Edge erosion of salt marshes due to surface waves and tide forcing is likely the chief mechanism that models marsh boundaries and by which salt marshes in worldwide coastal areas are being lost. In order to address this problem, experimental observations in a laboratory flume and field measurements in the lagoon of Venice were conducted to understand the main processes controlling marsh edge retreat, with a focus on the erosion mechanisms caused by the action of wind and tidal waves. A physical model reproducing a salt marsh bank was built inside a long wave current flume where random surface waves were generated according to a given wave spectrum. The physical model was constructed with the original soil and plants taken in a marsh of the lagoon of Venice, while the wave climate was reproduced according to field measurements. The experiments were conducted in the case of both unvegetated and vegetated bank: a first set of experiments was carried out considering only tidal wave; in the second, bank models experienced the effect of wind waves superimposed to the tide. The following data were collected during the experiments: wave climate interacting with the bank, flow velocity measurements in the eroded quasi-equilibrium configuration, pressure distribution along bank edge and internal pressure fluctuation and damping due to wave impact. Bank geometry profile and bottom topography at different times have also been collected to characterize the erosion rate with time and the evolution of bank retreat. Subsequent to laboratory activity wave climate was measured close to a marsh edge in the Lagoon of Venice with the aim at identifying wave forcing on the bank surface during a moderate wind event and comparing results with the wave stress experienced by bank models in laboratory tests. Several pressure transducers installed close to the bed were used to collect wave height and wave direction with respect to the edge of the marsh. Laboratory data and field measurement were analyzed and interpreted in order to develop a simple preliminary model describing the retreat processes of a bank edge subjected to wave attack and tidal forcing. The model applies to cohesive banks determining their temporal evolution under specific boundary and initial conditions. It takes into account processes induced by hydrodynamic forcing such as particle by particle erosion and mass failure triggered by the presence of tension cracks, whereas long time scale processes such as deposition and compaction are not considered.

Modeling the Retreat Processes of Salt Marsh Edge / Bendoni M.; Cappietti L.; Francalanci S.; Rinaldi M. ; Solari L.. - ELETTRONICO. - (2012), pp. ---. (Intervento presentato al convegno 2012 Fall Meeting tenutosi a San Francisco nel 3-7 dicembre).

Modeling the Retreat Processes of Salt Marsh Edge

BENDONI, MICHELE;CAPPIETTI, LORENZO;FRANCALANCI, SIMONA;RINALDI, MASSIMO;SOLARI, LUCA
2012

Abstract

Edge erosion of salt marshes due to surface waves and tide forcing is likely the chief mechanism that models marsh boundaries and by which salt marshes in worldwide coastal areas are being lost. In order to address this problem, experimental observations in a laboratory flume and field measurements in the lagoon of Venice were conducted to understand the main processes controlling marsh edge retreat, with a focus on the erosion mechanisms caused by the action of wind and tidal waves. A physical model reproducing a salt marsh bank was built inside a long wave current flume where random surface waves were generated according to a given wave spectrum. The physical model was constructed with the original soil and plants taken in a marsh of the lagoon of Venice, while the wave climate was reproduced according to field measurements. The experiments were conducted in the case of both unvegetated and vegetated bank: a first set of experiments was carried out considering only tidal wave; in the second, bank models experienced the effect of wind waves superimposed to the tide. The following data were collected during the experiments: wave climate interacting with the bank, flow velocity measurements in the eroded quasi-equilibrium configuration, pressure distribution along bank edge and internal pressure fluctuation and damping due to wave impact. Bank geometry profile and bottom topography at different times have also been collected to characterize the erosion rate with time and the evolution of bank retreat. Subsequent to laboratory activity wave climate was measured close to a marsh edge in the Lagoon of Venice with the aim at identifying wave forcing on the bank surface during a moderate wind event and comparing results with the wave stress experienced by bank models in laboratory tests. Several pressure transducers installed close to the bed were used to collect wave height and wave direction with respect to the edge of the marsh. Laboratory data and field measurement were analyzed and interpreted in order to develop a simple preliminary model describing the retreat processes of a bank edge subjected to wave attack and tidal forcing. The model applies to cohesive banks determining their temporal evolution under specific boundary and initial conditions. It takes into account processes induced by hydrodynamic forcing such as particle by particle erosion and mass failure triggered by the presence of tension cracks, whereas long time scale processes such as deposition and compaction are not considered.
2012
AGU Fall Meeting 2012
2012 Fall Meeting
San Francisco
Bendoni M.; Cappietti L.; Francalanci S.; Rinaldi M. ; Solari L.
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/790941
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