Date of Award
Master of Science (MS)
Civil and Environmental Engineering
David G. Chandler
Green Infrastructure, Hydrologic performance
Combined sewer systems and urbanization are significant concerns confronted by many aging cities, including the City of Syracuse, New York. This study addresses the role of impervious surfaces in the direct discharge of surface runoff, domestic and industrial wastewaters into Onondaga Lake and tributaries during wet weather events. Onondaga County addressed the combined surface overflow (CSO) problem in 2009 through a stormwater management program known as "Save the Rain” (STR)." This strategy involved adopting a combination of constructed (gray) and plant-soil-atmosphere based (green) infrastructure (GI) practices to address the CSO issue. GI practices are a proven viable option for stormwater management, however clear empirical evidence of in-field hydrologic performance at meaningful spatial and temporal scales is uncommon. Despite many successes, widespread adoption of these systems remains slow. This may reflect the limited availability of long-term empirical data to corroborate the claims of hydrologic benefits, and substantial variability in the performance data. There remains considerable discussion in the research literature regarding standard methods and metrics for quantifying the GI performance.
This study aims to clarify the performance characteristics of GI retrofit structures installed in Onondaga County NY over the period 2014-2015. The goal is to understand the hydrologic performance of three different types of green infrastructure retrofits through in-situ measurements of fluxes and any changes in structure performance over the period 2014-2019. The stormwater capture structures include rain gardens, infiltration trenches, and permeable pavements. The catch basins of 13 monitoring sites were instrumented with in-situ water-level sensors. Local precipitation data and areal extent of the contributing area for each GI contributing area were collected to estimate inflow and outflow volumes for each structure. Changes in catch basin stage relative to overflow drain to storm sewers were used to determine the infiltration rates and the percent runoff capture within the soil and gravel layers of these systems. The analysis also compares the percent runoff reduction and percent runoff capture.
The findings from these analyses indicated that site performance decreased in the order of permeable pavements, rain gardens and infiltration trenches. The regression analysis of infiltration rates and precipitation depth showed a positive increasing trend for all the sites. The infiltration rates provided by porous pavements ranged from 20 to 80 cm/hr, the infiltration rate provided by rain gardens ranged from 0.5 to 120 cm/hr, and the infiltration rate provided by infiltration trenches ranged from 0.05 to 25 cm/hr. The percent runoff capture varied from 40 to100% for rain gardens, 20 to 30% for infiltration trenches, and 80 to 100% for porous pavements. The percent runoff reduction ranged from 64 to 100% for Barker Park rain garden, 50 to 80% for the rain garden at the city parking lot 4, and 100% for all other rain gardens. The percent runoff reduction ranged from 90 to 100% at the Zoo parking lot, 80 to 100% at the Lewis basketball court, and 22 to 100% at Hughes Magnet School parking lot. The outflow from Barker Park rain garden showed a strong dependence on precipitation depth but the City Parking lot 4 rain garden showed a weaker relationship with precipitation depth. The percent runoff reduction at Barker Park showed a strong decreasing trend with precipitation depth whereas a weak trend was observed for City Parking Lot 4 rain garden.
The findings from the field evaluation of the green infrastructure controls helped identify the factors that were the cause for the variability of the hydrologic performance across and within structure types.
Rajashekar, Priyanka, "Retrospective Analysis of Hydrologic Performance of Green Infrastructure Systems of the Save The Rain (STR) Program in Syracuse, New York" (2020). Theses - ALL. 458.