Bigger Tides, Less Flooding: Effects of Dredging on Barotropic Dynamics in a Highly Modified Estuary

Ralston, David K.; Talke, Stefan A.; Geyer, W. Rockwell; Al-Zubaidi, Hussein A. M.; Sommerfield, Christopher K.

doi:10.1029/2018jc014313

Cited by 107 publications

(151 citation statements)

References 49 publications

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“…Lastly—on the topic of rivers—long‐term changes in discharge into the gulf could conceivably play a role, but the recent compilation of discharge data by Piecuch et al. () indicates a negligible trend in annual water level exported to the Gulf of Maine; it is possible that the seasonal cycle has shifted, as it has in other locations such as the Hudson River (Ralston et al., ).…”

Section: Discussionmentioning

confidence: 99%

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

Ray

Talke

2019

JGR Oceans

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Since the early twentieth century, the amplitudes of tidal constituents in the Gulf of Maine and Bay of Fundy display clear secular trends that are among the largest anywhere observed for a regional body of water. The M2 amplitude at Eastport, Maine, increased at a rate of 14.1 ± 1.2 cm per century until it temporarily dropped during 1980–1990, apparently in response to changes in the wider North Atlantic. Annual tidal analyses indicate M2 reached an all‐time high amplitude last year (2018). Here we report new estimates of tides derived from nineteenth century water‐level measurements found in the U.S. National Archives. Results from Eastport, Portland, and Pulpit Harbor (tied to Bar Harbor) do not follow the twentieth century trends and indicate that the Gulf of Maine tide changes commenced sometime in the late nineteenth or early twentieth centuries, coincident with a transition to modern rates of sea‐level rise as observed at Boston and Portland. General agreement is that sea level rise alone is insufficient to cause the twentieth‐century tide changes. A role for ocean stratification is suggested by the long‐term warming of Gulf of Maine waters; archival water temperatures at Boston, Portland, and Eastport show increases of ∼2 °C since the 1880s. In addition, a changing seasonal dependence in M2 amplitudes is reflected in a changing seasonal dependence in water temperatures. The observations suggest that models seeking to reproduce Gulf of Maine tides must consider both sea level rise and long‐term changes in stratification.

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Section: Discussionmentioning

confidence: 99%

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

Ray

Talke

2019

JGR Oceans

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“…A comparison of the salt flux mechanisms finds that while the steady salt flux is a slightly greater fraction of the total in the modern Hudson than in the shallower, shorter estuary before dredging, the tidal salt flux contributes less than half the total in both cases. Tidal amplitudes in the lower estuary have increased moderately with channel deepening (Ralston et al, ), and while this might be expected to increase the tidal salt flux, the increases in steady salt flux have been even greater. Increased tidal velocities would be expected to reduce the length of the salinity intrusion based on the steady salt flux scaling (equation ), but in the saline part of the Hudson (<120 km from the Battery), the increases in tidal amplitude have been relatively modest (10–40%) compared with those farther landward in the fresh tidal river (>100%; Ralston et al, ).…”

Section: Summary and Discussionmentioning

confidence: 99%

“…In that conceptual model sediment trapping is driven primarily by tidal asymmetry, but sediment trapping by the residual circulation could also be enhanced by deepening (Burchard et al, ). Tidal amplitude has more than doubled due to dredging in the tidal freshwater region of the upper ~60 km of the Hudson, but the increases in tidal amplitude in the harbor and lower estuary have been smaller (Ralston et al, ), so the corresponding effects on sediment transport are expected to be small. The increase in salinity intrusion is likely to increase the landward extent of sediment trapping, change the location of estuarine turbidity maxima, and increase the time scales for transport through the estuary (Ralston & Geyer, ).…”

Section: Summary and Discussionmentioning

confidence: 99%

“…The modern bathymetry was based on data from New York State Department of Environmental Conservation, the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Army Corps of Engineers (Ralston et al, ) and was projected onto the same regular grid. Bathymetric survey data were referenced to a tidal datum (mean lower lowwater (MLLW)) and converted to mean sea level (MSL) based on modern survey data (using NOAA's VDatum software) or tidal amplitudes from historical water level records and charts (Ralston et al, ). From the 1860s to 2015 MSL at the Battery increased by about 0.44 m (Talke et al, ), and the effect of this on estuary depth is incorporated in the bathymetry observations in addition to the more local changes.…”

