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CAPITOL HILL

LAKEUNION

Nor

th D

exte

r

Fairv

iew

Ave

East

Lak

e Av

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PROBLEM

Stormwater from Capitol Hill flows across streets and sur-faces collecting particles and contamination before the 475 acres (188 million gallons per year) of runoff head to the storm drain pipe that empties into to Lake Union. This process contami-nates the lake with silt, heavy metals, fertilizers, and patho-gens that affect plant and animal habitat as well as human conditions. Typical stormwater treatment plants designed to remove these pollutants are expensive and unattractive interruptions to the urban environment.

SOLUTION:

Stormwater will be treated through a vegetated fil-ter called a bioswale, an earth channel planted with erosion resistant and flood tolerant grasses, that re-moves contaminants collected in Capitol Hill while creating a neighborhood amenity in Cascade and improving the water quality conditions of Lake Union. This win-win situation takes advantage of new development to meet rising infrastructure demands of associated hardscape through a less invasive and more cost effective means. Stormwater from be-low ground pipes will be pumped into four street-lev-el bioswales that will naturally treat 188 million gal-lons of stormwater every year.

SOUTH LAKE UNION

Republican St

Harrison St

Thomas St

Yale

Ave

Pont

ius

Ave

SWA

LE

188 million gallons of Capitol Hill runoff willflow through the swales.

Swales remove 60% of contamination

The effect of this natural system will have an over-all impact of cleaning the lake by reducing con-taminants by 4%.

WATER RUNS FROM HIGH POINTS TO LOW

Runoff from the Capitol Hill drainage basin naturally flows towards the South Lake Union Neighborhood.

VEGETATION NATURALLY CLEANSES STORMWATER

Particulates and chemicals in rain water-runoff can be treated without mechanical means through planted channels called bioswales.

Pike Place market

CASC

AD

EN

EIG

HBO

RHO

OD

Denny Way

Valley St

convention center

WHERE IS IT?SEATTLE, SOUTH LAKE UNION AND CASCADE NEIGHBORHOOD

Yale AveRetail E

dge

New

Dev

elop

men

t

188 million gallons a year from Capitol Hill

72" main

24" to swales

Pre-treatment

Water flows into swales at a maximum 8 cubic foot/second

Stormwater run-off from Capitol Hill98 Mg/L total suspended solids TSS(low 49 Mg/L high 180 Mg/L)

Pre-treatment vault removes sediment, floating debris, and free oil

72" Main

Swales removeaverage 60% of total suspended solids. (Between 40% to 70%)

Pontius A

ve.

Yale

Ave

.

Thomas St.

Harrison St.

Republican St.

Swales have a 1%-2% slope12" pipe

Stormwater entering South Lake Union 39 Mg/L total suspended solids

12" pipe

Low water velocities combined with healthy strands of thin stemmed plants allow particles and pollution to settle out of stormwater. Swales es-sentially act as small constructed wet-lands.

SWALE REMOVAL RATES

PRE SWALE

POST SWALE

total suspend-ed solids

38%

100%

total phospho-rous

14%

37%

total nitrogen

14%

55%

nitratenitrogen

13%

44%

metals

9%

71%

SWALE BY NUMBERS4 blocks

2 streets

8 inches of water at full capacity

43 Tons of total suspended solids removed annually

188 million gallons of water treated annu-ally

$8 million construction costs

½ cost of effective water treatment projects

HOW DOES IT WORK?UNDERSTANDING THE SWALE

24" Drain pipe to swales

60'-0" ROW

the street above ground

the pipesbelow ground

“

’’

VASTRA HAMNEN HOUSINGMalmo Sweden

THE MERIWETHERPortland Oregon

VASTRA HAMNEN HOUSINGMalmo Sweden

THE MERIWETHERPortland Oregon

SWALESeattle Washington

“If all the world’s water were fit into a gallon jug, the fresh water available for us to use would equal only about a teaspoon.”

WHERE ELSE HAS IT BEEN DONE?

Give nature the space to grow and you’ll be amazed by the results.

VEGETATION NATURALLY FILTERS AND SLOWS STORMWATERPlants are natural filters. Particulates and chemicals in rain water runoff can be treated without mechani-cal means through planted channels called bioswales.

HEALTHY ECOLOGIES LEAD TO HEALTHY PEOPLEBiophilia describes the instinctive at-traction of humans to nature and oth-er living systems, an affiliation that is deeply rooted in our biology. Studies show that people who have regular access to and views of natural sys-tems are happier, healthier, and more productive.

SWALES ARE SWELL

Earth channels planted with ero-sion resistant and flood tolerant gas-ses have the capacity to retain pol-lutants, slow water velocity, and disconnect impervious areas from downstream waterways.

The Alcyon and P-Patch Community Gardens

Cascade Neighborhood, Seattle's pioneer of Sustainability

New Development

Swale

Yale Street

The Cairns

WHAT DOES IT DO?CREATES A HEALTHY URBAN ENVIRONMENT

looking north on yale street

view looking east accross yale from new home