Signatures of sea level changes on tidal geomorphology: Experiments on network incision and retreat

Abstract

[1] How do tidal networks respond to changes in relative mean sea level (RMSL)? The question on whether the morphological features of a tidal landscape retain signatures of past environmental forcings, or are in equilibrium with current ones, is critical to our prediction of the fate of residual tidal landforms. In the case of tidal networks, the issue is quite relevant owing to their fundamental role on landscape eco-morphodynamic evolution. Here we explore the response of tidal networks to cyclic variations in RMSL triggering tidal prism changes on the basis of laboratory experiments carried out in a synthetic lagoonal environment. A decrease in the tidal prism leads to network retreat and contraction of channel cross sections. Conversely, an increase in the tidal prism promotes network re-incision and re-expansion of channel cross sections: Network retreat and expansion tend to occur within the same planar blueprint. Our results show that the drainage density of tidal channels is linearly related to the landscape-forming prism, although this relation is speculated to hold with reasonable approximation as a statistical tendency rather than as a pointwise, instantaneous adaptation. Changes in tidal prism rapidly influence network efficiency in draining the intertidal platform and the related transport of water, sediments, nutrients and pollutants. This bears important consequences for quantitative predictions of the long-term ecomorphological adaptation of the tidal landscape to RMSL changes. Citation: Stefanon, L., L.Carniello, A. D'Alpaos, and A. Rinaldo (2012), Signatures of sea level changes on tidal geomorphology: Experiments on network incision and retreat, Geophys.

Analysis of the drainage density of experimental and modelled tidal networks

“…10). Initially, the tidal prism adapts to the morphological evolutions more rapidly than the drainage density does and then the two quantities vary with similar temporal scales, as also found by Stefanon et al (2012). Both the evolution of drainage density and the tidal prism displays asymptotic behaviour (Fig.…”

“…Moreover, the data obtained from these experiments (or after proper scaling analyses) can be utilised to benchmark numerical models (Tambroni et al, 2010). Stefanon et al (2010Stefanon et al ( , 2012 successfully reproduced the major features of the evolution of tidal networks in the laboratory, which are comparable to natural systems in terms of both the morphological development and the geomorphic characteristics. Zhou et al (2014) performed a comparative study between these laboratory experiments and numerical simulations at both laboratory and natural scales, exploring the effects of different parameterisations on the long-term morphological evolution of tidal networks.…”

“…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).…”

“…W , L and D represent width, length and depth scales of the basins; U denotes the typical velocity in tidal channels. Specifically, we will explore whether the numerically modelled channel networks are comparable with the experimental (Stefanon et al, 2010(Stefanon et al, , 2012 or natural ones from the perspective of drainage density. The variation of drainage density during the morphological development will also be examined in order to shed light on tidal network ontogeny.…”

“…5. Stefanon et al (2010Stefanon et al ( , 2012 carried out experiments under a range of different settings. One of these experiments (indicated by "Run 4" in Stefanon et al, 2010) was conducted considering a constant mean water level.…”