River Friendly Landscaping Low Impact Development Stormwater Management:

Permeable Paving, Stormwater Swales and Detention Wetlands

Presented by:

Ed Armstrong, RLA

Foothill Associates

“...because we no longer traveled in the wilderness as a matter of course,

we forgot that wilderness still circumscribed civilization and persisted

in domesticity. We forgot, indeed, that the civilized and the domestic

continued to depend upon wilderness -- that is, upon natural forces

within the climate and within the soil that have never in any meaningful

sense been controlled or conquered. Modern civilization has been built

largely in this forgetfulness.”

Wendell Berry, The Unsettling of America

LID Techniques

• Permeable Paving

– Pavers

– Permeable Asphalt

– Permeable Concrete

• Stormwater Swales

• Detention Wetlands

Permeable Paving

Stormwater Management Objectives

• Retain/infiltrate

stormwater runoff

• Capture “First Flush”

(typ. first ½ inch of rainfall)

• Control specific pollutants & metals

• Reduce amount of impervious cover

• Capture high percentage of storms

Brian McThorn, Calstone & the Interlocking Concrete Pavement Industry (ICPI)

Basic Permeable Paver Components

(optional)

Benefits of Permeable Pavers

• Help meet national/state stormwater regulations

• Conserves space: Usable pavement above detention facility

• 100% runoff reduction for low intensity storms

• Filter and reduce pollutants & metals

• Increase groundwater recharge

• Lower peak flows = reduce downstream flooding & erosion

• Reduce runoff temperatures

• Can be visually attractive

• Paver patterns can direct traffic

• Relatively easy to repair

• Filters oil drippings & petroleum residue

Paver Types

• Interlocking shapes/patterns

Joint Spacing

Plastic joint spacers

Spacers integral to

pavers

• ADA Compliance: Joints ½” or Less

Infiltration Rates Surface, Joints & Bedding

• Open surface area: varies with paver design/ pattern - 6% to 18%

• Required infiltration rate of openings: – Design storm, inches per hr / 0.06

– Example: 2 inches per hr / 0.06

– Required infiltration rate = 33 in/hr

• Measured infiltration rate of stone in openings: 300 to 500 in/hr

• Assume 10% lifetime efficiency: 30 to 50 in./hr

Base Infiltration Rates Open-Graded Base

• Effective Base Infiltration Rate

• Similar to an infiltration trench design

• Open-graded base stores/releases water

• Initial rate: over 1000 in/hr

• Base infiltration slows over time from sediment

Base Storage Capacity

• Base materials – No. 57 (crushed stone base

1.5 – ⅛ in. aggregate)

– No. 2 (crushed stone subbase 2½ in. – ¾ in. agg. )

• 30% to 40% void space

• Quarry or lab provides % of voids - ASTM C 29

• 3 inches of base stores about 1 in. of water – 60’ x 100’ parking lot w/12” base stores ~ 15,000 gals

• Design for 24 hour storage

Base

Design Options

• Full infiltration – Base stores water & drains to soil

– For sandy soils, typical permeability of > 0.5 in./hr

– No perforated drain pipes at bottom of Base

– Drain pipes for saturated/overflow conditions

• Partial infiltration – an infiltration & detention facility – Base stores water… Some drains to soil, some to pipes at bottom of base

– Most common design approach

– Many soils handle some infiltration

• Detention only, no infiltration – Impermeable liner

– Base filters only and then drains through liner

– Drain pipes at bottom of base

– Conditions for use: • High water table

• High bedrock

• Over fill soils and expansive soils

Full Infiltration

Partial Infiltration

No Infiltration

Areas To Avoid

• Drinking water wells (100 ft. min. distance)

• High water tables (< 1 meter from surface)

• Industrial sites / Fueling stations

• Do not exceed 5% slope (1 – 2% optimum)

