Peer ReviewedPostprint (published version

Arriaga García, Jaime

Falqués Serra, Albert

Ribas Prats, Francesca

Ruessink, Gerben

Rutten, Jantien

English

UPCommons

Modelling long-term morphodynamic evolution of mega-nourishments

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Geophysical Research AbstractsVol. 21, EGU2019-13472, 2019EGU General Assembly 2019© Author(s) 2019. CC Attribution 4.0 license.Modelling long-term morphodynamic evolution of mega-nourishmentsJaime Arriaga (1,2), Francesca Ribas (3), Albert Falqués (3), Jantien Rutten (2), and Gerben Ruessink (4)(1) National Autonomous University of Mexico, CONACYT-UNAM, Sisal, Mexico (JArriagaG@iingen.unam.mx), (2)National Autonomous University of Mexico, Institute of Engineering, Sisal, Mexico, (3) Universitat Politècnica de Catalunya,Physics Department, Spain (francesca.ribas@upc.edu), (4) Utrecht University, Department of Physical Geography, Utrecht,the NetherlandsThe Zandmotor (the Netherlands, installed in 2011) is the largest beach nourishment in the world and has thepurpose of mitigating the effects of climate change (de Schipper et al., 2014). Its long-term evolution was recentlyinvestigated with the Q2Dmorfo model (Arriaga et al., 2017), after calibrating and validating the model with 3-yrmeasured morphological data. The results shed light on its diffusion (e.g., predicting a lifetime three times largerthan the expected one in the initial design) and other properties such as its alongshore migration and the feeding ofsand to adjacent beaches. However, the role of the geometry of the mega-nourishment and the wave climate werenot analysed.In this contribution, a method to design an analytical mega-nourishment is applied that allows varying theinitial orientation, shape, and size. This is validated by comparing its evolution with that of the real Zandmotor byforcing both of them with a 50-yr real wave climate based on 5-yr historical data, using Q2Dmorfo model. Oncevalidated, the roles of orientation, shape and volume in the nourishment evolution are investigated. The resultsshow that the initial shape asymmetry only affects the asymmetry in the feeding to adjacent beaches. The beachat the side of the nourishment with the largest slope of the shoreline receives more sediment, not only in the shortterm but also in the long term. The nourishment volume and shape factors control the diffusivity. Smaller andwider nourishments are more diffusive than larger and narrower (more localized) ones.To examine the role of the wave climate, a simplified synthetic wave climate is constructed and validatedwith the evolution of the real Zandmotor bathymetry from January 2012. It is found that at least four waveincidence sectors must be considered, two representing low-angle waves and two representing high-angle waves,to have a good representation of the real climate. More incidence sectors do not improve significantly the results.The sensitivity of the nourishment evolution to the probability of occurrence of the oblique wave sectors issubsequently investigated. Results show that the wave angle has an important influence on the dynamics ofmega-nourishments and should be taken into account in their design. In particular, the diffusivity decreaseslinearly with increasing frequency of high-angle waves. If high-angle waves dominate (frequency above 80%)erosional hotspots are formed at the sides of the nourishment. This is especially strong when the high-angle wavescome mostly from one side, in which case a dramatic alongshore migration of the nourishment is also produced. Asmaller but significant migration can occur with bimodal wave climates that have a certain directional asymmetry,which at the same time produce an asymmetry in the feeding to adjacent beaches.References:J. Arriaga, J. Rutten, F. Ribas, B.G. Ruessink, A. Falqués (2017), Modeling the longterm diffusion andfeeding capability of a mega-nourishment, Coast. Eng., 121, 1–13.M.A. de Schipper, S. de Vries, J. Rutten, S. Aarninkhof (2014), Morphological development of a mega-nourishment; first observations of the Sand Engine, Coast. Eng., 111, 23–38.

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Modelling long-term morphodynamic evolution of mega-nourishments

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