This document provides an agenda and overview for a training module on rain gardens and bioretention. The agenda includes lectures and a design activity on bioretention and rain garden design examples, considerations for implementation, operations and maintenance, and vegetation. Bioretention is defined as a BMP that utilizes plants, soils and microbes to filter and infiltrate stormwater runoff, differing from a rain garden through the inclusion of an engineered underdrain system. Key components of bioretention design including pretreatment, ponding area, vegetation, soil mixture, underdrains and high flow structures are discussed.

1. BMP Training Module 3
Rain Gardens and Bioretention
Sponsored by: MARC
Presenters:
Andy Sauer, P.E. (CDM)
Natalie Postel, P.E. (CDM)
January 23, 2009

2. Agenda







8:30-9:30 Lecture 1: Overview of Rain Gardens & Bioretention

Review Module 1 and WQv definition

Define Bioretention

Define Rain Gardens
10 minute break
9:40-10:30 Lecture 2: Design Examples

Bioretention

Rain Garden
15 minute break
10:45 – 11:30 Design Activity
11:30 – 11:45 Design Activity Results
11:45 – 12:00 Lecture 3: Other considerations

Implementation

Operations and maintenance

Vegetation

Lessons learned

3. Best Management Practice
(BMP)



Best – State of the Practice
 No definitive answer
 Past experience, testing, research,
 Unique to site
Management – Responsible Parties

Improve water quality, meet NPDES Phase II
 Jurisdictional specific

Meet specific requirements of a regional
Practice – Action or Implementation

Practice = defined to carry out, apply, or to
do or perform often.

4. Basic BMP Principles

Plan for stormwater management




Mimic natural hydrology



Sustainable and “be green”
Provide a level of service
Improve water quality
Increase initial abstraction
Promote infiltration, retention & ET
“Treat” the stormwater runoff


Natural processes
Treatment trains

5. BMP Evaluation Process
PLAN
MIMIC
TREAT
Extended detention
(40 hours) to
increase treatment
and decrease peak
flows

6. TREAT
Retain, Infiltrate, Evaporate, and
ET

Retain


Infiltrate



Vadose Zone
Subsurface
Evaporate


At the source
Excess standing water
Evapotranspiration
(ET)


Plant Uptake
Transpiration

7. Structural BMP Consideration









Pollutant removal efficiency
Water quality volume
Site suitability
Tributary area (< 4 acres)
Dimensions (depth, length-width ratio)
Outlet
Emergency spillway
Maintenance easement
Routine and non-routine maintenance

8. an
Qu
er
er
Aesthetics/Amenity
y
tit
W
at
at
W
Qu
ali
ty
BMP Evaluation
General Rule

9. BMP Manual

10. Post Development BMP
Selection

11. BMP Level of Service

Reduce Volume
• Infiltration
• Evapotranspiration (ET)

Remove total suspended solids (TSS)
• Settling

Temperature Reduction
• Urban heat island

Remove oils and Floatables
• Screening and netting

12. BMP Selection Flowchart
Level Of Service
BMP Value Rating
Water Quality
Volume/sizing
Placement,
maintenance

13. Water Quality Volume (WQv)

Water Quality Volume
(WQv): The storage needed
to capture and treat 90% of
the average annual storm
runoff volume

Water Quality Storm: The
storm event that produces ≤
90% volume of all daily
storms in a year

Bioretention and rain
garden design is based on
the WQv
WQv

14. Kansas City Water Quality
Storm
Young and McEnroe
(http://kcmetro.apwa.net)
Daily Precipitation (in)
2.
7
2.
5
2.
3
1.
9
2.
1
1.
5
1.
7
1.
1
1.
3
0.
5
0.
7
0.
9
45
40
35
30
25
20
15
10
5
0
0.
1
0.
3
Water Quality
Storm = 1.37 in
# of days > or=
2003 Kansas City Precip events

