed cells separated by

check dam/weir overflows can provide more storage and infiltration than a

sloped facility.

– Grades on opposite sides within a facility should be similar to optimize ponding

across the entire basin/cell.

Hard Infrastructure

9/17/12 page 1/3


Bioretention Area

Design Guidance

Structure Design Guidelines

Are standard drawings

available?

Aggregate layer

Bioretention soil media

(BSM)

Design Guidance Review!

City of LA Manual

Yes, in a simplified drafting style, p.

35

Not shown on infiltration basin

drawing.

Described, not specified

City of Santa Barbara

Stormwater BMP Manual

Yes, drafted section of bioretention

area (may not be to scale), p. 6-26

Bioretention Guidelines and Standards

Comparison of Source Documents

Contra Costa C3 Manual LID Manual for So. California

Multiple graphics, but not one

standard detail for bioretention

area.

Yes, a very simple drafted detail, it

includes an underdrain, p. 80.

Yes, p. 6-24 Yes, p. 71 No

Yes, BSM specified, p.6-21, but does

not provide an infiltration rate for

the mix.

BSM compaction Did not locate Did not locate

BSM specified provided, Appendix

B, must achieve long-term, in-place

infiltration rate of ≥ 5"/hr.

General comment provided, but

not % compaction, p. B-2.

Generally comprised of 50% sand,

30% topsoil, and 20% organic

material (states infiltration rates of

specified soils may range from 25

– 130 in/hr.

LID Tech. Guid

for Puge

Yes, uses Seattle's,

drawings for diffe

and related com

option without u

shows 12" depth

available fo

Only shown w

unde

Yes, BSM specifi

spec. not use

performance p. 1

using 60% aggre

Did not locate Yes, compact to

BSM depth 2', 3' preferred 2', 3' preferred Min. 1'6" 2', 3', more where trees are planted

Bottom width Did not locate Not provided Did not locate Did not locate

Check dams

Design infiltration rate

Table provides distance between

check dams in sloped systems, p. 59

Provides how to calculate design

infiltration rate for a structure on p.

40.

Drawdown time 48 hrs.

Energy dissipation Required

States for use with longitudinal

slopes that exceed 6%, but I don't

think this is for biofiltration. See LA's.

Provides how to calculate design

infiltration rate for a structure in

Appendix D.

48 hrs. in soil, 72 hrs. in drain rock

layer, also gives 36-48 hours.

Include rock or other erosion

protection material at flow

entrance.

Ok between aggregate and soil

Yes, guidelines for distance apart

provided.

Long-term percolation rate 5"/hour

(appendix B).

72 hours

12"--24", > 24"

phosphorus, TKN

rem

Min. for swale

channe

Did not locate Did not

Not located for structure. See

bioretention soil mix above.

Varies by jurisdiction, but in the

range of 24-72 hours

Yes, shows a concrete apron, p. 72. Yes

Min. long-te

conductivity o

24 hours rec

Yes, rock or other

material. Avoi

because it is h

sedim

Where aggregate

filter fabric and ag


Expert Panel Review!

DRAFT

Low Impact Development Initiative (LIDI)

Bioretention Area Design Specifications (without underdrain)

Text in blue represents changes based on group comments.

Highlighted text indicates items related to discussion topics.

Facility Design/Dimensions

Develop narrative for each section?

� Bottom width – provide 2’ wide minimum flat bottom for facilities with side slopes

and longitudinal slope

� Drawdown time – 72 hours.

– Drawdown time is typically associated with mosquito vector control, and

varies by location. Confirm with local vector control agency to confirm

appropriate drawdown time for facility.

� Energy dissipation – provide an aggregate or concrete splash pad at inlet per

LIDI details.

– For aggregate: 6” depth, 3" – 6" rounded, washed cobble (CalTrans Class 2 or

3 Permeable)

– For sloped sided facilities, extend a cobble flow path from pad 1’ into

bioretention area bottom.

� Planter minimum widths are typically associated with their application.

Considerations influencing minimum widths include:

– 3’ minimum for planters in ROW with trees

– 2’ minimum for planters without trees

� Planter depth – (from pedestrian surface to top of facility planting surface) is

related to planter width. Planters can be deeper as they get wider, and need to

be shallower as they narrow. This is a perception and safety issue.

