Relative Sea Level, Tides, and Extreme Water Levels in Boston Harbor From 1825 to 2018

Abstract

Using newly‐discovered archival measurements, we construct an instrumental record of water levels and storm tides in Boston (MA) since 1825. After ascertaining the 19th century datum and correcting for a 0–0.03 m bias in the modern tide‐gauge record, we show that local, decadally‐averaged relative sea level (RSL) rose by 0.28 ± 0.05 m since 1826, with an acceleration of 0.023 ± 0.009 mm/yr2. Tide range decreased by 5.5% between 1830 and 1910, due in large part to dredging and filling of Boston Harbor, and trended slightly upward thereafter. An evaluation of storm events since 1825 suggests that trends in flood risk are driven by RSL rise, with a small contribution by tidal trends. Sea‐level rise also interacts with the 18.6 year nodal cycle in tide amplitudes to produce decadal fluctuations in hazard. Conditional sampling of the 1825–2018 record shows that storm tides with a 0.01–0.5 annual probability (100 and 2 year events) are 0.1–0.2 m larger during periods with above‐average tidal amplitudes. Similarly, the once‐in‐25 year event during elevated tidal forcing becomes a once‐in‐100 year event during periods of reduced tides. A plurality of historic flood events—including floods in 1851, 1978, and 2018—occurred near the peak of the tidal nodal cycle. Projections to the year 2100 suggest that decadal fluctuations in tide characteristics will interact with relative sea‐level rise to produce a fluctuating hazard over time, with periods of relative stationarity (e.g., the 2020s) bracketed by relatively abrupt increases in flood hazard (the early 2030s).

Nineteenth‐Century Tides in the Gulf of Maine and Implications for Secular Trends

“…Our three results at Eastport, Portland, and Pulpit/Bar Harbor consistently show that significant twentieth‐century trends in M 2 amplitudes do not extend back into the nineteenth century. The long time series collected at Boston since 1825 (Talke et al., ) is consistent with the three time series examined here, in the sense that Boston's MTR began increasing sometime in the early twentieth century, with a rate of about 2 cm per century according to Table . Before 1920, however, the Boston series (collected not at the present‐day site but at the Charlestown Navy Yard on the other side of Boston proper, a few kilometers away) gives an opposite trend: a remarkably large secular decrease in tidal range of about 20 cm per century (Figure 4 of Talke et al., ).…”

“…The long time series collected at Boston since 1825 (Talke et al., ) is consistent with the three time series examined here, in the sense that Boston's MTR began increasing sometime in the early twentieth century, with a rate of about 2 cm per century according to Table . Before 1920, however, the Boston series (collected not at the present‐day site but at the Charlestown Navy Yard on the other side of Boston proper, a few kilometers away) gives an opposite trend: a remarkably large secular decrease in tidal range of about 20 cm per century (Figure 4 of Talke et al., ). In keeping with suggestions noted long ago by Freeman (, Appendix 20), we suspect that such large changes in tide are related to large‐scale landfill (e.g., the extensive reclamation around Bass River and South Boston) and harbor changes that occurred at and around the Navy Yard (Seasholes, ).…”

The Tides They Are A‐Changin': A Comprehensive Review of Past and Future Nonastronomical Changes in Tides, Their Driving Mechanisms, and Future Implications

“…Changes in the tides over the last ~220 years have generally been studied using long tide gauge records. Only a small number of records are available with start dates during the first half of the nineteenth century; Brest (Pouvreau et al, ), Marseille (Wöppelmann et al, ), New York (Talke et al, ), and Boston (Talke et al, ) are notable examples from Europe and North America, respectively. Automatic tide gauges became more reliable and common during the second half of the nineteenth century (e.g., Talke & Jay, ), and such gauges were increasingly installed in many ports during the late nineteenth and early twentieth centuries.…”

“…In New York Harbor, measurements suggest that tide amplitudes decreased slightly from the 1840s to the early 1900s and increased thereafter by 5–10%, depending on location (Chant et al, ; Talke et al, ). In Boston, Talke et al () discussed, in the contexts of both local engineering changes and wider regional tidal changes, a large (~5.5%) decrease in MTR during the nineteenth century, after which it was relatively stable and even increased slightly after 1930 (see also Ray & Foster, ). The latter rate (19 mm per century) is somewhat less than half the rate of change in M 2 range (54 mm per century) reported for Boston by Ray () over the period 1935–2005, suggesting other tidal changes (such as altered M 4 and M 6 , as shown in Talke et al, ) are at work.…”

“…Only over the past 20 years (since the digitization, concatenation, and public dissemination of regional and global databases of tide gauge records; Woodworth et al, ) has it been determined that significant and widespread positive and negative trends in tidal levels (and tidal currents) are occurring at many locations around the world (e.g., Devlin et al, ; Feng et al, ; Flick et al, ; Jay, ; Müller et al, ; Ray, ; Talke et al, ; Talke & Jay, ; Woodworth, ). Remarkably, the rates of tidal level changes observed are of similar magnitudes to the rate of mean sea level (MSL) rise at some sites; for example, Mawdsley et al () found increases in tidal range at Astoria (USA), Wilmington (USA), Delfzijl (the Netherlands), Cuxhaven (Germany), and Calais (France) of >25 cm over the last century.…”