## 4 Discussion
### Local Morphodynamics  
Local morphodynamics often diverged from the general pattern of the coastal stretch as a whole, highlighting the importance of local approaches to erosion monitoring. Morpho-sedimentary dynamics were found to vary temporally, as well as spatially, with patterns depending on beach type and exposure. This was consistent with findings that sediment transport and budget will vary locally along a non-straight coastline due to uneven wave attenuation [27]. Variability between segments was high and the magnitude of change was of a similar order for the different periods analysed, from seasonal to decadal, showing how rapidly coastal morphology can change and recover. Over the last decade and from north to south, three zones could be distinguished: the rocky segments in the north, which were morphologically stable, as expected; a central zone of sandy beaches with rocky outcrops, displaying variable patterns but a tendency for erosion; and a southern part covering the beaches close to the city of Espinho that tended towards accretion (Figures 7-12). This pattern also occurred during the second winter (2009/2010), the second year (2010), the second 5-year period (2014-2019) and the last year (2018/2019). The first season and first year showed overall accretion in most segments (12-48), and erosion in some rocky segments (4-7) and the most southern segments (51-52), contradicting the pattern of the later periods. The observed sedimentary dynamics of the rocky shores were unexpected. Detailed analysis showed that differences were found on some sandy patches in the first segments, as well as between rocks, suggesting that there may be artefacts in the DEM due to shadow effects, which are particularly strong in the crevices between rocks (notice that surveys were always done during spring low tide, which may occur at different times of the day, causing more or less shadow) but also near the shoreline, where wave breaking and runup between the rocks and in crevices may have affected DEM precision. During the first 5-year period, the central part of the study area already showed erosion, but mostly in the upper central segments (16-23). The segments to the south of the Aguda breakwater (43-52) showed accretion, which could be (at least partly) attributed to a protective effect of the breakwater. In the second 5-year period, nearly all of the central segments showed erosion and shoreline retreat. In fact, comparing the two 5-year periods, many segments showed the opposite behaviour, particularly in terms of shoreline position (e.g., 28-31, 34, 40, 44). This suggested a change in the spatial pattern between 2008 and 2019, with a trend towards erosion in the central zone and a trend towards accretion for the southern zone of the studied coastal stretch. Notice, that there is a large groyne just south of the study area at Espinho, which may have contributed to the observed updrift accretion. However, this groyne has been there for decades with more or less success in retaining updrift sediments, suggesting that a change in hydrodynamics and/or sediment supply through increased artificial beach nourishments [34] supported the accretion in recent years. The temporal variability observed was likely a result of the different wave and wind patterns, which affected segments differently depending on the local conditions--i.e., geology, exposure, and updrift and downdrift structures. The wave incidence direction and wave impact will depend on the direction of the waves and the segment's orientation. [PERSON] and [PERSON] [49] evaluated the alongshore sediment flux for different wave angles and concluded that coastline segments with different orientations experience different alongshore sediment fluxes. Their results show that the wave angle that leads to the highest value of sediment transport is not necessarily the most oblique wave in shallow water. However, wave incidence will also depend on local hydrodynamics.