Physical models of small-scale geotechnical problems are thought-provoking didactic tools that facilitate the understanding of some physical phenomena and theoretical concepts. In a glass wall tank measuring 150 × 50 × 10 cm, classical two-dimensional seepage problems, such as the flow under sheet pile wall and through earth dams with and without drainage blanket, were reproduced on reduced model tests. Medium sand was used. The total seepage discharges were measured as well as the piezometric heads in certain points of the models. Dyes were applied to reveal the flow lines. The simple and well defined boundary conditions helped introducing methods for tracing flow nets by hand as well through numerical methods, such as the finite element method (FEM). FEM results were compared to the physical model measurements and the flow nets obtained by FEM were superimposed on model photos, enhancing the learning process. More complex phenomena, such as the flow in the unsaturated zone, could also be visualised. This article presents the use of these reduced models as a didactic tool in undergraduate and post postgraduate courses in Civil Engineering at UFRJ.
This article addresses the problem of sedimentation at the entrance of a harbour by evaluating and understanding the sediment dynamics in the adjacent beaches. The results of the methodology applied to acknowledge the beaches' sediment dynamics were used to diagnose the problem's cause and to interpret its evolution. The methodology includes analysis of data from a monitoring programme and process-based mathematical modelling of the alongshore and cross-shore beach dynamics. The integration of both allowed the authors to investigate the hydromorphological behaviour of the harbour-adjacent beaches and to conclude that (i) the harbour and adjacent beaches are a single morphological system, and thus require integrated management; (ii) the study area is exposed to a seasonal wave regime, which induces a local sediment transport pattern and consequently the main seasonal morphological characteristics of the study area; and (iii) the process of sand accumulation at the harbour entrance is irreversible without human intervention. Because harbours should be designed and constructed based on two criteria—capacity of depth self-maintenance and integration, with minimum impact on the local morphodynamics—this study highlights the need for monitoring and identifying the total extension of the active beach, particularly in coastal environments with seasonal hydromorphological variations, before deciding on harbour layout relative to the sedimentary littoral transit.
The protection against a storm event provided by nourishment to Costa da Caparica beaches near Lisbon, Portugal, is investigated numerically with a two-dimensional-horizontal morphodynamic model able to generate and propagate the longer infragravity waves. The beach has a groyne field and a multi-typology backshore. The nourishment of 106 m3 of sand was placed at the beach face and backshore. Pre- and post-nourishment topo-bathymetric surveys of the beach, which suffers from chronic erosion, were performed under a monitoring program. The morphodynamics of the pre- and post-nourished beach when exposed to a simulated historically damaging storm event and the post-storm morphologies were compared to evaluate the efficacy of the nourishment. Results indicate that the lower surface level of the beach face and backshore of the pre-nourished beach induces a larger erosion volume. The nourishment prevented the extreme retreat of the shoreline that occurred during the storm in the pre-nourished beach and reduced the storm-induced erosion volume by 20%, thus protecting the beach effectively against the storm. The beach backshore typology (seawall vs. dune) exerts differential influences on the sandy bottom. As a result, multi-typology backshores induce alongshore variability in cross-shore dynamics. The backshore seawalls exposed to direct wave action cause higher erosion volumes and a larger cross-shore extension of the active zone. The most vulnerable alongshore sectors of the beach were identified and related to the mechanisms responsible for the erosion phenomenon. These findings strengthen the importance of sand nourishment for the protection and sustainability of beaches, particularly those with a seawall at the backshore, where storm events cause higher erosion.
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