[1] Enhanced understanding of information propagation by waves in rivers is essential in the cont... more [1] Enhanced understanding of information propagation by waves in rivers is essential in the context of fluvial hydraulics and morphodynamics. Lanzoni et al. [2006] are complimented for their interesting contribution, which would help to understand the long waves in fluvial flows with sediment transport and morphological evolution. The investigation is formulated on the basis of a set of hyperbolic equations under the framework of shallow water hydrodynamics. However, the continuity equation of the fluid phase features a formal flaw. This comment presents the correct continuity equations, identifies the flaw, and briefly addresses its potential impact on the analysis of fluvial processes.
The Committee Firenze 2016, on the occasion of the 50th anniversary of the tragic 1966 flood, inv... more The Committee Firenze 2016, on the occasion of the 50th anniversary of the tragic 1966 flood, invited six engineers and scientists to form an International Technical Scientific Committee (ITSC) to assess the current status of flood protection for the city of Florence and identify steps to reduce the risk of flooding facing the city. In this final Report, ITSC concludes that Florence remains at risk to significant flooding and this risk grows each day. It is not a question of whether a flood of the magnitude of 1966 or greater will occur, but when. In fact, the level of protection that exists in Florence now is not on a level appropriate to the citizens and treasures that rest within the city. If, under current conditions, a 1966-like flood occurred, the consequences to human lives, treasures, properties and community infrastructure could be much more catastrophic than they were in 1966.
We survey the problem of the response of coastal wetlands to sea level rise. Two opposite views h... more We survey the problem of the response of coastal wetlands to sea level rise. Two opposite views have traditionally been confronted. According to the former, on the geological time scale, coastal lagoons would be ‘ephemeral’ features. The latter view maintains that marshes would keep pace with relative sea level rise as, increasing the rate of the latter, the sedimentation rate would also increase. In any case, the timescale of morphodynamic evolution is of the order of centuries, which makes it not easily perceived. For example, in Venice, the diversion of the rivers debouching into the lagoon undertaken in the Renaissance has taken centuries to display its consequences (shift from depositional to erosional environment). This process accelerated in the last two centuries due to effects of the industrial revolution and of an enhanced sea level rise. Recent research has employed powerful computational techniques and advanced models of marsh vegetation. Zero-order modeling suggests tha...
ABSTRACT We explore the problem of morphodynamic equilibrium of tidal channels, bounded seaward b... more ABSTRACT We explore the problem of morphodynamic equilibrium of tidal channels, bounded seaward by a tidal sea and shoaling landward as observed in coastal lagoons and estuaries. These channels are typically landward converging, meandering and bounded by tidal flats periodically flooded by the tidal wave. We then attempt to provide an answer to the following questions. How is equilibrium defined for tidal channels? Do tidal channels have an equilibrium length with a predictable bed profile? Why are channels typically converging? What fundamental differences exist between lagoon channels and estuaries? We identify three distinct cases. The first (coastal) case concerns the 'short' tidal channels observed in coastal wetlands and lagoons: their dis-tinct feature is the absence of a fluvial supply of fresh water and sediments. This case has been fully explored. In particular, Seminara et al. (2010) showed that rigorous conditions of static equilibrium exist and require that the sediment flux must vanish at each instant throughout the tidal cycle. The equilibrium length is proportional to the inlet depth and decreases as convergence, roughness or tidal amplitude increase. These channels satisfy the so called O'Brien law. Results have been substantiated by detailed laboratory measurements of Tambroni et al. (2005a). The second (fluvial) case concerns the transition of a river into a tidal channel characterized by fairly 'small' tidal oscillations. We derive a perturbation solution for flow and bed topog-raphy showing that equilibrium arises from a balance between the aggrading effect of channel divergence and the opposite effect of the residual sediment flux driven by tide propagation. The third (estuarine) case concerns the transition of a river into a tidal channel characterized by fairly 'large' tidal oscillations. We derive a numeri-cal solution for flow and bed topography able to describe conditions intermediate between the two limit cases discussed previously. Results show that the model is able to describe a wide class of settings: ranging from fluvial dominated estuaries to tidally dominated estuaries, where the equilibrium profile tends to the 'coastal' profile, with some correction needed in order for the hydrodynamics to accommodate the fluvial transport.
