Experimental delta evolution in tidal environments: Morphologic response to relative sea‐level rise and net deposition

Abstract

Tide‐influenced deltas are among the largest depositional features on Earth and are ecologically and economically important as they support large populations. However, the continued rise in relative sea level threatens the sustainability of these landscapes and calls for new insights on their morphological response. While field studies of ancient deposits allow for insight into delta evolution during times of eustatic adjustment, tide‐influenced deltas are notoriously hard to identify in the rock record. We present a suite of physical experiments aimed at investigating the morphological response of tide‐influenced deltas subject to relative sea‐level rise. We show that increasing relative tidal energy changes the response of the delta because tides effectively act to remove fluvially deposited sediment from the delta topset. This leads to enhanced transgression, which we quantify via a new methodology for comparing shoreline transgression rates based on the concept of a ‘transgression anomaly’ relative to a simple reference case. We also show that stronger tidal forcing can create composite deltas where distinct land‐forming processes dominate different areas of the delta plain, shaping characteristic morphological features. The net effect of tidal action is to enhance seaward transfer of bedload sediment, resulting in greater shoreline transgression compared to identical, yet purely fluvial, deltaic systems that exhibit static or even regressive shorelines. © 2019 John Wiley & Sons, Ltd.

Effect of Small Tidal Fluctuations on the Stability and Equilibrium Configurations of Bifurcations

“…According to Seminara et al (2012), the effect of the tide is to induce a progressive erosion wave that, proceeding landward from the channel mouth, migrates upstream along the estuary. Even just fairly small tidal amplitude is responsible for this erosive process observed theoretically (Bolla Pittaluga, Tambroni, et al, 2015;Seminara et al, 2012), experimentally (Finotello et al, 2019;Lentsch et al, 2018), in field-case study (Kästner et al, 2017;Leonardi et al, 2015;Shaw & Mohrig, 2014;Wagner & Mohrig, 2019), and with the utilization of process-based morphodynamic models (e.g., Delft3D) (Rossi et al, 2016), entailing an increase in transport capacity in each branch. As a consequence, provided the flow discharge partition at the bifurcation is the same, the tidal branches are deeper than their pure fluvial counterpart.…”

“…Recently, Seminara et al (2012) and Bolla Pittaluga, Tambroni, et al (2015) tackled analytically and numerically the more general case of natural streams in which both river and tides concur. This case has been also subject to a series of laboratory and numerical investigations in a single channel (Leuven et al, 2018) and in a built-up physical tide-influenced delta (Finotello et al, 2019;Lentsch et al, 2018;Rossi et al, 2016).…”

Reading tidal processes where their signature is cryptic: The Maastrichtian meandering channel deposits of the Tremp Formation (Southern Pyrenees, Spain)

“…Blind tidal channels are dominant landscape features in the macrotidal Bay of Mont St. Michel (France) (Belliard, 2014), across the meso‐tidal and macro‐tidal British salt‐marshes (Pethick, 1969), and also along the microtidal Southeast US Atlantic and Gulf of Mexico coastlines, where blind tidal channels are found as far as 20 km from the shoreline (Wiegert & Freeman, 1990). Blind tidal channels are widespread also on deltas (see Finotello et al ., 2019b), such as the macro–mesotidal delta of Ganges–Brahmaputra–Meghna (Bangladesh, Passalacqua et al ., 2013; Wilson et al ., 2017), and the micro–mesotidal Mahakan delta plain (Indonesia, Allen et al ., 1979), where heads of blind tidal channels are found 70 km and 15 km upland from the coastline, respectively.…”

River, Coastal and Estuarine Morphodynamics Selected papers from the 10th anniversary of the RCEM Symposium

“…The 17 collected contributions include four state-of-science papers concerning the most recent advances in computational morphodynamic modelling of coupled flow-bed-sediment systems (Shimizu et al, 2019), a critical analysis of existing data on vegetation-flow-sediment interactions obtained through both laboratory experiments and field campaigns (Tinoco et al, 2020), a review of existing moving-boundary theories of shorelines with two extensions to allow inclusion of firstorder effects of waves and tides (Voller et al, 2020), and an overall assessment of the role played by wave forcing on the hydro-morphodynamics in shallow nearshore areas and at river mouths (Brocchini, 2019). The other 13 papers cover different topics about morphodynamics, spanning multiple environments, tackling concepts and processes with the aid of refined theoretical and numerical tools (Redolfi et al, 2019;Tambroni et al, 2019), grounding the results on laboratory data (Finotello et al, 2019;Geng et al, 2019;Matoušek et al, 2019, Porcile et al, 2020 and field observations (Fogarin et al, 2019;Tommasini et al, 2019), and making use of interdisciplinary approaches (Calvani et al, 2019;Chen et al, 2019;Pivato et al, 2019;van de Vijsel et al, 2020) also to develop new conceptualizations (Schlömer et al, 2020).…”

“…Overall, flood-dominated tides favour the formation of small-scale channel branches in the upper basin zone, while long-lasting ebb-dominated tides result in more complex, wider and deeper tidal networks. The formation of tidal channel networks in depositional, fluvio-deltaic settings was investigated by Finotello et al (2019), who address the morphological response of tide-influenced deltas subject to relative sea-level rise. They demonstrate that the action of tidal forcing can create composite deltas where distinct land-forming processes dominate different areas of the delta plain, shaping characteristic morphological features such as funnelled distributary channels and branching networks of tidal channels.…”