Applied Research, Informed Design Standards for Stormwater - - PowerPoint PPT Presentation

Applied Research, Informed Design Standards for Stormwater Management

Bill Hunt, PE, PhD, D.WRE

Associate Professor & Extension Specialist NC State University

www.bae.ncsu.edu/stormwater

Minnesota Clean Water Summit – 13-Sep-12

Acknowledgements

• NCDENR & NCDOT

– For listening to me & Funding me

• Slew of Graduate

Students & Staff

• Many Granting

Entities & Project Host Communities

The Static Stormwater Design Manual…

• Written with (even at the time) dated material
• Serves a Community (State) for 5 to 10 years
• Is the Norm in nearly every state

– Including North Carolina from 1997 to 2006

www.bae.ncsu.edu/stormwater

Our Stormwater Practices could…

• Mitigate Peak Flow
• Be designed solely by

an engineer

• Be a liability/ attractive

nuisance The only stormwater practice regulators and designers felt comfortable with were Big Muddy Practices (BMPs) called Wet Ponds.

Our stormwater practices couldn’t

• Infiltrate

– Soils too clayey

• Reduce volumes of

water

• Be anything but Typha

(Cattail) jungles

• Be located next to

people

• Be driven on?!

www.bae.ncsu.edu/stormwater

But then came the Hurricanes…

www.bae.ncsu.edu/stormwater

www.bae.ncsu.edu/stormwater

And then the fish kills…

• Nothing inspires action

(and perhaps innovation) like a crisis – A political one, particularly

And politicians reacted and told regulators: thou must remove nutrients

www.bae.ncsu.edu/stormwater

Images: NCSU CAAE

Call for Change…Who’s at the Table?

• Designers wanted tools
• Environmentalists

wanted protection

• Regulators wanted to

be careful

• Researchers wanted

solutions – And work

www.bae.ncsu.edu/stormwater

Comment #1 – You won’t let us use permeable pavement (2000)

www.bae.ncsu.edu/stormwater

Response: Because they don’t work!

www.bae.ncsu.edu/stormwater

Permeable Pavement?

www.bae.ncsu.edu/stormwater

“We Bring Engineering to Life”

What is Permeable Pavement?

• AKA: Pervious pavement, porous pavement
• Several Types:

Permeable Interlocking Concrete Pavers (PICP) Concrete Grid Pavers (CGP)

“We Bring Engineering to Life”

Types of Permeable Pavements

Pervious Concrete Pervious Asphalt

“We Bring Engineering to Life”

Types of Permeable Pavements

Plastic Reinforcing Grids (PG) Gravel Filled Soil Filled for Grass Growth

Kinston, NC, Block Paver Study

• Sandy Soil (K > 8

in/hr or 0.056 mm/sec)

• Seasonal High Water

Table > 2 m from surface

• Employee Parking Lot

(ADT = 30)

• Average Slope = 0.5%

www.bae.ncsu.edu/stormwater

BAE Stormwater Engineering Group

www.bae.ncsu.edu/stormwater

Hurricane Dennis Hyetograph & Hydrograph – 15 min intervals

2 4 6 8 10 12 0:00 4:00 8:00 12:00 16:00 20:00 0:00

Time (04Sep99) Rainfall/Runoff (mm)

Rainfall Runoff

126 mm

Wilmington, NC, Permeable Concrete Study

• Loamy Sand Soil–

Coastal NC

• Water table > 1 m

from surface

• Day Use Recreation

(40 ADT)

www.bae.ncsu.edu/stormwater

www.bae.ncsu.edu/stormwate r

Permeable Concrete Wilmington NC

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 < 12 hour Rainfall (in) Runoff (in) Runoff from an Impermeable Lot Runoff from Permeable Concrete Lot LESS THAN 0.1 in/hr INFILTRATION

Pavement Storage

Infiltration Rate

Compaction of Subgrade Suspected

Swansboro PICP study

~50 cm

• f

Gravel Storage Layer

www.bae.ncsu.edu/stormwater

Swansboro Data

• No Runoff from March to December 2004

– Five events > 50mm (2 in) – Largest Event: 88mm (3.5 in) – 90 events (>0.25 mm)

• Average NRCS Curve Number: 44

– Limited by rainfall total

• Rational Coefficient (for Qpeak): 0

www.bae.ncsu.edu/stormwater

Still not satisfied?

