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Abstract: We have monitored and analyzed, through remote sensing and ancillary field surveys, the rapid (O(1) year) development of a tidal network within a newly established artificial salt marsh in the Venice Lagoon. After the construction of the salt marsh, a network of volunteer creeks established themselves away from an artificially constructed main channel (with mean and maximum annual headward-growth rates of 11 m/yr and 18 m/yr, respectively). The rapid formation of this system of tidal creeks provides a unique opportunity to test the reliability of a model of tidal network initiation and development, previously proposed by the authors. The restored marsh presents the characteristics of a controlled environment analogous to a large-scale field laboratory, as it allows comparison of the morphologic features of real and simulated network structures under the reasonable assumption of neglecting accretion and deposition processes over the timescales of observation. Our results compare favorably with observational evidence, showing that the model proves reasonably capable of reproducing the main features of the actual channel-network patterns. The model reproduces statistical network characteristics of eco-morphodynamic and hydrodynamic relevance and captures the dominant modes of the network-incision process. [Copyright &y& Elsevier]

Debris flow events in gullies generate the formation of multiple deposits along the main riverstream, with a consequent increase in the hydraulic susceptibility of the surrounding areas. For the early emergency response a rapid assessment of the debris flow deposit stability and if possible of its resilience (function of the deposit interaction with the river water discharge) is needed. Moreover, considering the fact that debris flow deposits can form in many different locations along the river network, a speedy procedure for effective assessment of stability of debris dam, to be applied over large areas would be particularly useful.Debris dam assessments are usually carried out adopting indexes, which have been developed considering morphometric or on the physically-based approaches. These indexes are difficult to be applied mainly because they are strongly dependent on the local environmental settings (i.e., channel width and slope) or on quantities that vary significantly during a given event (e.g., the main stream water discharge and the debris flow discharge). The aim of the present research is to propose a deposit resilience stability index to forecast hazard scenarios at regional scale by using Earth-Observation data, such as aerial photos or satellite images. Considering that the deposit shape is the final result of the interplay between the physical forces that drive debris flow dynamics and deposition, we based this index on the shape characteristics of the debris deposits. In particular, elliptical Fourier descriptor analysis has been applied to study the morphometry of the deposit contours. More symmetrical shapes indicate more stable deposits. The standardizing procedure of the elliptical Fourier coefficients is adopted in order to have a scale-invariant index applicable to both large and small mountain basins. The index proposed has been calibrated on the basis of data provided by a systematic series of flume tests and then evaluated by using aerial pictures of debris flow deposits formed after extreme rainfall events in the Sichuan province, China (Tang et al. 2011, Landslide). The proposed resilience index allows to take advantage of the possibility given by remote sensing for individuation of the limiting conditions and the deposit resilience status (low/high) as well as the blockage class (no blockage, partial blockage, full blockage).The resilience index proposed seems to provide robust estimates of the resilience of sediment deposits to erosion by the water flow. In particular, the index appears to appropriately describe the state of different sediment deposits observed at the field scale, occurring under complex environmental conditions with varying channel slope, channel width, sediment size. [ABSTRACT FROM AUTHOR]

Abstract: The present paper describes observations, analyses and models of salt-marsh channel network and vegetation patterns with the aim of contributing to the development of predictive models of ecological and morphological co-evolution. Existing and new observations are described, with particular emphasis on remote sensing and ancillary field surveys, which are shown to allow reliable, accurate and repeatable quantitative characterizations of landform and vegetation properties over the spatial scales of interest. The observed channel network morphological characters are then used as the basis and validation of models describing the emergence of channel network and vegetation spatial patterns. In particular, with reference to observations performed in the Venice Lagoon, the note describes: (i) new, 2-cm resolution, characterizations of channel network geometry obtained from “proximal sensing” photographic observations; (ii) the reliable quantitative maps of salt-marsh vegetation which may be retrieved from hyperspectral remote sensing data and field ancillary observations; (iii) a synthesis of recent and new analyses of the statistical properties of vegetation and landform spatial organization, that may be inferred from the maps so derived; (iv) recent and new conceptual and quantitative ecological and geomorphic models developed and validated by remote-sensing and field observations. A coherent observational and theoretical eco-morphodynamic framework is then proposed. [Copyright &y& Elsevier]