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
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
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
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.
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
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
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
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
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
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
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
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.
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
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
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
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
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
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
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
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
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
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.
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
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
Best Management Practices (BMPs) is a familiar term we use when talking about water quality, NPDES Phase II permits, and education to the public. We all have are own understanding of the term and use it maybe more than we should and too often forget the true meaning and intent of the acronym. The action word in the acronym is PRACTICE. Practice if you go to a dictionary is defined as to carry out, apply, or to do or perform often. Therefore what should w carry out regularly (often) to improvement water quality in our region? This and other BMP manuals often focus on the actions that are BEST not the ones that should be perform regularly. Therefore this primer is a discussion on what we should do regularly to improve water quality. Other items in this manual will focus on specific structural practices that can be implement for a specific site. This section will focus on regular practices that should be consider as key part in a stormwater management program to improve water quality.
Add pic of wqv
Better Pictures
Change picture
Need picture with native species
Need picture with native species
Plant pics
Plant pics
Added first bullet
Picture
Picture
Changed permanent to temporary
Changed permanent to temporary
Changed title removed “Provide a valve or cap at end of underdrain
Longer retention of water for plant uptake and groundwater recharge” put in underdrain section
New pictures or better copies of these
Added statement on when to use filter strip and channel
The value should be 0.053. the equation used what 1.4/12*.99*.5?
Can you just scale this up for larger tributaries?
Can you just scale this up for larger tributaries?