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!