15. Why Use the WQv to size
BMP?

Retain runoff long enough to get
water quality benefits



Infiltrate
Maintain vegetation
Reducing erosive flows from
smaller runoff events

Less applicable

16. Water Quality Volume
Calculation

Two methods

Short-Cut Method
•
•

Sites < 10 acres
Only 1 predominant cover type
Small Storm Hydrology Method
•
Larger or more heterogeneous drainage
areas

17. WQv Calculation

Short-Cut Method
WQv = P*Rv



P = 24 hour Water Quality Storm (inches)
Rv = Volumetric run coefficient =
0.05+0.009(I)
I = % site Imperviousness = 100%
Rv = 0.95
WQv = 1.37 in * 0.95 = 1.3 in

18. WQv Calculation

Water Quality Volume

WQv = 1.37 in * 0.95 = 1.3 in

Driveway Example
20 ft x 30 ft = 600 ft2
1.3 in / 12 x 600 ft2 = 65 ft3 (486 gal)
65 ft3 = 10 ft x 10 ft x 0.65 ft

Residential Street Example
(28 ft / 2) x 100 ft = 1400 ft2
1.3 in / 12 x 1400 ft2 = 152 ft3 (1135 gal)
152 ft3 = 10 ft x 10 ft x 1.52 ft

19. WQv Calculation

Water Quality Volume

WQv = 1.37 in * 0.95 = 1.3 in
Typical Home
Roof Area = 2,100 ft2 (varies)
1.3 in / 12 x 2,100 ft2 = 227.5 ft3 (1,702 gal)
Assume 4 downspouts with equal area
228 ft3 / 4 = 57 ft3 (426 gal)
57 ft3 = 10 ft x 10 ft x 0.57 ft

20. Typical Lot – BMPs in ROW

Insert Lot Layout Figure
970
971
970
972
973
969

21. Typical Lot – BMPs in Private
970
971
970
972
973
969

22. Questions?

23. Bioretention
Topeka KS

24. What is bioretention?


A BMP that utilizes
natural chemical,
biological, and physical
properties of plants,
microbes, and soils to
filter, treat, and infiltrate
stormwater runoff.
Bioretention differs
from a rain garden in
that is has an
engineered underdrain
system.

25. Bioretention Plan view
Pretreatment
sheet flow
Underdrain
Bioretention
soil mix
High flow
inlet
Vegetation
Outflow
Overflow
Weir

26. Bioretention

Designed to filter WQv in 1-3 days
High Flow Inlet
(slanted grate in side slope
preferred)
Underdrain
Cleanout
Pollu
ted R
unof
f
3” Shredded
Hardwood Mulch
(free of debris)
Bioretention Soil
Mixture (BSM)
2.5ft – 4ft
45° Wye
Fitting
4’’ Min. HDPE
Underdrain
(min. slope
0.5%)
Ponding Depth
6” Typical
Geotextile Fabric
on top of #7
Stone
Geotextile
Fabric Under
#57 Stone
Overflow Weir
Elevation

27. Bioretention
10’ Min. Grass
Filter Strip
10-15’ Min.
(recommended)
Curb Cut
24”
Rock
Diaphragm
3” Shredded
Hardwood Mulch
(free of debris)
12”
2.5’ Min. Bioretention Soil
Mixture (BSM)
12”
11”
12” Wide Geotextile Fabric on top of #7
Stone
4” Min. HDPE Perforated Underdrain
Geotextile Fabric Under #57 Stone

28. Bioretention Pretreatment


Sheet flow entering the site is best
Concentrated flow requires energy
dissipaters



Decrease velocity
Particle settling
Options



Baffle boxes
Surge stone
Filter Strips
Topeka KS

29. Vegetative Pretreatment

Sheet flow: Vegetated filter strip

Concentrated flow: Vegetated channel
Filter Strip
Leawood KS
Channel
Olathe KS

30. Pretreatment - Vegetated
filter strip



Acts as a pre-filter
Reduces flow velocity
Can be planted with native grass or turf
Kansas City MO