Recommended ratios are:

– Need further input. Will provide a table with width/depth or bulleted

guidelines.

� Ponding depth - Min. 6", max. 12"


Design Specifications!

• Facility Design and Dimensions

– width, depth, slope, ponding!

• Hard Infrastructure

– inlets, check dams, overflow structures!

• Facility Media

– soil, aggregate base, mulch !

• Landscape

– plant selection, irrigation!


• Facility Type

– planter!

Standard Details!

– sloped sided!

• Elements related to facility

– walls!

– curb inlets!

– overflows!

– check dams!


Standard

Details!

BIORETENTION DESIGN NOTES

1. Overflow structure required for in-line systems without overflow bypass, Detail

140.

2. Provide spot elevations on civil plans (TBSM, OE, GIE, IE). See Detail 120.

3. Edge condition will vary for new and retrofit projects. Curb details may be

modified for project by civil and geotechnical engineers.

4. If check dams are needed, see Concrete Check Dam Detail 131.

5. If Caltrans Class 2 Permeable is not available, substitute Class 3 Permeable with

an overlying 3" deep layer of 3/4" (No. 4) open-graded aggregate.

6. Bioretention Soil Media (BSM) specification per BASMAA Soils for Biotreatment

or Bioretention Facilities.

7. Plant Selection per LIDI Plant Guidance for Bioretention Areas Technical

Assistance Memo (TAM).

8. Mulch (optional) per LIDI Plant Guidance for Bioretention Areas TAM. Grading to

allow for specified soil and mulch depths while achieving finished elevations per

civil plans.

9. Locate energy dissipation cobble only as specified in inlet details - avoid

decorative use.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

Bioretention Area

Planter

CONSTRUCTION NOTES

1. Scarify subgrade before installing bioretention

area aggregate and BSM.

2. Compact each 6" lift of BSM with landscape

roller or by lightly wetting. If wetting, allow to

dry overnight before planting.

3. Never work within bioretention area limits

during rain or under wet conditions.

4. Keep all heavy machinery outside bioretention

area limits.

detail number

100


Facility Design & Dimensions !

• Bottom width – provide 2’ wide minimum flat bottom

for facilities with side slopes and longitudinal slope

• Allowable standing water – 72 hours.

– Allowable ponding time is typically associated with

mosquito vector control, and varies by location. Confirm

with local vector control agency to confirm appropriate

drawdown time for facility.!

• Energy dissipation – provide an aggregate or

concrete splash pad at inlet per LIDI details.

– For aggregate: 6” depth, 3" – 6" rounded, washed cobble !

– For sloped sided facilities, extend a cobble flow path from

pad 1’ into bioretention area bottom.!


100

Bioretention w/ Flat Bottom (Planter)!

BIORETENTION DESIGN NOTES

1. Overflow structure required for in-line systems without overflow bypass, Detail

140.

2. Provide spot elevations on civil plans (TBSM, OE, GIE, IE). See Detail 120.

CONSTRUCTION NOTES

1. Scarify subgrade before installing bioretention

area aggregate and BSM.

2. Compact each 6" lift of BSM with landscape

roller or by lightly wetting. If wetting, allow to


Bioretention w/ Sloped Sides


BIORETENTION DESIGN NOTES

(rain garden, linear swale)!

CONSTRUCTION NOTES

1. Overflow structure required for in-line systems without overflow bypass, Detail 140. 1. Scarify subgrade before installing bioretention


• 3:1 max

– needs shoulder!

• 4:1 recommended

Side Slope Grades!


Bioretention w/ Sloped Sides!

BIORETENTION DESIGN NOTES

CONSTRUCTION NOTES

1. Overflow structure required for in-line systems without overflow bypass, Detail 140. 1. Scarify subgrade before installing bioretention


Facility Elevations!

• Overflow elevation

• Curb gutter inlet

elevation

• Top of curb

• Adjacent surface

• Finished grade in

facility

photo: bluegreenbldg.org


Bioretention w/

Underdrain

Planter!

• Class 2

permeable

• No filter fabric

• No filter layer

• Underdrain

– PVC SDR 35!

– holes downward!

– cleanout!

