3. PROJECTCREDITS
ii
A special thank you to :
Jim Adams - Director of Utilties
Minakshi M. Amundsen - University Planner
Lester Cook - Facilities Designer
David Cutter - Campus Landscape Architect
Frank M. Popowitch - GIS & Data Manager
for your help in submitting files and documentation necessary for the
completion of this manual
7. MANAGEMENTPRACTICES
6
Bioretention systems incorporate shallow landscaped depressions to temporarily store
and infiltrate stormwater runoff for filtration. The systems are to manage water quality volume
(WQv) from residential, commercial, and institutional sites. In addition to an aesthetic value, they
remove fine sediments, heavy metals, nutrients, bacteria, organics, and reduce thermal pollution
from runoff across pavement surfaces. The drainage area per cell is typically not more than five
acres. Larger drainage areas should be divided into smaller sub-areas with numerous, individual
bioretention systems to maintain the functionality of the watershed.
The systems include rain gardens and bioretention cells. A rain garden relies on modified soils with
good percolation rates. In addition to a modified soil matrix, bioretention cells typically include
a rock chamber and subsurface drainage system tied into adjacent storm drains. Stormwater
runoff collected in the upper layer of the facility is slowed and filtered by vegetation, mulch and
soil layer, and then stored temporarily in a stone aggregate base layer. The water quality volume
(WQv) is drained from the aggregate base by infiltration into the underlying soils and/or to an
outlet through a perforated pipe subdrain. They are designed with a combination of plants that
may include grasses and forbs, flowering perennials, shrubs, or trees. In the case of bioretention
cells, the systems can operate either off-line or online and generally include an integrated upstream
treatment facility such as a perimeter grass filter strip or grass swale for initial capture of sediment.
8. A. Description
7
Bioretention cells are structural stormwater systems that slow the WQv using soils and
vegetative massing in shallow depressions to remove pollutants from stormwater runoff. The
facilities are intended to model the hydrologic functions of a native ecosystem. Some of the
major processes that occur through bioretention include: interception, infiltration, settling, evapo-
transpiration, filtration, absorption, thermal attenuation, and hydrocarbon and organic matter
decomposition. They remove pollutants through a variety of physical, chemical, and biological
processes in the upper engineered soil layer and the underlying native soils. The design can
impact the processes and their function. Example applications of bioretention cells and rain
gardens are illustrated in Figure 1. The components of the bioretention cell and rain garden are
diagramed in Figures 2 and 3, respectively.
Each component of the bioretention cell is important. The engineered soil layer provides filtration
and holds water and nutrients for the plants, and enhances biological activity and root growth
through the voids within the soil particles. The plant material evapo-transpires stormwater, creates
pathways for percolation through the soil, and improves soil structure and aesthetics. The mulch
layer acts as a filter for pollutants in runoff, protects underlying soil from drying and erosion, and
provides an environment for microorganisms to degrade organic pollutants.
Vegetation and engineered soils function as a treatment area to accept runoff from various
surfaces. Stormwater flows into the cell, ponds on the surface, and slowly infiltrates into the
modified soil layer. The filtered runoff can be allowed to either percolate into the underlying soils
or be temporarily stored in the aggregate subdrain system and discharged at a controlled rate to
the storm sewer or a downstream open channel. Runoff can be controlled closer to where it is
generated by the uniform distribution of bioretention cells to break up the area in manageable
sub-watersheds. Higher flow events (>Q2
), and runoff volume that exceed the infiltration capacity
of these systems can be returned to the conveyance or safely bypassed.
Plants in bioretention cells enhance infiltration and provide an evapotranspiration component.
Properly selected plants provide resistance to moisture changes, insects, and disease; enable water
and pollutant uptake; and maintain high organic matter content in the soil matrix. The mulch
layer and organic matter component of the soil matrix provide filtration and a place for beneficial
microbial activity. Aerobic conditions are necessary to maintain bacterialogical activity for
processing pollutants.