• All of the pavements

you studied were young

• Won’t they still clog

with time?

www.bae.ncsu.edu/stormwater

www.bae.ncsu.edu/stormwate r

Study on Surface Infiltration Rates

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Surface Infiltration Rates

• 48 sites

– CGP (17) – PICP (14) – PC (11) – PA (5) – PG (1)

• 2 to 21 yrs
• ld

Funded by ICPI

www.bae.ncsu.edu/stormwater

Procedure

• Modified Soil Infiltration

Rate Procedure

– ASTM D3385-03 – Falling Head; Sealed

• Double Ring

– Inner and Outer Rings filled to 125 – 175 mm

(5 – 7 in)

– Depth measured every 5 - 10 min

www.bae.ncsu.edu/stormwater

PICP: Surface Infiltration

www.bae.ncsu.edu/stormwater

www.bae.ncsu.edu/stormwater

Permeable Interlocking Concrete Pavers

5000 10000 15000 20000 25000 30000 35000 40000 Site 18 Site 19 Site 20 Site 21 Site 22 Site 23 Site 24 Site 25 Site 26 Site 27 Site 28 Site 29 Site 30 Site 31

Infiltration Rate (mm/h)

Site

10000 mm/hr

Permeable Interlocking Concrete Pavers

100 200 300 400 500 600 Site 18 Site 19 Site 20 Site 21 Site 22 Site Infiltration Rate (mm/h)

2300

100 mm/hr

PICP Results

 PICP Exposed to Fines:

SIR = 80 mm/h

 PICP not Exposed to

Fines: SIR = 20000 mm/h

 99% confidence

statistically significant difference

Clogged Sites’ Infiltration Rate Reflected that of Nearby Soil

www.bae.ncsu.edu/stormwater

2005 – State of NC Regulators: The Moment of Truth

• Permeable Pavement ≠

Impermeable Pavement!

• Incentives Given for

Developers to use Permeable Pavement

• But amount of incentive

somewhat conservative

www.bae.ncsu.edu/stormwater

Where Permeable Pavements were Most Easily Employed

www.bae.ncsu.edu/stormwater

Bringing Findings to the Design Community

• Workshop Series held

across North Carolina in 2006 & 2007

• 100’s of designers

attended

• Several Muni’s updated

codes

• Permeable Pavement is

among the most popular practices in some cities

www.bae.ncsu.edu/stormwater

The Saga Continues…

Jonathanlack.com

Plan View – Boone, NC

www.bae.ncsu.edu/stormwater

Separator Walls Finished…

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“Ripping” the Subsoil from Tyner et al. (2009)

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Preliminary Results - Hydrology

www.bae.ncsu.edu/stormwater

100 200 300 400 500 600

Normal Deep Shallow Total Volume (cubic feet)

ESTIMATED INFLOW DRAINAGE

48% Reduction 99% Reduction 95% Reduction

The Importance and Conduct of Workshops

• Tentative Design

Standards Presented

• NCSU leads
• NC DENR (regulators)

always a part

• Attendees ask/ make

recommendations

• Design Standards

finalized 3-6 months later

www.bae.ncsu.edu/stormwater

Regulators (& Many Designers) Comment: You Can’t Infiltrate in Clay Soils

• Much of North Carolina

has clay-ey soils.