BIORETENTION DESIGN NOTES

1. Overflow structure required for in-line systems without overflow bypass, Detail 140.

2. Provide spot elevations on civil plans (TBSM, OE, GIE, IE). See Detail 120.

3. Edge condition will vary for new and retrofit projects. Curb details may be modified

for project by civil and geotechnical engineers.

4. Provide capped, threaded PVC cleanout for underdrain, 4" min. dia. with sweep

bend.

5. If check dams are needed, see Concrete Check Dam Detail 131.

6. If Caltrans Class 2 Permeable is not available, substitute Class 3 Permeable with

an overlying 3" deep layer of 3/4" (No. 4) open-graded aggregate.

7. Bioretention Soil Media (BSM) specification per BASMAA Soils for Biotreatment or

Bioretention Facilities.

8. Plant Selection per LIDI Plant Guidance for Bioretention Areas Technical

Assistance Memo (TAM).

9. Mulch (optional) per LIDI Plant Guidance for Bioretention Areas TAM. When used,

excavate to allow for specified soil and mulch depths and achieve finished

elevations as shown on plans.

10. Locate energy dissipation cobble only as specified in inlet details - avoid

decorative use.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

Bioretention Area

Planter w/ Underdrain

DRAFT

CONSTRUCTION NOTES

1. Scarify subgrade before installing bioretention

area aggregate and BSM.

2. Install underdrain with holes facing down.

Underdrain discharge elevation shall be near

top of aggregate layer. Underdrain slope may

be flat.

3. Compact each 6" lift of BSM with landscape

roller or by lightly wetting. If wetting, let dry

overnight before planting.

4. Never work within bioretention area limits

during rain or under wet conditions.

5. Keep all heavy machinery outside bioretention

area limits.

detail number

102


Bioretention w/

Underdrain

Side Slope!

• Underdrain

design

considerations

– design w/ future

modification!

– adjustable orifice!

– open/close drain!

BIORETENTION DESIGN NOTES

1. Overflow structure required for in-line systems without an overflow bypass, Detail 140.

2. Provide spot elevations on civil plans (TBSM, OE, GIE, SIE). See inlet details 121, 122.

3. Max. longitudinal slope 6% with check dams. See details 130, 131.

4. Edge condition will vary for new and retrofit projects. Curb, wall, and sidewalk details may

be modified for project by civil and geotechnical engineers.

5. If Caltrans Class 2 Permeable is not available, substitute Class 3 Permeable with an

overlying 3" deep layer of 3/4" (No. 4) open-graded aggregate.

6. Bioretention Soil Media (BSM) specification per BASMAA Soils for Biotreatment or

Bioretention Facilities.

7. Plant Selection per LIDI Plant Guidance for Bioretention Areas Technical Assistance

Memo.

8. Mulch (optional) type/depth per LIDI Plant Guidance for Bioretention Areas TAM. Grades

to allow for specified soil and mulch depths while achieving finished elevations per civil

plans.

9. Locate energy dissipation cobble only as specified in inlet details - avoid decorative use.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Bioretention w/ Side Slope and

Underdrain

Municipality

Department Name

DRAFT

CONSTRUCTION NOTES

1. Scarify subgrade before installing bioretention

area aggregate and BSM.

2. Install underdrain with holes facing down.

Underdrain discharge elevation shall be near

top of aggregate layer. Underdrain slope may

be flat.

3. Compact each 6" lift of BSM with landscape

roller or by lightly wetting. If wetting, let dry

overnight before planting.

4. Never work within bioretention area limits

during rain or under wet conditions.

5. Keep all heavy machinery outside bioretention

area limits.

detail number

103


• Hard Infrastructure

Design Specifications!

Hard Infrastructure

� Inlet curb cut design – per details 120, 121,122,123

� Check dams – provide for facilities with bottom slope

– Per check dam details 130,131

– Use LIDI check dam spacing detail (under development detail 132).

� Overflow structure – required for on-line systems without an overflow bypass

– Per overflow structure details 140, 141


Edge

Infrastructure!

BIORETENTION DESIGN NOTES

1. Special design consideration or structural review may be required

for longer swale edge spans. Steel reinforcement or additional

concrete check dams may be needed for stability.

2. When sidewalk drains to planter, provide 6" wide notch openings

spaced to convey flows.

