TRACING THE FATE OF SEDIMENTS IN GSI

Dr. Virginia Smith and Dr. Kristin Sample-Lord
Villanova University

ABSTRACT:

Green stormwater infrastructure (GSI) mitigates stormwater runoff through natural processes. In bioinfiltration GSI, stormwater is infiltrated through the soil and evapotranspirated through vegetation. For bioinfiltration systems to remain effective over time the soil must continue to adequately infiltrate, filtrate, and store water to meet requirements for runoff volume reduction and water quality improvement. Major challenges surrounding service life and resilience of bioinfiltration GSI include erosion and channelization due to high bed shear stresses developed during large storm events, and sedimentation causing clogging and reduced infiltration. Understanding the geomorphology, shear stress, and sediment flux in GSI can help inform design and predict maintenance needs associated with erosion and deposition. To investigate the fate of sediments in GSI and address longevity concerns for bioinfiltration soils, sites draining portions of I-95 constructed as part of PennDOT’s I-95 Revive Project have been continuously studied since 2017. Temporal and spatial soil dynamics are being studied through comprehensive field testing, laboratory analysis, and modeling. Sediment collection, soil core sampling, and field infiltration tests were performed at multiple locations at each site at regular intervals over the last four years. Results of laboratory testing showed sediment deposition to date has had negligible impact on the texture of the underlying soil column. Accordingly, infiltration rates have remained relatively constant at the sites and there is no evidence of clogging in most of the soil. However, additional soil samples collected from the surface at visually-identified depositional areas indicated a higher percentage of fines in the upper 4 cm than the rest of the underlying soil media. These results suggest that the bioinfiltration soil is effectively acting as a graded filter, resulting in development of a finer soil layer near the surface over time and restricting migration of particles deeper into the soil column. Thus, hydraulic properties of the original soil media have been maintained, and the need for future sediment removal and maintenance would likely be limited to the upper surface of the GSI. To better understand the fate of the sediments and predict such future maintenance needs, a geomorphic sediment transport model, FaSTMECH, was combined with the Green-Ampt infiltration model to model GSI morphodynamics through time. A comparison of observed and predicted ponding depths shows good agreement and demonstrates the ability of this novel model framework in predicting the hydraulics and morphology within a GSI. The data and framework from this ongoing study opens the door for planning and evaluating design alternatives to minimize impacts due to excessive erosion or deposition within a GSI and maximizing longevity of bioinfiltration systems.

SPEAKER BIOS: 

Dr. Smith is an Assistant Professor of Water Resources in the Civil and Environmental Engineering Department.  She received her PhD studying hydrology, fluvial geomorphology, and sediment transport at the Jackson School of Geosciences at the University of Texas at Austin (UT). Prior to earning her PhD Dr. Smith received a master’s degree in civil engineering from UT and her BS from Georgia Institute of Technology in civil and environmental engineering. After finishing her graduate work Dr. Smith worked in international development in Asia, the South Pacific, and Afghanistan, overseeing water and natural resource management projects.  Since starting at Villanova University Dr. Smith has leveraged her experiences in her research focusing on rivers, floodplains, and flooding dynamics, particularly in urban settings. She also has several funded research projects investigating sediment transport into and through green stormwater infrastructure. She is the winner the of the Early Career Award from the University Council on Water Resources (2020) and the Villanova College of Engineering Excellence in Teaching Award (2021).

Dr. Sample-Lord is an Assistant Professor of geotechnical and geoenvironmental engineering in the Civil and Environmental Engineering Department at Villanova University. She received her PhD and MS from Colorado State University. Her research focuses on geotechnical aspects of green infrastructure and clay-based hydraulic barriers for geoenvironmental containment. She currently holds multiple national leadership positions within the professional geotechnical community, including Vice President of the International Geosynthetics Society of North America, Board Member of the United States Universities Council on Geotechnical Education and Research, and leadership positions within the ASCE Geoenvironmental Engineering Technical Committee. She also received the Excellence in Teaching Award from the College of Engineering for her teaching in soil mechanics, engineering geology, and other geotechnical courses at Villanova.

Engineers:

This seminar does qualify for 1.0 Professional Development Hour (PDH). A Certificate of Attendance will be available for AWRA-PMAS members only. The meeting price for non-members who wish to receive a Certificate of Attendance for the PDH is $10.00 ($3.00 for meeting + $7.00 for certificate).  

Please note: Presentation is to be given through Zoom at the link below. PDH's will be issued through PDFs. Please allow extra time to register through Zoom and get software set up. Presentation will start at noon. Early participants will be in a Waiting Room until noon. Participants must email AWRA.PMAS@gmail.com to request PDH Certificate after the event.

Presentation at:  https://us02web.zoom.us/j/89898533531

Thank you!