Section: Methods and Data Sourcesmentioning

confidence: 99%

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Response to Channel Deepening of the Salinity Intrusion, Estuarine Circulation, and Stratification in an Urbanized Estuary

Ralston

Geyer

2019

JGR Oceans

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Modifications for navigation since the late 1800s have increased channel depth (H) in the lower Hudson River estuary by 10–30%, and at the mouth the depth has more than doubled. Observations along the lower estuary show that both salinity and stratification have increased over the past century. Model results comparing predredging bathymetry from the 1860s with modern conditions indicate an increase in the salinity intrusion of about 30%, which is roughly consistent with the H5/3 scaling expected from theory for salt flux dominated by steady exchange. While modifications including a recent deepening project have been concentrated near the mouth, the changes increase salinity and threaten drinking water supplies more than 100 km landward. The deepening has not changed the responses to river discharge (Qr) of the salinity intrusion (~Qr−1/3) or mean stratification (Qr2/3). Surprisingly, the increase in salinity intrusion with channel deepening results in almost no change in the estuarine circulation. This contrasts sharply with local scaling based on local dynamics of an H2 dependence, but it is consistent with a steady state salt balance that allows scaling of the estuarine circulation based on external forcing factors and is independent of depth. In contrast, the observed and modeled increases in stratification are opposite of expectations from the steady state balance, which could be due to reduction in mixing with loss of shallow subtidal regions. Overall, the mean shift in estuarine parameter space due to channel deepening has been modest compared with the monthly‐to‐seasonal variability due to tides and river discharge.

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“…Worldwide, the most dramatic recent changes in tidal properties have occurred in estuaries and tidal rivers (Talke & Jay, ; Winterwerp, ). For example, tidal ranges have more than doubled since the late nineteenth century in the upper reaches of the Hudson and Ems Rivers (Ralston et al, ; Schureman, ; Talke & Jay, ; Winterwerp, ) and the Cape Fear River at Wilmington (Familkhalili & Talke, ). Tidal ranges have similarly doubled for high flows (above 10,000 m 3 /s) in the tidal river part of the Columbia River estuary (Jay et al, ).…”

Section: Potential Mechanisms Causing Changesmentioning

confidence: 99%

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

Haigh

Pickering

Green

et al. 2020

Reviews of Geophysics

175

173

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Scientists and engineers have observed for some time that tidal amplitudes at many locations are shifting considerably due to nonastronomical factors. Here we review comprehensively these important changes in tidal properties, many of which remain poorly understood. Over long geological time scales, tectonic processes drive variations in basin size, depth, and shape and hence the resonant properties of ocean basins. On shorter geological time scales, changes in oceanic tidal properties are dominated by variations in water depth. A growing number of studies have identified widespread, sometimes regionally coherent, positive, and negative trends in tidal constituents and levels during the 19th, 20th, and early 21st centuries. Determining the causes is challenging because a tide measured at a coastal gauge integrates the effects of local, regional, and oceanic changes. Here, we highlight six main factors that can cause changes in measured tidal statistics on local scales and a further eight possible regional/global driving mechanisms. Since only a few studies have combined observations and models, or modeled at a temporal/spatial resolution capable of resolving both ultralocal and large‐scale global changes, the individual contributions from local and regional mechanisms remain uncertain. Nonetheless, modeling studies project that sea level rise and climate change will continue to alter tides over the next several centuries, with regionally coherent modes of change caused by alterations to coastal morphology and ice sheet extent. Hence, a better understanding of the causes and consequences of tidal variations is needed to help assess the implications for coastal defense, risk assessment, and ecological change.

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Bigger Tides, Less Flooding: Effects of Dredging on Barotropic Dynamics in a Highly Modified Estuary

Cited by 107 publications

References 49 publications

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

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

Response to Channel Deepening of the Salinity Intrusion, Estuarine Circulation, and Stratification in an Urbanized Estuary

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

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