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Monitoring and modeling of the hydrologic performance of the Carroll Street Right-of-Way Bioswale
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Monitoring and modeling of the hydrologic performance of the Carroll Street Right-of-Way Bioswale

Wei Chen
Master of Science (M.S.), Drexel University
Aug 2014
DOI:
https://doi.org/10.17918/etd-6060
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Chen_Wei_20141.72 MBDownloadView
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Abstract

Combined sewer overflows Urban runoff--Management--New York (State)--New York Environmental Engineering
Like many old cities in the United States, New York City (NYC) suffers from combined sewer overflows (CSOs) where untreated stormwater and wastewater overflow from sewers during wet-weather rain-events. To manage this environmental issue, New York City is underway with efforts to implement Green Infrastructure (GI) throughout the city which seeks to capture stormwater in green space while reducing the load on sewer systems. The main focus of this project is the application of computer simulated hydraulic models SWWM5 and Visual MODFLOW to evaluate the performance of an actual NYC Department of Environmental Protection Right of Way Bioswale (DEP ROWB). The bioswale performance metrics evaluated are volume reduction (SWMM) and influence on groundwater i.e. groundwater mounding (Visual MODFLOW). The actual ROW bioswale evaluated in this study is installed on Denton place & Carroll Street in Brooklyn, New York. The site is instrumented with monitoring equipment for continuous time-series measurement of piezometric head. Monitoring data used in the analyses occurred over a roughly one year observation period between 2013 and 2014. Field measured data was used to calculate infiltration rates using Darcy's Law and to calibrate the SWMM model. Results from the calibrated SWMM model were used as inputs to the Visual MODFLOW model to simulate the groundwater mounds beneath ROW bioswale. Models were run on an event basis (using one inch design storms) and continually over one year period (using the 1988 precipitation record). The SWMM Model results reveal that, as currently configured, the ROW bioswale at Carroll Street can capture approximately 6% to 7% of the stormwater runoff generated from its catchment area during a 1 inch (25.4 mm) rain event. This bioswale could capture a higher percentage of the runoff generated by this particular storm, if it had smaller tributary drainage area. The Visual MODFLOW output demonstrates that, during a typical rainfall year, the maximum height of simulated groundwater mounding occurs under the center of the bioswale, and that the average height of all mounds generated during a representative year of rainfall is 0.46 m. In this particular setting, it appears unlikely that this magnitude of mounding could flood basements or negatively impact nearby underground utilities.

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