Loading...
2 results
Search Results
Now showing 1 - 2 of 2
- Coastal ridge constructive processes at a multi‐decadal scale in Barreta Island (southern Portugal)Publication . Herrero, Xabier; Costas, Susana; Kombiadou, KaterinaMultiple ridges across prograding coasts may display variable geometries, commonly expressed through varying elevations. Changes in ridge elevation have been traditionally related to the occurrence of fluctuating progradation rates, which might, in turn, be driven by shifting environmental conditions. Here, we explore the geometry and growth mechanisms of multiple ridges, generated at Barreta Island (Ria Formosa, southern Portugal), as a consequence of the rapid progradation of the island over the last 70 years, following the artificial fixation of the downdrift Faro-Olhao inlet with jetties in 1955. The variability in the morphology of these features was analysed in combination with available wind and wave data, in order to better distinguish growth mechanisms and understand the main parameters determining the final geometry of the observed ridges. The results suggest that (1) most of the identified ridges fall in the beach ridge classification, as they have been mostly built by marine processes, and (2) the parameters derived from, or closely related to wave climate variability (e.g. progradation rates, storm occurrence) can jointly explain most of the observed morphological changes, while aeolian processes played a secondary role. Indeed, ridge geometry appears mainly controlled by progradation rates, with higher ridges associated with lower progradation rates. Progradation rate, in turn, is mostly related to longshore wave power, storminess, and the occurrence storm groups. Yet, the final configuration of ridges can also be affected by runup levels and onshore winds. Therefore, establishing the relation between ridge geometry and wave climate is not a straightforward task, because of the complex processes and interactions that control coastal morphodynamics.
- Exploring controls on coastal dune growth through a simplified modelPublication . Kombiadou, Katerina; Costas, Susana; Roelvink, DanoProcess-based morphodynamic models can be useful in understanding coastal dune responses to disturbances, as well as possible evolutionary patterns. To this aim, we employ Duna, a simplified 1D morphodynamic model, to assess the influence of dune morphology (height and slope) on sand transfer and deposition across the dune profile for different beach widths and wind incidence angles through idealized experiments. Simulations of real conditions show good model performance, both in wind flow reproduction and in topographic change along the dune profiles tested. The idealized experiments show that wind speed increases and sand accumulation decreases logarithmically with dune height and linearly with stoss slope along the dune profile. Fetch and cosine transport limiting parameters are reflected in the sand accumulated windwards from the toe, while sand transfer to the dune appears controlled by multiple factors; the higher the dune and/or the narrower the beach, the likelier that maximum accumulation occurs under oblique winds. Results point to two different types of evolution for high dunes. Either the vegetation is dense enough to maintain the stoss position, in which case vertical growth near-ceases and seaward progradation is promoted, or the stoss is eroded and landward retreat dominates, in which case sand transfer to the crest and lee continues as a mixture of low input from the beach and recycled sand from the stoss. Coastal dunes are sensitive ecosystems whose survival depends on their adaption to changing conditions. Thus, it is important to understand how dune characteristics (i.e., shape, vegetation type, and cover) and prevailing conditions (i.e., wind speed and direction, beach width) determine where and when sand is deposited onto the dune, promoting growth. This is the result of a complex balance between winds that bring sand to the dune from the adjacent beach (main sand provider), the dune topography (decelerating winds near the dune toe and accelerating them along the slope, up to the dune crest) and dune plants (slowing winds down in their vicinity and trapping wind-blown sand). The main controls on these complex interactions have been incorporated into the Duna model for aeolian sand transport. After tuning parameters and verifying that simulated results are accurate, Duna is used to assess the impacts of dune shape (height and slope), beach width, vegetation coverage and wind angles to wind flow and topographic changes on the dune. Results show that both wind speed and sand accumulation vary logarithmically with dune height and linearly with slope. The simulated sand distribution along the dune is used as a basis to draw generalized dune growth patterns. Duna morphodynamic model is calibrated and validated against Computational Fluid Dynamics model results and field dataThe influence of dune shape (height and slope), wind incidence, vegetation density and beach width on dune growth is investigatedDune height and plant cover are the main factors controlling accumulation patterns, sand recycling and vertical growth