Coastal Evolution in a Wetland Affected by Large Tsunamigenic Earthquakes in South-Central Chile: Criteria for Integrated Coastal Management

Abstract

The coastal evolution of the microtidal Tubul-Raqui wetland in south-central Chile (36° S), which historically has been affected by large earthquakes and tsunamis, particularly the 1960 (Mw = 9.5) and 2010 (Mw = 8.8) subduction earthquakes and their associated tsunamis, is analyzed. Historical aerial photographs and topographic and bathymetric surveys from the 1961–2017 period, as well as salinity, sediment, and flora data obtained following the 2010 earthquake were used for comparison with data from prior to the event. A steady state of the shoreline was established, with an average erosion rate of −0.016 m/year in the 1961–2017 period. However, erosion predominated in the period between these two large earthquakes (1961–2009), with an average rate of −0.386 m/year. The wetland dried up, partially recovered saline intrusion a year later, and recovered the salinity conditions it had before the earthquake two years later. The postearthquake effects on the floristic composition were not significant, with the species Spartina densiflora, which presented a high tolerance to these types of changes, predominating. Moreover, 75 percent of the taxa in pre- and postearthquake conditions coincided, with the halophyte species Spartina densiflora, Sarcocornia fructicosa, and Cotula coronopifolia predominating, while the best-conserved community was Spartina-Sarcocornia association located in the saltmarsh. Seven years after the earthquake, the shoreline presented an accretion rate of 2.935 m/year; if the current tectonic conditions prevail, an erosive trend can be expected in the coming decades. The morphological variability and the changes associated with the shoreline in this wetland are strongly controlled by tectonic factors. Criteria aimed at integrated coastal management to promote its occupancy and use in accordance with its evolutionary dynamics are proposed.

Coastal Erosion and a Characterization of the Morphological Dynamics of Arauco Gulf Beaches under Dominant Wave Conditions

“…Furthermore, this uplift destabilized the system, so it is expected that the beach will present more significant coast-line variability than the rest of the Arauco Gulf beaches. In light of this, Martínez et al [33] analyzed the spatio-temporal changes in the coastline after the earthquake of 27 F/2010, establishing the steady state of the shoreline, with an average erosion rate of −0.016 m/year in the 1961-2017 period. However, erosion predominated in the period between these two large earthquakes , with an average rate of −0.386 m/year.…”

“…Some studies have shown that the region's beaches are very sensitive to the uplift and subsidence tectonics associated with earthquakes [30,33,59,60]. Moreover, the increase in the frequency and magnitude of coastal storms in Chile has generated a rise in the erosion rates of the beaches, which explains why they cannot recover [29].…”

“…However, their study had a qualitative approach because they did not quantify the transported sediment. Meanwhile, Martinez et al [33] analyzed the impact on the morphodynamics of the Tubul beach of the uplift of the terrain during the earthquake of 27 February 2010 (Mw = 8.8) through numerical modeling. Their results show a change in the morphological response of the beach for regular wave conditions, increasing the tendency to accretion on the post-tsunami beach.…”

Morphology Recovery and Convergence of Topographic Evolution in the Natori River Mouth after the 2011 Tohoku Tsunami

“…Within the context of this the study and the recent countermeasures proposed by the national government against future tsunamis, long-term coastal and riverine adaptation planning for the Natori River is expected to be approached by the government authorities in the near future in order to make this area a more resilient coastal region against future disasters and climate change issues [71,72]. Furthermore, with regard to the concerns of the resilience of modern coastal regions against large-scale disasters after urbanizing [12,73], this study also emphasizes the importance of extensive interdisciplinary research into the future management in disaster-prone areas.…”

“…Some recent studies have been able to numerically investigate the post-tsunami morphological changes and sediment movements. Monecke et al [11] simulated the cross-shore profile change under the prevailing hydrodynamic conditions to investigate the recovery process, while Martínez et al [12] applied a more complicated sediment transport model (Delft3D) in conjunction with morphology and topography data analysis to discuss the erosive behavior of the microtidal Tubul-Raqui wetland in south-central Chile. In Japan, more thorough and multidisciplinary research of the coastal and riverine damage and recovery after the tsunami was conducted using the sufficient availability of both pre-and post-tsunami data [13][14][15][16][17][18][19][20][21].…”