31. Pretreatment - Vegetated
Channel


Same benefits as filter strip
Can be planted with native grass or turf

32. Bioretention Ponding Area



Temporary storage as water filters through
soil mixture
Minimize depth required to hold WQv
Maximize surface area for infiltration
Lenexa KS

33. Bioretention Vegetation


Water volume reduction through transpiration and
increased infiltration through root pathways
Pollutant and nutrient removal through plant uptake
Broadleaf Arrowhead,
Sagittaria latifolia
Robert H. Mohlenbrock @ USDANRCS PLANTS Database
Lenexa KS

34. Bioretention Vegetation
Types




Should be tolerant to both
extended wet and dry
periods
Aesthetics are important
Approximately 6 species
Native grasses and other
ground cover

35. Bioretention Soil Mixture
High Flow Inlet
(slanted grate in side slope
preferred)
Underdrain
Cleanout
Pollu
ted R
unof
f
3” Shredded
Hardwood Mulch
(free of debris)
Bioretention Soil
Mixture (BSM)
2.5ft – 4ft
45° Wye
Fitting
4’’ Min. HDPE
Underdrain
(min. slope
0.5%)
Ponding Depth
6” Typical
Geotextile Fabric
on top of #7
Stone
Geotextile
Fabric Under
#57 Stone
Overflow Weir
Elevation

36. Bioretention Soil Mixture
(BSM)






Appendix A contains specifications for BSM
Must have permeability greater than 1 ft/day
A mix of compost, planting soil, and sand
Free of stones, stumps, roots
Free of brush or seeds from noxious weeds
Organic mulch layer to cover the BSM


Prevents erosion of BSM, retains moisture, aids
biological growth and decomposition, and filters
pollutants
Pine mulch, wood chips, or grass clippings should
NOT be used

37. Bioretention Underdrain
High Flow Inlet
(slanted grate in side slope
preferred)
Underdrain
Cleanout
Pollu
ted R
unof
f
3” Shredded
Hardwood Mulch
(free of debris)
Bioretention Soil
Mixture (BSM)
2.5ft – 4ft
45° Wye
Fitting
4’’ Min. HDPE
Underdrain
(min. slope
0.5%)
Ponding Depth
6” Typical
Geotextile Fabric
on top of #7
Stone
Geotextile
Fabric Under
#57 Stone
Overflow Weir
Elevation

38. Bioretention
10’ Min. Grass
Filter Strip
10-15’ Min.
(recommended)
Curb Cut
24”
Rock
Diaphragm
3” Shredded
Hardwood Mulch
(free of debris)
12”
2.5’ Min. Bioretention Soil
Mixture (BSM)
12”
11”
12” Wide Geotextile Fabric on top of #7
Stone
4” Min. HDPE Perforated Underdrain
Geotextile Fabric Under #57 Stone

39. Bioretention Underdrain

Increases the soils ability to drain

Soil remains in an aerobic state

Increases number of appropriate plant species

Surround with an aggregate followed by a
sand layer

Clean out drain

40. Bioretention Underdrain
Lenexa KS

41. Bioretention Underdrain
Lenexa KS

42. Bioretention Outlet

Attach to underdrain and possibly high flow
drain

Connect to conventional storm water system
or create a non-erosive outfall using energy
dissipation structures

43. Bioretention High Flow
Structures
High Flow Inlet
(slanted grate in side slope
preferred)
Underdrain
Cleanout
Pollu
ted R
unof
f
3” Shredded
Hardwood Mulch
(free of debris)
Bioretention Soil
Mixture (BSM)
2.5ft – 4ft
45° Wye
Fitting
4’’ Min. HDPE
Underdrain
(min. slope
0.5%)
Ponding Depth
6” Typical
Geotextile Fabric
on top of #7
Stone
Geotextile
Fabric Under
#57 Stone
Overflow Weir
Elevation

44. Bioretention High Flow
Structures




A bigger concern in commercial areas
 Parking lot runoff
Design to allow 1% event to pass through or
around facility

