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

Minnesota Clean Water Summit – 13-Sep-12 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

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

And then the fish kills… • Nothing inspires action (and perhaps innovation) like a crisis – A political one, particularly www.bae.ncsu.edu/stormwater

And politicians reacted and told regulators: thou must remove nutrients Images: NCSU CAAE www.bae.ncsu.edu/stormwater

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

What is Permeable Pavement? • AKA: Pervious pavement, porous pavement • Several Types: Concrete Grid Pavers Permeable Interlocking Concrete Pavers (PICP) (CGP) “We Bring Engineering to Life”

Types of Permeable Pavements Pervious Asphalt Pervious Concrete “We Bring Engineering to Life”

Types of Permeable Pavements Plastic Reinforcing Grids (PG) Soil Filled for Gravel Filled Grass Growth “We Bring Engineering to Life”

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

Hurricane Dennis Hyetograph & Hydrograph – 15 min intervals 12 Rainfall/Runoff (mm) 126 mm 10 8 Rainfall 6 Runoff 4 2 0 0:00 4:00 8:00 12:00 16:00 20:00 0:00 Time (04Sep99) BAE Stormwater Engineering Group www.bae.ncsu.edu/stormwater

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

Permeable Concrete Wilmington NC 4.00 Compaction of Subgrade 3.50 Suspected 3.00 2.50 Pavement Runoff (in) Infiltration Storage 2.00 Rate 1.50 LESS THAN 0.1 in/hr INFILTRATION 1.00 0.50 0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 < 12 hour Rainfall (in) www.bae.ncsu.edu/stormwate r Runoff from an Impermeable Lot Runoff from Permeable Concrete Lot

Swansboro PICP study ~50 cm of 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 Q peak ): 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

Study on Surface Infiltration Rates www.bae.ncsu.edu/stormwate r www.bae.ncsu.edu/stormwater

Surface Infiltration Rates • 48 sites – CGP (17) – PICP (14) – PC (11) – PA (5) – PG (1) • 2 to 21 yrs old 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

Permeable Interlocking Concrete Pavers Permeable Interlocking Concrete Pavers 2300 600 500 Infiltration Rate (mm/h) 400 Infiltration Rate (mm/h) 300 40000 35000 200 30000 100 100 25000 mm/hr 20000 0 15000 Site 18 Site 19 Site 20 Site 21 Site 22 10000 mm/hr Site 10000 5000 0 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 Site www.bae.ncsu.edu/stormwater

PICP Results  PICP Exposed to Fines: SIR = 80 mm/h  PICP not Exposed to Fines: SIR = 20000 mm/h  99% confidence statistically significant Clogged Sites’ Infiltration difference 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… www.bae.ncsu.edu/stormwater

“Ripping” the Subsoil from Tyner et al. (2009) www.bae.ncsu.edu/stormwater

Preliminary Results - Hydrology ESTIMATED INFLOW DRAINAGE 600 Total Volume (cubic feet) 99% 95% Reduction Reduction 500 48% 400 Reduction 300 200 100 0 Normal Deep Shallow www.bae.ncsu.edu/stormwater

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

Louisburg: Joyner Park www.bae.ncsu.edu/stormwate r

Our First Examination of Rain Gardens/ Bioretention (10 years ago) www.bae.ncsu.edu/stormwater

Conventional Drainage Configuration v. Internal Water Storage Zone (IWS) Internal Conventional Storage Increase TN reduction? Reduce Total Outflow? “We Bring Engineering to Life” www.bae.ncsu.edu/stormwater

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/ NO 2-3 . Site Avg Influent Avg Effluent TN (mg/L) 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… Site # Events # Events w/ Media IWS Monitored Outflow Depth (m) Depth (m) Greensboro 1 63 18 1.2 0.6 Greensboro 2 63 40 1.2 No IWS • Not all inflow = outflow in either cell, AND • The cell with the IWS reduced outflow. www.bae.ncsu.edu/stormwater

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. Passeport et al. 2009 4 N S IN TN Concentration (mg/L) 3.5 3 2.5 2 1.5 1 0.5 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Event www.bae.ncsu.edu/stormwater

Question: They Can’t Work in the Mountains www.bae.ncsu.edu/stormwater

Answer: They can. 40 Jones and Hunt, 2009 35 Temperature (°C) 30 25 20 15 10 05/01/06 08/09/06 11/17/06 02/25/07 06/05/07 09/13/07 Median Inlet Median Outlet Max Inlet Max Outlet www.bae.ncsu.edu/stormwater