The Parking Forest: As if Mother Nature Designed a Parking Lot

The Parking Forest BMP:Linear Tree Wells Using Structural Soil in Parking Lots

Sustainability for all the places between the buildings

503.334.8634www.greengirlpdx.com

[email protected] certified women business enterprise

Agenda

• What is the purpose of a Parking Forest?• What is a Parking Forest?• Why should there be more Parking Forests?• What is it made of and how does it work?• Why do we expect this to actually grow healthy trees in

parking lots?• Where can it be installed?• How did we innovate to lower costs and improve

function?• How much did each demonstration project cost?

More Informationwww.parkingforest.org

• Partners• Benefits• Design Criteria• Specifications• Plans & Details• Monitoring & Adaptive Management• Photo Galleries• Additional Resources• Press• Frequently Asked Questions

What is the purpose of a Parking Forest?

www.parkingforest.org

To increase canopy and manage stormwater …without losing parking spaces

What is a Parking Forest?


The Parking ForestAn Assembly of Common Materials

12 foot wide x 2 foot deep continuous trench

Two Demonstration Sites

Watershed base map courtesy of Tualatin River Watershed Council

Redevelopment

Retrofit

THPRD Sunset Swim CenterRedevelopment with Pervious Concrete

Pervious concrete

Amended native soil topped with crushed

rock (4 foot wide)

Pervious Concrete

THPRD Sunset Swim Center in PlanRedevelopment with Pervious Concrete

PCC Sylvania Lot 10Retrofit with Conventional Asphalt

Conventional impervious

asphalt

Amended native soil topped with crushed

rock (4 foot wide)


Ignore the piles of dirt. They’re

gone.

Line of pavement removal and replacement


Tree trunks lined up with striping to

protect trees

4’ wide amended native soil trench

Why should there be more Parking Forests?


1. There are lots of conventional parking lots

1. There are lots of conventional parking lots(and I’m not the only who thinks so)

Source: Clean Water Services Healthy Streams Plan

Effective Impervious Areas in the Tualatin Watershed6% Sidewalks (1,028 acres)

14% Roads (2,319 acres)

31% ParkingLots

(5,136 acres)

1% Misc(156 acres)

48% BuildingFootprints

(7,840 acres)

2. Conventional parking lots impact water quality.

Before development in Western Oregon…

Before development in Western Oregon…

25% base flow

(shallow infiltration)

50%

ev

apor

ation

0.5% runoff

100%

XX”

ave

rage

annu

al ra

infa

ll

25%

gro

undw

ater

(dee

p in

filtr

ation

)

Water Balance AFTER DevelopmentEVERYWHERE

redu

ced

evap

orati

on

98% runoff

2%

evap

orati

on

Redu

ced

infil

trati

on

100%

ave

rage

annu

al ra

infa

ll

No

infiltration

Water Balance Runoff Compared

0.5% runoff (Oregon)Up to 10% (nationally)

98% runoff

Additional Runoff Volumes from a Watershed Perspective

Additional runoff volumes scour stream banks, impacting water quality downstream.Additional durations of flow impact habitat further.

Please! Keep your runoff volume to

yourself!

Why Should YOU Care About Water Quality?

$Funding for stormwater projects is made available to meet regulations (319 Grants)

3. For Business Owners, Parking Spaces = $$$

Other vegetated stormwater facilities take up parking spaces.

Some people try to park in them anyway

4. Other institutions can’t afford to lose parking spaces either

At PCC, parking is so limited that people park in front of the islands.

5. We need better behaved trees

To be low maintenance and safe, trees need lots of soil.

Photo Source: gratefulmommy.com

Trees Need Lots of Soil to Grow

Graph Source: USDA Forest Service Center for Urban Forest ResearchSlide courtesy of Todd Prager ,Todd Prager & Associates

33326720013367Soil Area Needed Assuming a 3ft min depth (ft2)

Trees Need Soil to GrowAfter 20 years or so…

5 ft crownIn 40 cu ft soil

20 ft crownIn 450 cu ft soil

40 ft crownIn 2000+ cu ft soil

Photos and observations courtesy of Todd Prager, Todd Prager & Associates

Callery Pear Pin Oak Pin Oak

6. We need more trees. Trees are awesome.

Just ask anyone at this conference.

What are Parking Forests made of and how do they work?


The Parking ForestAn Assembly of Common Materials

12 foot wide x 2 foot deep continuous trench

Structural Soil (dry)

The Parking ForestClose Up

Pavement outside of

Parking Forest

Pavement over structural soil4 ft wide, both sidesTree

Structural Soil (wet)Amended native

clayey soilUndisturbed native clayey soil

Crushed aggregate

Wheel stop

12’ wide by 2’ deep continuous trench

Structural Soil: Our Preferred Method for Providing Adequate Soil Volume

Source: Cornell University – CU Structural Soil - http://www.hort.cornell.edu

Loading or Compaction Effort

Stone particle

Soil particle

Air or water pore

Stone contact points where load is transferred

Why Structural Soil versus “Real” Soil and Supports?

