Changes in wave climate and its impact on the coastal erosion in Samborombón Bay, Río de la Plata estuary, Argentina

Abstract

The loss of coastal wetlands, such as salt marshes, seems to be one ofthe consequences of the climatic change, because their locations withinthe intertidal zone make them vulnerable to erosive processes.Consequently, in the face of new environmental conditions, the coast isgradually adjusted to the long-term effects (Nicholls, 2011). In general,salt marshes are in a delicate balance between the lateral erosion oftheir edges and its vertical evolution. This last responds to the balanceamong the sedimentation, erosion, and relative sea level increase(Marani et al., 2011). The lateral erosion of the marsh edges, andconsequently the loss of wetlands, was observed in many sites of theworld highlighting the important role of waves in driving erosionprocesses (Downs et al., 1994; Wray et al., 1995; Day et al., 1998; vande Koppel et al., 2005; Wolters et al., 2005; Ravens et al., 2009; Cowartet al., 2010; Fagherazzi et al., 2013; Francalanci et al., 2013; Leonardiand Fagherazzi, 2014; McLoughlin et al., 2015). In addition, the connectionbetween the wave power and the marsh edge retreating can beappreciated in several coastal areas in the world (e.g. Schwimmer,2001; Marani et al., 2011; Leonardi and Fagherazzi, 2015). It was alsodocumented that waves are able to erode the marsh edge scarp evenwithout a noticeable sea level rise (Fagherazzi et al., 2013; Mariotti andFagherazzi, 2013).More than 4000 km of the Argentine coast (from approximately5000 km of its total length) are being affected by gradual, natural andevident erosive processes (Codignotto et al., 1992; Codignotto andAguirre, 1993). Kokot (1997) reported an increase in the erosive processesalong the coast of Buenos Aires province during the last threedecades of the 20th Century. This author linked the enhanced erosion tochanges in atmospheric and oceanic processes which seem to be aconsequence of climate change. Barros et al. (2000, 2006) found thatthe western border of the South Atlantic High and the atmosphericcirculation over South-eastern South America have slowly shifted towardsthe south during the last decades. This displacement produces ahigher frequency of easterly winds over the Río de la Plata region(SMN, 1992; Simionato et al., 2005; SMN, 2009; Codignotto et al.,2012). The possibility that wind wave heights are actually increasing inthe South-eastern South American Continental Shelf was investigatedby Dragani et al. (2010) who found that the most significant increaseoccurred between the 80´s and the 90´s, and the largest difference betweenboth decades (0.20 m, 9%) was observed to the east of the Río dela Plata mouth (around 34° S 48° W). The wave height increase resultedslightly lower (7%) over the continental shelf and the outer Río de laPlata (Fig. 1). Several works have shown evident changes in the windwave climate in the World Ocean, for example, Cox and Swail (2001)and Young et al. (2011), among others. In addition, regional changes inthe wind wave climate were also investigated in different places of theworld as, for example, on the Australian coast (Hemer et al., 2007) andin Central and South America (Izaguirre et al., 2013; Reguero et al.,2013).