Tidal meanders

Abstract

.[1] Observational evidence is presented on the geometry of meandering tidal channels evolved within coastal wetlands characterized by different tidal, hydrodynamic, topographic, vegetational and ecological features. New insight is provided on the geometrical properties of tidal meanders, with possible dynamic implications on their evolution. In particular, it is shown that large spatial gradients of leading flow rates induce important spatial variabilities of meander wavelengths and widths, while their ratio remains remarkably constant in the range of scales of observation. This holds regardless of changes in width and wavelength up to two orders of magnitude. This suggests a locally adapted evolution, involving the morphological adjustment to the chief landforming events driven by local hydrodynamics. The spectral analysis of local curvatures reveals that Kinoshita's model curve does not fit tidal meanders due to the presence of even harmonics, in particular the second mode. Geometric parameters are constructed that are suitable to detect possible geomorphic signatures of the transitions from ebb-to flood-dominated hydrodynamics, here related to the skewness of the tidal meander. Trends in skewness, however, prove elusive to measure and fail to show detectable patterns. We also study comparatively the spatial patterns of evolution of the ratios of channel width to depth, and the ratio of width to local radius of curvature. Interestingly, the latter ratio exhibits consistency despite sharp differences in channel incision. Since the degree of incision, epitomized by the width-to-depth ratio, responds to the relevant erosion and migrations mechanisms and is much sensitive to vegetation and sediment properties, it is noticeable that we observe a great variety of landscape carving modes and yet recurrent planar features like constant width/curvature and wavelength/width ratios.

Tidal estuary width convergence: Theory and form in North Australian estuaries

“…Marani et al (2002) fi tted Equation (1) to seven tidal channels, and noted that the value of L b varied in a highly site-specifi c manner, while the ratio of L b to the channel length tended to be larger in short channels than in long channels. Woodroffe and Mulrennan (1993, p 106) considered the changes in the width profi les of estuarine channels in the Mary River plains during the Holocene, and found that the convergence lengths of palaeochannels and modern channels were reasonably similar despite huge differences in channel size.…”

A stochastic model for the formation of channel networks in tidal marshes

“…These intertwined processes hinder the tendency of the system to develop a self-organized configuration [Rinaldo et al, 1999b]. Tidal channels are also highly sinuous, with meanders that are geometrically similar to the meanders developing in rivers [Marani et al, 2002]. However, the bidirectionality of the discharge in tidal channels often implies a meander evolution that departs from terrestrial meanders [Fagherazzi et al, 2004].…”

Salt marsh ecohydrological zonation due to heterogeneous vegetation–groundwater–surface water interactions

“…Intertidal marsh surface water hydrology is characterized by tidal flood and ebb in the channel network [Fagherazzi et al, 1999;Marani et al, 2002Marani et al, , 2003. During especially high tides, the channels fill beyond bankfull capacity and tidal waters flood across the marsh plain, influenced by vegetation roughness [Temmerman et al, 2005;van Proosdij et al, 2006].…”