This document discusses how to construct rain gardens and bioswales to mitigate stormwater runoff. It begins by providing data on average monthly and annual rainfall in St. Louis to illustrate the large volumes of water that fall. Design considerations for rain gardens include the size based on the impervious surface drainage area and depth based on soil percolation rates. Native plants suitable for the bottom, sides, and edges of rain gardens are recommended. Bioswales can include engineered soil mixes and underdrains to drain water more quickly. The document emphasizes distributing green infrastructure near rainwater sources to reduce sedimentation and implement low impact development techniques.
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Constructing Rain Gardens & Bioswales (Keynote)
1. Constructing
Rain Gardens
& Bioswales
By Tom Barrett
Green Water Infrastructure, Inc.
www.ThinkGWI.com
Tom.Barrett@ThinkGWI.com Follow us on Twitter @TomBarrett_GWI
3. How Much Rain Falls in St. Louis?
January
-
1.83" Image of Rain Falling
February
-
1.85"
March
-
2.88"
April
-
3.58"
May
-
4.10"
June
-
4.72"
July
-
3.56"
August
-
3.51"
September
-
3.17"
October
- 2.96"
November
-
2.35"
December
-
1.85"
Total
36.36"
4. How Much Water Falls in St. Louis?
2,500 sq. ft. Roof
January
-
,852 gallons
2 Image of Rain Falling
February
-
,883
2
March
-
,488
4
April
- 5,579
May
-
,390
6
June
-
7,356
July
-
,548
5
August
-
,470
5
September
-
,940
4
October
-
,613
4
November
-
3,662
December
- 2,883
Total
6,664
5
5. How Much Water Falls in St. Louis?
3 Acre Commercial Property
January
-
49,075 gallons
1 Image of Rain Falling
February
-
50,705
1
March
-
34,611
2
April
- 291,634
May
-
33,994
3
June
-
384,501
July
-
90,005
2
August
-
85,932
2
September
-
58,235
2
October
-
41,128
2
November
-
191,436
December
- 150,705
Total
2,961,961
6. How Much Water Falls in St. Louis?
City Block
(5 acres)
January
-
48,459 gallons
2
February
-
51,176
2
March
-
91,018
3
April
- 486,057
May
-
56,657
5
June
-
640,834
July
-
83,341
4
August
-
476,553
September
-
30,391
4
October
-
01,879
4
November
-
319,061
December
- 251,176
Total
4,936,602
13. Peak Flow
(1 Acre Site)
Grass Field Roof
1 Year Storm 1.4 cfs 4.3 cfs
2 Year Storm 2.1 cfs 5.4 cfs
10 Year Storm 4.3 cfs 8.0 cfs
25 Year Storm 5.7 cfs 9.5 cfs
100 Year Storm 8.0 cfs 12.0 cfs
cfs – cubic feet per second
14. Peak Flow
(1 Acre Site)
Grass Field Roof
1 Year Storm 10.5 gps 32.2 gps
2 Year Storm 15.7 gps 40.4 gps
10 Year Storm 32.2 gps 59.8 gps
25 Year Storm 42.6 gps 71.1 gps
100 Year Storm 59.8 gps 89.8 gps
gps – gallons per second
15. Peak Flow
(1 Acre Site)
Grass Field Roof
1 Year Storm 630 gpm 1,932 gpm
2 Year Storm 942 gpm 2,424 gpm
10 Year Storm 1,932 gpm 3,588 gpm
25 Year Storm 2,556 gpm 4,266 gpm
100 Year Storm 3,588 gpm 5,388 gpm
gpm – gallons per minute
16. Peak Flow
(2,500 sq. ft. Roof)
Grass Field Roof
1 Year Storm 0.08 cfs 0.25 cfs
2 Year Storm 0.12 cfs 0.31 cfs
10 Year Storm 0.25 cfs 0.46 cfs
25 Year Storm 0.33 cfs 0.55 cfs
100 Year Storm 0.46 cfs 0.69 cfs
cfs – cubic feet per second
17. Peak Flow
(2,500 sq. ft. Roof)
Grass Field Roof
1 Year Storm 0.60 gps 1.85 gps
2 Year Storm 0.90 gps 2.32 gps
10 Year Storm 1.85 gps 3.43 gps
25 Year Storm 2.44 gps 4.08 gps
100 Year Storm 3.43 gps 5.15 gps
gps – gallons per second
18. Peak Flow
(2,500 ft. sq. Roof)
Grass Field Roof
1 Year Storm 36 gpm 111 gpm
2 Year Storm 54 gpm 139 gpm
10 Year Storm 111 gpm 206 gpm
25 Year Storm 147 gpm 245 gpm
100 Year Storm 206 gpm 309 gpm
gpm – gallons per minute
19. Change in Peak Runoff Flow Before and after Development
300%
225%
150%
75%
0%
1 Year Storm Year Storm Year Storm Year Storm Year Storm
2 10 25 100
Stormwater Effects of Urbanization
25. Location
Rain gardens are
Plant Choices often located at the
end of a roof or
Choose plants based drain spout.
on the need for light
and soil type.
Depth Size Soil
A Rain Garden usually A tpical mix is 65%
A typical Rain Garden
five to ten percent sand, 15% top soil,
is between four to
of the impervious 25% organic matter.
eight inches deep.
surface area.
RAIN GARDENS
37. Criteria
Near the Rainwater Distributed Evenly
Source Across the Site
Avoid “End-of Pipe” Small Tributary Areas
because of (usually 1 acre or less)
Sedimentation Issues
Typically 10’ to 20’
from Buildings
58. Green • Water • Infrastructure
Green • Water • Infrastructure
Green • Water • Infrastructure
Green • Water • Infrastructure
Green • Water • Infrastructure