columbus stormwater planters
TRANSCRIPT
Columbus
Stormwater Planters LARCH 770, Dr. Jesus Lara
L.Russell and S. Lawson
5/15/2012
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Contents
OVERVIEW ....................................................................................................................... 2 SOILS ................................................................................................................................. 5 PLANTS ............................................................................................................................. 6
FENCES .............................................................................................................................. 6
ASSESSMENT ................................................................................................................... 8
FUTURE PROJECT ........................................................................................................... 8 REFERENCES ................................................................................................................. 10
Cover image: City of Columbus Department of Public Service Transportation Division, River South Street Improvements drawings prepared by EMH&T
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OVERVIEW
he City of Columbus Ohio installed bioretention basins and planters on several
streets in downtown Columbus, and we focused on some of those located in the
River South District. Revitalizing downtown was a goal of the 2002 Downtown
Business Plan. Certain redevelopment projects are required to include stormwater quality
and quantity controls. This means reducing the amount of pollutants and slowing the rate
of flow. The 39-acre River South District will include new high-density residential and
neighborhood retail uses, necessitating an upgrade to the stormwater infrastructure.
The engineering firm, EMH&T
designed the River South bioretention
basins and they were required to capture
and treat at least 20% of the runoff or
decrease the amount of impervious surface
according to the Columbus Stormwater
Drainage Manual (Manno, 2012). Water
quality and quantity standards are similar in
manuals across municipalities because they
all are based on standards set by the Ohio
EPA.
Funding sources for the River South
basins came from several sources,
including: $5.5 million from ARRA, the
American Recovery and Reinvestment Act
T
Figure 1 – Map of the River South District. Dark
Lines are the boundary, green is part of the Scioto
Mile Project, pink is the Phase 2 area.
Source: Doyle-Ahern of EMH&T.
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(the ‘stimulus’); $5.0 million from the Ohio Public Works Commission; and $17.2
million from the City of Columbus for design, construction, and right-of-way acquisition.
The 27.7 million dollar River South revitalization project began in 2008. A portion of
Front Street was converted to 2-way travel, and alternate modes of transportation were
accommodated. The goals were to improve economic activity and provide neighborhood
amenities for Downtown residents. The city’s River South infrastructure renovation
project coincides with separate public and private investment in the area, including the
Scioto Mile Park, the new West Main Street bridges, and Lifestyle Communities $25
million housing project (City of Columbus). Ultimately, all combined sewers in this
district will be disconnected and all the stormwater will be directed into the Scioto River.
EMH&T considered the Portland Bureau of Environmental Science’s evaluation of the
effectiveness of various stormwater best management practices. This study revealed that
bioretention basins are very effective in multiple areas of stormwater concern, including
Image 1 – Town Street before stormwater improvements.
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reduction in volume, flow, total suspended solids, and total phosphorous (Doyle-Ahern).
In order to effectively meet the stormwater requirements of redevelopment as set forth in
the Columbus Stormwater Drainage Manual, bioretention facilities were designed
throughout the River South district (see Figure 2 below). The Columbus Stormwater
Drainage Manual describes bioretention systems as consisting of “a soil bed planted with
native vegetation located above an underdrained gravel layer. Stormwater runoff entering
the bioretention system is filtered first through the vegetation and then the soil bed before
being conveyed downstream through the underdrain system, slowing the runoff velocity
and treating stormwater runoff by absorption, decomposition, and filtration. Bioretention
facilities are often sited adjacent to and used to treat runoff from paved surfaces such as
parking lots.” (City
of Columbus, 2006).
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On the section of Front between Rich and Town Streets, and Rich between Ludlow and
Front Streets, as well on portions of other streets, additional amenities included brick and
concrete sidewalks with granite curbs, ADA ramps, benches, bike racks, trees with
grates, and rain gardens.
SOILS The first mix of engineered soil was based on the Columbus Stormwater Design
Manual’s formula (Manno, 2012). The peat moss and sand mixture held water but the
designers had to change the mix to native soil, sand, and composted yard waste in order
to achieve the desired infiltration rate. The soil media was manufactured off-site. Central
Ohio’s native clay soil alone would not have worked well because infiltration and
removal of pollutants is poor.
Figure 2 – Stormwater street improvements in River South showing the locations
of bioretention facilities. Source: Doyle-Ahern of EMH&T.
Figure 3 – Diagram of street improvements along Rich Street in River South district, including bike racks and
benches on the southern end and the bioretention basins along the northern end. Source: City of Columbus,
prepared by EMH&T.
