Trade-offs and synergies in river-coastal restoration for the Ebro case (Spanish Mediterranean) Agustín Sánchez-Arcilla, Luis Garrote, Vicente Gracia, Iván Cáceres, Xavier Sánchez-Artús, et al. Nature Conservation, 2025 The paper tackles some of the major challenges associated with coastal risk reduction, based on restored river-delta-coast continuums. The presented approach builds on the Ebro River-Delta system, located in the Spanish Mediterranean coast, where available data and results from hands-on restoration actions provide quantitative evidence on the synergies and trade-offs when implementing restoration. The work addresses the evolution of climatic- and human-induced risks driven by recent deltaic evolution, starting in the 1960s, when socioeconomic development increased and river regulation by large dams in the lower river course started. Such development has driven up freshwater demand, consequently diminishing both liquid and solid discharges in the river system, which has affected the natural deltaic evolution, compounded by sea-level-rise and changes in storminess due to global warming. Evolving erosion and flooding risks (problem symptoms) consider the decrease in sediment input to the delta and the increase in mean sea level (problem origin). To address the origin of the problem, we address sediment availability and transport in the lower river coast and reservoirs, followed by an assessment of sediment transport and deficit at the coastal fringe. The proposed solutions consider reservoir by-pass techniques, sediment mobilisation and downstream transport, as well as downstream transport capacity under present and future climates. Regarding the problem symptoms, we analyse the alternatives to enhance coastal resilience by means of restored coastal roughness resulting from embryonic dunes, lagoons and ridge and runnel topography. The analysis also considers coastal sediment recycling, based on a combination of wind and wave induced transports that provide a natural conveyor belt in dynamic equilibrium. Finally, the paper systematises the main synergies and trade-offs that must be considered in any coastal restoration plan, targeting a low carbon reduction of coastal risks while maintaining the important socio-economic assets in the river-delta-coast system. The conclusion section briefly explores the extrapolation of the proposed approach to other vulnerable coastal regions in Europe.
Coarse Sand Transport Processes in the Ripple Vortex Regime Under Asymmetric Nearshore Waves N. Fritsch, G. Fromant, D. Hurther, I. Cáceres Journal of Geophysical Research Oceans, 2024 Large‐scale wave flume experiments are conducted in the ripple vortex regime to study near bed coarse sand transport processes below asymmetric surface waves typical of the coastal nearshore region. For this purpose, a set of complementary acoustic instruments were deployed under regular nearshore wave conditions. Time‐resolved velocity, sand concentration and sand flux profiles are measured across both the dense bedload and dilute suspension layers with an Acoustic Concentration and Velocity Profiler. The equilibrium 2D suborbital ripples are in good agreement in terms of dimensions, shape and onshore migration rate with Wang and Yuan (2018, https://doi.org/10.1029/2018jc013810, 2020, https://doi.org/10.1016/j.coastaleng.2019.103583). Stoss ripple vortex entrainment around the trough‐to‐crest flow reversal (FR+) is found to be more energetic in terms of sand pick‐up into suspension compared to the counter rotating lee side vortex around the FR‐ flow reversal, as a consequence of the onshore skewed wave acceleration. Ripple vortex driven nearbed velocity phase leads around both flow reversals exceed typical bed friction induced values found in turbulent Wave Boundary Layers. Intrawave sand erosion events can be distinguished locally at the two ripple vortex positions around the flow reversals and two events more uniformly distributed along the ripple profile at wave crest and trough. Spatial fields of sand flux reveal the origin of the net onshore directed suspended and bedload transport. Good agreement is found with the mechanism identified under asymmetric oscillatory flows in Wang and Yuan (2020, https://doi.org/10.1016/j.coastaleng.2019.103583). Differences with ripple vortex regime under skewed shoaling waves and symmetric oscillatory flows are highlighted.
Study of Velocity Changes Induced by Posidonia oceanica Surrogate and Sediment Transport Implications Carlos Astudillo-Gutierrez, Iván Cáceres Rabionet, Vicente Gracia Garcia, Joan Pau Sierra Pedrico, Agustín Sánchez-Arcilla Conejo Journal of Marine Science and Engineering, 2024 An analysis of the interactions between wave-induced velocities and seagrass meadows has been conducted based on the large-scale CIEM wave flume data. Incident irregular wave trains act on an initial 1:15 sand beach profile with measurement stations from the offshore of a surrogate meadow until the outer breaking zone, after crossing the seagrass meadow. The analysis considers variability and peaks of velocities, together with their skewness and asymmetry, to determine the effects of the seagrass meadow on the near bed sediment transport. Velocity variability was characterized by the standard deviation, and the greatest changes were found in the area right behind the meadow. In this zone, the negative peak velocities decreased by up to 20.3%, and the positive peak velocities increased by up to 11.7%. For more onshore positions, the negative and positive peak velocities similarly decreased and increased in most of the studied stations. A progressive increase in skewness as the waves passed through the meadow, together with a slight decrease in asymmetry, was observed and associated with the meadow effect. Moving shoreward along the profile, the values of skewness and asymmetry increased progressively relative to the position of the main sandbar. The megaripple-like bedforms appeared earlier when the meadow was present due to the higher skewness, showing a belated development in the layout without the meadow, when skewness increased further offshore due to the proximity of the breaker sandbar. To assess the sediment transport capacity of a submerged meadow, the SANTOSS formula was applied, showing that in front of the meadow, there was a higher sediment transport capacity, whereas behind the meadow, that capacity could be reduced by up to 41.3%. In addition, this formula was able to produce a suitable estimate of sediment transport across the profile, although it could not properly estimate the sediment volumes associated with the bedforms generated in the profile.