10% storm passes through high flow inlet

1% storm passes through overflow weir
Minimize ponding of water above WQv
Options
 Yard drain catch basin
 Stabilized channel
 Weir

45. Bioretention High Flow
Structures
Lenexa KS

46. Bioretention High Flow
Structures
Topeka KS

47. Bioretention Siting
Considerations





Off-line, outside of stream corridor
Tributary area must be stabilized against erosion
Not on fill sites or steep slopes (unless
enhanced)
Minimum 20’ setback from maximum water
surface to surrounding structures
Use fences and landscaping to impede access as
needed to protect public safety

48. Bioretention Siting
Considerations






Off-line, outside of stream corridor
Tributary area must be stabilized against erosion
Route stormwater around BMP until plants are
established
Not on fill sites or steep slopes (unless
enhanced)
Minimum 20’ setback from maximum water
surface to surrounding structures
Use fences and landscaping to impede access as
needed to protect public safety

49. Bioretention Installation
Considerations

Rototill bottom of excavation area to at least 6
inches prior to adding planting soil

Except in areas that will support the underdrains

Plant vegetation in early spring to take advantage
of spring rains

Do not bring on-line until plants are established
(45 days minimum from planting date)

Water plants as needed during the first year

50. Bioretention Maintenance


Relatively low maintenance
Biannual inspection






Erosion of pretreatment areas
Spot mulching
Dead or diseased vegetation removal
Trash removal
Check Overflow structures
Inspect for wet boggy areas

51. Bioretention Advantages








Minimal land area requirements
Flexibility in design themes
Pollutant uptake by vegetation
Groundwater recharge
Reduction of downstream peak runoff rate and
volume to be managed
Creation of wildlife habitats
Recreational and aesthetic benefits
Reduction in downstream water temperature

52. Bioretention Disadvantages





Sediment can quickly clog a bioretention facility
Not suitable in areas with high water table (1-2
feet from ground surface)
Flood control features are not easily incorporated
Serve only small
tributary areas
(< 4 acres)
BSM must meet soil
specifications for
permeability & to
support plants
Lenexa KS

53. Bioretention Lessons Learned




Establishing Vegetation
takes time (1-3 years)
Erosion of banks can be
significant
Consider by-pass for first
2-6 months after
construction based on
vegetation growth
Filter strip or other pretreatment before inflow
increases performance

54. Questions?

55. Rain Gardens
Lenexa, KS

56. Rain Gardens



Small depression planted
with native wetland and
prairie vegetation
Collect and infiltrate
stormwater
Can be placed in
many settings



Residential yards
Public areas
Commercial sites
10,000 Gardens (www.rainkc.com)

57. Bioretention vs. Rain
Gardens
Similarities
 Collection and infiltration of rainwater water
quality volume (WQv)

Biomass removes pollutants by filtration and
uptake
Kansas City MO

58. Bioretention vs. Rain
Gardens
Differences
 Size of facility




Max runoff area for a
rain garden ~1 acre
Excavation
Bioretention soil
mixture (BSM)
versus on-site soils
Engineered
underdrain system

59. Rain Gardens in Public Areas
http://www.dof.virginia.gov/mgt/resources/pub-Rain-Garden-Tech-Guide_01.pdf

60. Rain Gardens in Residential
Yards
10,000 Rain gardens (www.rainkc.com)
Maplewood, MN

61. Rain Gardens
Vegetation
Impervious
Surface
Grass
buffer
Ponding
Area
Augmented Soil
http://fairfaxcounty.gov/nvswcd/youyourland/landscape.pdf

62. Rain Garden Soil

Existing soil may need to be augmented to
increase permeability and encourage plant
growth. Should be a combination of:



Loam
Sand
Clay
UMKC Rain garden Project

63. Rain Garden Vegetation


Deep rooted native perennials provide greatest
stormwater capture and infiltration
Species should be tolerant of drought and
periodic flooding

64. Rain Garden Mulch


Cover soil and surround plants with a layer of
mulch to reduce erosion, retain moisture and help
filter pollutants
Should be shredded hardwood not pine
Olathe KS