A complementary upstream practice is provided to reduce the sediment loading to the
bioretention cell. Bioretention cells are often built with grass or rock filter strips around the
bioretention area. These filters remove particulates and reduce runoff velocity. Filter strips also
prevent crusting of pore spaces with fines and reduce maintenance. Furthermore, a freeboard
storage area may also be designed for runoff prior to infiltration, evaporation, and uptake.
Mosquitoes are not a problem because bioretention cells do not retain standing water long enough
for mosquito reproduction (4 to 10 days). Bioretention cells are designed to infiltrate standing
water within 4 to 12 hours.
9. MANAGEMENTPRACTICES
8
There are many ways to incorporate bioretention cells into new construction projects or to
retrofit existing urban areas. Bioretention can be used in residential yards, as interior or perimeter
structures in parking lots and sidewalks, for rooftop drainage at residential and commercial
building sites, along highways and roads, within larger landscaped pervious areas, and as
landscaped islands in impervious or high-density environments.
Bioretention Cell in Parking Lot Rain Garden in a Residential Neighborhood
Curb Extensions Along a Pubic Road Commercial Roof Top Drainage Swale
Figure 1: Example Applications of Bioretention Cells and Rain Gardens
10. Routine landscape maintenance (removal of dead plant debris
and weeds); mulch and plant replacement as needed
Non-erosive flow velocities are crucial at inlet points and
overflow spillway
Inlet and Outlet
Supplies water and nutrients to support plant life. Stormwater
pollutants are removed through filtration, plant uptake,
adsorption, and microbial decomposition
Planting soil depth = 1.5-2.5ft; Total cell depth = 3.5-5.5ft
Example soil mixture: medium sand(50-60%), sandy/clay
loam (20-25%), leaf compost (20-25%)
Organic matter content of 10%
Maximum clay content of < 5%
Provides for temporary surface storage before runoff infiltrates
into the soil matrix. Mainly limited to a depth of 6-9 inches.
During larger events (Q2
), additional freeboard depth should be
provided for online systems to allow surcharge above overflow
weir.
B. Design Components
9
Reduce velocity and capture heavier sediment and debris.
Example pre-treatment practices include grass filter strips,
vegetated swales, mechanical treatment systems, sediment
traps, level spreaders, and ditch checks.
Protects soil from erosion, retains moisture in the root zone,
provides a medium for microbial growth and organic matter
decomposition, provides some filtration of larger sediment and
controls weeds
The aggregate subbase layer provides additional storage
capacity for the captured runoff after filtration.
An open-graded, clean, durable aggregate of 1-2 inch
diameter will provide a porosity of 35-40%
Depth of the aggregate layer can be varied to provide more
storage volume
A nominal depth of 12 inches is typically provided
Perforated pipe underdrain is necessary when subsurface
percolation rates are limited
Native species generally recommended
System is sized to retain the WQv, runoff volumes in excess of
the WQv are usually bypassed; check capability to provide some
peak flow attenuation for larger runoff events up to the Q5
Pre-treatment Area
Ponding Area
Organic Mulch Layer
Modified Soil Layer
Stone Aggregate Subbase
Subdrain
Plant Materials
Maintenance
Hydrologic Design
11. MANAGEMENTPRACTICES
10
Figure 2: Typical Bioretention Cell Components
Curb Cut
Grass Filter Strip
Plant Material
Ponding Depth
Mulch Layer
Soil Matrix
Filter Fabric 3/8”Stone Layer
3/8”Stone Layer
Plant Material
No
2 Stone Layer
No
2 Stone Layer
Perforated Pipe
Perforated Pipe
Figure 3: Typical Rain Garden Components
13. MANAGEMENTSUITABILITY
12
Bioretention cells are primarily designed for stormwater quality. In addition, they can
provide limited runoff quantity control. As a result, the facilities may be sometimes used to partially
or completely meet channel protection requirements. Bioretention cells will generally need to be
positioned in conjunction with another structural control to provide channel protection standards.
As a result, it is important to ensure that a bioretention cell safely bypasses higher flows.
