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(Seattle, WA w/ZGF) A project to build four swales in Seattle's South Lake Union area within the Cascade neighborhood. A partnership between the private developer Vulcan and Seattle Public Utilities, this project highlights a public/private approach integrating a public drainage system with private property redevelopment. In doing so, the project maximizes construction efficieincies, creates a mechanism for sharing maintenance requirements, and reduces overall project costs. Not only will the swales provide a much needed benefit for the water quality of Lake Union, but it will also enhance the neigborhood with surface water, plants and wildlife.
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I-5
I-5
CAPITOL HILL
LAKEUNION
Nor
th D
exte
r
Fairv
iew
Ave
East
Lak
e Av
e
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