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Extensive loss of salt marshes in back‐barrier tidal embayments is ongoing worldwide as a consequence of land‐use changes, wave‐driven lateral marsh erosion, and relative sea‐level rise compounded by mineral sediment starvation. However, how salt‐marsh loss affects the hydrodynamics of back‐barrier systems and feeds back into their morphodynamic evolution is still poorly understood. Here we use a depth‐averaged numerical hydrodynamic model to investigate the feedback between salt‐marsh erosion and hydrodynamic changes in the Venice Lagoon, a large microtidal back‐barrier system in northeastern Italy. Numerical simulations are carried out for past morphological configurations of the lagoon dating back up to 1887, as well as for hypothetical scenarios involving additional marsh erosion relative to the present‐day conditions. The progressive loss of salt marshes significantly impacted the lagoon hydrodynamics, both directly and indirectly, by amplifying high‐tide water levels, reducing wind‐wave energy dissipation, and critically affecting tidal asymmetries across the lagoon. Restoration projects and manmade protection of marsh margins, which have been implemented over the past few decades, limited the detrimental effects of marsh loss on the lagoon hydrodynamics, while not substantially changing the risk of flooding in urban lagoon settlements. Compared to previous studies, our analyses suggest that the hydrodynamic response of back‐barrier systems to salt‐marsh erosion is extremely site‐specific, depending closely on the morphological characteristics of the embayment as well as on the external tidal and wind forcings. Key Points: Effects of salt‐marsh lateral erosion on the characteristics of tides and waves are investigated for the microtidal Venice LagoonSalt‐marsh loss primarily enhances mean high water levels and wave heights due to reduced friction and longer wind fetchesHydrodynamic changes depend on salt‐marsh spatial distribution and elevation, as well as on the characteristics of tidal and wind forcings [ABSTRACT FROM AUTHOR]

Tidal channels form the pathways for tidal currents to propagate and distribute clastic sediments and nutrients, thus providing a primary control on tidal‐landscape ecomorphodynamics. Most tidal channels in both estuarine and lagoonal environments have a tendency to meander, yet very few studies exist that investigate the full spectrum of processes controlling tidal meander morpho‐sedimentary evolution. The Venice Lagoon (Italy) offers a unique opportunity to shed light on this topic, because a long record of morphological and sedimentary data is available, which allows one to relate tidal channel evolution to the hydrodynamic and morphological changes undergone by the lagoon. In particular, during the last 130 years, feedback between rising relative sea levels and anthropogenic interventions has caused severe modifications of the Lagoon hydro‐ and morphodynamics. Here we investigate how these modifications fed back into the morpho‐sedimentary evolution of a meandering tidal channel located in the northern lagoon. Combining extensive datasets of aerial photographs, topographic and bathymetric surveys, geophysical investigations, sedimentary core analysis, and numerical modelling, we show that enhanced local tidal ranges and water discharges determined adjustments of channel cross‐sectional geometries proportional to increasing tidal prisms, while changes in local tidal asymmetries caused modifications of the local sediment transport regime, resulting in the development of bar–pool patterns according to the dominant tidal phase. Such bar–pool patterns eventually determined channel migration through a bar‐push mechanism controlled by a fluvial‐like, quasi‐linear relationship between local channel curvature and lateral migration rates. Critical differences in sediment transport regime are, however, highlighted between fluvial and tidal meanders the latter being potentially characterized by high concentrations of suspended sediment during periods of slack waters when wind‐driven sediment transport processes are not negligible. This could hamper the formation of high‐relief bedforms, with profound implications for the sedimentology of tidal point‐bar deposits. [ABSTRACT FROM AUTHOR]

Brambilla, W.; van Rooijen, A.; Simeone, S.; Ibba, a.; DeMuro, S., 2016. Field observations, coastal video monitoring and numerical modeling of coastal processes at Poetto Beach, Italy. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 825-829. Coconut Creek (Florida), ISSN 0749-0208. This work presents an analysis of hydrodynamics and morphological evolution during one year at Poetto Beach (South Sardinia, Gulf of Cagliari - Italy). The results, in the form of a numerical model, Delft3D, were validated using data obtained from a very reproducible low-cost video monitoring system. Subsequently, the model was used to study local hydrodynamics (Delft3D) during wave events. Poetto Beach is a wave-dominated urban beach system characterized by an inner shelf with Posidonia oceanica meadows. Bathymetric and topographic surveys were carried out every three months in order to understand the beach morphology. Sediment grain samples were taken alongshore/cross-shore in correspondence with the main morphologies. The Delft3D model was used to simulate waves and hydrodynamics. The numerical simulation (Delft3D) showed good agreement with the field data and video image analyses for the distribution and direction of the rip and longshore currents. This approach, which can be easily replicated on other urban beaches, could provide beach managers with useful information on how to prevent and minimize the effects of storms and flooding. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to propose an integrated low cost system for monitoring the performance of beach defence works during storms. For this purpose, the site of Igea Marina, Northern Adriatic Sea, Italy, which is protected by low crested detached breakwaters, is selected. The monitoring system is composed by a video installation, for the identification of the shoreline position and of the intertidal bathymetry at high space and time resolution, and a 2DH numerical model, to reconstruct the hydrodynamics induced by coastal defenses. The accuracy of the monitoring system is verified against available measurements of waves and currents performed during a field campaign with acoustic Doppler profilers. Assimilation of data on the shoreline position in 2DH model operatively working is challenging in the improvement of the production of risk maps. These show the current intensities and flooded areas during forecasted storms. First promising results suggest the possibility of setting up an early warning tool. [Copyright &y& Elsevier]

