Using records of water levels, tides and high-water marks that had been untouched for over 100 years, a researcher at Portland State University and his colleagues found that sea levels in Boston Harbor rose by nearly a foot over the past 200 years, with the greatest increase occurring since 1920.
The researchers noted that Boston’s biggest floods occurred when high tides combined with a major storm event. In reviewing the 200-year record of floods and tide cycles, they concluded that the flooding in January and March of this year occurred partially because of the 18-year cycle of tides.
In an article named "Relative Sea Level, Tides, and Extreme Water Levels in Boston Harbor From 1825 to 2018," PSU engineering professor Stefan Talke and his collaborators from the University of Massachusetts Amherst and Tufts University, evaluated sea level rise and storm events in Boston since 1825. Published in the Journal of Geophysical Research – Oceans, the study revealed that changes in flood risk since the 1800s are driven in part by tidal trends but primarily by sea-level rise.
“Determining long-term trends in sea-level, tides and high water marks gives us the potential to make better decisions about infrastructure investment,” said Talke. “Understanding the past helps us prepare much better for the future.”
Talke, whose research focuses on the flow of water, worked with his collaborators to report on the recovery, data reconstruction, digitization, quality assurance and analysis of 50 years of pre-1920 tide records from Boston Harbor found in documentary archives at Harvard University, MIT and other sources.
The authors used daily water-level data from the inner part of Boston Harbor plus archival notes, correspondence and other reports for their study.
“When combined with available National Oceanic and Atmospheric Administration measurements since 1921, these records span the period of 1825-2018 to form the longest known water-level record outside of northwest Europe,” said Talke.
The findings also note that in Boston, sea level rise is a combination of climate change and land still sinking that is linked to the last ice age in the area.
Co-author Jonathan Woodruff of UMass Amherst said, “In the 2020s, nature is working with us,” referring to the 18.6 year nodal cycle in tides. “But in the 2030s it will be working against us. We are coming up to a decade where flooding is slightly less likely. That means we have a window of opportunity to be prepared for the 2030s when flooding associated with tides becomes more likely.”
Talke’s other collaborator was Andrew Kemp from Tufts. Their study was funded by U.S. Army Corps of Engineers, the National Science Foundation, and Massachusetts Sea Grant.