Modelling Tsunami-Induced Sediments Transport in the Bay of Tangier - Morocco

The NE Atlantic (NEA) is prone to tsunami impact of tectonic origin. Previous studies and tsunami catalogs report the occurrence of significant events namely the 1 November 1755 and the 28 February 1969. In the NEA, the most impacted areas are the coastal zone of Portugal, Morocco and the Cadiz Gulf in Spain. In this study, we focus on the inland tsunami propagation and the changes in coastal morphology due to sediments transport, erosion, and deposition processes. To do this, we implemented a coupled hydrodynamic and morpho-dynamic numerical code, based on two open sources codes: COMCOT and Xbeach. COMCOT solves the shallow water equations to calculate the tsunami generation, propagation and inundation. The Xbeach solves the advection-diffusion equations to determine the amount of sediments eroded, transported and deposited, taking into account the bed-load and suspended load transport of non-cohesive sediments and suspended load of cohesive sediments. We employ the coupled model for an earthquake-generated tsunami in the Gulf of Cadiz and assess the morphological changes in the Bay of Tangier, Morocco. We simulate different earthquake scenarios and the correspondent tsunami impact using a high-resolution digital terrain model of the Bay of Tangier. Additionally, we use information on the present-day sediment layers characteristics (grain size, type of sediment, thickness, etc.). Our results show that in the case of large tsunami events the Bay of Tangier is vulnerable to tsunami-induced morphological changes. The sediment volume transported by a 1755-like event is circa 35000 m3. Additionally, our results give an insight on the consequences of tsunami impact on the coastal morphology, showing the need to consider erosion/deposition processes as an important component of tsunami hazard assessment. This work is supported by the EU project ASTARTE - Assessment, Strategy And Risk Reduction for Tsunamis in Europe, Grant 603839, 7th FP (ENV.2013, 6.4-3) and the EU project TSUMAPS-NEAM - Probabilistic TSUnami Hazard MAPS for the NEAM Region, Agreement Number: ECHO/SUB/2015/718568/PREV26.