Intertidal floodplain controls on centennial-scale morphological channel development

<p>Intertidal areas disappear in deltas worldwide because of land reclamations. This greatly impacts delta morphology because the presence and physiological characteristics of intertidal areas determine the tidal regime and, as a result, residual sediment transport patterns in tidal basins. Understanding how the interaction between intertidal areas and channels in tidal basins influence morphodynamics is therefore important to predict morphological development and to assess the resilience of delta’s to changing boundary conditions.</p><p>In the Ems estuary (The Netherlands), the gradual embankment of a large intertidal embayment altered the planform and cross-sectional geometry of the estuary, leading to changes in the tidal regime and associated residual sediment transport patterns. As early as 1952, it was already suggested that these changes eventually caused a shift towards an alternative historical development of the geometric configuration of the channels; from a multiple to a single channel system.</p><p>This study shows through centennial-scale morphological modelling that the observed system shift can be hind-casted, while conserving model validity by comparison to the observed gross morphodynamics trends. The results indicate that the system shift is indeed driven by land reclamations. This provides a unique case to study the processes leading to the observed developments and evaluate the value of tidal-asymmetry based stability relationships to predict regime shifts in estuarine development.</p>

Arctic Ocean tidal regime change across the Bolling-Allerod onset

<p>Although currently microtidal, the Arctic Ocean is known to have been megatidal at Last Glacial Maximum (LGM) due to the Arctic Ocean basin being nearly entirely enclosed, with only Fram Strait connecting it to the global ocean. This allowed for the propagation of a gravest mode coastal Kelvin wave traveling anti-clockwise around the Arctic ocean. The transition from the megatidal regime at LGM to the mircotidal regime observed today is not well understood, and the factors which control the amplitude of the semidiurnal tidal constituents in the Arctic Ocean have not been fully determined in the literature. We investigate the Arctic tidal regime across the Bolling-Allerod (B-A) onset, 14.6-14.1 ka, finding that the Arctic Ocean is megatidal prior to B-A onset and weakens considerably thereafter. The period of time during which the Arctic tidal regime is enhanced is precisely the time at which high Arctic ice streams begin to deglaciate, indicating that the tides may play a causal role in forcing the rapid deglaciation of the sector of the Laurentide abutting the Arctic Ocean. We further show that the deglaciation of the Laurentide ice sheet, through the mechanisms of Glacial Isostatic Adjustment (GIA) and gravitationally self-consistent local reduction in sea level, causes an increase in the amplitude of the principal lunar and solar semidiurnal tidal constituents in the Arctic Ocean. Additionally, it is the collapse of the Barents sea ice sheet which significantly weakens the Arctic Ocean tidal regime. We report the contribution of each major terrestrial ice sheet to the relative sea-level rise at each of Barbados, Tahiti, and Sunda Shelf, finding that the gravitationally self-consistent GIA model employed accurately predicts the RSL change at each of these sites and determines that the contribution at Barbados from the Laurentide is smaller than the contribution at Tahiti or Sunda Shelf due to the flow of ocean water away from the deglaciating Laurentide and into the "far field."  We further show that the contribution to RSL at Barbados due to the collapse of the Barents Sea ice sheet is significant. </p>

Variability of Currents and Water Column Structure in a Temperate Estuarine System (Sado Estuary, Portugal)

The circulation in estuaries promotes the transport of organisms, nutrients, oxygen and sediments. Simultaneously, the mixture of fresh and salt water leads to variations of the physicochemical and biological components of the region. Therefore, it is important to further understand the hydrodynamic patterns of an estuary as one of the bases to understand the whole dynamic of these systems, ecologically important regions that must be preserved. However, little is known about the hydrodynamics of some estuarine systems. In order to bridge the knowledge gap about the Sado estuary, sampling was conducted with the purpose of evaluating some circulation patterns of the estuary and classifying it according to the stratification of the water column. The campaigns were conducted to collect monthly data on the intensity and direction of the currents, and on the temperature and salinity of the water column, between September 2018 and September 2019. The data indicated that water circulation in the Sado estuary, occurred through the two main navigation channels (North and South), according to the tidal regime. Both the temperature and the salinity were homogeneous along the water column, revealing little stratification. The analysis suggests possible hydrodynamic changes of the estuary in the past years.

Coastal wetlands can be saved from sea level rise by recreating past tidal regimes

Climate change driven Sea Level Rise (SLR) is creating a major global environmental crisis in coastal ecosystems, however, limited practical solutions are provided to prevent or mitigate the impacts. Here, we propose a novel eco-engineering solution to protect highly valued vegetated intertidal ecosystems. The new ‘Tidal Replicate Method’ involves the creation of a synthetic tidal regime that mimics the desired hydroperiod for intertidal wetlands. This synthetic tidal regime can then be applied via automated tidal control systems, “SmartGates”, at suitable locations. As a proof of concept study, this method was applied at an intertidal wetland with the aim of restabilising saltmarsh vegetation at a location representative of SLR. Results from aerial drone surveys and on-ground vegetation sampling indicated that the Tidal Replicate Method effectively established saltmarsh onsite over a 3-year period of post-restoration, showing the method is able to protect endangered intertidal ecosystems from submersion. If applied globally, this method can protect high value coastal wetlands with similar environmental settings, including over 1,184,000 ha of Ramsar coastal wetlands. This equates to a saving of US$230 billion in ecosystem services per year. This solution can play an important role in the global effort to conserve coastal wetlands under accelerating SLR.

Characterisation of the Water Renewal in a Macro-Tidal Marina Using Several Transport Timescales

In this paper, we investigate the water renewal of a highly populated marina, located in the south-west of France, and subjected to a macro-tidal regime. With the use of a 3D-numerical model (TELEMAC-3D), three water transport timescales were studied and compared to provide a fully detailed description of the physical processes occurring in the marina. Integrated Flushing times (IFT) were computed through a Eulerian way while a Lagrangian method allowed to estimate Residence Times (RT) and Exposure Times (ET). From these timescales, the return-flow (the fraction of water that re-enters the marina at flood after leaving the domain at ebb) was quantified via the Return-flow Factor (RFF) and the Return Coefficient (RC) parameters. The intrinsic information contained in these parameters is thoroughly analysed, and their relevance is discussed. A wide range of weather-marine conditions was tested to provide the most exhaustive information about the processes occurring in the marina. The results highlight the significant influence of the tide and the wind as well as the smaller influence of the Floating Structures (FS) on the renewal. Besides, this study provides the first investigation of the water exchange processes of La Rochelle marina. It offers some content that interest researchers and environmental managers in the monitoring of pollutants as well as biological/ecological applications.