# NE Siskiyou Green Street Project
NE Siskiyou Street between NE 35 th 

### Pl. and NE 36 th 

### Ave., Portland, Oregon

Project Summary

Projec t T y pe : Sto r m w ater ret r ofit to an ex istin g resi de nt i a l st reet – dem o n s t r at i on p r o j ect
Technol o gy: A pai r of st o r m w at er c u r b e x t e nsi o ns

Ma j o r Bene fit s : • The e x tensi o ns capture runoff fr om approxi m ately 9,300 s q

. ft. of pa ve d surfaces, treating and in filtratin g a larg e propo rtion o f th e runo ff (see Flow Test R e p o rt 1 ).

• The c u r b e x t e n s i ons co n v ert e d a b o u t 59 0 sq uare feet of pa vem e nt t o l a n d s cape.

• Th ey are attractiv e add itio n s to th e n e i g hbo rh ood , im prove the urban environm ent, and i n crease p e d e strian safety at th e in tersectio n

. Co st: The t o t a l p r o j e c t cost , i n cl u d i n g m a nagem e nt , desi gn , a n d c onst r uct i o n wa s $ 2 0

, 0 0 0 of w h i c h $ 3

, 0 0 0 i s attrib u t ed to ancillary street an d sid e walk rep a irs co st s t h at m a y n o t b e n e ed ed fo r o t h e r si m ilar p r oj ect s. To tal co st fo r th e st o r m w ater cu rb ex ten s i o ns on ly w a s $17,00 0 or $1 .8 3 per sq u a r e f o o t o f im p e r v io us ar ea

m a naged

. Constr ucted : City crews co nstru c ted th e ex t e n s ion s i n two weeks in Oct o b e r 200 3.

Main ten a nce Po rtlan d Park s an d Recreation will m a in tain th e facilities d u ring th e two

- year estab lish m e n t p e riod (un til Octob e r 200 5); th e sou r ce of l o ng-term m a in ten a n ce serv ices is to b e d e termin ed

.

Features

N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005 M a r c h 2005 • This was Portland’s first Gr een Street project to u s e landscap ed s t orm w ater curb ex tensions to m a nage street runoff.

• The design provides water qua lity treatm e nt but also

m a xi m i zes infiltration of the runoff. Each facility has four com p artm ents separated by check dam s to prom ote infiltration.

• The project dem onstrates one of the sim p lest types of Green Street retrofits. Th e exis ting s t reet cu rb was left intact and no m odifications were m a de to the
storm w ater collection sy stem

.

• The design integrates well with its surroundings. The low evergreen plantings bl end with landscape areas on the adjacent residen t ial p r operties.

• The adjacen t neighbo rs have played a m a jor role in

m a intaining the two f acilities, prov iding seasonal watering and weeding.

1 Flo w Test Re p o rt fo r t h e Siskiy ou Cu rb E x tensio n, Octo b e r 20 0 4 ; BES

### Background

The Environm ental Services Sustainable Managem e nt Tea m undertook the proj ect in 2003 as part of an on-going evaluation of technique s for m a naging runoff from str eets. Urban storm w ater runoff pollutes r i ve rs and strea m s and contributes to co mbined sewer overf lows (CSOs) to the W illam e tte River. It can also cause localized backups of the com b ined sewer during large storm s

.

Storm w ater curb extensions hold particular promis e as a sustainable practice for m a naging runoff from existing stre ets. These n a tura l sys t e m s capture a nd f ilter run o f f and allow it to inf i ltr ate in to the ground. They are an alternative to tradition a l s t ormwater sumps for m a naging street runoff. In addition to treating and disposing of runoff, they inte grate well with existing neighborhood vegetation and generally im prove the urban environm ent. Portland has constructed m a ny curb extensions over the years to im prove pedestrian safety; this new vers ion of the curb extension provides m a ny additional benefits.

The project on Siskiyou was the first retrofit to an existing street in Portland. Environm ental Services built a secon d set of curb extens ions on Ankeny Stree t (a t SE 56 th ) in 2004, and by 2005 both the City and private developers were im plem enting a num b er of sim ilar projec ts. These typ e s of f

acilities can be constructed in a variety of configurations, as retrofits or as part of new development, and are referred to alternatively as bum p-out swales, pocket swales, or street stormwater planters.