Supported Parking Area

. Photo courtesy of Jim Labbe

Another Way of Providing Tree Roots with Adequate Soil Volume Under Pavement


. Photo courtesy of Jim Labbe


Photo courtesy of Jim Labbe

My Personal Reason:Structural Soils are All Natural

How do we know Structural Soils work?Olympia, WA: Results 8 Years Later

Control Trees Planted in Compacted Native Soil

Trees Planted in Structural Soil

Palo Alto, CA is hooked

Jan 29, 2004 presentation by Dave Dockter, Managing Arborist , Planning Division

Palo Alto, CA is hooked

Jan 29, 2004 presentation by Dave Dockter, Managing Arborist , Planning Division

Apparently many other places are hooked, too

Constructing the Trench Assembly

Place the structural soil in an 8-inch lift on either side of the 12’ wide trench.


Place the amended native soil (middle). Here, the structural soil (left and right) is being wetted down in preparation for light compaction.


Test for adequate compaction on both sides of the structural soil every 25 feet. Remember, cars will drive on this!

Assembly Procedure

Each lift of amended native soil is water compacted.

Assembly Procedure

Lifts are added, compacted, tested three times to reach a full depth of 2 feet.

Assembly Procedure

Place pavement over structural soil.

Assembly Procedure

Place crushed rock down the middle of the amended native soil section, plant trees, park cars, and ENJOY!

How did we innovate to lower costs and improve function?


A Common Structural Soil Detail

Cornell University Horticulture Department

3 feet of structural soil

Compacted subgrade

Drains to storm system without

significant volume

reduction

We hired a geotechnical engineer

To minimize the pavement section for our traffic load

The Parking ForestStormwater and Cost-Saving Innovation

Undisturbed (i.e. not compacted or “prepared”) native clayey soil

2 feet of structural soil needed for structural

stability

3 feet of soil depth for tree roots is still available!

Were the demonstration projects cost-effective?


Cost depends on how you look at it

Redevelopment with pervious

concrete

Retrofit in conventional

asphalt

Area [sf] 2,400 400

Construction & permit costs ~$21,000 $9,446.93

# of trees 15 3



concrete


asphalt

Area [sf] 2,400 400


# of trees 15 3

Cost per tree $1,400 $3,148.98



concrete


asphalt

Area [sf] 2,400 400


# of trees 15 3

Cost per tree $1,400 $3,148.98

Cost per square foot $105 $23.62



concrete


asphalt

Area [sf] 2,400 400


# of trees 15 3

Cost per tree $1,400 $3,148.98

Cost per square foot $105 $23.62

Cost per square foot of area managed for stormwater $105 $1.55

Conclusion: Stormwater Management Retrofit was Cost Effective

6133 sf

1919 sf

754 sf

615 sf

2815 sf

6103 sf

Parking Lot

Sidewalk

<50% Grass HSG C

Woods, Good HSG C

L Street

To lower costs next time, we could mix our own structural soil

Photo Source: www.greelysand.com/cu-soil.html

Olympia, WA Soil Recipe

4 cubic yards Crushed Rock ¾”-1¼” + 1 cubic yard Loam/organic topsoil + 1 pound Soil Binder “Stabilizer” + 46 gallons water__________Makes 4.6 cubic yards Structural Soil

Structural Soil Costs - Olympia

“The price to supply, deliver and install the structural soil material per cubic

yard ranged from $19 to $85 with an average bid of $42, the median price

was $39.50.

The city paid $24 per cubic yard for the structural soil material to the low

bidder.

This compare to a price quote we received for the supply of CU structural

soil at $65 per cubic yard plus delivery. The source was over an hour’s drive

away and delivery charges were $85 per hr with a truck and trailer hauling 22

cubic yard. The expected cost delivered was $72 per cubic yard.”

Excerpted from “Structural Soil Demonstration Project”

http://olympiawa.gov/~/media/Files/CPD/Urban%20Forestry/Forms/StructuralSoil.ash

x

Source: City of Olympia -Structural Soil Demonstration Project

What if downtown Charlotte…

…could look more like the Dilworth neighborhood?

Thank You! Partners Who Donated In-Kind

Services/Products

Alder Geotechnical Services

Thanks!

Sustainability for all the places between the buildings

503.334.8634www.greengirlpdx.com

[email protected] certified women business enterprise

The Parking Forest: As if Mother Nature Designed a Parking Lot

Environment

Transcript of The Parking Forest: As if Mother Nature Designed a Parking Lot