3. Concrete and expansion joints shall meet the requirements of the

municipality.

CONSTRUCTION NOTES

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

1. Finish all exposed concrete surfaces.

detail number

Deep Curb 111


Edge

Infrastructure

for Sloped

Sides!

BIORETENTION DESIGN NOTES

1. Special design consideration or structural review may be required

for longer swale edge spans. Steel reinforcement or additional

concrete check dams may be needed for stability.

2. Concrete and expansion joints shall meet the requirements of the

municipality.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

CONSTRUCTION NOTES

1. Finish all exposed concrete surfaces.

detail number

Thickened Edge Sidewalk 112


Curb Cut Inlets

for Planters!

• Inlet design has

evolved

A

PLAN VIEW

SECTION A-A

A

BIORETENTION DESIGN NOTES

1. For use with stormwater facilities with flat

bottoms.

2. Provide spot elevations on plans (TBSM, OE,

GIE, IE). See Detail 100.

3. Refer to municipal standard drawings and

match gutter pan of adjacent curb and gutter.

CONSTRUCTION NOTES

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

Curb Cut Inlet

for Planters

PERSPECTIVE VIEW

1. After construction place sand bags at gutter

openings to keep storm flows from entering

facility until vegetation is established.

detail number

120


Concrete Splash Pad!


Curb Cut Inlets

for Sloped

Sides!

City of Portland, Environmental Services

A

PLAN VIEW

SECTION A-A

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

Curb Cut Inlet

for Side Slopes

(rain garden or swale)

A

PERSPECTIVE VIEW

BIORETENTION DESIGN NOTES

1. For use with stormwater facilities with side

slopes.

2. Provide spot elevations on plans (TBSM,

OE, GIE, IE). See Detail 100.

3. Refer to municipal standard drawings and

match gutter pan of adjacent curb and

gutter.

CONSTRUCTION NOTES

1. After construction place sand bags at gutter

openings to keep storm flows from entering

facility until vegetation is established.

detail number

121


Curb Cut Inlets

w/ Gravel!

A

PLAN VIEW

BIORETENTION DESIGN NOTES

1. For use with stormwater facilities with

sloped sides or flat bottoms.

2. Provide spot elevations on plans (TBSM,

OE, GIE, IE). See Details 100, 101.

3. Drop from inlet to aggregate pad will be

greater for planters.

4. Refer to municipal standard drawings and

match gutter pan of adjacent curb and

gutter.

CONSTRUCTION NOTES

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Curb Cut Inlet

with Gravel Energy Dissipation

Municipality

Department Name

A

SECTION A-A

1. After construction place sand bags at gutter

openings to keep storm flows from entering

facility until vegetation is established.

detail number

122


• Use it for energy

dissipation

– at inlets!

Energy Dissipation Cobble!

– sloped sides/extend

down to facility bottom!

• Avoid decorative use

– difficult to maintain!

– weeds can establish

in sediment/cobble!


SW 12 th Ave., Portland, Kevin Perry

Inlet w/ Grate! A

A

B

B

PLAN VIEW

SECTION B-B

BIORETENTION DESIGN NOTES

1. For use with stormwater facilities with sloped sides or flat bottoms.

2. Provide spot elevations on plans (TBSM, OE, GIE, IPE). See Details 100, 101.

3. Refer to municipal standard drawings and match gutter pan of adjacent curb and gutter.

4. If sloped sides, extend cobble from splash pad 1' into bottom of facility.

5. Base material for curb, gutter, and sidewalk per municipal standards.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

GRATE AND FRAME

SECTION A-A

CONSTRUCTION NOTES

1. After construction place sand bags at gutter

openings to keep storm flows from entering

facility until vegetation is established.

detail number

Inlet with Grate 123


Gravel Check

Dam!

• Mild longitudinal

slope

City of Portland, Environmental Services

BIORETENTION DESIGN NOTES

SECTION A-A

1. For use with stormwater facilities with sloped sides.

2. Best suited for facilities with > 2% longitudinal slope.

3. Provide elevations and stationing and/or

dimensioning for check dams.

4. Space check dams per detail 132.

5. Ensure that check dam elevations do not cause

stormwater to overflow to sidewalk.

A

A

CONSTRUCTION NOTES

1. Do not work during rain or under wet

conditions.

