Date of Submission

12-2025

Document Type

Thesis

Degree Name

Master of Science in Environmental Engineering

Department

Civil and Environmental Engineering

Advisor

Nandan Shetty, Ph.D, P.E.

Committee Member

Cameron Oden, Ph.D.

Committee Member

Christian Conroy, Ph.D.

Keywords

Green Stormwater Infrastructure, Bioswale, Soil Moisture Dynamics, Infiltration

LCSH

Stormwater infiltration, Bioswales, Watersheds, Soil moisture conservation, Soil infiltration rate

Abstract

Effective stormwater management is essential for enhancing the resilience of urban environments facing challenges from climate change, aging infrastructure, and increasing impervious surfaces. As cities adopt green stormwater infrastructure such as bioswales to relieve these pressures, understanding the hydrologic behavior within these systems becomes essential. This study investigated soil moisture dynamics in New Haven, Connecticut by analyzing the seven critical points (A, B, C, D, E, F′, and F) that describe pre-storm, during storm and post storm drying behavior within bioswale systems. A total of 77 bioswale sites were monitored during May and June 2025, covering 14 storm events. Soil moisture was measured using HOBO MX2306 sensors and rainfall depth was recorded using a HOBO data-logging rain gauge. Spearman’s rank correlation analysis was used to examine bivariate relationships between soil moisture, watershed area, and rainfall depth across the seven hydrologic points. Results show a consistent positive association between soil moisture and watershed area throughout the hydrologic cycle, while relationships between soil moisture and rainfall depth varied across storm stages, with weaker associations observed at peak saturation. To evaluate the combined influence of watershed area and rainfall depth, linear regression models were applied to three soil-moisture indicators: peak moisture at point C, the infiltration indicator (C-D), and the evapotranspiration indicator (E-F). Regression results indicate that watershed area is a statistically significant predictor of peak soil moisture, while rainfall depth also contributes to peak saturation variability. However, the model explains a limited portion of overall variance reflecting substantial site to site variability. In contrast, infiltration and evapotranspiration indicators show non significant relationships with watershed area and rainfall depth, suggesting that post storm moisture loss processes are influenced more strongly by site-specific factors such as soil properties and local conditions. Overall, these findings demonstrate that while watershed size contributes to peak saturation behavior, bioswale hydrologic performance during infiltration and drying phases cannot be predicted using drainage area and rainfall depth alone, highlighting the importance of site specific controls in green stormwater infrastructure design and management.

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