JAWRA article - Rain Gardens

• Project Type: General OWC
• Title: Performance Assessment on Rain Gardens
• Date: 12/15/2009
• Water Conservation - Doc Type: Reports

PERFORMANCE ASSESSMENT OF RAIN GARDENS
Distribution of Kset in Rain Gardens
100
90
1 (Burnsville)
-- -
7
(Cottage
Grove)
9
(RWMWD
#1)
11
(Thompson
Lake)
12
(UM -
Duluth)
Number of
23
-'
'
80
-E-2,589 (RWMWD
12
c
#4, #5, #1)
measurements
70
"i-6 (U of M, St. Paul)
Arithmetic mean
1.8 x 10 -2
3.2 x 10 -3
a
w 60
4.3 x 10 -3
2.4 x 10 -2
7.5 x 10 -3
1.2 x 10 -2
9.1 x 10 -3
(cm /s)
x
w
-I--7 (Cottage Grove)
0 50
Geometric mean
1.1 x 10 -2
9.0 x 10 -4
1.2 x 10 -3
x
2.0 x 10 -2
5.1 x 10 -3
__
2.0 x 10 -3
(cm/s)
40
11 (Thompson Lake)
X
Median (cm /s)
1.3 x 10 -2
4.0 x 10 -3
8.1 x 10 -4
2.9 x 10 -3
2.0 x 10 -2
:3 30
° (U of M, Duluth)
1.6 x 10 -3
SD (cm /s)
X
2.1 x 10 -3
4.9 x 10 -3
!
1.4 x 10 -2
X
1.5 x 10 -2
E
20
CV ( %)
100
U
148
87.7
57.4
X
123
178
10
5.5 x 10 -4
1.0 x 10 -5
1.8 x 10 -4
;X
4.0 x 10 -3
8.2 x 10 -4
7.0 x 10 -7
<7.0 x 10 -7
Max. (cm/s)
8.1 x 10 -2
X
1.6 x 10 -2
1.5 x 10 -2
5.4 x 10 -2
2.6 x 10 -2
5.4 x 10 -2
�
Range (cm /s)
8.1 x 10 -2
4.7 x 10 -3
1.6 x 10 -2
1.0E -07 1.0E -06 1.0E -05 1.0E -04 1.0E -03 1.0E -02 1.0E -01
Ksat (cm /s)
FIGURE 8. Distribution of Measured Ksat Values for Eight Rain Gardens. Note that the three rain
gardens at the RWMWD (2, 5, and 9) site were combined into one dataset for the plot.
TABLE 3. Statistics for Measured Ksat Values From Eight Rain Gardens
Statistical
Parameter
1
(Burnsville)
2
(RWMWD
#4)
5
(RWMWD
#5)
6
(UM - St.
Paul)
7
(Cottage
Grove)
9
(RWMWD
#1)
11
(Thompson
Lake)
12
(UM -
Duluth)
Number of
23
4
15
41
20
12
30
34
measurements
Arithmetic mean
1.8 x 10 -2
3.2 x 10 -3
3.3 x 10 -3
4.3 x 10 -3
2.4 x 10 -2
7.5 x 10 -3
1.2 x 10 -2
9.1 x 10 -3
(cm /s)
Geometric mean
1.1 x 10 -2
9.0 x 10 -4
1.2 x 10 -3
2.3 x 10 -3
2.0 x 10 -2
5.1 x 10 -3
2.7 x 10 -3
2.0 x 10 -3
(cm/s)
Median (cm /s)
1.3 x 10 -2
4.0 x 10 -3
8.1 x 10 -4
2.9 x 10 -3
2.0 x 10 -2
5.4 x 10 -3
5.3 x 10 -3
1.6 x 10 -3
SD (cm /s)
1.8 x 10 -2
2.1 x 10 -3
4.9 x 10 -3
3.8 x 10 -3
1.4 x 10 -2
7.1 x 10 -3
1.5 x 10 -2
1.6 x 10 -2
CV ( %)
100
67.4
148
87.7
57.4
94.6
123
178
Min. (cm/s)
5.5 x 10 -4
1.0 x 10 -5
1.8 x 10 -4
<7.0 x 10 -7
4.0 x 10 -3
8.2 x 10 -4
7.0 x 10 -7
<7.0 x 10 -7
Max. (cm/s)
8.1 x 10 -2
4.7 x 10 -3
1.6 x 10 -2
1.5 x 10 -2
5.4 x 10 -2
2.6 x 10 -2
5.4 x 10 -2
6.4 x 10 -2
Range (cm /s)
8.1 x 10 -2
4.7 x 10 -3
1.6 x 10 -2
1.5 x 10 -2
5.0 x 10 -2
2.5 x 10 -2
5.4 x 10 -2
6.4 x 10 -2
Notes: CV, coefficient of variation (CV = SD /Mean); RWMWD, Ramsey - Washington Metro Watershed District; SD, standard deviation; UM
University of Minnesota.
greater extent than they influenced drainage time. As
the drainage progresses, the region around the
perimeter of the basin would no longer remove pooled
water because of its higher elevation.
The median and geometric mean Ksat values
obtained from the infiltration rate tests were also
used to predict the drain times for comparison with
the measured values from the synthetic drawdown
tests (based on the same initial test volumes). The
predicted drain times based on the median Ksat value
and geometric mean Keat value at RWMWD #5 (5)
were both in better agreement with the observed
drain time than the predicted drain time based on
the mean Ksat value. The same is true for the Cottage
Grove (7) site, although the predicted and measured
drain time times were all very brief. The UM - St.
Paul (6) rain garden drain times predicted from the
median and geometric mean Ksat values were in
slightly better agreement with the measured drain
time than the predicted drain time based on the
mean Ksat value. The large differences between the
predicted and measured drain times for the UM - St.
Paul (6) rain garden are likely due to the influence of
the restrictive soil layer on drainage when the rain
garden is filled to capacity during synthetic draw -
down testing. The MPD Infiltrometer tests infiltra-
tion rates in the upper 15 -20 cm. The limiting soil
layer would thus not be a factor because of the small
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1029 JAWRA