Tides and Coastal Geomorphology: The Role of Non-Stationary Processes
Résumé
Tidal motions play a major role in emplacement of sedimentary deposits in a variety of realms, from tidal rivers to the deep ocean. Here we focus on non-stationary tides in coastal environments; i.e., tidal rivers, estuaries, deltas, bays, beaches, and continental shelves and slopes. Although certain deposits are likely the result of periodic tidal motions, many of the sediment packages preserved in modern and ancient tidal settings are not solely constructed of these deposits. Thus, much of the geologic tidal record is potentially produced from the interactions of tides with river currents and waves, or the complete overprinting of tidal products by these forces. Over the last several decades, this notion has in part motivated research into the interplay between tides and the various factors that render them non-stationary on multiple time scales. Relevant processes include: (a) interaction of tides with non-tidal events like floods and storm surges; (b) seasonal fluctuations in tides, driven by both hydrological and oceanic processes; (c) response of tides to engineering changes imposed on rivers, deltas, estuaries and ports; and (d) decadal (and longer) scale evolution of tides in response to changing ocean and coastal conditions, frequently in a climate-change context. We review astronomical tidal forcing, coastal tidal phenomena, interactions of tides with other processes from river flow to sea level rise, analysis methods for non-stationary tides, and how non-stationary tidal processes may appear in the sedimentary record.