Groundwater Flow Modeling of ROW Bioswales Adjacent to Residential Buildings 2016 AWRA Summer Specialty Conference: GIS and Water Resources IX Zachary Benedetto Arup
Outline Background on NYC Green Infrastructure Program Issues during construction Groundwater Modeling for Risk Analysis Next Steps 2
Outline Background on NYC Green Infrastructure Program Issues during construction Groundwater Modeling for Risk Analysis Next Steps 3
CSOs
30 billion gallons combined sewer overflow from 490 outfalls in NY Harbor each year Background
NYC Waterways
NYC DEP Green Infrastructure 7 NYC DEP Green Infrastructure
8 ROW Bioswale
9 ROW Bioswale
Arup NYC Green Infrastructure Projects
Tributary Drainage Area Analysis high points low points slopes catch basins Sidewalk width type Site Selection pictures offsets LIRR NYCT Rail Coordination Amtrak CSX Geotechnical Investigation borings permeability tests bedrock groundwater Survey utilities properties offsets grades sizes efficiency Design Documents trees coordinates obstructions plantings Construction submittals RFIs 12 Project Phases
Outline Background on NYC Green Infrastructure Program Issues during construction Groundwater Modeling for Risk Analysis Next Steps 13
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Outline Background on NYC Green Infrastructure Program Issues during construction Groundwater Modeling for Risk Analysis Next Steps 16
Sites with Issues during Construction - 0061f - Adjacent buildings have a history of basement water leakage. - Structural defects likely contributed to water issue - 0097b - Seepage into basement occurred after the location was excavated. - 0433e - pit was excavated, and was in the process of being filled with the bioswale material, when the flooding occurred - Infiltration causing groundwater levels to rise to basement floor vs. lateral flow in unsaturated zone from bioswale to basement wall during large storm events 17
Site Selection Geotechnical Investigation Site Survey Design & Construction Seepage Rejection 18 Current Workflow
Site Selection Geotechnical Investigation Site Survey Groundwater Modeling Design & Construction Seepage Rejection 19 Ideal Workflow
22 Data Collection
Available Data from Bioswale Soil Boring Logs Permeability Tests Soil Samples w/ Lab Results Bioswale Design Infiltration Rates Bioswale and proposed site dimensions 23
Available Data from Overall Site Rainfall Rates Soils Types Groundwater Levels Overall History of Issues Historic Boring Tests 24
Groundwater Modeling Software GeoStudio 2012 Suite - Geo-Slope International - SEEP/W - 2D finite element model that allows for both unsaturated zone flow and transient flow simulations - analyzes groundwater flow within porous materials. Its formulation enables analyses ranging from simple saturated steady-state problems to sophisticated saturated/unsaturated timedependent problems. 25
SEEP / W First Steps - Build and run test model with base case cross section and data assumptions - Expand to case study bioswales and their unique data - Validate - Run tests for proposed bioswales 26
27 Model Domain
28 4 hour storm duration in bioswale (modeled as constant head)
29 Pore water pressure profile t = 4 hrs (end of storm event) Fully saturated soil conditions beneath bioswale
30 Pore water pressure profile t = 10 hrs (post storm) Saturated conditions progressively moving vertically through soil (declining in size)
31 Pore water pressure profile t = 3 days Partially saturated conditions as water progressively fills voids
32 Pore water pressure profile t = 20 days
Outline Background on NYC Green Infrastructure Program Issues during construction Groundwater Modeling for Risk Analysis Next Steps 33
Next Steps Refine models with site data and determine if they align with what happened on site during construction Propose this risk analysis modeling to NYC DEP Conduct the modeling on proposed sites that are nearby to adjacent underground structures Pre-emptively reject seepage prone sites before incidents occur 34
Thank you! Questions? Contact Info - Zachary Benedetto - Civil Engineer - Zachary.Benedetto@arup.com - Vincent Lee - Project Manager - Vincent.Lee@arup.com 35