Mg. Villagrán-Valenzuela, Mauricio

The understanding of morphological processes controlling the evolution of sand spit reformation after a tsunami impact is a challenging and interesting topic, especially in highly energetic and micro tidal environments. A field campaign performed during December 2012 at the Mataquito River mouth in Chile, allowed us to simultaneously monitor topo-bathymetry evolution, wave climate, tidal range, swash zone dynamics and upper beach face evolution over a portion of its sand spit. A video system was set up for a continuous and long-term monitoring of the evolution of the river mouth and sand spit. Primarily, in this work we focus on the application of a video-derived shoreline detection method to assess shoreline evolution and beach cusps migration at hourly scales. We test the method performance on short-term episodic migration of beach cusps recorded during the campaign. Beach face variations at a daily scale were observed, which can be attributed to the migration of beach cusps in the alongshore direction, and linked to wave forcing and alongshore sediment transport.

The capability to predict the long term evolution of coastal state parameters can be severely affected by neglecting major geomorphic forcings. Among these, the effect of tsunamis as been largely neglected along the Chilean coast. In this contribution, we present a qualitative and descriptive assessment of the sudden change induced by the tsunami on a coastal location in Central Chile, and the consequent recovery process. The latter is driven mostly by strong wave forcing, with a very fast recovery capactity. The necessity and consequences of including tsunamis in long term evaluations fo coastal morphology are briefly discussed.