65. Rain Garden Site Selection

Existing low spot in
yard

Where downspouts
will drain into it

Setback from building
foundations by at
least 10 ft
10,000 Rain gardens (www.rainkc.com)

66. Rain Garden Maintenance

Water plants about every other day for the first
two to three weeks


Once native plants are established, they require
little or no additional watering
Do not fertilize


Overgrowth results in plants falling over
Fertilizer stimulates weed growth

67. Rain Garden Advantages





Low cost
Minimal excavation
Promote infiltration near the source
Lot level amenity
Public education and outreach tool

68. Rain Garden Disadvantages





Small contributing area (< 1 ac)
Private property
Performance can vary
Long term implementation
Require property owner maintenance

69. Questions?
10 minute break

70. Lecture 2: Design Example
Topeka KS

71. Bioretention
Pretreatment
sheet flow
Underdrain
Bioretention
soil mix
High flow
inlet
Vegetation
Outflow
Overflow
Weir

72. Bioretention Design Criteria

Pretreatment







Vegetated filter strip if runoff enters as sheet
flow
Vegetated channel if runoff is concentrated or
channelized
Other options available
Planting soil bed and ponding area
Underdrain
Overflow
Vegetation

73. Bioretention Design Example


Design a bioretention BMP to treat a 0.5
acre parking lot.
Use the Bioretention Soil Mixture (BSM)
specifications detailed in Appendix A.

74. Water Quality Storage
Volume
Bioretention Design Procedure Form
i.
ii.
Tributary area to bioretention cell = 0.5 acres
Calculate water quality storage volume

75. Water Quality Storage
Volume
ii.
Calculate Water Quality Storage Volume (WQv)
Short-Cut Method
WQv = P*Rv

P = 24 hour Water Quality Storm (inches)
P = 1.37 inches (Kansas City)


Rv = Volumetric runoff coefficient = 0.05+0.009(I)
I = % site imperviousness

76. WQv Example Short-cut
Method

Given:
 A
Tributary = 0.5 acres

%impervious = 99%
WQv = P * Rv*Area
= (1.37in)*(1ft/12in) * (0.05 + 0.009 * 99%)*0.5 ac

77. Bioretention Pretreatment


For sheet flow use a vegetated filter strip
For concentrated flow use a vegetated channel

78. Bioretention Vegetated filter
strip
Lfs

79. Bioretention Vegetated filter
strip


Determine the maximum inflow approach length,
equal to overland flow length from tributary area
Use the following table to identify minimum filter
strip length (Lfs) slopes <2% and >2%.

Slope not to exceed 6 percent
Table 13 Pre-treatment Filter Strip Sizing Guidance
Parameter
Impervious Parking
Residential Lawns
Lots
Maximum inflow
approach length
(feet)
35
Filter strip slope
≤ 2% ≥ 2%
Filter strip minimum
length (feet)
10
75
15
≤2
%
20
75
150
≥ 2% ≤ 2% ≥ 2% ≤ 2% ≥ 2%
25
10
12
15
18

80. Bioretention Vegetated filter
strip
Table 13 Pre-treatment Filter Strip Sizing Guidance
Parameter
Impervious Parking
Lots
Maximum inflow
approach length
(feet)
Filter strip slope
Filter strip minimum
length (feet)
35
≤ 2%
10
Residential Lawns
75
75
≥ 2% ≤ 2% ≥ 2%
15
20
25
≤ 2%
10
150
≥ 2% ≤ 2% ≥ 2%
12
15
18

81. Bioretention Vegetated
Channel

82. Bioretention Vegetated
channel

Determine the percent imperviousness of the
tributary area


This can be different than the %impervious used for the
WQv calculation
Use Table 14 to identify minimum length (LVC) for
channels slopes <2% and >2%

