Long-term morphodynamic evolution of the Llobregat Delta under climate change conditions
Tipus de documentTreball Final de Grau
Data2020-11-24
Condicions d'accésAccés obert
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Abstract
Global warming will produce important effects at the coasts mainly due to sea level rise, which will increase the amount of inundation events and the erosion trends. The delta planes are particularly vulnerable because of their low altitudes, and this is especially critical if they are highly populated as occurs in the Llobregat delta (Barcelona). The present project focuses on the southern side of the delta, which consists of a long stretch of sandy coast ranging from the Garraf Mountain chain up to the groin of the Llobregat outfall. It includes the sandy beaches of the cities of Castelldefels, Gavà, Viladecans and El Prat. The management of such coastal erosion problems would strongly benefit from a good knowledge of the time dynamics of the system under different climate change scenarios. The long-termevolution of sandy coasts is caused by gradients in the sediment transport, a very complex (and partially unknown) process driven by surface wave orbital motion and wavedriven mean currents. The corresponding sediment erosion and deposition patterns change the shoreline position and the sea bed, which in turn affects the wave and current dynamics. This can produce strong feedback processes and a rich nonlinear dynamical behaviour. The nonlinear Q2Dmorfo model (Arriaga et al., 2017) is adequate to capture these mechanisms and hence to reproduce the evolution of the coast at scales from years to decades. It describes the propagation of monochromatic waves over the variable bathymetry using linear ray theory, computes the corresponding wave-driven alongshore sediment transport and includes the cross-shore transport in a simplified way. The essential simplification is that it does not resolve the full surf zone hydrodynamics. So far, the model has been mostly used assuming a constant sea surface level. However, the slow sea level rise due to global warming can influence the dynamics at such long-term time scales. Storm surges, that is, the mean sea level rise at the coast due to storms, can also play a role. Some improvements have been recently incorporated in the model (e.g., solid lateral boundary conditions, a variable sea level and alongshore-variable wave conditions). The Q2Dmorfo model, written in Fortran77 language, has been developed by the UPC research group where this TFG was done. The model was first applied to the past observations at the southern side of the Llobregat delta data in order to validate it for a 5 year-long period (2012-2017). Finally, the model was forced with offshore data of the future 50 yr corresponding to different scenarios of climate change (including sea level rise). Thewave conditionswere based on measured past data. The available past data included hourly (alongshore-variable) wave conditions in front of the coast (at 10-20 mdepth), hourly sea surface level at the Barcelona harbour, yearly shoreline positions extracted from aerial ortophotos, several topographies measured with LIDAR and a few bathymetries. The three latter data sets were provided by researchers form the Institut de Ciències del Mar (ICM, CSIC, Barcelona). The future sea level datawas provided by researchers from the Institut Mediterrani d?Estudis Avançats (IMEDEA, Mallorca) and are based on the global projections made by Kopp et al. (2014). Although most of the performed simulations blew up before reaching to predict for the desired lapse of time (due to an instability recently described in Falqués et al. (2020)), some general guidelines on the characteristic morphodynamic behaviour of the site have been established. All the sea level rise scenarios studied predict an overall regression of the domain shoreline, particularly accentuated in the region closest to the Llobregat mouth. For the most likely climate change scenario, a loss of 43 % of the initial dry beach area is predicted to occur by 2075.
MatèriesProspecting -- Geophysical methods, Sediment transport, Climatic changes, Prospecció -- Mètodes geofísics, Sediments (Geologia) -- Transport, Canvis climàtics
TitulacióGRAU EN ENGINYERIA FÍSICA (Pla 2011)
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Long-term morph ... mate change conditions.pdf | 5,810Mb | Visualitza/Obre |