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PLANTS Plants used in the Columbus bio-basins include Ilex Glabra ‘Densa’ Inkberry (a
holly), Clethra alnifolia ‘Sixteen Candles’ summersweet, Buxus sempervirens ‘Green
Velvet’ boxwood, and Panicum virgatum switchgrass (Manno, 2012).The landscape
architects balanced the plants’ needs with the high pH of the engineered soil mix and
other growing conditions in the basins. For example, Ilex glabra prefers a lower pH, but
tolerates the higher pH. The evergreen is native to eastern U.S. wooded swamps and
tolerates urban conditions, including transplanting, drought, heat and sun or shade,
making it a good selection overall (American Beauties Native Plants). ‘Sixteen Candles’
summersweet is a cultivar of the native Clethra alnifolia shrub and loves wet locations, is
cold hardy and is an aggressive grower (American Beauties Native Plants). The selected
boxwood, ‘Green velvet’ is also vigorous, cold hardy, and tolerates shade. Switchgrass is
a tough native prairie grass, adaptable to many growing conditions and excellent at
capturing and storing the greenhouse gas carbon dioxide (Silzer, 2000). In winter, the
Columbus vegetated bio-basins have infiltration capacity, but capacity is reduced when
the plants are dormant (Doyle-Ahern).
Image 2 – Dormant conditions of planter vegetation on
the left, and Summer conditions on the right. Source:
L. Russell (left) and EMH&T (right).
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FENCES Some of the deepest bioretention basins on Front at Town are enclosed with
decorative black fences made from salt-tolerant steel. These basins are deeper because
the leftover space available for them was narrow. Buildings are at zero setbacks and a
liberal sidewalk width was maintained, leaving a narrow strip between the street curb and
the sidewalk. To meet water quality goals, they must impound a certain volume of water,
and in this case it was 18 inches deep. Two basins in the area are ‘dummy’ basins for
aesthetic balance. Because of the natural terrain’s slope westward to the Scioto River,
basins on the east side of Front Street will not capture stormwater runoff from the street.
Image 3 – Fenced basins along Front Street. Source: L.
Russell.
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ASSESSMENT A rough cost estimate per Columbus basin or unit is approx. $15,000, based on
$12,500 for the basin and $22/ft for plantings (Doyle-Ahern). In Portland Oregon, the
average cost was $30,000 each. The Columbus budgets limited the designs, but future
bio-basin projects will benefit from the sophistication gained from experience and the
availability of pre-cast modular systems.
As in Portland, the most important environmental benefit of Columbus’
bioretention basins is combined sewer overflow mitigation. Local statistics are not
available but analysis from other cities comparable to Columbus show that street
bioretention basins will remove from the combined sewer system 100% of all rain events
of one inch or less and will keep 91% of all rainfall annually from the combined sewer
system (Doyle-Ahern). General citywide improvement efforts in Columbus will be
ongoing through a 40 year $2.5 billion Wet Weather Management Plan which began in
2005 and was approved by the OEPA in 2009 (City of Columbus). Environmental and
economic benefits are both tied to CSO mitigation. Columbus statistics are not available,
but one could model, or sample, how much water is filtering through the bio-basins and
thus diverted from the city sewer system (Manno, 2012).
FUTURE PROJECTS EMH&T is again working with the City of Columbus on new education complex
south of downtown near the Scioto River. Because the soil is silt loam, gravelly clay
loam, and gravelly sand and drains to the river, engineers can take advantage of the
natural infiltration and are designing a ‘zero discharge site’ on which no stormwater
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leaves the site though a pipe (Franklin Soil and Water Conservation District, 2012). So
far, there have been no shared stormwater management facilities in Columbus as there
have been in Portland. Innovative private/public agreements may be a way to further the
city’s goals in a cost-effective way while also bringing awareness of stormwater
management to residents and local businesses.
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REFERENCES
American Beauties Native Plants. (n.d.). Ilex glabra . Retrieved from:
http://www.abnativeplants.com/index.cfm?fuseaction=plants.plantdetail&plant_id=39
City of Columbus. (n.d.). Retrieved from: http://utilities.columbus.gov/
City of Columbus. Division of Sewerage and Drainage Department of Public Utilities.
(2006). Stormwater drainage manual. Retrieved from:
http://publicutilities.columbus.gov/uploadedFiles/Public_Utilities/Document_Library/Pub
lications/Sewer/StormwaterDrainageManual.pdf
Franklin Soil and Water Conservation District. (2012, May). Innovative stormwater
design at new school. The Urban Review, 10(2), Retrieved from:
http://www.franklinswcd.org/wp-content/uploads/2010/10/May-2012-newsletter.pdf
Doyle-Ahern, S. (n.d.). Green infrastructure stormwater management options in an ultra-
urban redevelopment. EMH&T presentation at OWEA Session 3.
Manno, F. of EMH&T. (2012, May 8). Interview by L Russell [Personal Interview].
Silzer, Tanya. (2000). "Panicum virgatum L., Switchgrass, prairie switchgrass, tall panic
grass". Rangeland Ecosystems & Plants Fact Sheets. University of Saskatchewan
Department of Plant Sciences.