14. A. Management Concerns
13
Each component of the bioretention cell is designed to
perform a specific function thereby increasing the efficiency of
bioretention as a whole:
Pretreatment practices reduce velocity and filter fines from
incoming runoff
Ponding area provides temporary storage prior to
evaporation, infiltration, or plant uptake
Mulch layer provides filtration and an environment conducive
for microbial communities beneficial to hydrocarbon and
organic material degradation
Soil matrix provides filtration; Micropores created by clays
provides adsorption sites for hydrocarbons, heavy metals,
nutrients, and other pollutants
Plant material uptakes runoff and pollutants, stabilizes soils,
but requires maintenance practices
Aggregate subbase yields positive drainage, aerobic
conditions, and supplies a final polishing treatment media
Water Quality (WQv)
Bioretention cells may be designed to capture entire volume
in either an off-line or online system. For larger sites, another
structural control must be constructed to provide the CPv while
still directing the WQv to the bioretention cell
Use another control in conjunction with the bioretention cell
to reduce post-development flows of storms above the 5 year
storm (Qp) to pre-development levels
Cells must provide other structural diversions and/or be
designed to protect again extreme storm flows
Channel Protection (CPv)
Overbank Flood
Protection
Extreme Flood Protection
15. Despite uncommonly observed across all landscapes, bioretention practices provide a
suitable means for harnessing stormwater runoff in commercial, high-density urban, and single-
family residential sites. However, they are more generally confined to areas that generate higher
levels of hydrocarbons and trace metals in stormwater runoff. In these high concentration
“hotspots”, stormwater must be prevented from entering the groundwater table and numerous
bioretention practices may be necessary. The following are sites where stormwater management
practices should be taken seriously for proper hydrologic function:
Vehicular fueling, service, storage and equipment cleaning facilities
Industrial Site
Marinas
Outdoor loading facilities
Hazardous material storage facilities
Commercial nurseries and golf courses
B. Pollutant Removal
C. FEASIBILITY
MANAGEMENTSUITABILITY
14
Fertilizers such as nitrogen and phosphorous are common pollutants in residential and other
landscaped places. Other controls may need to be constructed in conjunction with a bioretention
cell to ensure sufficient removal rates of pollutants. The following data depict pollutant removal
efficiency levels commonly observed by bioretention cells (Table 1) and percent removal by depth
(Table 2):
Table 1: Pollutant Removal Efficiency Data
Table 2: Cumulative Percent Removal by Depth
80%
65-85%
50%
70-100%
45-95%
Total Suspended Solids
Total Phosphorous
Total Nitrogen
Pathogens
Heavy Metals
Depth Cu Pb Zn P TKN NH4
NO3
TN
1 ft
2 ft
3 ft
93 99 98 73 60 86 -194 0
90 93 87 0 37 54 -97 -29
93 99 99 81 68 79 23 43
17. DESIGNCRITERIA
16
Stormwater quality should be the priority when designing for bioretention cells. In
addition, they can provide limited runoff quantity control by slowing the flow of water through
plant evapotranspiration and soil infiltration.
18. 18
A.Planning
CONSIDERATIONS
What are the requirements for water quality and quantity control?
What level of storm is required to meet the stormwater
management criteria?
Will the bioretention cell be used for quantity control in addition to
water quality?
Are there any surface pollutants? If yes, what is the level of
concentration? Are there any specific requirements to handle the
polluted runoff?
Will the bioretention cells be used independently or will they be
part of a large network of BMP’s ?
What level of storm is required to meet the stormwater
management criteria?
Will the bioretention cells be On- or Off-line? - meaning will the cells
have a direct connection to the existing storm infrastructure?
Before designing the Bioretention cell it is important to first
think about the existing site conditions and any local and state
requirements. In the end these conditions and guidelines will inform
the design process. Below are just a few examples of some things to
consider when evaluating the suitability of the bioretention cell.
19. DESIGNCRITERIA
19
LOCATING/SITING Identify existing site features that could be incorporated into
or informed by the site. These could be:
• Ditches, ponds, depressions
• Existing bodies of water - lakes, rivers, ponds, streams,
wetlands
• Local vegetation/wildlife
• Existing infrastructure - natural or man-made
Prevent from damaging existing vegetation such as trees. If
disrupted plan to replace with alike species.
