ABSTRACT

Tidal environments are dynamic and delicate systems, usually characterized by highly heterogeneous physical and biological properties (e.g. Perillo 1995; Allen 2000; Friedrichs & Perry 2001). To address issues of conservation of tidal environments it is of critical importance to improve our understanding of the origins and evolution of tidal networks, strikingly interesting landforms (see e.g. Figure 1) which exert a fundamental control on the hydrodynamics and on sediment and nutrient exchanges within tidal systems. A number of authors have described the hydrodynamics of tidal channels and creeks, the consequences of tidal currents and asymmetries on sediment dynamics and other morphological characteristics of tidal channels (e.g. Boon 1975; Speer & Aubrey 1985; Friedrichs & Aubrey 1988; Friedrichs 1995; Lanzoni & Seminara 2002). Morphometric analyses of tidal networks have been carried out (e.g. Myrick & Leopold 1963; Steel & Pye 1997; Fagherazzi et al. 1999; Rinaldo et al. 1999a,b; Marani et al. 2002, 2003), and sedimentation and accretion patterns in salt marshes have been studied (e.g. Leonard & Luther 1995; Christiansen et al. 2000), together with ecological dynamics and patterns in salt marshes (e.g. Silvestri & Marani 2004). Moreover, simplified models have been proposed to simulate the morphological behavior of tidal basins and to describe either the vertical growth of a marsh platform relative to a datum or such movement combined with the growth of the vertical sequence of

underlying sediments (e.g. Beeftink 1966; Pethick 1969; Allen 1990, 1995, 1997; French 1993; Rybczyk et al. 1998). The large body of knowledge available on tidal environments can be used to develop a model of

long-term morphological evolution of tidal systems, capable of describing the planimetric development of tidal channel networks coupled with the vertical accretion of the adjacent marsh surface, as a consequence of tidal forcings, varying sediment inputs and relative sea level changes. Several ingredients related to the description of the delicate balance and strong feedbacks characterizing hydrodynamics, morphological and ecological dynamics should be included in such a model. As a first step towards a complete morphodynamic model of evolution of tidal systems, D’Alpaos et al.(2005a) have addressed the problem of channel network ontogeny and early development. Their model, which is strictly valid for relatively short tidal embayments, does not include soil production processes nor any other morphodynamic interaction of physical, chemical and biological nature, acting on timescales longer than those involved in the elaboration of the early tidal network. The model imposes a null along-channel gradient in net sediment transport resulting in stable channeled shapes whose proxy is the local tidal prism. In this note we extend some of the analyses carried out by D’Alpaos et al. (2005a), focusing on the capability of the model to develop tidal patterns whose geomorphic features resemble the ones of observed tidal morphologies. The note is organized as follows: Section 2 reports on observational evidence, analyzed in previous works, which will be used to develop and test the model. In Section 3 we recall the physical assumptions and the mathematical structure of the model by D’Alpaos et al. (2005a). Section 4 then presents and discusses the main results obtained by applying the model under different initial conditions. The final Section deals with conclusions and some remarks on future developments.