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
TABLE 2. Summary of the Soil Properties Determined at Each Rain Garden
ID
Rain Garden Name
Soil Cover
Soil Profile
Soil Color
Bulk Density (g /cm
1
Burnsville
Thick wood mulch 0 -31 cm — Sandy loam
IOYR 2/2
1.128 ± 0.218 (n = 23)
31 -119 cm — Sand w /large rocks
10YR 3/4
2
RWMWD #4
Wood mulch
0 -38 cm — Sandy loam
5YR 2.5/1
1.323 ± 0.068 (n = 2)
38 -51 cm — Sandy loam
IOYR 3/4
51 -119 cm — Sand
IOYR 3/4
3
A
None
0 -15 cm — Silt loam
10YR 3/2
NA
15 -23 cm — Silty clay loam
IOYR 4/4
23 -119 cm — Sand
10YR 4/4
4
B
None
0 -5 cm — Organic matter
Gley 2.5/N
NA
5 -38 cm — Silt loam
IOYR 3/2w /red mottles
38 cm — Hard surface
5
RWMWD #5
Wood mulch
0 -38 cm — Sandy loam
5YR 2.5/1
1.193 ± 0.163 (n = 8)
38 -51 cm — Sandy loam
10YR 3/4
51 -119 cm — Sand
10YR 3/4
6
UM — St. Paul
Wood mulch
0 -20 cm — Sandy loam
10YR 2/2
1.182 ± 0.127 (n = 21)
20 -48 cm — Silt loam
lOYR 2/1
48 -119 cm — Sand
10YR 6/4
>119 cm — Silt loam w /coarse sand
2.5YR 3/3
7
Cottage Grove
None
0 -76 cm — Sand
IOYR 3/2
1.573 ± 0.076 (n = 8)
76 -102 cm — Sand
10YR 4/4
102 -119 cm — Gravel
8
C
None
0 -6 cm — Organic matter
5Y 2.5/1
NA
6 -18 cm — Sand
IOYR 4/3
18 -28
cm — Sandy clay loam
Gley 4 /10Y w /red mottles
28 -119 cm — Loamy sand w /rocks
5YR 4/3
9
RWMWD #1
Wood mulch
0 -38 cm — Sandy loam
5YR 2.5/1
1.202 ± 0.084 (n = 7)
38 -51 cm — Sandy loam
10YR 3/4
51 -119 cm — Sand
10YR 3/4
10
D
None
NA
NA
NA
11
Thompson Lake
Wood mulch
0 -13 cm — Loamy sand
10YR 2/2
1.096.t 0.175 (n = 10)
13 -43 cm — Sand w /rocks
10YR 5/4
43 -119 cm — Silt loam
10YR 3/1
12
UM — Duluth
Wood mulch
0 -46 cm — Sandy loam
10YR 2/2
0.947 ± 0.106 (n = 8)
46 -117 cm — Clay
5YR 4/4
>117 cm — Clay
5YR 4/4 w /gray mottles
Notes: n, number of samples; RWMWD, Ramsey - Washington Metro Watershed District; UM, University of Minnesota; w/, with
1 10YR 2/2 is the notation used to describe the hue, value, and chroma of the soil color (Foth, 1990).
1998). By comparing the bulk density measurements
to the texture of the soils, compaction did not appear
to be a problem for any of the eight functioning rain
gardens.
Infiltration Rate Tests
Infiltration rate tests, using the methods described
in the Methods and Analysis section for infiltration
rate testing, were performed at the eight functional
rain gardens. Rain gardens A (3), B (4), C (8), and D
(10) were not included in these tests because they
failed the Level 1 assessment based on the existence
of hydric soils and wetland plants, therefore infiltra-
tion rates were assumed to be poor and/or inhibited
at those sites. Six MPD Infiltrometers were used
simultaneously allowing infiltration rate testing to be
completed within 8 h at each rain garden, with the
exception of UM — Duluth (12) due to its large size.
The number of locations where measurements were
made using the MPD varied among the rain gardens
due to differences in rain garden size. The time
required for each individual MPD test to be com-
pleted ranged from 1.5 min to 8.6 h with an average
time of 1.3 h. Only 1% of the tests took 8 h or longer
to drain completely, while 78% of the tests were com-
pleted in less than 2 h. One percent of the MPD tests
were terminated at the UM — St. Paul (6) and UM —
Duluth (12) sites due to minimal change in water
level over a period of more than 8 h.
The Burnsville (1) rain garden (Figure 2) contained
the highest measured Ksat value of 8.1 x 10 -2 cm/s
and the median for the entire rain garden was the
second highest of the eight sites. Not surprisingly,
the MPD Infiltrometer tests were finished within
15 min at 57% of the locations. The highest measured
Ksat values were typically near the shrubs and
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 1025 JAWRA