Slope not to exceed 6 percent
Table 14 Pretreatment Grass Channel Sizing Guidance for a 1.0-Acre Tributary Area
Parameter
Channel Slope
Grass Channel
Minimum Length
(feet)
≤ 33%
Impervious
34% to 66%
Impervious
≥ 67%
Impervious
≤ 2%
≥ 2%
≤ 2%
≥ 2%
≤ 2%
≥ 2%
25
40
30
45
35
50

83. Bioretention Vegetated
channel
Table 14 Pretreatment Grass Channel Sizing Guidance for a 1.0-Acre Tributary Area
Parameter
Channel Slope
Grass Channel
Minimum Length
(feet)
≤ 33%
Impervious
34% to 66%
Impervious
≥ 67%
Impervious
≤ 2%
≥ 2%
≤ 2%
≥ 2%
≤ 2%
≥ 2%
25
40
30
45
35
50

84. Bioretention Planting soil bed and
ponding area

85. Bioretention Planting
Soil Bed

Set planting soil bed depth (df)



Must be between 2.5 to 4 feet
Soil bed must be 4 inches deeper than the bottom
of the largest root ball
Test soil permeability (k)

Must be at least 1 ft/day

86. Bioretention Ponding Area

Set max water ponding depth (hMAX)


Between 3 to 6 inches (hMAX = HWQ)
Calculate average water ponding depth (h)
h = hMAX / 2

87. Bioretention Planting Soil Bed
and Ponding Area
Max
(K) Measured
Max
= 0.5 / 2

88. Bioretention Planting Soil
Bed and Ponding Area

Select time for WQV to filter through planting
soil bed (tf)


3 days is recommended
Calculate required filter bed surface area (Af)
Af = (WQv * 43,560 * df) / [K * tf * (havg + df)]

89. Bioretention Planting Soil
Bed and Ponding Area

Calculate length and width of bed

Length = (L:W Ratio * Af)0.5, L:W must be > 2

Width = (W:L Ratio * Af)0.5, W:L must be < 0.5

Ensure that length > 40 ft and width > 15 ft

90. Bioretention Planting Soil
Bed and Ponding Area
= (0.0537*43,560*4)/[1.0*3*(0.25+4)]
= (2*735)1/2 = 38
= 735/40

91. Bioretention Underdrain

92. Bioretention Underdrain
Pollu
ted
Underdrain
Cleanout
Runo
ff
3” Shredded
Hardwood Mulch
(free of debris)
Bioretention Soil
Mixture (BSM)
2.5ft – 4ft
45° Wye
Fitting
4’’ Min. HDPE
Underdrain
(min. slope 0.5%)
Geotextile Fabric
on top of #7 Stone
Geotextile Fabric
Under #57 Stone

93. Bioretention Underdrain

Set underdrain diameter (Du)

At least 4 inches
nPERF >= 4

Use at least 4 perforations rows
around the drain pipe (nPERF)

Use perforation diameter (DPERF) of at least
0.375 inches
Du = 4 inches

Use a longitudinal spacing between
perforations (SPERF) of 6 inches on center

Set depth of gravel blanket around
underdrain

At least 8 inches and greater or
= Du + 2 inches
DPERF = 0.375 inches

94. Bioretention Underdrain
6
8
0.375
6
5

95. Bioretention Underdrain

Ensure underdrain grade is at least 0.5 percent

Provide a clean-out for each pipe run or every 50’

Provide a valve or cap at end of underdrain


Longer retention of water for plant uptake and
groundwater recharge
Connect underdrain to stormwater system or
suitable outfall

96. Bioretention Underdrain

If planting soil bed width > 20 ft, then add
transverse collector pipes


Spacing of transverse collector pipes (Su) < 10 ft
Number of transverse collector pipes
(npipe) = planting soil bed length / Su
For example:
npipe = 120 ft / 10ft = 12 transverse collector pipes
120ft
60ft
10ft

97. Bioretention Underdrain
NO
NA
0
0.5
YES

98. Bioretention Overflow




Bioretention BMPs must be
able to safely route or
bypass runoff up to the 1%
event
If the 1% event is routed
through, flow velocity must
be kept below 3 fps to
prevent erosion
If a bypass is used, it must
be able to route all events
up to and including the 1%
event
Overflow can be a vegetated
or stabilized channel or a
yard inlet catch basin
Topeka KSC
UMKC Rain garden
Project

