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Columbus Stormwater Planters LARCH 770, Dr. Jesus Lara L.Russell and S. Lawson 5/15/2012

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Page 1: Columbus stormwater planters

Columbus

Stormwater Planters LARCH 770, Dr. Jesus Lara

L.Russell and S. Lawson

5/15/2012

Page 2: Columbus stormwater planters

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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.