Abstract: This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide. The long-term deposition (or erosion) rate in a given location is expressed as proportional to the difference between the local transport concentration and the local equilibrium concentration, depending in turn on the local stirring action by waves and currents. The two-dimensional model is able to reproduce the ontogeny of a tidal lagoon as a consequence of a breaching of the littoral dune line. During the ontogenetic phase, the system tends rapidly toward a quasi-equilibrium condition apparently characterized by a stable planimetric configuration of the channel network. The structure of the channels and their watersheds is qualitatively similar to the Venice Lagoon''s ones. After the relatively fast ontogenetic phase, the subsequent morphological evolution of the bottom continues at a slower pace until a stable bathymetric configuration of the lagoon is reached. The model is able to reproduce the morphological effects of subsequent perturbations of natural or anthropogenic origin. [Copyright &y& Elsevier]

Abstract: A number of morphological models, often referred to as regime or hybrid models, require the equilibrium relationship between form and hydraulics to be prescribed in some way. In general, the well documented relationship between tidal prism and the cross-sectional area of the channel has been adopted. In this paper an alternative approach is proposed. First, a description of an idealised 3D morphology has been developed based on the equilibrium form of the constituent parts, namely the plan form, low water channel cross-section and intertidal profile. This is then modified to take account of waves acting on the shores of the constituent channels. A key feature of the model is that it only uses attributes that are exogenous to the system, or can be defined a priori (although there is some discussion as to how well this objective is fulfilled in relation to the sedimentary properties). The model is applied to the three inlets that make up Venice Lagoon. The quality of fit obtained is sufficient to justify a more detailed examination of the model''s ability to predict the gross properties of the system (volumes and surface areas of the channels and intertidal flats), and an assessment of modelled changes in basin hypsometry against observed changes. [Copyright &y& Elsevier]

Abstract: Large gravel-bed braided rivers show a highly dynamic evolution, where even moderate flow pulses can produce significant morphological adjustment. An estimation of network variations is needed by river authorities as well as by ecologists for better managing river ecosystems. However, few field investigations have been performed to measure the effect of unsteady discharges in braided rivers. In this paper we report on the morphological changes induced by six different floods in a 1-km-long reach of the Tagliamento River, Italy. Topographic surveys were performed after each significant flood, and an automatic digital camera continuously monitored the planimetric configuration. Repeated measurements of cross section profiles allowed the quantification of the transported sediments volume and, in particular, provided a basis to estimate the percentage of the floodplain subject to morphological evolution. Data analysis showed a good relationship between peak flow level, active width, and mean bed level changes. Similarly, lateral channel shifting is likely to increase for larger floods. Monitoring of a range of discharges up to bankfull conditions revealed a fundamental difference between flow pulses (events on the average occurring one or more times per year) and flood pulses (with a return period larger than two years). The morphological evolution in the former case is mainly limited to a few active branches and is locally driven by bank erosion at the bend apex. On the other hand, larger floods induce a complete reworking of the network configuration, where bifurcations and confluences play a crucial role. Single morphological units (like branches, nodes, bars) are no longer recognizable after this type of event. Braided rivers are therefore characterized by the occurrence of two different spatial and temporal scales that force the ecosystem dynamics. [Copyright &y& Elsevier]

Abstract: Recent studies of sediment dynamics and clinoform development in the northern Adriatic Sea focused on winter 2002–2003 and provided the data and motivation for development of a detailed sediment-transport model for the area near the Po River delta. We used both idealized test cases and more realistic simulations to improve our understanding of seasonal sediment dynamics there. We also investigated the relationship between physical processes and the observed depositional products; e.g. the accumulation of sediment very near the Po River distributary mouths. Sediment transport near the Po River was evaluated using a three-dimensional ocean model coupled to sediment-transport calculations that included wave- and current-induced resuspension, suspended-sediment transport, multiple grain classes, and fluvial input from the Po River. High-resolution estimates from available meteorological and wave models were used to specify wind, wave, and meteorological forcing. Model results indicated that more than half of the discharged sediment remained within 15 km of the Po River distributary mouths, even after two months of intensive reworking by winter storms. During floods of the Po River, transport in the middle to upper water column dominated sediment fluxes. Otherwise, sediment fluxes from the subaqueous portion of the delta were confined to the bottom few meters of the water column, and correlated with increases in current speed and wave energy. Spatial and temporal variation in wind velocities determined depositional patterns and the directions of sediment transport. Northeasterly Bora winds produced relatively more eastward transport, while southwesterly Sirocco winds generated fluxes towards both the north and the south. Eastward transport accounted for the majority of the sediment exported from the subaqueous delta, most likely due to the frequent occurrence of Bora conditions. Progradation of the Po River delta into the Adriatic Sea may restrict the formation of the Western Adriatic Coastal Current, increasing sediment retention at the Po delta and reducing the supply of sediment to the Apennine margin. A positive morphodynamic feedback may therefore be present whereby the extension of the delta into the Adriatic increases sediment accumulation at the delta and facilitates further progradation. [Copyright &y& Elsevier]

