Managing stable waterways at bridges

Peggy Johnson
The Pennsylvania State University

Abstract

Bridges over streams and rivers are susceptible to erosional processes during a wide range of flows. Local and contraction scour erodes sediment from bridge piers and abutments, potentially affecting the safety of the bridge. There has been considerable focus on assessing scour, designing countermeasures to protect bridges against scour, and designing foundations to resist scour. Stream channel instability, on the other hand, includes bank failure, lateral migration, and bed degradation, has the potential to impact safety at bridges as much or more than local and contraction scour. However, predicting and preventing channel instability at bridges has is a more difficult task.

The complexities and unique characteristics of bridge-waterway crossings have eluded computational modeling thus far. In addition, maintaining a safe and stable waterway opening under the conditions of an unstable stream channel has also proven to be difficult due to spatial limitations, lack of experience, and other constraints. Although national guidelines exist, each state tends to take different approaches to this problem. Thus, the feasibility of and confidence in each of the various possible solutions is not well known.

Selection of possible designs and countermeasures is a function of multiple factors, including effectiveness, cost, maintenance, constraints, and the ability to detect failure. Some countermeasures have been systematically tested, while others may have been laboratory tested, but not field tested. Others cannot be used effectively within existing right-of-ways. There is a wide range of costs associated with the initial design and construction of the stabilization measures, in addition to maintenance costs. The ability to detect failure or impending failure of a stream stabilization project or its components is important to assuring that the bridge will be protected during high flow events. In addition, movement of sediment through the bridge opening is important to avoid deposition that limits flow or changes the direction of flow.

Bio

Peggy Johnson is currently the Dean of the Schreyer Honors College and a Professor of Civil Engineering at Penn State University, where she had been a faculty member since 1996. As the Dean of the Schreyer Honors College, she oversees Honors Scholars, representing the top 2% of Penn State students across all disciplines. From 2006 to 2015, she was the Head of the Civil and Environmental Engineering Department at Penn State. She has served on the CEE faculty at Penn State since 1996.

Prior to coming to Penn State, she served on the faculty of the Civil and Environmental Engineering Department at the University of Maryland. Over her nearly three decades as a Professor in Civil Engineering, she has conducted research and taught classes in the areas of hydraulic engineering, bridge scour, stream restoration, reliability analyses, and river mechanics. Now, as the Dean, she teaches courses on leadership.

She has published numerous papers in peer-reviewed journals on bridge scour, stream restoration, uncertainty in hydraulics, bridge scour, and stream restoration, and the probability of bridge failure due to scour. She has conducted work on the stability and vulnerability of stream channel designs at bridges. Her method for assessing stream stability at bridge-stream intersections is incorporated as part of the Federal Highway Administration’s manual on stream stability at bridges (HEC-20).

Johnson has supervised the dissertations and theses of dozens of PhD, MS, and BS students. She is the Past-President and a Fellow of the ASCE Environmental and Water Resources Institute (EWRI), the largest institute within ASCE with more than 23,000 members. She received the ASCE Hans Albert Einstein award in 2016 for her contributions in the use of sediment transport for the evaluation and design of in-line control structures and stream restoration projects and the use of uncertainty and risk management for scour analyses. She also received the ASCE-EWRI Outstanding Woman of the Year award in 2012. In addition to winning several teaching awards, Johnson won the National Science Foundation Young Investigator award and in 1995, she won the NSF Presidential Faculty Fellow award.

She received a Master’s Degree in 1988 and a PhD in 1990, both from the Civil and Environmental Engineering department at the University of Maryland.