Role of the forcing sources in morphodynamic modelling of an embayed beach

Abstract. The sensitivity of a 2DH coastal area (XBeach) and a reduced-complexity (Q2Dmorfo) morphodynamic models to using different forcing sources is studied. The models are tested by simulating the morphodynamic response of an embayed beach in the NW Mediterranean over a 6-month period. Wave and sea level forcing from in-situ data, propagated buoy measurements, hindcasts as well as combinations of these different data sources are used and the outputs are compared to in-situ bathymetric measurements. Results show that when the two models are calibrated with in-situ measurements, they accurately reproduce the morphodynamic evolution with a "Good" BSS (Brier Skill Score). The wave data propagated from the buoy also produces reliable morphodynamic simulations but with a slight decrease in BSS. Conversely, when the models are forced with hindcast wave data the mismatch between the modelled and observed beach evolution increases. This is attributed to a large extent to biased mean directions in hindcast waves. Interestingly, in this small tide site the accuracy of the simulations did not depend on the sea-level data source, and using filtered or non-filtered tides also yielded similar results. These results have implications for long-term morphodynamic studies, like those needed to validate models for climate change projections, emphasizing the need of using accurate forcing sources such as those obtained by propagating buoy data.