South Curb Extension North C urb E xtension

NE Siskiyo u Street

NE Siskiyou Green Street Plan View

N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005

### Site Selection Criteria

• Traffic I m p a cts: City tr af f i c engine ers cons ider ed the low- tr af f i c residen tia l setting ideal f o r a dem onstration project. The street is 28 feet wide. The addition of tw o 7-foot wide curb extensions created an acceptab l e qu euing config uration.

• Stormw ater Catchment Areas: The size of the catchm ent, a little over 9,000 sq. ft., was considered fairly representative of conditions in the surrounding neighborhood.

• Utility Conflic ts: W a ter lines were th e only subsu r face util ities within the proj ect area and did not present obstacles. See a detailed di scussion under “System Configuration.”

• Loss of Parking Spaces: The project did not elim inate on- street p a rking. Adjacent p r operty owners can park in front of their houses on SE 35 th Place.

• Street Slop e: The m ode rate street slope (2%) was suita ble for a first test of the technology.

• Suitability For Monitoring: The configuration of the local co m b ined sewer allowed f o r placem ent of a flow monitor. There is also a rain gage near the project.

• Soil Infiltra tion Rates: Specialized infiltration tests were no t requ ired a t the site. See “Storm water Capacity and System Configuration” for details.

• Space Available for the Facilities: The space availab l e for the curb ex tensions – len g th of curb unbroken by driveways o r near a fire hydrant – is c onsidered represen tativ e of conditio ns in other

areas.



### Storm w a t er Capacity a nd System Configuration

Stormw ater Management Goals The objectiv e was to m a xim i ze the capture,
trea tm ent, and inf iltratio n of street ru nof f while providing a visual am enity for the neighborhood and im proved pedestrian safety.

Geotechnical Evaluation An inf iltra t ion test was not requ ired bef o re construction. Adequate docum e ntation of characteristics of the local soils already existed. The Natural Resources C onservation Service (NRCS) soil survey for Multnom ah County class i fies th e soils as 51A-Urban Land and well-drained Multnom ah soils. The s u rface horizon typically is dark brown silt loam about 25” thick. S o il below this depth is gravelly silt loam and gravelly sand to a depth of approxim a tely 60”.
March 2005

N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005NE Siskiyou Green Street (Cross Section)

N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005System Configuration W ith f e w exception s , the two curb ex tensions are identical in configuration.

Catchment Areas (pavement, driveways) :

• North curb extension: 3,000 square feet

• South curb extension: 6,300 square feet Street Slope: Approximately 2% Facility Dim e nsions ( applies to each facility) :

• Length: 60 feet; width: 7 feet

• Total area: 275 square feet

• Depth at curb: 6 inches

• Depth at center: 12 inches

• Maxim u m ponding depth: 7 inches at center Internal Storage Volume : 120 cubic feet Overflow : O v erflow exits through a curb cut at the west end of the facility, drain i ng to the com b ined sewer via the street gutter and the exis ting street inlet. No modif i cation s were m a de to the inle t. Check Dams : Each curb extension ha s three checkdam s , with four separate com p art m ents for ponding runoff and slowing its passage th rough the facility. Additiona l I n

formation :

• The asphalt crown on Siskiyou Street is north of the center of the street, a large factor in the difference in catchm e nt sizes.

• The gravel subgrade under the asphalt on Siskiyou Stree t is abo u t 4 inche s thick.

• The two extensions were excavated to a depth of 14 inches be lo w grade. The nativ e soil was tilled pr ior to im porting 8 inches of soil m i x and then the m a terial was tilled a second tim e . There is not a gravel trench underlying the facility (a common fe ature of some designs).

• Excavation in the north exte nsion intersected the top of a gravel-f illed trench containing a water utility line. The trench runs the length of the m i ddle of the facility, abo u t 3 feet fro m the pre-ex isting curb. Excavation of the southern extension did not intersect the adjacent water utility trench, which runsunderneath the new curb (about seven feet off the preexisting curb).

• The check d a m s were co nstructed of com p acted clay and covered with pea gravel and river rock to

m i ni m i ze erosion. See “Success and Lessons Learned” for details.

• The first co mpartm ent (forebay) in each curb extension has the sam e configuration and pl antin g regim e as the other co mpartm ents.