Influence of Beach Slope on Morphological Changes and Sediment Transport under Irregular Waves Sara Dionísio António, Jebbe van der Werf, Erik Horstman, Iván Cáceres, José Alsina, et al. Journal of Marine Science and Engineering, 2023 This paper presents new data from large-scale wave flume experiments. It shows the beach profile evolution and sediment transport for two different bed slopes (1:15 and 1:25), and three irregular high-energy erosive wave conditions and one low-energy accretive wave condition. The bulk cross-shore net sediment transport was investigated for the total active profile and for the surf and swash zone separately. It is shown that the steep slope is morphologically more active than the gentle slope, with faster and more pronounced morphological changes and larger sediment transport rates. For both slopes, the total and surf zone net sediment transport were offshore-directed for erosive waves and onshore-directed for the accretive wave condition. However, the net swash zone transport for the erosive wave conditions was offshore-directed for the steep slope and onshore-directed for the gentle slope. The direction and magnitude of the total and surf zone sediment transport correlate well with the slope-corrected Dean criterion with increasing offshore-directed sediment transport (erosion) observed for increasing wave energy and bed slope. This relation does not hold for the swash zone sediment transport along the gentle slope, suggesting that swash zone sediment transport processes are not well captured when using a simple predictor such as the (modified) Dean number. Differences in sediment transport in the swash for the different slopes are likely influenced by differences in incoming wave energy, wave–swash interactions and the relative importance of long- and short-waves.
Effectiveness of Dune Reconstruction and Beach Nourishment to Mitigate Coastal Erosion of the Ebro Delta (Spain) Giuseppe Pio Costa, Massimiliano Marino, Iván Cáceres, Rosaria Ester Musumeci Journal of Marine Science and Engineering, 2023 Coastal areas facing increasing erosion are resorting to sand displacement strategies to mitigate the erosive impact, which is exacerbated by climate change. In the face of climate change, coastal managers are more frequently resorting to sand displacement strategies to recover eroding coastlines. These vulnerable coastal zones require innovative approaches to minimize the need for frequent sand replenishment, extend their effectiveness and lower their maintenance expenses. This study undertakes a comparison of four primary nourishment strategies—a conventional uniform nourishment technique and the placement of a single sand dune evaluated at three different positions—in contrast to a scenario where no intervention is carried out. The investigation employs the XBeach numerical model to assess the outcomes of these diverse strategies under both low- and high-energetic storm conditions. The case study is a degraded coastal beach in the Ebro Delta (Spain). The results reveal a significant decrease in erosion when the dune is positioned closest to the shoreline. However, this erosion mitigation effect diminishes as the dune is situated further inland. Conversely, the sand nourishment measure exhibits minimal fluctuations in the volume of eroded sand when compared to the scenario with no intervention.
Force Measurements on Storm Walls Due to Overtopping Waves: A Middle-Scale Model Experiment Koen Van Doorslaer, Alessandro Romano, Giorgio Bellotti, Corrado Altomare, Iván Cáceres, et al. Coastal Structures and Solutions to Coastal Disasters 2015 Resilient Coastal Communities Proceedings of the Coastal Structures and Solutions to Coastal Disasters Joint Conference 2015, 2015
Large scale experiments on beach evolution induced by bichromatic wave groups with varying group period Proceedings of the Coastal Engineering Conference, 2014
A hybrid numerical model for coastal engineering problems Proceedings of the Coastal Engineering Conference, 2014
Sandt-pro: Sediment transport measurements under irregular and breaking waves Proceedings of the Coastal Engineering Conference, 2014
Influence of surf-beat on beach morphology and sediment transport 34th IAHR Congress 2011 Balance and Uncertainty Water in A Changing World Incorporating the 33rd Hydrology and Water Resources Symposium and the 10th Conference on Hydraulics in Water Engineering, 2011
3D wave field behind impermeable low crested structures Journal of Coastal Research, 2009
Mobile-bed tests. the sands project Iván Cáceres, Joachim Grüne, Leo Van Rijn, Agustín Sánchez-Arcilla, Alireza Ahmari, et al. Proceedings of the Coastal Engineering Conference, 2009
Comparative study of the hydro-morphodynamic behavior of emerged and submerged structures Ingenieria Hidraulica En Mexico, 2007
Coastal dynamics around a submerged barrier Iván Cáceres, Agustín Sánchez-Arcilla, José-María Alsina, Daniel González-Marco, Joan Pau Sierra Coastal Dynamics 2005 Proceedings of the Fifth Coastal Dynamics International Conference, 2006
