[1] We propose an ecomorphodynamic model which conceptualizes the chief land-forming processes operating on the intertwined, long-term evolution of marsh platforms and embedded tidal networks. The rapid network incision (previously addressed by the authors) is decoupled from the geomorphological dynamics of intertidal areas, governed by sediment erosion and deposition and crucially affected by the presence of vegetation. This allows us to investigate the response of tidal morphologies to different scenarios of sediment supply, colonization by halophytes, and changing sea level. Different morphological evolutionary regimes are shown to depend on marsh ecology. Marsh accretion rates, enhanced by vegetation growth, and the related platform elevations tend to decrease with distance from the creek, measured along suitably defined flow paths. The negative feedback between surface elevation and its inorganic accretion rate is reinforced by the relation between plant productivity and soil elevation in Spartina-dominated marshes and counteracted by positive feedbacks in multispecies-vegetated marshes. When evolving under constant sea level, unvegetated and Spartina-dominated marshes asymptotically tend to mean high water level (MHWL), different from multiple vegetation species marshes, which can make the evolutionary transition to upland. Equilibrium configurations below MHWL can be reached under constant rates of sea level rise, depending on sediment supply and vegetation productivity. Our analyses on marine regressions and transgressions show that when the system is in a supply-limited regime, network retreat and expansion (associated with regressions and transgressions, respectively) tend to be cyclic. Conversely, in a transport-limited regime, network reexpansion following a regression tends to take on a new configuration, showing a hysteretic behavior.Citation: D'Alpaos, A., S. Lanzoni, M. Marani, and A. Rinaldo (2007), Landscape evolution in tidal embayments: Modeling the interplay of erosion, sedimentation, and vegetation dynamics,

No abstract

Looking across a tidal landscape, can one foresee the signs of impending shifts among different geomorphological structures? This is a question of paramount importance considering the ecological, cultural and socio-economic relevance of tidal environments and their worldwide decline. In this Letter we argue affirmatively by introducing a model of the coupled tidal physical and biological processes. Multiple equilibria, and transitions among them, appear in the evolutionary dynamics of tidal landforms. Vegetation type, disturbances of the benthic biofilm, sediment availability and marine transgressions or regressions drive the bio-geomorphic evolution of the system. Our approach provides general quantitative routes to model the fate of tidal landforms, which we illustrate in the case of the Venice lagoon (Italy), for which a large body of empirical observations exists spanning at least five centuries. Such observations are reproduced by the model, which also predicts that saltmarshes in theVenice lagoonmay not survive climatic changes in the next century if IPCC’s scenarios of high relative sea level rise occ

[1] We identify a previously undetected link between the river network morphology and key recession curves properties through a conceptual-physical model of the drainage process of the riparian unconfined aquifer. We show that the power-law exponent, a, of −dQ/dt vs. Q curves is related to the power-law exponent of N(l) vs. G(l) curves (which we show to be connected to Hack's law), where l is the downstream distance from the channel heads, N(l) is the number of channel reaches exactly located at a distance l from their channel head, and G(l) is the total length of the network located at a distance greater or equal to l from channel heads. Using Digital Terrain Models and daily discharge observations from 67 US basins we find that geomorphologic a estimates match well the values obtained from recession curves analyses. Finally, we argue that the link between recession flows and network morphology points to an important role of low-flow discharges in shaping the channel network.

Abstract. Through the new method for automatic extraction of a tidal network from topographic or bathymetric fields described in a companion paper [Fagherazzi et al., this issue], we analyze the morphology of aggregated patterns that we observe in nature in different tidal environments. Specifically, we define, on the basis of a hydrodynamic analysis, a procedure for watershed delineation and for the identification of the "divides" for every subnetwork and look at the resulting drainage density and its related scaling properties. From the systematic, large-scale plots of drainage density and channel width versus watershed area we address the issue of a possible geomorphic criterion that corresponds to the parts of the tidal landscape that are characterized by river-like features. We also analyze the relationship of total contributing tidal basin area to channel widths and to mainstream lengths (Hack's law). We study comparatively probability distributions of total drainage areas and of "botanical" mass (the area of the channelized landscape upstream of a given section) for tidal and fluvial patterns and find altered scaling features of tidal landforms that reflect the complex interactions of different mechanisms that shape their geometry. Simple geomorphic relationships of the types observed in the fluvial basin (e.g., power laws in the watershed area versus drainage density, mainstream length, or channel width relationships) do not hold throughout the range of scales investigated and are site-specific. We conclude that tidal networks unlike rivers exhibit great diversity in their geometrical and topological forms. This diversity is suggested to stem from the pronounced spatial gradients of landscape-forming flow rates and from the imprinting of several crossovers from competing dynamic processes. IntroductionIn this paper, the second in a series of three, we quantify various tidal network properties including common power law relationships which have been well documented for terrestrial river systems [Rodriguez-Iturbe and Rinaldo, 1997]. Our goals here are both to explore tidal channel scaling properties and to infer, based on scaling breaks, possible changes in dominant formative process through a network. We anticipate that spatial variation in the dominance of ebb versus flood tides and in erosional resistance associated with vegetation and sediment texture could give rise to limited scaling compared to that found in terrestrial systems (where single power law relationships typically apply across many orders of magnitude). Hence we propose to apply common power law relationships quantified for terrestrial systems to tidal systems and use these analyses to identify possible geomorphic "signatures" of dominant processes. In order to perform morphometric analysis of tidal networks, we need an objective procedure for delineating the drainage area to any link. Here we first introduce a new method, based on flow hydrodynamics, for delineating drainage directions and contributing areas throughout the tidal network...