1

Green Infrastructure in New York CityStormwater Source Control Performance

John McLaughlin, NYCDEPJulie Stein, NYCDEPSandeep Mehrotra, PE, Hazen and SawyerWilliam Leo, PE, HDR-HydroQualMatthew Jones, PE, PhD, Hazen and Sawyer

September 14, 2012

2

Acknowledgements

NYC DEP

Horsley-Witten

GeoSyntec

Brooklyn College

3

NYC Green Infrastructure Plan

Build cost‐effective grey infrastructure

Optimize the existing wastewater system

Institutionalize adaptive management, model impacts, measure CSOs, and monitor water quality

Sustain stakeholder engagement55

Control runoff from 10% of impervious surfaces through green infrastructure and other source controls

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4

Stormwater Pilot StudyObjectives

Develop stormwater pilot designs

Construct and maintain pilots within NYC

Evaluate pilot performance

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Stormwater Pilot Highlights

B Public Housing PilotsC Storage Building Blue RoofM Roadway Median BioretentionP Permeable Pavement

6H&

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2011 Precipitation Patterns

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0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Storm Rainfall D

epth (in)

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0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

5‐min Peak Ra

infall Intesity 

(in/hr)

Percentile

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Bioretention

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Bioretention:Example 0.4” Storm

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1.00.00.20.40.60.81.01.21.4

8/21/11 12:00 8/21/11 16:48 8/21/11 21:36 8/22/11 2:24

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Surf

ace

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age

(in)

Flow

(gpm

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Inflow Rate Outflow Rate Surface Storage

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Bioretention:Example 4.8” Storm

10H&

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Bioretention 1-4: Vol. Retained

Bio 1 - 7:1 Bio 2 - 6:1

Bio 3 - 9:1 Bio 4 - 17:1

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Bioretention:Preliminary Observations

Bioretention areas retaining much of the water they receive– Most outflow associated with storms >1”

Curb cuts are not 100% effective at runoff captureLeaf and litter pickup part of routine maintenanceCommunity frequently comments on BMPs and are interested in project

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Subsurface Detention & Infiltration

North Parking Lot

South Parking Lot

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Stormwater Chambers:Example 4.8” Storm

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0034

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Stormwater Chambers:Inflow and Outflow

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Stormwater Chambers:Volume Retained

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Stormwater Chambers:Preliminary Observations

Subsurface systems effective at capturing runoff (no bypass)

Chamber system not generating consistent outflow

Outflow rates have been below design target (0.25 cfs)

No substantial maintenance needs

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Roadway Median Bioretention

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Median Bioretention:Example 1.1” Storm

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Median Bioretention: Vol. Retained

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N&S Conduit Bioretention:Preliminary Observations

Most storms have been fully retainedApparent infiltration losses along conveyance swales

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Permeable Pavement

22Porous Asphalt Standard Asphalt FilterPave

Permeable Pavement

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Permeable Pavement

0%20%40%60%80%

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me

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aine

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Rainfall Depth (in)

Standard Asphalt

Porous Asphalt Filterpave

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Permeable Pavement:Preliminary Observations

No measured flow from filterpave and porous asphalt underdrainsOn-site tests suggest porous asphalt may be generating surface runoff

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Multiple Blue Roof Systems

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Blue Roofs:Example 1.9” Storm

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Uncontrolled

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Control Trays

Blue Roofs:Example 1.9” Storm

Uncontrolled Modified Inlet

Check Dams Trays

28H&

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ile: 9

0034

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Blue Roof: Peak Flow Reduction

Uncontrolled

Check Dams Trays

Modified Inlet

29H&

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ile: 9

0034

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Uncontrolled

Check Dams Trays

Modified Inlet

Blue Roof: Volume Retained

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Blue Roof:Preliminary Observations

All roof types (including uncontrolled) providing some level or retention and detention

Trays and check dams appear to be providing more detention than uncontrolled and modified inlet

Modified inlet performance possibly inhibited by lack of available rooftop storage due to 2% roof slope

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Monitoring Study Summary

Preliminary observations indicate pilots are providing benefits range of benefits

Findings will be validated and expanded upon through further data collection and analysis

Further data analysis and metrics will providing greater insight into CSO planning

Information on maintenance needs and qualitative performance informing future implementation efforts

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Questions?

www.nyc.gov/html/dep/html/stormwater/index.shtml

Matthew Jones, EI, PhDHazen and Sawyer, PCmjones@hazenandsawyer.com