The morphology of sandy coasts, including the shoreline position and the bathymetry of the surf and shoaling zones, quite often displays complex and intriguing patterns. These patterns are sometimes nearly periodic alongshore or at least showing some sort of regularity with an alongshore recurrence length, L, and are then known as rhythmic coastal morphologies. Some types have been defined in the literature (Short, 1999;Ribas et al., 2015) but the extreme complexity of beach dynamics and the increasing capacity and frequency of beach monitoring and field observations often challenge their traditional classification (Guillén et al., 2017).Transverse sand bar systems is one type of those patterns. The term transverse bar (TB) is generically applied to sand bars extending perpendicularly to the coast or with an oblique orientation (Shepard, 1952). They usually occur in patches of a few of them up to tens, they are separated by troughs and they are typically attached to the shore. The alongshore spacing, L, is defined as the distance between successive bar crests. With a dominant longshore current they tend to migrate downdrift with migration rates up to 40 m/d (Ribas and Kroon, 2007;Pellón et al., 2014). They sometimes show an asymmetry of their cross-section (the down-current flank being steeper than the upcurrent flank, Pellón et al., 2014).Several types of transverse bars have been reported in the literature (see, e.g., Pellón et al., 2014;Ribas et al., 2015). The first ones are TBR bars, which are associated to the Transverse Bar and Rip (TBR) state in the standard beach state classification (Wright and Short, 1984). They are typically wide and short-crested and their origin is the merging of the horns of a crescentic bar into the beach. The second type are medium energy finger bars, MEFB, which are sometimes observed in open microtidal beaches under medium-energy conditions (

Field data of a harbour basin are compared with analytical formulations for predicting maximum scouring depth due to propeller jets. Spatial data analysis of seven-year biannual bathymetries quantifies the evolution of the scouring hole along with the sedimentation process within a harbour basin. The maximum scouring depth is found to be of the order of the propeller diameter with a maximum scouring rate within the first six months of docking manoeuvring. Three of the analysed expressions yielded realistic results while observed discrepancies between the theoretical predictions and field data are related to scaling factors. The outcomes of this analysis can be extrapolated to other harbours to improve their management. The obtained results highlight the importance of field data in developing combined physical and numerical models.

The growth of marine traffic in harbors, and the subsequent increase in vessel and propulsion system sizes, produces three linked problems at the harbor basin area: (i) higher erosion rates damaging docking structures; (ii) sedimentation areas reducing the total depth; (iii) resuspension of contaminated materials deposited at the seabed. The published literature demonstrates that there are no formulations for twin stern propellers to compute the maximum scouring depth. Another important limitation is the fact that the formulations proposed only use one type of maneuvering during the experimental campaign, assuming that vessels are constantly being undocked. Trying to reproduce the real arrival and departure maneuvers, 24 different tests were conducted at an experimental laboratory in a medium-scale water tank using a twin propeller model to estimate the consequences and the maximum scouring depth produced by stern propellers during the backward/docking and forward/undocking scenarios. Results confirm that the combination of backward and forward scenario differs substantially from the experiments performed so far in the literature using only an accumulative forward scenario, yielding deeper scouring holes at the harbor basin area. The results presented in this paper can be used as guidelines to estimate the effects of regular vessels at their particular docking location. reducing its operability for larger draft vessels and the area has to be dredged often enough for safe navigation (with sufficient keel clearance). Moreover, an environmental problem can also arise from the scouring effects of stern twin propellers of the vessels, and the increase in marine traffic in ports is also increasing the accumulation of heavy contaminants in some areas of the harbor. One of the engineering solutions to improve the water quality of the harbor is to trap the contaminated sediment below a layer of coarser gravel [2]. However, as reported by [3,4], the action of stern propellers over the seafloor can negate the solution and free the contaminated sediment creating an important issue that correlates sediment resuspension of contaminants due to the stern propellers' effects and water quality requirements of the cruise shipping industry.Therefore, the growth of marine traffic in harbors and its subsequent increase in vessel and propulsion system sizes produces three linked problems at the seabed of the harbor basins: (i) higher erosion rates damaging docking structures; (ii) sedimentation areas reducing the total depth of the harbor basin and its operability; and (iii) resuspension of contaminated materials deposited at the seabed.The formulation published and used so far to investigate the erosion rates of ship's propellers is based on empirical equations with a dependent variable named efflux velocity, V 0 . Efflux velocity is defined as the average velocity of the flux nearby a single propeller in a plane parallel to the propeller blades. The first empirical equation for V 0 was developed by [5,6], and detailed the expression ...

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