Take into consideration features that will affect the overall
design strategies.
• Topography/slope
• Geologic formations
• High water tables - seasonal
Identify existing infrastructure
• Utilities
• Storm - public and private
• Water lines
• Sanitary
• Combined sewers
Review site land use, traffic, and circulation along with other
possible water quality hazards.
Soil Testing should be performed on site. Below is a short list
of some of the possible test.
• Infiltration
• Nutrients and Metals
• Drainage
• Aggregate stability
• pH
20. B. Physical Specifications
20
The design should maintain a length to width ratio of at
least 2:1
The Surface area of the bioretention cell is sized using
Darcy’s law.
A = (WQ ) ( d ) / [ (k) (h + d ) ( t )]
A
WQ Water Quality Volume(cf)*
d Filter bed depth (ft)
k Coefficient of permeability of filter media(ft/day)
h Average height of water above filter bed (days)
t Design filter bed drain time (days)- recommend
drain time is 2 day(48 hrs)
* The following equation can be used to determine the
WQ ( water quality Storage volume)
WQ = (P) (Rv)(A) / 12
P = 90% Rainfall Event Number
R = 0.05 + 0.009(I), where I is percent impervious cover
A = site area in acres
The treatment system shall be sized to temporarily hold at
least 75%
Drainage area : 5 acres maximum for individual cell
.5 - 2 acres preferred, if larger than 5 acres
then additional cells are recommended
SIZING
f f f f fv
v
f
f
f
f
2
Surface area of filter bed (ft )
v
v
v
21. DESIGNCRITERIA
21
REQUIRED ELEMENTS (As Observed on Page 9)
DESIGNCRITERIA
21
Routine landscape maintenance (removal of dead plant debris
and weeds); mulch and plant replacement as needed
Non-erosive flow velocities are crucial at inlet points and
overflow spillway
Inlet and Outlet
Supplies water and nutrients to support plant life. Stormwater
pollutants are removed through filtration, plant uptake,
adsorption, and microbial decomposition
Planting soil depth = 1.5-2.5ft; Total cell depth = 3.5-5.5ft
Example soil mixture: medium sand(50-60%), sandy/clay
loam (20-25%), leaf compost (20-25%)
Organic matter content of 10%
Maximum clay content of < 5%
Provides for temporary surface storage before runoff infiltrates
into the soil matrix. Mainly limited to a depth of 6-9 inches.
During larger events (Q2
), additional freeboard depth should be
provided for online systems to allow surcharge above overflow
weir.
Reduce velocity and capture heavier sediment and debris.
Example pre-treatment practices include grass filter strips,
vegetated swales, mechanical treatment systems, sediment
traps, level spreaders, and ditch checks.
Protects soil from erosion, retains moisture in the root zone,
provides a medium for microbial growth and organic matter
decomposition, provides some filtration of larger sediment and
controls weeds
The aggregate subbase layer provides additional storage
capacity for the captured runoff after filtration.
An open-graded, clean, durable aggregate of 1-2 inch
diameter will provide a porosity of 35-40%
Depth of the aggregate layer can be varied to provide more
storage volume
A nominal depth of 12 inches is typically provided
Perforated pipe underdrain is necessary when subsurface
percolation rates are limited
Native species generally recommended
System is sized to retain the WQv, runoff volumes in excess of
the WQv are usually bypassed; check capability to provide some
peak flow attenuation for larger runoff events up to the Q5
Pre-treatment Area
Ponding Area
Organic Mulch Layer
Modified Soil Layer
Stone Aggregate Subbase
Subdrain
Plant Materials
Maintenance
Hydrologic Design
22. C. PLANTING MATERIAL
22
Peltandra virginica Osmunda cinnamomea
Schizachyrium scoparium Spartina alterniflora
Cephalanthus occidentalis Clethra alnifolia
Magnolia virginiana Betula nigra “Heritage”
Green Arrow Arum Cinnamon Fern
Little Bluestem Smooth Cordgrass
Buttonbush Summersweet Clethra
Sweet Bay Magnolia Multi-Stem River Birch
treesshrubsherbaceousgrasses
25. COORNELLUNIVERSITYPOTENTIALS
25
Currently, only a few bioretention practices are observed on Cornell University’s campus. Of
those basins, many are not living up to their potential due to poor plant selection or improper
maintenance such as over mowing. The following attempts to outline hot spots or potential sites
for future bioretention practices in hopes of creating a brighter and more ecologically friendly
campus. Furthermore, the proposed sites should be in well populated/traversed areas to provide a
means for educating the public.