99. Bioretention Overflow
High Flow Inlet
(slanted grate in side slope
preferred)
1% Storm
Pollu
ted R
10% Storm
unof
f
WQv
Bioretention Soil
Mixture (BSM)
2.5ft – 4ft
Overflow Weir
Elevation

100. Grading

Side slopes 4:1 or flatter for entire bioretention or rain
garden area
UMKC Rain Garden Project

101. Bioretention Vegetation

Purpose





Removal of water by evapotranspiration
Creation of infiltration pathways via root
development
Pollutant uptake
Aesthetic value
Specify



Species
Amount
Spacing
Topeka KS

102. Bioretention Vegetation

Plant a mix of Redbud and White Mulberry with 6-foot
spacing between trunks and at least 6 feet from facility
edges. Plant an even mix of Yellow Coneflower, little
bluestem, and side-oats grama with 2-foot spacing
between plants. Plant Indiangrass in and around other
species to fill out facility. These species are perennial
and tolerant of dry and wet conditions and sunlight. This
mix provides a multi-layered canopy and aesthetic
appearance from green, yellow, purple, and white
flowers.

103. Bioretention Maintenance







Similar to any landscaped area
Inspect overflow structures
Inspect, prune, remove vegetation
Inspect for erosion
Spot mulch
Remove trash
Inspect after storm
events > 0.5in
Topeka KS

104. Questions?

105. Rain Gardens
UMKC rain garden
Project

106. Rain Gardens

107. Rain Gardens

108. Rain Gardens
Vegetation
Impervious
Surface
Grass
buffer
Ponding
Area
Augmented Soil

109. Rain Garden Design Sites

Maximum drainage area is ~ 1 acre
Garden should be at least 30% as large as
impervious area

Typical sites



Residential yards
Community areas
10,000 Rain Gardens
(www.rainkc.com)

110. Rain Garden Design Sites

Minimum of 10ft from structures

Should complement natural drainage of area
Kansas City MO

111. Rain Garden WQv

Same Water Quality Volume calculation as
Bioretention

Use short-cut method

112. Regional Soil Classifications

113. Rain Garden Max Depth
USDA
Soil Texture
Classification
(Ksat)
Infiltration
Rate
(in/hr)
24 hr
Max Ponding
Depth
(in)
48 hr
Max Ponding
Depth
(in)
Sand
9.28
222.6
445.2
Loamy Sand
2.35
56.5
113.0
Sandy Loam
0.86
20.6
41.2
Loam
0.52
12.5
24.9
Silt Loam
0.27
6.4
12.9
Sandy Clay Loam
0.12
2.8
5.7
Clay Loam
0.08
1.9
3.8
Silty Clay Loam
0.08
1.9
3.8
Sandy Clay
0.05
1.1
2.3
Silty Clay
0.04
0.9
1.9
Clay
0.02
0.6
1.1

114. Clayey Soil Infiltration Rates
Three dimensional plot of infiltration rates for
clayey soil conditions. (Pitt, et. al, 2002)

115. Sandy Soil Infiltration Rates
Three dimensional plot of infiltration rates
for sandy soil conditions. (Pitt, et. al, 2002)

116. Building a Rain Garden
Volume

Ponding depth of WQv is dependent on the soils
(Typically 4-6 inches)

Ponded water should be infiltrated within 24-48
hrs

A slightly deeper area can be incorporated to hold
water longer

Side slopes should be flatter than or equal to 4:1

117. Rain Garden Soil

Amend clay soils with organic material to improve
drainage



Loam, peat, compost
Sand
Add a 3 inch layer of untreated, shredded
hardwood mulch

