Implementing LID on Large Sites: Two Case Studies

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Implementing LID on Large Sites Two Case Studies
Central Ohio Stormwater and Erosion Control Expo
2007

• OhioHealth Dublin Methodist Hospital, Dublin,
  Ohio
• New Hilliard High School in the Big Darby
  Watershed
• Eco-Design and Engineering, Ltd
• Scott E Sonnenberg, PE, LA, CPESC

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• Low Impact Design
• Minimize Impervious Impacts
• Maximize Flow Lengths
• Maximize Infiltration
• Provide Water Quality Filtration
• Minimize Flow Velocities
• Provide Controlled Flood Storage

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• Obstacles to LID
• Owners Cost and Schedule Delay
• Design Consultants I dont experiment.
• Government Zoning/Standards dont allow.
• Contractors I know how to manage a site.

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Existing Site Data Total Area 71 ac Farmed
65 ac Wooded 6 ac Slopes 1 to .25 Soils
40 hydric, 60 type C silt loam
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Existing Watersheds 5 Subwatersheds City
Stormwater Master Plan
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Future Site 13 ac
Proposed Site Areas Hospital Site 45.5 ac
New Road ROW 2.5 ac
Future Interchange 10 ac
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North 11.4 ac

West 11.8 ac
East 21.4 ac
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• Stormwater Regulations
• Post lt Pre Runoff Rate
• Pre Rate set by City STW Master Plan
• Critical Storm 1-Yr Volume Increase
• NPDES Phase II State Regulations
• ¾ WQv hold gt 24 hours
• No Infiltration or Volume Regs

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EX NORTH SUBWATERSHED
1-YR
1
100-YR
10-YR
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• Proposed LID Measures
• Minimize Impervious Impacts
• Impervious runoff into 28 vegetated areas and 26
  grassed basins
• Maximize Flow Lengths
• Sheet flow, curb cut, grass swale, basin, wetland
  swale, pond
• Maximize Infiltration
• 26 grass detention basins, 5 wetland swales, 5
  wetland ponds gt 4 days
• 33 to 50 infiltration of 1 to 1-yr storm
  runoff
• Provide Water Quality Filtration
• 3.5 ac ft WQ volume in grass basins, wetland
  swales, and wetland ponds
• Minimize Flow Velocities
• Wetland swales at 0.1 slopes and undersized
  storm drain pipes
• Provide Controlled Flood Storage
• Multiple basins throughout site provides gt 18
  acft storage

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Proposed Site Data Total Area 45.5 ac Roof
Paving 18.4/9.4 ac (61) Green Space 17.7 ac
(39)
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95 Curb Cuts
7 Outlets
5 Wetland Ponds
54 Inlets/3 CBs
5 Wetland Swales
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• Obstacles to LID
• Owners Cost and Schedule Delay
• Design Consultants I dont experiment.
• Government Zoning/Standards dont allow.
• Contractors I know how to manage a site

• Opportunities
• Lower SD Cost and Quicker Permit Approval
• Typical Landscape Near Building / Wild at
  Perimeter
• Green Space and Setbacks use for Stormwater
  Management
• Low/Wet areas away from Building Pad and Pavements

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PROPOSED NORTH SUBWATERSHED
1-YR
1
10-YR
100-YR
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SITE
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UNDER CONSTRUCTION
17
UNDER CONSTRUCTION
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119 Ac New Hilliard High School Hamilton
Ditch/Hellbranch/Big Darby Creek Watershed
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119 Ac New Hilliard High School Hamilton
Ditch/Hellbranch/Big Darby Creek Watershed
EXISTING SITE 119.5 Total Acres DESCRIPTION SOIL
TYPE AREA COEF INF VOL Forest C 3.0 15.6
46.8 Row Crop C 46.8 11.9 556.9 LD Res (12) C
1.0 14.2 14.2 Road ROW (30)C 1.0 11.2
11.2 Forest D 4.0 14.6 58.4 Row
Crop D 63.7 8.1 516.0 TOTAL INFILTRATION
VOLUME (INCHES) 1203.5 VOLUME (ACFT) 100.3
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PROPOSED SITE DESCRIPTION SOIL TYPE AREA COEF INF
VOL Forest C 3.0 15.6 46.8 Commercial C/D 55
.0 4.3 236.5 Urban Grasses C 21.0 14.2
298.2 Urban Grasses D 20.5 12.7
260.3 Meadow C 8.0 15.4 123.2 Meadow D 8.0 14.4
115.2 Forest D 4.0 14.6 58.4 TOTAL
INFILTRATION VOLUME (INCHES) 1138.6 VOLUME
(ACFT) 94.9   VOLUME DEFICIT 5.4
22 Rain Gardens 3 Water Quality Basins 1
Extended Detention
Annual Infiltration Volume Calculation
Infiltration Vol/1 Rain Vol X 90 of Annual Rain
Vol 1" Rain Volume 1"/12" X 117 AC 9.75 acft
(storms 1 and less 90 of annual
rainfall) 14,390 CF 0.33 acft 3.4 OF 1" Rain
Volume (minimum of rain held in basins) Annual
Rain Volume 38.5"/12" X 117 AC 375.4
acft 3.4 X 90 OF 375.4 acft 11.4 acft per
year potential infiltration volume Evapotranspirat
ion may reduce the volume by up to
50   Effective infiltration volume 5.7 acft
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Proposed Stormwater Management System

• Parking Island Rain Gardens-11
• Basin Rain Gardens - 11
• Water Quality Basins - 3
• Wetland Channel Systems 9
• Vegetated Basins - 2
• Extended Wetland Detention 1
• 20.5 Ac Greenspace for Stormwater
• 5.4 AcFt Water Quality Volume
• 48.4 AcFt Flood Storage
• Daylighting Farm Tiles 3000 LF
• Open Channel Systems 8000 LF

Proposed Sediment and Erosion Control System
Parking Island Rain Gardens 70-90 Basin Rain
Gardens 85-98 Water Quality Basins
50-70 Wetland Channels 10-20 Extended Wetland
Detention 80 Overall Trap Efficiency in Series
99.7