Abstract: Since 1988, geomorphologic research based on field surveys and photo-geological analysis, has been conducted in southern Tuscany (Italy), in areas characterised by very rapid morphological evolution. In the area outcrop Pliocene marine claystones uplifted during the Quaternary up to 750 m above sea level, now undergoing intense erosion processes, leading to considerable badlands formation. Morphodynamic analysis, conduced by direct and indirect measurements in a sample area, were taken in order to quantify the erosion rate in badland areas. The “Torrente Piantrafolla” sample area was chosen as representative of the study area; it was most recently monitored during the period Nov. 2000–Feb. 2004. At this time, morphographic and morphometric analyses carried out in selected measurement stations located on slopes, identified gravity as the main morphogenetic process responsible for slope shaping. The calanchi badland areas are characterised by constant and rapid shrinking of their edges resulting from landslides which occur in autumn and winter as a consequence of intense rainstorms. Selected measurement stations indicate an erosion rate value range from 5 to 7.5 cm/y. The comparison between 1976 and 1994 digital elevation models (DEM), obtained from photogrammetric restitution, indicated a mean erosion rate of about 5 cm/y in a nineteen year period. This value, considerably higher than the values measured in other Italian basins, indicate a very rapid evolution of the slopes, due mainly to small earth flows inside calanchi badlands. [Copyright &y& Elsevier]

In the present paper the morphodynamics of sand waves in the Messina Strait, Italy, is analysed by comparing data gathered during two different surveys carried out in 1991 and 2001, respectively. In particular, a morphometric analysis on the most recent data and a qualitative analysis of the differences between bottom bedform patterns, are carried out. At locations characterised by greater depths, only minor changes to the planimetric configuration of the field, i.e. crest orientation (which is seen to be orthogonal to the direction of net gross sand transport) and wave length are observed, while differences in wave length and crest direction are more evident in more shallow areas. On the other hand, wave height has significantly increased in the whole field. A possible explanation of such a change, based on the previsions of a theory which relates sand-wave growth and migration to the main components of the tidal ellipse, is provided. [ABSTRACT FROM AUTHOR]

The high water level and extreme waves that occur during a storm may threaten coastal landscapes, including densely populated zones that may also suffer from erosion, increasing the flooding magnitude and the total risk level. Climate change and future sea-level rise may result in an increased impact of storms due to the changes in the frequency and/or magnitude of the extremes of these water levels and/or waves. Coastal dunes and their associated vegetation communities act as a barrier to storm surges and wind waves, reducing flooding and coastal erosion. Therefore, nature-based solutions to protect coastal areas have gained attention in the last years. This contribution aims at evaluating the effectiveness of dune system rehabilitation as a Disaster Risk Reduction (DRR) measure under the current and future sea level scenarios at a rapidly eroding coastline in Bellocchio (Italy, Northern Adriatic Sea). The design of the dune reconstruction and revegetation was performed according to the morphodynamics and ecosystem characteristics of the current dune system. The effectiveness of the DRR was assessed based on numerical tests. The hydro-morphodynamic model XBeach reproduced morphological changes and inundation caused by a recent extreme event. The proposed DRR results in an increase of 22% of the sediment budget of the dune-beach system under the current sea level, and of the 57% and 82% under future sea level rise, for low and high hazard scenarios, respectively. The maximum water volume of the flooding is reduced by 42% in the current sea level. The expected increase of maximum flooding water volume under future high hazard and low hazard scenarios is reduced of 25% and 59%, respectively. These benefits are discussed along with a simplified cost analysis. It is concluded that the complete rehabilitation (reconstruction and revegetation) of the dune system represents a proper Disaster Reduction Solution under current and future sea level rise scenarios. Image 1 • Numerical modelling of the role of dune vegetation on controlling storm impact. • Dune rehabilitation was tested as a measure to reduce coastal flooding and erosion. • An assessment of a nature-based solution to counteract sea level rise scenarios. • Vegetation increases sediment budged of beach-dune system under overwash conditions. • Reduction of the flooding extension and magnitude by dune system reconstruction. [ABSTRACT FROM AUTHOR]