Bedrock rivers link climate, tectonics, and topography, and drive landscape evolution. Sediment i... more Bedrock rivers link climate, tectonics, and topography, and drive landscape evolution. Sediment in bedrock channels plays a major role in their dynamics, because bedrock abrasion due to impacts from saltating bedload particles is an important, and sometimes dominant, erosive mechanism. However, because bedrock channels are characterized by conditions where sediment supply is less than the channel's transport capacity, morphodynamic theory that has provided valuable insights on alluvial rivers cannot readily be applied to bedrock systems. Here I present some recent work aimed at improving our ability to model and understand the morphodynamics of bedrock rivers, particularly the effects of sediment on channel evolution. I will present a theoretical framework for the morphodynamics of bedrock-alluvial channels that overcomes the restrictive assumption of sufficient sediment supply by reformulating the sediment continuity equation to account for temporal changes in the areal concent...
Evaluating the implications of common features that we observe in meandering landforms on Mars an... more Evaluating the implications of common features that we observe in meandering landforms on Mars and on the Earth in a variety of hydrodynamic and geomorphic environments is crucial for our understanding of the relevant dynamic and morphologic processes, and possibly relevant to the ongoing debate over martian waters. A theoretical framework and martian data from accurate geomorphic analyses, jointly with the results of a famous dataset on earth meandering forms, provide striking evidence for common structures of meanders regardless of gravity, basic erosional properties, relevant dynamics and fluid properties. Evidence for a link between the martian and earth landforms, and for the immaturity of martian meanders, appears to suggest the past existence on Mars of massive and ephemeral outbursts of fluid (not necessarily water) driven by gravity or density gradients.
Stability of salt marshes is a very delicate issue depending on the subtle interplay among hydrod... more Stability of salt marshes is a very delicate issue depending on the subtle interplay among hydrodynamics, morphodynamics and ecology. In fact, the elevation of the marsh platform depends essentially on three effects: i) the production of soil associated with sediments resuspended by tidal currents and wind waves in the adjacent tidal flats, advected to the marsh and settling therein; ii) production of organic sediments by the salt marsh vegetation; iii) soil 'loss' driven by sea level rise and subsidence. In order to gain insight into the mechanics of the process, we consider a schematic configuration consisting of a salt marsh located at the landward end of a tidal channel connected at the upstream end with a tidal sea, under different scenarios of sea level rise. We extend the simple 1D model for the morphodynamic evolution of a tidal channel formulated by Lanzoni and Seminara (2002, Journal of Geophysical Research-Oceans, 107, C1) allowing for sediment resuspension in the...
[1] Enhanced understanding of information propagation by waves in rivers is essential in the cont... more [1] Enhanced understanding of information propagation by waves in rivers is essential in the context of fluvial hydraulics and morphodynamics. Lanzoni et al. [2006] are complimented for their interesting contribution, which would help to understand the long waves in fluvial flows with sediment transport and morphological evolution. The investigation is formulated on the basis of a set of hyperbolic equations under the framework of shallow water hydrodynamics. However, the continuity equation of the fluid phase features a formal flaw. This comment presents the correct continuity equations, identifies the flaw, and briefly addresses its potential impact on the analysis of fluvial processes.
The Committee Firenze 2016, on the occasion of the 50th anniversary of the tragic 1966 flood, inv... more The Committee Firenze 2016, on the occasion of the 50th anniversary of the tragic 1966 flood, invited six engineers and scientists to form an International Technical Scientific Committee (ITSC) to assess the current status of flood protection for the city of Florence and identify steps to reduce the risk of flooding facing the city. In this final Report, ITSC concludes that Florence remains at risk to significant flooding and this risk grows each day. It is not a question of whether a flood of the magnitude of 1966 or greater will occur, but when. In fact, the level of protection that exists in Florence now is not on a level appropriate to the citizens and treasures that rest within the city. If, under current conditions, a 1966-like flood occurred, the consequences to human lives, treasures, properties and community infrastructure could be much more catastrophic than they were in 1966.
We survey the problem of the response of coastal wetlands to sea level rise. Two opposite views h... more We survey the problem of the response of coastal wetlands to sea level rise. Two opposite views have traditionally been confronted. According to the former, on the geological time scale, coastal lagoons would be ‘ephemeral’ features. The latter view maintains that marshes would keep pace with relative sea level rise as, increasing the rate of the latter, the sedimentation rate would also increase. In any case, the timescale of morphodynamic evolution is of the order of centuries, which makes it not easily perceived. For example, in Venice, the diversion of the rivers debouching into the lagoon undertaken in the Renaissance has taken centuries to display its consequences (shift from depositional to erosional environment). This process accelerated in the last two centuries due to effects of the industrial revolution and of an enhanced sea level rise. Recent research has employed powerful computational techniques and advanced models of marsh vegetation. Zero-order modeling suggests tha...
