The Future of Stormwater Management in North Carolina: Aiming to be the BestNorth Carolina
Dr. Bill Hunt, PE Associate Professor & Extension Specialist
Biological & Agricultural Engineering
Project Objectives
• Select small urban watersheds in 8 North Carolina cities for analysis
• Identify potential retrofit opportunities in each watershed
• Estimate pollutant load removals and flow volume/peak flow reductions – single BMP- and watershed-scale
• Perform cost-benefit analysis for each retrofit and watershed
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
465 ac (0.727 mi2)
www.bae.ncsu.edu/stormwater
BMP
• Only applies to ‘treated’ runoff
• Does not vary by region (volume reduction does)
• Percent removal based on mass
INFLOW
OUTFLOW
OVERFLOW
TREATED
(mg/L) TSS TN TP
Bioretention 10 0.92 0.14 Blue Roof 10 1.08 0.12 Daylight Downspouts 17 1.20 0.15 Dry Detention Pond 10 1.20 0.20 Green Roof 25 1.01 1.03 Level Spreader 17 1.20 0.15 Permeable Pavement 7 0.95 0.05 Proprietary BMP 40 1.30 0.10 Rainwater Harvesting 25 1.63 0.15 Sand Filter 10 0.92 0.14 Street Sweeping n/a n/a n/a
Underground Detention 10 1.08 0.12
Vegetated Swale 14 1.21 0.26 Wet Pond 9 1.01 0.11 Wetland 20 1.08 0.12
www.bae.ncsu.edu/stormwater
$30 per 1 ft3 of volume treated
Proprietary BMP $17,000 per acre of impervious surface
treated Bioretention (greater than 2,500 ft2)
$10.50 per 1 ft3 of volume treated
Rainwater Harvesting
Blue Roof $15 per 1 ft2 of surface
area Sand Filter
Daylight Downspouts $50 per downspout Street Sweeping $375,000 per streetsweeper
Green Roof $225 per 1 ft3 of volume treated
Underground Detention
$65 per 1 ft3 of volume treated
Level Spreader $1500 each Vegetated Swale $12.50 per 1 ft3 of
volume treated
Wetland $19,440 per acre of impervious surface
treated
(CWP, 2007; Hunt and Lord, 2003; Erickson et al., 2009)
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
Conclusions, Part I
• Land use type, regardless of geographic location, tends to dictate the most appropriate type of retrofits
• Neighborhood characteristics Number/type of retrofit possibilities
• Residential ≠ Residential, Commercial ≠ Commercial, etc.
www.bae.ncsu.edu/stormwater
Wetland Vegetated Swale Water Harvesting Wetland
Bioretention Streetsweeping (High Dens.) Permeable Pavement Water Harvesting
Sand Filter Level Spreader/Filter Strip Underground Detention Bioretention
Proprietary Device Permeable Pavement Blue Roof Underground Detention
Green Roof Sand Filter Streetsweeping Blue Roof
Proprietary Device Green Roof Proprietary Device
www.bae.ncsu.edu/stormwater
• Large, undeveloped tracts of land = wetlands
www.bae.ncsu.edu/stormwater
www.bae.ncsu.edu/stormwater
0
10
20
30
40
50
60
70
80
$0
$10
$20
$30
$40
$50
$60
$70
$80
www.bae.ncsu.edu/stormwater
• All watersheds studied could meet 8% and 5% TN and TP reductions, respectively.
• None of the watersheds could meet TN and TP reductions of 40% and 77%, respectively.
• Certain land uses and unique combinations of those land uses can lead to higher potential reductions
(>30% TP, >10% TN).
• Attaining these reductions are technically feasible only in a limited number of urban watersheds.
• Higher potential reductions = extraordinary costs
• No visible difference between site-specific BMPs and regional BMPs
www.bae.ncsu.edu/stormwater
• Laura Lord • Natalie Bouchard
• Will Pluer • Matthew Webb
• Amelia Clark • Ross Perry
Funding provided by:
www.bae.ncsu.edu/stormwater
Questions?
kathy_debusk@ncsu.edu