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

Sumith Yesudasan, Ph.D.

Keywords

Bioswales, Green Infrastructure, Runoff, Infiltration, Watershed, Stormwater

LCSH

Bioswales, Green infrastructure, Runoff, Stormwater infiltration, Watersheds, Stormwater management

Abstract

Bioswales are a major component of New Haven’s green infrastructure network, designed to intercept roadway runoff and promote infiltration. Their hydrologic performance, however, varies widely due to differences in watershed loading, surrounding land use, vegetation condition, and sediment accumulation at inlets. Understanding these sources of variability is essential for improving maintenance strategies and guiding future bioswale placement. This study evaluates the hydrologic behavior of 281 roadside bioswales using field-measured infiltration rates, GIS-based watershed delineation, parcel-level land-use classification, vegetation assessments, and inlet-outlet comparisons. Contributing drainage areas were delineated from a 2-ft LiDAR derived Digital Elevation Model, land-use context was assigned using the Connecticut CAMA parcel dataset, and infiltration was measured at bioswale inlet and outlet locations using a Turf-Tec double-ring infiltrometer. Across the network, infiltration at inlet zones was consistently lower than at outlets, with inlet rates typically around 3-4 cm/min compared with 5-6 cm/min at outlets. Average vegetation cover across sites was approximately 70%, and bioswales with denser vegetation infiltrated slightly faster. Watershed size showed substantial variability, ranging from 81 m² to over 2,400 m², and infiltration increased modestly with watershed area (ρ ≈ 0.12). Land-use differences were also evident: residential bioswales exhibited higher median initial infiltration (4.45 cm/min) compared with commercial (4.00 cm/min) and mixed-use (3.75 cm/min) areas. Overall, the results show that bioswale performance is jointly shaped by watershed loading, land-use context, vegetation structure, and inlet sedimentation. These findings provide guidance for improving bioswale siting, maintenance prioritization, and long-term stormwater planning in New Haven.

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