2. Keep all heavy machinery outside

bioretention area limits.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

detail number

Gravel Check Dam 130


Concrete

Check Dam!

Pittsburgh Courthouse, photo: bluegreenbldg.org

BIORETENTION DESIGN NOTES

1. For use with bioretention planters or sloped sided

swales/rain gardens.

2. For check dams longer than 12' specify rebar overlap

length.

3. Space check dams per detail 132.

4. Provide elevations and stationing and/or dimensioning

for check dams.

5. Ensure that check dam elevations do not cause

stormwater to overflow to sidewalk.

6. Show planter wall embedded in existing subgrade or

drainrock.

CONSTRUCTION NOTES

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

1. Embed #3 rebar 3" into curb and planter

wall.

2. Do not work during rain or under wet

conditions.

3. Keep all heavy machinery outside

bioretention area limits.

detail number

Concrete Check Dam 131


Concrete Check Dams!

• Work w/ steep

longitudinal slope

• Series of bathtubs

photo: Tracy Tackett, SPU


Check Dams!

• Other rigid materials

– steel!

– clear plexiglass!

– concrete w/ wood!


Overflow

Structure w/

Beehive Grate!

• Required for systems

without overflow bypass

• Overflow raised to allow

ponding

• Connects to

downstream structure or

stormdrain

photo: SvR Design

BIORETENTION DESIGN NOTES

1. Provide grate overflow elevation on plans.

2. To incorporate flexibility into design

overflow elevation or correct elevation of an

existing structure, install overflow collar, per

detail 141.

Overflow Structure

w/ Beehive Grate

CONSTRUCTION NOTES

1.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

detail number

140


Overflow

Structure w/

Collar!

photo: Kevin Perry

BIORETENTION DESIGN NOTES

1. Provide collar overflow elevation (COE) on

plans.

Overflow Structure

Collar

CONSTRUCTION NOTES

1. Center collar on overflow grate.

LOW IMPACT DEVELOPMENT STORMWATER MANAGEMENT STANDARD DETAILS

Municipality

Department Name

detail number

141


Location of Overflow!

• Not adjacent to inlet

• Raised to allow for

design ponding

TOP

10


Design

Specifications!

• Facility Media

• Landscape

� Overflow structure – required for on-line systems without an overflow bypass

– Per overflow structure details 140, 141

Facility Media (soil, aggregate base, mulch)

� Aggregate layer – where an aggregate layer is included in the design (optional, use

based on project requirements, depth based on sizing calculations), specify “CalTrans

Class 2 Permeable.”

– CalTrans Class 2 Permeable does not require an aggregate filter course between

the aggregate storage layer and the bioretention soil media above.

– When CalTrans Class 2 Permeable is not available, substitute CalTrans Class 3

Permeable.

• Class 3 Permeable requires an overlying 3” deep layer of ¾” (No. 4) open

graded aggregate (between Class 3 and bioretention soil media above).

Bioretention soil media - use BASMAA Specification of Soils for Biotreatment or

Bioretention Facilities (Attachment L).

– Using performance specification for alternative bioretention soil mix is not

recommended.

� BSM depth – 18” minimum depth, 24” recommended.

– Where aggregate layer is used and trees are specified, increase bioretention soil

media depth in tree planting areas.

– Per detail XXX (tree in bioretention detail TBD)

� Filter fabric - do not use fabric between BSM and aggregate layer

– Per details 100,101

� Mulch depth – 2” – 3”

– Optional below ponding high water mark.

– Do not apply mulch in ponding zone just prior to or during rainy season.

– When mulch is used, excavation must allow for specified soil and mulch depths and

achieve finished elevations as shown on plans.

� Mulch type - when used in ponding zone, must be aged, stabilized, non-floating mulch,

such as a specified compost mulch.


Aggregate!

• Optional use – per project requirements

• Cal Trans Class 2 Permeable

• No filter fabric

– potential for clogging!

– inhibits infiltration!

• Aggregate filter layer not needed for Class 2

• If Class 2 not available, substitute Class 3

– provide 3” depth filter layer for Class 3 !


Future Standard Details!

• Layout details for bioretention

– street edge with parking!

– curb extensions!

– bioretention with pedestrian

crossing!

– parking lot layouts!


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