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PLAN TYPICAL SWALE SECTION
UNDERDRAIN SECTION
NOTES:
1.LONGITUDINAL SLOPE, 1% TO 6%. IF THE LONGITUDINAL SLOPE IS LESS THAN 1.5%, UNDERDRAINS MUST BE PROVIDED OR THE SWALE MUST BE DESIGNED AS A
WET BIOSWALE. IF THE LONGITUDINAL SLOPE EXCEEDS 6 PERCENT, CHECK DAMS WITH VERTICAL DROPS OF 12 INCHES OR LESS SHALL BE PROVIDED.
2.UNDERDRAIN MUST INFILTRATE OR DRAIN FREELY TO AN ACCEPTABLE DISCHARGE POINT. UNDERDRAIN TO BE PVC PERFORATED PIPE, SDR 35 PER ASTM D3034.
3.THE DIVIDER SHALL EXTEND FROM THE FLOW SPREADER AT THE INLET FOR AT LEAST THREE-QUARTERS OF THE SWALE LENGTH. THE DIVIDER SHALL BE
CONSTRUCTED OF A FIRM MATERIAL THAT WILL RESIST WEATHERING AND NOT ERODE, SUCH AS CONCRETE, COMPACTED SOIL SEEDED WITH GRASS, UNTREATED
HEARTWOOD CEDAR, OR UNTREATED WHOLE DE-BARKED CEDAR LOGS.
4.ACCESS ROAD SHALL MEET REQUIREMENTS IN STD. PLAN 234.50.
5.IF NATIVE SOIL HAS LESS THAN 1% ORGANIC CONTENT, 2" COMPOST PER STD. PLAN 262.60 SHALL BE TILLED INTO 6" NATIVE SOIL
6.SEE CONSTRUCTION PLANS FOR SPECIFIC PROJECT REQUIREMENTS.
FLOW SPREADER PER STD.
PLAN 242.00 OR 242.10
MID SWALE FLOW
SPREADER
(RECOMMENDED) PER STD.
PLAN 242.00 OR 242.10
BIOFILTRATION SWALE BOTTOM
(MIN SWALE LENGTH = 100 FT)
ACCESS ROAD, SEE NOTE 4 AND TABLE 6.3.1.B
BOTTOM WIDTH (B)
2' MIN.
16' + DIVIDER WIDTH MAX.
WATER QUALITY DESIGN DEPTH (Y), 4" MAX.
(2" FOR FREQUENTLY MOWED AREAS)
COMPOST AMENDED SOIL,
SEE NOTE 5
SWALE DIVIDER FOR WIDTH > 10',
HEIGHT = Y+1", SEE NOTE 3
SWALE
BOTTOM
FILTER FABRIC 6" MIN. DIA. PERFORATED UNDERDRAIN PIPE
CENTERED BENEATH SWALE, SEE NOTE 2
5/8" CLEAN DRAIN ROCK OR GRAVEL
BACKFILL FOR DRAINS PER WSDOT STD.
SPECIFICATION SECTION 9-03.12(4)
FILTER FABRIC, WRAP TOP,
SIDES, AND BOTTOM PER WSDOT
STD. SPEC. 9-33.2(1)
UNDISTURBED NATIVE SOIL
6" MIN. OVER PIPE
UNDERDRAIN SECTION
FOR SLOPES <1.5%
MIN. 6" DIA. PERFORATED
UNDERDRAIN PIPE
CENTERED BENEATH
SWALE, SEE NOTE 2
UNDISTURBED NATIVE SOIL
3
1
3
1
5/8" CLEAN DRAIN ROCK OR GRAVEL
BACKFILL FOR DRAINS PER WSDOT STD.
SPECIFICATION SECTION 9-03.12(4)
COMPOST AMENDED SOIL,
SEE NOTE 5
COMPOST AMENDED SOIL,
SEE NOTE 5
TABLE 6.3.1.B - REQUIREMENTS FOR BIOSWALE ACCESS ROAD
SWALE BOTTOM AREA¹: L x W (SF)ACCESS ROAD LENGTH²
200-1000 1/2 SWALE LENGTH L
1000-1600 2/3 SWALE LENGTH L
OVER 1600 ENTIRE SWALE LENGTH L
¹ THE SWALE AREA USED FOR COMPUTING ACCESS ROAD LENGTH MAY BE THE BOTTOM AREA
² CITY STREETS AND PAVED PARKING AREAS ADJACENT TO THE TOP OF SLOPE MAY BE COUNTED AS ACCESS
BIOFILTRATION SWALE SCHEMATIC,
CROSS SECTION, AND UNDERDRAIN
DETAIL
STD. PLAN - 243.00
PUBLIC WORKS
DEPARTMENT
APPROVED:
DATEMartin Pastucha
Public Works Administrator
UNLESS OTHERWISE NOTED, DRAWING IS NOT TO SCALE (NTS)
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8/13/2020 | 8:48 AM PDT