Rain Garden Research

1. Rain Garden Research and
Current Issues
Michael Dietz, Ph.D.
CT NEMO | Cooperative Extension
Univ. of Connecticut
Managing Stormwater from Impervious Surfaces: Green Infrastructure
Solutions for New Jersey
The Heldrich | New Brunswick, NJ
January 27, 2011

2. Monitoring-Began November 2002

3. Installation: 9‐19‐02

5. Rain Garden Materials Detail
(Based on PGC RG Manual, 2001)
• Three native shrub species:
– Chokeberry (Aronia prunifolia)
– Winterberry (Ilex verticillata)
– Compact inkberry (Ilex glabra compacta)
• Native soil mix
– Loamy sand
• Roughly 5 cm of bark mulch

6. Monitoring Equipment

7. Methods
•Lab analysis of water samples for:
•Nitrate‐N, ammonia‐N, total Kjeldahl‐N, total
phosphorus, copper, lead, zinc
•Water level in each garden measured
•Temperature measured at inlet and outlet
(underdrains)
•Weekly measurements of soil moisture,
redox potential (Eh), and frost depth

8. Flow balance
cm % of Inflow
Inflow
Roof Runoff 1202 79.7
Precipitation 306 20.3
Total 1507
Outflow
Underdrain 1438 95.4
Overflow 13 0.8
Total 1451
Residual 56 3.7
99% of inflow
retained!

9. Percent retention
NO3-N NH3-N TKN TP TN ON
g
Total In 388 30 250 9 647 211
Total Out 128 5 186 20 316 181
% Retention 67 82 26 -108 51 14
-Two years of results (year 1 much less)
-Remember: 99% of inflow was retained

10. Total Phosphorus
0.25
Roof runoff
Underdrain average
Exponential (Underdrain average)
0.2 Linear (Roof runoff)
Total Phosphorus (mg/L)
0.15
0.1
0.05 R2 = 0.47
R2 = 0.06
0
Sep-02 Dec-02 Mar-03 Jun-03 Oct-03 Jan-04 Apr-04 Aug-04 Nov-04 Feb-05
Date

11. Comparison with other research
• Consistent with North Carolina
– Hunt et al., 2006. Evaluating bioretention hydrology and nutrient removal at three field
sites in North Carolina. Journal of Irrigation and Drainage Engineering, Vol. 132(6), pp.
600‐608.
• Consistent (N) & inconsistent (P) with
Maryland
– Davis et al., 2006. Water quality improvement through bioretention media: nitrogen and
phosphorus removal. Water Environment Research, Vol. 78(3), pp. 284‐293.
• Consistent with New Hampshire
– Roseen, et al., 2009. Seasonal performance variations for storm‐water management
systems in cold climate conditions. Journal of Environmental Engineering, Vol. 135 (3),
pp. 128‐137.
• Lots of variability in results!

12. Second year
• Modification to encourage denitrification and
increase treatment of NO3‐N
• Saturated zone created in bottom of rain
garden (after Kim, et al., 2004)

13. Modification
Ponding depth

14. Saturated zone
Monitoring
tank
1m Underdrain

15. Impact on NO3‐N
• No statistically significant reduction in NO3‐N
concentrations
– Lots of samples below detection limit
• Percent of outflow samples below detection
before/after change:
– Before = 19%
– After = 56%
– Significant using chi‐square statistic

16. What happens in the winter?

17. Frost Tube
After Ricard, et al. (1976)

18. Frost Tube Detail

19. Winter performance
• Measured frost depth
• Did not impact annual performance
• http://www.youtube.com/watch?v=cq6WB6VKeac
• Similar findings at UNH Stormwater Center
– Roseen, et al., 2009. Seasonal performance variations for storm‐water management
systems in cold climate conditions. Journal of Environmental Engineering, Vol. 135 (3),
pp. 128‐137.

20. Some Current Issues
• Filter fabric use
– DON’T USE IN BIORETENTION!
– Prone to clogging
• Sizing
– Water quality volume vs. curve number vs. ?

21. Thank You!!
Questions??
michael.dietz@uconn.edu

22. Two year ANOVA/mean separation
Bulk Underdrain Overflow1
Variable n Unit Deposition Roof Runoff Treatment Control Treatment Control
*** -1
NO3-N 73 mg L 0.7 bcd 0.9 abc 0.2 d 0.4 cd 2.0 ab 2.1 a
-1
NH3-N*** 78 mg L 0.04 a 0.04 a 0.01 b 0.01 b 0.08 a 0.04 a
TKNns 79 mg L
-1
0.5 a 0.6 a 0.4 a 0.5 a 0.6 a 0.3 a
TN*** 72 mg L
-1
1.3 abc 1.6 ab 0.7 c 0.9 bc 2.7 a 2.4 a
ONns 77 mg L
-1
0.4 a 0.5 a 0.4 a 0.5 a 0.5 a 0.2 a
TP*** 80 mg L
-1
0.009 b 0.015 b 0.039 a 0.043 a 0.009 b 0.016 b
-1
Cutotal ns 26 µg L 3a 5a 3a 4a 3a -
-1
Pbtotal ns 26 µg L 3a 3a 3a 3a 3a -
-1
Zntotal ns 26 µg L 11 a 9a 10 a 5a 8a -
*** p=0.001
ns=ANOVA comparison non significant
1
n=4 for overflow samples
Means followed by the same letter are not significantly different at p=0.05