Assessing the Effectiveness of Floodplain Modifications for Flood Mitigation in Swatara Creek, Pennsylvania

open_access
Open Access
Author:
Pillay, Anushka
Area of Honors:
Environmental Systems Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Lauren Mc Phillips, Thesis Supervisor
Jeremy Michael Gernand, Thesis Honors Advisor
Keywords:
Environmental Engineering
Nature-Based Solutions
Flood Mitigation
Hydraulic Modeling
Abstract:
Communities across Pennsylvania are experiencing more frequent and intense flooding as extreme precipitation events continue to rise. In response, nature-based solutions (NBS), including floodplain terrain modification and vegetation-based land cover change, have gained attention as alternatives to traditional flood control strategies. However, few studies examine how these two floodplain modifications perform in combination. This study uses a 2D HEC-RAS hydraulic model to evaluate the effectiveness of combined floodplain terrain extraction and vegetation-based roughness modifications across seven sites along Swatara Creek, Pennsylvania. Three extraction depths (3, 5, and 10 ft) and three Manning's n values (0.027, 0.045, and 0.08) were tested under both low- and high-discharge conditions, producing 18 modified scenarios compared against 2 unmodified baseline. Results indicate that all modified scenarios reduced flood extent relative to the baseline, with percent reductions ranging from 6.01% to 15.77%. Overall, terrain extraction emerged as the strongest control on flood reduction, with larger extractions consistently yielding greater percent reductions. Manning’s n had a relatively modest influence, with lower roughness values generally contributing to slightly improved outcomes. These findings support combined floodplain modification as a viable nature-based mitigation strategy and provide a foundation for more targeted floodplain management along flood-prone watersheds in central Pennsylvania.