Ecomorphodynamic evolution of salt marshes: Experimental observations of bank retreat processes

• We observed erosion of salt marshes subjected to tidal and wind wave oscillations.
• Experiments were performed with both vegetated and unvegetated salt marshes.
• The formation of tension cracks on the top of the bank triggered mass failures.
• Wave impact causes slides and slab/toppling failure events.
• The effect of the vegetation was to delay mass failures.

This paper addresses the problem of the erosion of salt marsh edges. Flume laboratory experiments were carried out aimed at reproducing the instability and retreat of the scarps that typically delimit the salt marshes under the attack of wind waves during the tidal cycle. The bank model and hydrodynamic forcing in the flume were such as to simulate the conditions observed in the field in Venice Lagoon. Experiments were conducted for the same hydrodynamic forcing in the case of two identical banks but with and without the inclusion of the vegetation. Experimental results show that bank retreat involves a variety of processes (including particle erosion, cantilever and slide failures). The effect of the vegetation was to produce a delay in the mass failures, related to a certain growth of plant roots, thus providing an overall stabilizing effect. Bank instability was related to the formation of tension cracks at the bank top and to the impulsive effects associated with wave energy dissipation.