Revisiting mobile bed tests for beach profile dynamics

The levels of uncertainty for morphodynamic analysis in the present state of art require field measurements and, whenever possible, large scale mobile bed tests to reproduce what happens in Nature under controlled conditions. Following this idea, the paper will revise the procedure to design reduced scale mobile bed tests, including the criteria for scaling and those for selecting an experimental facility.This will be followed by the description of a set of carefully designed erosion and accretion beach profile tests, carried out at 2 different scales (prototype, large and small scales) and in three different wave flumes in such a way that the results should be fully compatible. From here we shall discuss the fundamental issues about test repeatability, error bounds and the feasibility to extrapolate to other scales.The paper will present next the measurements carried out within the swash zone in one of the flumes. This zone, relatively less studied until recently in the state-of-art, is now the focus of considerable research attention. Its reduced dimensions and the fact that it is alternatively wet and dry will serve to review the advanced observational systems used in the hydraulic tests, and which have allowed recording swash/surf zone processes with an unprecedented level of resolution and accuracy.The paper will end with some discussion about the present and future role of mobile bed tests.