Changing Tides: The Role of Natural and Anthropogenic Factors

Abstract

Tides are changing worldwide at rates not explained by astronomical forcing. Rather, the observed evolution of tides and other long waves, such as storm surges, is influenced by shelf processes and changes to the roughness, depth, width, and length of embayments, estuaries, and tidal rivers. In this review, we focus on processes in estuaries and tidal rivers, because that is where the largest changes to tidal properties are occurring. Recent literature shows that changes in tidal amplitude have been ubiquitous worldwide over the past century, often in response to wetland reclamation, channel dredging, and other environmental changes. While tidal amplitude changes are sometimes slight (<1%) or even negative, we identify two types of systems that are particularly prone to tidal amplification: ( a) shallow, strongly damped systems, in which a small increase in depth produces a large decrease in effective friction, and ( b) systems in which wave reflection and resonance are strongly influenced by changes to depth, friction, and convergence. The largest changes in amplitude occur inland, some distance from the coast, and can sometimes be measured in meters. Tide changes are a leading indicator that the dynamics of storm surges and river flood waves have also changed and are often associated with shifts in sediment transport, salinity intrusion, and ecosystem properties. Therefore, the dynamics of tidal evolution have major implications for coastal management, particularly for systems that are sensitive to changes in geometry induced by sea-level rise and anthropogenic development.

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

“…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, ).…”

“…Strong convergence of width (or depth) modifies the H dependence, and frictional effects dominate if the channel is rough enough (Jay, ). More details are found in the review of Talke and Jay ().…”

“…For a system with a channel and flats, both the width of the channel and flat influence the tidal amplitude, such that amplitudes scale as b (Jay, 1991). More details are found in the review of Talke and Jay (2020).…”

“…Leaving aside these dynamical complexities, changes to either length or depth of an estuary can alter tidal amplification. As discussed in Talke and Jay (2020), the largest changes occur in systems that were highly damped historically but have been significantly deepened. For example, construction of a weir in 1900 altered the length of the Ems estuary and produced an amplification in upriver tides (Chernetsky et al, 2010;Keller, 1901;.…”

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

“…There have been decreases in the length of tributary estuaries; for example, three were shortened by up to 30 km in the 1960-1970 era by road and causeway construction, with subsequent formation of large mudflats on the seaward side (Daborn & Dadswell, 1988). As is typical for a system near resonance (Talke & Jay, 2020), the Gulf of Maine may be quite sensitive to changes in length and energy dissipation over shallow water (see also Holleman & Stacey, 2014). Environmental (and ecological) changes caused by trawling (Kenchington et al, 2007) may have exerted a not-yet-explored, system-scale impact on seabed roughness and frictional dissipation.…”