118. Rain Garden Vegetation

119. Rain Garden Vegetation

120. Rain Garden Vegetation

Other resources

Appendix A in BMP
manual

10,000 Rain Gardens
• www.rainkc.com

121. Rain Garden Maintenance

Biannually



Inspect for erosion
Mulch
Annually



Year 1
Inspect spillway
Prune, remove,
inspect vegetation
Year 5
Similar to
Bioretention
St. Stephens School, Alexandria Virginia

122. Questions?
Break (15 minutes)

123. Bioretention Design Activity

124. Activity
Design a bioretention area to capture the WQv from a
2 acre tributary area with 85 % imperviousness.
Stormwater enters the facility as sheetflow off
impervious surfaces with a maximum inflow length of
75 feet. Use the BSM specified in Appendix A to
determine the dimensions of the bioretention area.

125. Activity Solution

126. Lecture 3: Follow up,
Lesson’s Learned, Review
Criteria
Kansas City MO

127. Follow up, Review Criteria,
Maintenance, Plants

Phases of BMP development





Key points of emphasis for each party




Preliminary Plan
Final Plan
Construction
Operation and Maintenance
Designer
Reviewer
Stakeholder
Maintenance

128. Designer
Review Team
Planning Phase
– Environmental Site
Assessment
– Select Post
Construction BMPs
– Flood Control Study
– Establish Long-term
Maintenance Agreements
Plat
Approval
Planning
Engineering
Parks & Recreation
Environmental Specialists
Attorney
Design Phase
– Erosion and
sedimentation
controls
– Post-construction
BMPs
– Flood control
improvements
Building
Permit
Review Team
Planning
Engineering
Code Compliance
Inspectors
Review Team
Planning
Engineering
Parks & Recreation
Environmental Specialists
Operations & Maintenance
Construction Phase
– Inspect and maintain
BMPs for construction
activities
– Construct Post
Construction BMPs
– Maintain agreements for
post-construction BMPs
Occupancy
Permit

129. General Maintenance




Event Inspection (> 0.5 inches)

Inspect facility operation, especially outlet structure

Remove trash & debris

Document potential problems
Monthly Inspection

Inspect & repair erosion

Water plant material during dry periods (1st Year)
 Perform routine plant maintenance (pruning, weeding, etc.)
Semi-Annual Inspection

Remove and replace dead or diseased vegetation

Re-landscape/re-mulch any area areas
Annual Inspection

Inspect inlet & outlet structure condition

Record assessment of planted species & evidence of invasive
plant species

Perform comprehensive safety inspection

130. Other Maintenance
Consideration





Maintenance access - 15 feet wide strip around the
perimeter of the site
May need to harvest excess plants
Erosion issues
Sedimentation
Remove trash/floatables
Olathe KS

131. Vegetation


Use plants listed in the BMP Manual Appendix A
“Recommended Plant Materials for BMPs”
Narrow down from this list by:



Native/Non-Native
Treatment only, habitat creation / biodiversity,
aesthetics?
Evaluating site conditions - soil quality, climate,
wetness, pollution
• Hardier plants would work better in areas with poorer
site conditions

132. Vegetation

Narrow down from this list by (cont):

Speaking with local nursery or botanists
•
•
•

What plants are available for purchase?
Which plants have the best survivability?
Which plants would be best candidates for wet areas,
variable moisture, poor soils, etc.?
Visit at natural wetland in the area
• What plants are naturally favored in local area?
• Are there specific invasive species that need to be
managed?

Check municipal codes to ensure all plant materials
are approved for the area

133. Native versus Non-native
Plants

Native plants are
recommended





Adapted to environmentgrowing season
corresponds to wet
season
Dense, deep root system
Increase infiltration
More drought tolerant
Disease resistant

134. Vegetation Resources
http://plants.usda.gov




Appendix A in the MARC BMP manual
Local nurseries
www.kansasnativeplantsociety.org
www.grownative.org

135. Upcoming Training Sessions

Module #4 – Extended Dry Detention & Infiltration
(Pervious Pavements)


Date: February 20, 2009
Location: Helzberg Auditorium, KCPL

136. Questions?