Experimental Investigation on Beach Morphodynamics in the Presence of Subsidence

In this paper, we present a model study on beach morphodynamic processes under the combined action of waves and controlled subsidence settlement. A special facility was designed to reproduce controlled seabed movements of a few millimetres. Vertical settlement is obtained with the use of wedges driven by the Archimedean screw. A prototype to model mechanical scale in this particular experiment showed the difficulties of reproducing a test duration that in the prototype could vary from 10 to 100 years. To solve this problem, tests were carried out reproducing only wave conditions able to give significant seabed movement. Measurements of wave heights, beach profiles, and shorelines were made. Results highlight the different effects of subsidence on beach profiles under storm surge, annual average wave conditions, and morphologic wave. Beach profiles and shorelines show a relevant increase in erosion, more evident in the vicinity of the still-water level because of the combined action of waves and subsidence. The net beach recession accompanying sea level rise by Bruun's Rule is different from that obtained under laboratory-controlled settlement. Equations describing quantitatively the erosion caused by settlement in the presence of wave subsidence were found.