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Rain Garden Design & Monitoring
Jay Martin, Ph.D., and Derek Schlea
Ohio State University
What the results will be used for
• Increase guidance
– Lack of information on networks
• Engineering design standards
• Retrofits
• Promote the technology
Table 1. Summary of individual and laboratory studies of benefits of rain gardens or bioretention areas related to storm water flow
and quality (Davis et al. 2009). Previous results have reported reductions of metals (Davis et al. 2003, Hunt et al. 2008)
Site location /
descriptionParameter Load Reduction (%) Citation
Stormwater Flow Results
Burnsville, MN flow 90 Barr Engineering 2006
Haddam, CN flow 98 Dietz and Clausen 2006
Greensboro, NC flow ~50 Hunt et al. 2006
College Park, MD flow 49-58 Davis 2008
Charlotte, NC flow 96 Hunt et al. 2008
Water Quality Results
College Park, MD TSS 59 Davis 2007
College Park, MD TSS 54 Davis 2007
Durham, NH TSS 97 UNHSC 2006
Villanova, PA TSS 99 USEPA 2006
Haddam, CN Total N 32 Dietz and Clausen 2006
Greensboro, NC Total N 40 Hunt et al. 2006
Chapel Hill, NC Total N 40 Hunt et al. 2006
Louisburg, NC Total N 65 Sharkey 2006
Durham, NH Total N 97 UNHSC 2006
Pilot boxes Total N 30-99 Davis et al. 2006
College Park, MD Total P 79 Davis 2007
College Park, MD Total P 77 Davis 2007
Haddam, CN Total P -111 Dietz and Clausen 2006
Greensboro, NC Total P -240 Hunt et al. 2006
Chapel Hill, NC Total P 65 Hunt et al. 2006
Louisburg, NC Total P 69 Sharkey 2006
Villanova, PA Total P 28 USEPA 2006
Pilot boxes Total P 50-99 Davis et al. 2006
Laboratory columns Total P 63-85 Hsieh et al. 2007
College Park, MD Zn 54 Davis 2007
College Park, MD Zn 69 Davis 2007
Villanova, PA Zn 74 USEPA 2006
Durham, NH Zn 99 UNHSC 2006
Goals and Objectives
• Hydrology
– Quantify volume and peak flow reductions
– Compare to control neighborhood
• Water Quality
– Quantify nutrient reductions
• Modeling
– Application to additional watersheds
Garden
Locations
Street-Side Garden Design
• Retrofit
– Space limited
– Utilities
– Tile drainage
Street-Side Garden Design
• Sizing
• Terracing
Street-Side Garden Construction
• Excavate
– In situ clay soil
• Backfill
– Higher % sand
– 20% organic matter
• Plant
• Mulch
Monitoring – What to Measure
• Hydrology
– Rainfall
– Volume, peak flow, time to peak
– Rise in water table in gardens
• Water Quality
– Nutrients
– Solids
Monitoring - Equipment
• Tipping bucket rain gauge
• Storm sewer flow meters
Monitoring - Equipment
• Water quality grab samples
– Storm events
– Various locations
– Time intervals
Monitoring - Equipment
• Water level logger / pressure transducers
– Piezometers
Preliminary Results – Hydrology
• Water level “hydrograph”
Preliminary Results – Hydrology
Controlled Experiments
• What?
– Observe garden response to known water
volume and rate inputs
– Water balance equation
Controlled Experiments
• Eliminate the unknowns of water balance
– Inflow volume
– Bi-pass flow
– Tile drain flow
Controlled Experiment (12-10-10)
Controlled Experiment (12-10-10)
Controlled Experiment Results
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00
Time
Wate
r D
ep
th,
feet
bg
s
0
5
10
15
20
25
30
Infl
ow
, g
pm
K
L
Inflow
Controlled Experiment Results
• Water
balance
• Tile
drainage
Next Steps
• Quantify maximum volume retention
= depth * width * length * porosity
• Quantify seepage losses
• Better estimations of water balance
• Compare with outfall flow data
• Mass balance for nutrients
– Load reductions
Ongoing Learning
• Modify methods to increase accuracy
• Develop a model
– Use data we have
– Gather data we need
Current Status
• Observations show the gardens are
working
• Working to quantify these observations
• Continuing controlled experiments
– More data
– Predict infiltration rates for different inflows
Thank you!