Constructi
ng Rain
Gardens &
BioswalesBy Tom Barrett Green Water Infrastructure, [email protected]
@TomBarrett_GWIFollow us on Twitter @TomBarrett_GWI
The GREENEconomy
How Much Rain Falls in St. Louis?January - 1.83"
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"
Image of Rain Falling
How Much Water Falls in St. Louis?
January - 2,852 gallons
February - 2,883
March - 4,488
April - 5,579
May - 6,390
June - 7,356
July - 5,548
August - 5,470
September - 4,940
October - 4,613
November - 3,662
December - 2,883
Total 56,664
Image of Rain Falling
2,500 sq. ft. Roof
How Much Water Falls in St. Louis?
January - 149,075 gallons
February - 150,705
March - 234,611
April - 291,634
May - 333,994
June - 384,501
July - 290,005
August - 285,932
September - 258,235
October - 241,128
November - 191,436
December - 150,705
Total 2,961,961
Image of Rain Falling
3 Acre Commercial Property
How Much Water Falls in St. Louis?
January - 248,459 gallons
February - 251,176
March - 391,018
April - 486,057
May - 556,657
June - 640,834
July - 483,341
August - 476,553
September - 430,391
October - 401,879
November - 319,061
December - 251,176
Total 4,936,602
City Block (5 acres)
Low Impact Site Development
Stormwater Mitigation
Stormwater Mitigation
Stormwater Mitigation
Stormwater Mitigation
Stormwater Mitigation
• Image of Rain Falling
Pesticide IssuesAtrazine, Nitrogen, Phosphorous
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
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
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
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
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
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
Stormwater Effects of Urbanization
Planting Trees
Stormwater Mitigation
– Collection runoff near the source
– Slow it down
– Soak it in
– Filter it
– Apply it to the landscape
– Create habitats
Rain Garden
A Low Spot
Catches Stormwater
Deep Rooted Plants
Simple Rain garden
Bioswales
Engineered Soils
Underdrain
Rain Gardens
Plant Choices
Choose plants based on the need for light and
soil type.
Location
Rain gardens are often located at the end of a roof or drain spout.
Depth
A typical Rain Garden is between four to eight inches deep.
Size
A Rain Garden usually five to ten percent of the impervious surface
area.
Soil
A tpical mix is 65% sand, 15% top soil, 25% organic matter.
Rain Garden
Rain Garden
BioswalesBurnsville, Minnesota
Native Vegetationwww.epa.gov/greenacres/ www.for-wild.org
Street Edges & Medians
Street Median
Parking Lot Edges
Parking Lot Islands
Driveway Edge
Downspout
Neighborhoods
Meet Stormwater Regulations
Detention Volume
Fix Drainage Issue
Fix Erosion Issue
Utility Clearance
Soil Investigation
Percolation Test
Criteria
Criteria
Near the Rainwater Source
Avoid “End-of Pipe” because of Sedimentation Issues
Typically 10’ to 20’ from Buildings
Distributed Evenly Across the Site
Small Tributary Areas (usually 1 acre or less)
Soil Investigation• Soil Profile to Five
Feet• Soil Compaction
Level• Depth to
Groundwater and Bedrock
Percolation Test• Soil Infiltration Rate• Key Design
Parameter• Percolates water in
24 Hours
Sizing
Determine Design Goals
Calculate Runoff Volume
Determine Allowable Depth
Calculate Surface Area
Native vs. Engineered Soil Assessment
Sizing
Runoff Volume = Precipitation x Drainage Area x Runoff Coefficient
RV=Pr x D(area) x C(un
Depth
Based Upon Infiltration Rate
Infiltration in One Day
Avoid Misquotes
Maximum Depth 18” for Safety
Surface Area
Area of Rain Garden (ft2) = Runoff Capture Volume (ft3) / Average Depth (ft)
A=V/D(average)
Engineered Soils
Bioretention
Space Available
Volume of Stormwater
Drain Faster(the garden can be deeper and not as wide)
Plants - BottomPalm SedgeSoft RushTussock SedgeMarsh Milkweed Blue Flag IrisJoe-Pye Weed
Plants - SidesPurple ConeflowerShowy GoldenrodSmooth Phlox
Plants - EdgesButterfly MilkweedLittle BluestemAromatic Aster
Inlets
Outlets
Curb Cut & Filter StripControls Sedimentation
Splash BlocksPrevents Erosion and Gullies
Functional Landscapes
Thank You
