Turning the tide: experimental creation of tidal channel networks and ebb deltas

Abstract

Tidal channel networks, estuaries and ebb deltas are usually formed over a period longer than observations cover. Much is known about their characteristics and formation from linear stability analyses, numerical modelling and field observations. However, experiments are rare whilst these can provide data-rich descriptions of morphological evolution in fully controlled boundary and initial conditions. Our objective is to ascertain whether tidal basins can be formed in experiments, what the possible scale effects are, and whether morphological equilibrium of such systems exists.We experimentally created tidal basins with simple channel networks and ebb deltas in a 1.2 by 1.2 m square basin with either a fixed or self-formed tidal inlet and initially flat sediment bed in the tidal basin raised above the bed of the sea. Rather than create tides by varying water level, we tilted the entire basin over the diagonal. The advantage of this novel method is that the bed surface slopes in downstream direction both during flood and ebb phases, resulting in significant transport and morphological change in the flood phase as well as the ebb phase. This overcomes the major problem of earlier experiments which were entirely ebb-dominated, and reduces the experiment time by an order of magnitude.Ebb deltas formed in sand were entirely bedload dominated whereas the lightweight plastic sediment was intermittently suspended. Channels bifurcated during channel deepening and backward erosion to form a network of up to four orders. For initially dry tidal plains, the tidal prism increased as more sediment eroded from basin to ebb delta, so that evolution accelerated initially. The rate of change, the size of the channels and the final length of channels and delta were very sensitive to the tidal amplitude, tidal period and initial water depth in the basin. Most experiments with sand terminated with all sediment below the threshold for motion, whilst lightweight sediment remained mobile in the inlet region and firstorder channels, suggesting that sustained morphodynamics are feasible in experiments. We discuss how this novel experimental setup can be extended to produce tidal deltas, estuaries and other tidal systems and study their dynamics as a function of their forcing.

Analysis of the drainage density of experimental and modelled tidal networks

“…Based on scaling arguments (Stefanon et al, 2010), we set up numerical simulations in an attempt to understand the evolution of drainage density of tidal networks from a numerical modelling point of view and also examine to which degree numerical model results agree with the scaling laws. Quantitatively, the numerically simulated tidal networks resemble those obtained in the laboratory experiments (Stefanon et al, 2010(Stefanon et al, , 2012Kleinhans et al, 2012) and some natural back-barrier tide-dominated systems (e.g. the Venice Lagoon and the Dutch Wadden Sea).…”

“…Rinaldo et al, 1999a;Marani et al, 2003;Novakowski et al, 2004;Vandenbruwaene et al, 2012a, b), have confirmed that tidal networks show distinctive landscapes and geometric characteristics, because of the highly complicated interactions between various processes such as waves, tides, biological activities and sea level rise. By limiting the number of active processes, controlled laboratory experiments provide an important alternative to gain insight (Stefanon et al, 2010(Stefanon et al, , 2012Vlaswinkel and Cantelli, 2011;Kleinhans et al, 2012;Iwasaki et al, 2013). Moreover, the data obtained from these experiments (or after proper scaling analyses) can be utilised to benchmark numerical models (Tambroni et al, 2010).…”

Quantifiable effectiveness of experimental scaling of river- and delta morphodynamics and stratigraphy

“…Postma et al, 2009;Eggenhuisen and McCaffrey, 2012), tidal experiments (e.g. Tambroni et al, 2005;Stefanon et al, 2010;Kleinhans et al, 2012) and planetary experiments with sediment flows, surface runoff and groundwater outflow (e.g. Kraal et al, 2008;de Villiers et al, 2013;Marra et al, 2014).…”

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

“…funnel-shaped tidal channels, tidal mouth bars, etc.) Physical experiments can help bridge this knowledge gap, allowing one to capture delta evolution at a spatial and temporal resolution otherwise impractical in the field (Malverti et al, 2008;Paola et al, 2009;Kleinhans et al, 2012Kleinhans et al, , 2014aStefanon et al, 2012;Braat et al, 2018;Lentsch et al, 2018;Leuven et al, 2018). Physical experiments can help bridge this knowledge gap, allowing one to capture delta evolution at a spatial and temporal resolution otherwise impractical in the field (Malverti et al, 2008;Paola et al, 2009;Kleinhans et al, 2012Kleinhans et al, , 2014aStefanon et al, 2012;Braat et al, 2018;Lentsch et al, 2018;Leuven et al, 2018).…”

“…are typically not well preserved (Dalrymple and Choi, 2007). Recent studies demonstrated that physical experiments are capable of reproducing several typical tidal features, such as ebb deltas (Kleinhans et al, 2012), tidal channel networks (Stefanon et al, 2010;Vlaswinkel and Cantelli, 2011) and tidal estuaries (Kleinhans et al, 2014a). Recent studies demonstrated that physical experiments are capable of reproducing several typical tidal features, such as ebb deltas (Kleinhans et al, 2012), tidal channel networks (Stefanon et al, 2010;Vlaswinkel and Cantelli, 2011) and tidal estuaries (Kleinhans et al, 2014a).…”