• This “claim” repeated

world-wide.

www.bae.ncsu.edu/stormwater

Bioretention & The Role of Serendipity

www.bae.ncsu.edu/stormwater

www.bae.ncsu.edu/stormwate r

Louisburg: Joyner Park

Our First Examination of Rain Gardens/ Bioretention (10 years ago)

www.bae.ncsu.edu/stormwater

“We Bring Engineering to Life”

Conventional Drainage Configuration v. Internal Water Storage Zone (IWS)

Conventional Internal Storage

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Increase TN reduction? Reduce Total Outflow?

We initially called this an “Anaerobic Zone” Configuration

• And studied it in

Greensboro, NC from 2001-2004

• Underlying Soils: HSG

C (rather tight clays)

• Media Depth 1.2 m
• S.A. Approx 5% of

contributing Catchment

www.bae.ncsu.edu/stormwater

We thought our Bioretention Cells (Rain Gardens) would remove TN/ NO2-3.

Site Avg Influent TN (mg/L) Avg Effluent TN (mg/L) Greensboro-1 1.35 4.38 Greensboro-2 1.27 5.23 Chapel Hill 0.97 1.65

www.bae.ncsu.edu/stormwater

However, we noticed…

• Not all inflow = outflow in either cell, AND
• The cell with the IWS reduced outflow.

www.bae.ncsu.edu/stormwater

Site # Events Monitored # Events w/ Outflow Media Depth (m) IWS Depth (m) Greensboro 1 63 18 1.2 0.6 Greensboro 2 63 40 1.2 No IWS

We had created an infiltration enhancer… in HSG C soils!

www.bae.ncsu.edu/stormwater

We repeated the Design Concept

• Charlotte: 40-50%

Infiltration + ET Loss

– 1.2 m media depth

• Louisburg: 20-30%

Infiltration +ET Loss

– 0.6 m media depth

• Graham: 18 of 40 Flow

Events eliminated

– 0.9 m media depth

• All sites HSG B/C

underlying soils

www.bae.ncsu.edu/stormwater

Other Bioretention Questions: They can’t be grassed (2006)

www.bae.ncsu.edu/stormwater

Answer: They Can.

www.bae.ncsu.edu/stormwater

0.5 1 1.5 2 2.5 3 3.5 4 1 2 3 4 5 6 7 8 9 10 11 12 13 Event TN Concentration (mg/L)

N S IN

Passeport et al. 2009

Question: They Can’t Work in the Mountains

www.bae.ncsu.edu/stormwater

www.bae.ncsu.edu/stormwater

Answer: They can.

10 15 20 25 30 35 40 05/01/06 08/09/06 11/17/06 02/25/07 06/05/07 09/13/07 Temperature (°C) Median Inlet Median Outlet Max Inlet Max Outlet

Jones and Hunt, 2009

Other Questions Answered for the Design Community and/or NCDENR

• Minimum Media Depth
• Fill Media Type & Composition
• Runoff Volume Reduction

Potential

• IWS Sizing
• Regional Performance (Coastal

Plain Sands and Loamy Sands

• Proportional Sizing

www.bae.ncsu.edu/stormwater

The Communication + Design Protocol

• And Every 6 months…
• We meet with our regulatory officials

– Provide updates and research direction

• And Every 2 years…

– A new design standard has emerged for bioretention

• And immediately post 1st Draft Design

Standard

– A (well attended) workshop series was offered

www.bae.ncsu.edu/stormwater

Take Home Point #1: A Flexible Design Manual

• Static Manuals are a thing of

the past

– In North Carolina

• Enough information to adjust

some chapters every 2 years

• (Nearly) Every Year this is

some change

• And, yet, not everyone is

happy.

www.bae.ncsu.edu/stormwater

Take Home Point #2: “Talk Through This”

• Feelings are hurt without

proper communication

• That involves providing a

mediated forum

– Workshops

• Need a Trusted Mediator

– NC State University

• And the Knowledge that

people are listening

– Adjustments to Design Standards

www.bae.ncsu.edu/stormwater

www.bae.ncsu.edu/stormwater

Thank you and Questions