ABSTRACT We explore the problem of morphodynamic equilibrium of tidal channels, bounded seaward b... more ABSTRACT We explore the problem of morphodynamic equilibrium of tidal channels, bounded seaward by a tidal sea and shoaling landward as observed in coastal lagoons and estuaries. These channels are typically landward converging, meandering and bounded by tidal flats periodically flooded by the tidal wave. We then attempt to provide an answer to the following questions. How is equilibrium defined for tidal channels? Do tidal channels have an equilibrium length with a predictable bed profile? Why are channels typically converging? What fundamental differences exist between lagoon channels and estuaries? We identify three distinct cases. The first (coastal) case concerns the 'short' tidal channels observed in coastal wetlands and lagoons: their dis-tinct feature is the absence of a fluvial supply of fresh water and sediments. This case has been fully explored. In particular, Seminara et al. (2010) showed that rigorous conditions of static equilibrium exist and require that the sediment flux must vanish at each instant throughout the tidal cycle. The equilibrium length is proportional to the inlet depth and decreases as convergence, roughness or tidal amplitude increase. These channels satisfy the so called O'Brien law. Results have been substantiated by detailed laboratory measurements of Tambroni et al. (2005a). The second (fluvial) case concerns the transition of a river into a tidal channel characterized by fairly 'small' tidal oscillations. We derive a perturbation solution for flow and bed topog-raphy showing that equilibrium arises from a balance between the aggrading effect of channel divergence and the opposite effect of the residual sediment flux driven by tide propagation. The third (estuarine) case concerns the transition of a river into a tidal channel characterized by fairly 'large' tidal oscillations. We derive a numeri-cal solution for flow and bed topography able to describe conditions intermediate between the two limit cases discussed previously. Results show that the model is able to describe a wide class of settings: ranging from fluvial dominated estuaries to tidally dominated estuaries, where the equilibrium profile tends to the 'coastal' profile, with some correction needed in order for the hydrodynamics to accommodate the fluvial transport.
Bedrock rivers link climate, tectonics, and topography, and drive landscape evolution. Sediment i... more Bedrock rivers link climate, tectonics, and topography, and drive landscape evolution. Sediment in bedrock channels plays a major role in their dynamics, because bedrock abrasion due to impacts from saltating bedload particles is an important, and sometimes dominant, erosive mechanism. However, because bedrock channels are characterized by conditions where sediment supply is less than the channel's transport capacity, morphodynamic theory that has provided valuable insights on alluvial rivers cannot readily be applied to bedrock systems. Here I present some recent work aimed at improving our ability to model and understand the morphodynamics of bedrock rivers, particularly the effects of sediment on channel evolution. I will present a theoretical framework for the morphodynamics of bedrock-alluvial channels that overcomes the restrictive assumption of sufficient sediment supply by reformulating the sediment continuity equation to account for temporal changes in the areal concent...
Evaluating the implications of common features that we observe in meandering landforms on Mars an... more Evaluating the implications of common features that we observe in meandering landforms on Mars and on the Earth in a variety of hydrodynamic and geomorphic environments is crucial for our understanding of the relevant dynamic and morphologic processes, and possibly relevant to the ongoing debate over martian waters. A theoretical framework and martian data from accurate geomorphic analyses, jointly with the results of a famous dataset on earth meandering forms, provide striking evidence for common structures of meanders regardless of gravity, basic erosional properties, relevant dynamics and fluid properties. Evidence for a link between the martian and earth landforms, and for the immaturity of martian meanders, appears to suggest the past existence on Mars of massive and ephemeral outbursts of fluid (not necessarily water) driven by gravity or density gradients.
Stability of salt marshes is a very delicate issue depending on the subtle interplay among hydrod... more Stability of salt marshes is a very delicate issue depending on the subtle interplay among hydrodynamics, morphodynamics and ecology. In fact, the elevation of the marsh platform depends essentially on three effects: i) the production of soil associated with sediments resuspended by tidal currents and wind waves in the adjacent tidal flats, advected to the marsh and settling therein; ii) production of organic sediments by the salt marsh vegetation; iii) soil 'loss' driven by sea level rise and subsidence. In order to gain insight into the mechanics of the process, we consider a schematic configuration consisting of a salt marsh located at the landward end of a tidal channel connected at the upstream end with a tidal sea, under different scenarios of sea level rise. We extend the simple 1D model for the morphodynamic evolution of a tidal channel formulated by Lanzoni and Seminara (2002, Journal of Geophysical Research-Oceans, 107, C1) allowing for sediment resuspension in the...
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Papers by Giovanni Seminara