Design Steps

• Assess site and soil conditions

• Compute runoff from watershed

• Determine the depth of the base for storage

• Compute the maximum allowable base

depth for drainage in 24 hours

• Determine base thickness for traffic

Performance Monitoring

• Observation well at lowest point

• Min. 6 in. diameter perf pipe w/cap

• Monitor drainage rate, sediment, water

quality

Construction

Construction sequence:

1. Excavation & Sediment control

2. Soil subgrade compaction

3. Geotextile (or impermeable liner if no infiltration)

4. Drain pipes as required

5. Concrete curbs

6. Base installation – Max 4 in. lifts

7. Compaction: initial vibration, 10 T static roll

8. Bedding course: max. 2 in. thick (Geotextile under bedding course not recommended)

9. Pavers placed, joints filled, surface swept and compacted

10. Joints filled, surface swept, pavers compacted again

11. Remove excess stone

Sediment cannot

contaminate base materials!!

Installing Geotextile

Adding Base

Compacting Base

Installing Bedding Course

• Screeding bedding layer over stone base

Installing Pavers

• Edges cut, placed

then compacted

Compacting Pavers

Filling Joints

• Filling the openings with No. 9 stone before

second compaction

Excess stones removed, then final compaction

Maintenance

• Annual

– Inspection of observation well after

major storm, vacuum and sweep

surface – improves infiltration

• True vacuum sweeper

– Very powerful

– Restores clogged

surfaces

PICP Costs

• Assumptions:

– 80mm (3.2”) thick pavers

– 2 in. leveling course

– 12 in. open graded base

– 10,000+ sf

• $12 to $17/sf (Union / Prevailing wages)

• Larger projects may be mechanically installed to lower unit costs

Permeable Asphalt

University of New Hampshire,

Stormwater Center

SECTION FOR STORAGE & INFILTRATION

Permeable Asphalt

University of New Hampshire, Stormwater Center

SECTION WITH FILTER COURSE FOR WATER QUALITY

Permeable Asphalt

• Effectiveness

– Infiltration up to 80% of annual runoff (with proper installation and maintenance)

– Can remove between 65 and 85 percent of undissolved nutrients and up to 95% of sediment

Sierra College Boulevard @

Miner’s Ravine

Permeable Asphalt

• University of New Hampshire, Stormwater

Center research has found:

– Water quality performance is strong to

excellent, depending upon design

– Hydraulic performance is excellent

– Little removal of nitrogen

– No removal of many common ionic forms

Permeable Asphalt

Design Considerations:

• Soil permeability/infiltration rate – EPA recommends 0.5”/hour

– 0.1”/hour still OK

• Depth to bedrock > 2’

• Depth to high water > 3’

• Fill – not recommended

• Frost – Pavement section should exceed frost depth

• Slope – Limit surface slope to 5%

– Terrace when necessary

– Use conventional HMA for steeper slopes

Permeable Concrete

• Concrete with little or no sand and sufficient cementious material to bind aggregates.

• Contains 15% and 25% voids

• Can be used in most locations concrete pavement is used.

• Limitations:

– Less strength than standard concrete.

– Not for heavily travelled roadways due to surface raveling.

Permeable Concrete

• Effectiveness:

– Flow rates are

typically around 480

in./hr, although they

can be much higher.

From NPR’s Science Friday website

Permeable Asphalt and Concrete

Permeable Pavement Performance

Permeable Pavement Costs

• DMA $75-100/ton, PA $89-125/ton placed by machine for parking and

residential road and driveways (2009 costs)

• DMA $3,456/parking stall, PA $4,455/parking stall (2008 UNH installation)*

• PC costs approximately 18% greater than PA, 31% greater than DMA;

however, pervious concrete may last up to 40 years before requiring

resurfacing, whereas porous asphalt and conventional asphalt may need to be

replaced after 8 to 10 years*

• Complicated jobs with handwork are more expensive

• Costs offset by lack of stormwater infrastructure

• Cost break even is achieved when designing for quantity management ~Q10-

Q25

PA = Porous Asphalt, DMA = Dense-Mix Asphalt, PC = Permeable Concrete

*Source: Kristopher M. Houle, Master’s Thesis, Winter

Performance Assessment of Permeable Pavements,

University of New Hampshire

Permeable Pavement Maintenance

• PA: Use porous or dense asphalt for

patching

– If using dense, repair should not exceed 10% of

total porous pavement paved area

• Cracks can be repaired using crack sealant

• Regular cleaning

– Flush or jet wash

– Vacuum sweeping

Maintenance Effectiveness

Stormwater Swales

• Types:

– Cobbled or vegetated or both: vegetation adds

benefit of evapotranspiration & filtration, but

requires more maintenance & summertime

irrigation

– Detention or pass-through: defined by at-grade

vs. elevated outflow structure

• At grade can be curb-cut or catch basin grating

• Elevated is typically catch basin grating on riser

Swales

• Can be designed for full infiltration, partial retention or infiltration with subsurface drainage

• Inlet is usually curb cut or flush-curb street

• Carefully control inlet grade if curb-cut to avoid debris accumulation

Stormwater Swale Effectiveness

• Swales are most effective at removal of

Total Suspended Solids (TSS)

• Consider swales as an above-ground

stormwater conveyance system

• Reduce cost of below-ground infrastructure

as well as provide some filtering benefits

LID Effectiveness

Detention Wetlands

• Wetland vs. Basin

– Detention wetland is

meant to handle low-

flow, nuisance flow &

first-flush

– Detention basin is

designed to detain

large flows

Detention Wetland Effectiveness

• Wetlands are effective at removing bacteria, metals, organics, suspended sediment and phosphorus

• Wetlands are less effective at removing nitrogen or improving BOD

• NPS reductions*: – Suspended solids > 60%;

– Total nitrogen ~ 25 to 76%;

– Metals removal ~ variable, but lead generally shows at least 75% reduction; and

– Phosphorus removal ~ 30 to 90%, with an average of 50%

*http://www.water.ncsu.edu/watershedss/info/wetlands/manage.html#cons

Detention Wetlands Design Criteria

• Design for good mosquito management – Complex microtopography (also increases treatment effectiveness)

• Treatment distances of 60-120 feet or more

• Retention times of 5-20 days ideal

• 1 to 3 treatment cells

• Several small wetlands may be better than one large one

• Ideal proportions for stormwater retention are 50% shallow marsh, 30% deep marsh & 20% deep open-water

• Contaminant treatment wetlands should consist of 50-70% very shallow depths

Examples - Permeable Paving

Nevada Beach Day Use Area,

Roundhill, NV

Permeable Paving

Lowe’s Home Center Olympia, WA

Permeable Paving

Rio Vista Water

Plant, Santa

Clarita, CA

Auburn Streetscape,

Auburn, CA

Stormwater Swales

Stormwater Swales

Four Seasons, El Dorado Hills, CA

Stormwater Swales

South Sacramento

Community, CA

Stormwater Swales

Sunrise Boulevard Complete Streets,

Citrus Heights, CA

Tempo Park, Citrus Heights, CA

Stormwater Swales

Village Homes,

Davis

Detention Wetlands

Del Paso Regional Park,

Sacramento, CA

Detention Wetlands

Longview Oaks, Sacramento, CA

Detention Wetlands

Anatolia Preserve, Rancho Cordova, CA

Detention Wetlands

Laguna Stonelake, Elk Grove, CA

Additional Information

• Permeable Pavers: – Brian McThorn, consulting / installation, 209-786-8002 main/fax,

hardscapes101.com, brian@hardscapes101.com

• Permeable Asphalt: – http://www.coastal.ca.gov/nps/lid/Milar-

PorousAsphaltPavements.pdf

– http://www.unh.edu/unhsc/presentations

• Permeable Concrete: – http://www.perviouspavement.org/

• Swales & Detention Wetlands – Ed Armstrong, Foothill Associates, 916-435-1202,

ed.armstrong@foothill.com