N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005Landscaping

C u r b c u t s :

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( bot t o m ) The facilities were excavate d throughout to 14 inches below grade and backfilled with a 3-way m i x of sand, topsoil, and com post. The m i x was tilled into th e native soil and sp read to create a sh allow parabolic cross section (see illustration).

The plants were selected for their drought tolerance, evergreen foliage, and short st atu r e. The typical m a ture height of the plants is less than two feet. These characteristics were a priority in order to m i nim i z e

m a intenance and address safety concerns. The most common plants, including sedges, rushes, ferns, and broadleaf evergreen shrubs, are native species. T h e planting plan also included som e non-native plants, prim arily to provide seas onal colo r accents. Rush es are the dom inant plan t in th e lo west portions of the two f

acilities. Th eir s tif f struc t ur e helps slow the passage of water and th ey thr i ve in the variable moisture co nditions. There is no perm anent irrigation sys t em in the curb extensions.

The plants were installed at a density greater than required by the Environm ental Services Storm w ater Managem e nt Manual in order to reduce weeding and other m a intenance requirem ents and to quickly create an aesthetically appealing landscape.

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N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005

### Project Costs

The final project cost w a s $20,000 for design, m a nage m e nt, construction activities, and ancillary sidewalk r e p a irs.

I. Budget Elements

1. Construction Management and Overhead Project and construction m a nagem e nt cost $4,500 or 23% of the total.

2. Construction Activities (Curb Extensions Only) Curb extension construction and landscap ing cost $12,500 or 62% of the total budget.

• Curb Extension Construction

The core construction activities cost $8,250 or 41% of the total project cost. This included sawcutting and rem oving existing asphalt, excavat ion, concrete curb installation, soil import and preparation, grading, and safety painting and reflectors on the curbs.

• Landscape Construction

Landscape construction cost $4,250 or 21% of the total project costs. This included check dam construction, fine grading, plant procurem ent, plant m a terial, and m u lch installation.

3. Ancillary Construction Activit i e s Miscellaneous street and sidewalk repair work cost $3,000 or 15% of the total.

II. Budget Discussion It’s likely that design and project m a nagem e nt costs will decline for curb extension projects as they becom e m o r e routine. T h e project in cluded one -tim e costs such as the developm ent of outreach materials and standa rd drawings. Ancilla ry co nstruc tion ta sks – repa ir to the ad jace nt pavem e nt as well as the sidewalk – m a y have also m a de this projec t m o re expensive than subsequent projects.

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N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005

### Maintenance and Monitoring

Maintenance Adjacent p r operty owners have volu n tarily m odified their hom e irrigation system s to help water the curb extensions. In the long term, the City is responsible for providing any irrigation required. Given the shady location of the curb extensions, irrigation after the 2-year startup period should be mi n i ma l

.

Portland Pa r k s and Recr eation will m a intain the curb extensions for two years afte r construction, ending October 2005. Maintenance includes hand weeding (non-chem ical applic ation s ), tr imm i ng plants, p l ant replacem ent, and m a jor leaf and debris rem oval as needed. E nvironm ental Services will re-evalu ate m a intenance requ irem ents in Decem ber 2005 and m a ke arrangem e nts for long-term m a intenance services.

Monitoring Environm ental Services will m onitor hydraulic p e rfor m a nce, m a intenance requirem e nts, the succes s of the planting regim e , and comments from neighborhood residents. Environm ental Services conducted a first flow test in summ er 2004. See Flow Test Report: Siskiyou Curb Extensions, August 4 th , 2004 online a t www.portlandonline.com / shared/cfm /i m a ge.cfm ? i d=63097

.



### Successes and Lessons Learn ed

• The data sug g est th at th e curb extensions on Siskiyou are cap turing and in filtrating a large proportion of the runoff that drains to them

. • The plants grew vigorously during the firs t year and little weeding was required.

• In the f i rs t y ear th e vegetated f o rebay s f illed tw ic e with sed i ment and deb r is (to a depth of 4-6 inches). C ity staff rem o ved the sediment by hand with a shovel and rakes. The cleanings typically required about 30 m i nutes per forebay.

• The earth en checkdam s are susceptible to erosio n during large storm s , as observed during the hose test in August 2004. A more substantial structur al design should be em ployed in the future.

N E Sisk iyou Gr een Str eet Proj ect Repo r t: C o m p le ted Ap r il 2 005