26. A. Site Analysis
26
VEHICULAR CIRCULATION
PARKING
ROADWAYS
FFSFDFSDFSDFSDFDSFSDFSF
Fall Creek Watershed
Fall Creek Gorge
Cornell University is located within the Fall creek Watershed. The campus consists of numerous
roadways and other impervious surfaces situated in close proximity to the Fall Creek Gorge. This
unique layout contributes a high sediment load and other deleterious elements into the gorge and
Cayuga Lake.
27. COORNELLUNIVERSITYPOTENTIALS
27
CURRENT STORMWATER PRACTICES on Campus
Below are examples of current stormwater management practices
within campus parking lots. Most the stormwater is handled by
traditional methods of guiding stormwater to catch basins. However,
some newer tactics are recently emerging by way of curb cuts and
swales. These methods seem to appear on some of the newer parking
lots throughout the campus.
28. We identified several sites based on their function and connections to major pedestrian routes. The
areas were characterized based on one of three different Stormwater BMP’s. Bioretention cells were
used for large areas( i.e. park lots) where water quantity would be the highest. Rain Gardens were
proposed in areas that could receive more localized runoff from sidewalks and pathways. Lastly,
curb extensions were suited for sites to collect runoff from roadways.
PROPOSED ECO-BASIN
BIORETENTION CELL
RAIN GARDEN
CURB EXTENTION
FFSFDFSDFSDFSDFDSFSDFSF
B. Potential Bioretention Sites
28
Noyes Lodge
University Ave
Balch Hall A LOT CC LOT Appel Commons
Rand Hall Tower Road Crescent Parking Lot Friedman Parking Lot
29. COORNELLUNIVERSITYPOTENTIALS
29
A LOT is a heavily used campus parking lot designated for faculty members. The Parking lot is
located on the outer edge of Cornell University’s North Campus. Along with vehicle traffic there are
several bus stops in and around the area. The site is roughly six acres in size. The runoff is handled
by catch basins and ultimately deposited into local streams. This lot was selected due to usage, size,
physical features, and few underground utilities that would limit the design and/or construction of
a Bioretention Cell(s).
A LOT - Existing Site Conditions
C. Selected Sites
Electrical lines Water Lines Sewer Lines
30. 30
The parking lot has several catch basins located near the southwestern corner of each isle.
Currently, there are open lawns within the parking medians that could provide a potential for
future bioretention practices.
A LOT - Existing Site Conditions Cont.
Outflow Pipe
Standard Catch Basin - Park Isle
31. COORNELLUNIVERSITYPOTENTIALS
31
A LOT - Sizing of Cell
Total Surface Area( impervious surface) - 263, 930 sq ft. / 43,560 sq ft(acre) = 6.05 Acres
Step 1: finding the WQv
WQv = (P)(Rv)(A)/12
WQv = Water quality Volume
P = 90% rainfall event
Rv = .05 + .009(I), I is percent of impervious surface cover
A = Area in acres
WQv = .9(.05 + .009(80)(6)/12
.9(.77)(6)/12
4.158/12 = .34 acre - feet or 14,810
Step 2: compute filter bed area using
Af = (WQv)(Df)/[(K)(Hf + Df)(Tf)]
Af Surface area of bed
WQv 14,810
d 2ft
k .5 ft/day
h .5 ft
t 2 days
Total filter bed area = 9147.6 sq ft
Total area of site designated for Bioretention cell = 9533sq ft
Based on the 6 acre size of the lot, the site we have chosen (in red) would fulfill the sizing
requirements. If a second area is needed, the median in the middle of the lot (in orange) could also
be used
