PAST, PRESENT, AND EXPECTED HYDRO-MORPHOLOGIC EVOLUTION OF THE BAHIA DE SAMBOROMBON (ARGENTINA) BY REMOTE SENSING DATA

BRAGA F.; CAROL E; CARRETERO S; KRUSE E; POUSA J; RIZZETTO F.; TEATINI P.; TOSI L.

Bologna

Congreso; 7th EUREGEO; 2012

Hydro-geomorphologic setting of coastal areas is the result of complex interactions between marine and continental processes. Lowland morphologies make coastlands the zones at highest hydrogeological risk because of flooding, land subsidence, and saltwater contamination. As many studies have predicted a significant increase of eustacy, sea level rise (SLR) is the most relevant problem affecting coastal lowlands. The wetland of the Samborombon Bay (Argentina) is a Ramsar natural reserve affected to periodic floods due to rainfall, runoff, tidal fluctuations, and storm surges. In this work, we show preliminary results of a project aimed at understanding the effect of expected SLR scenarios on the hydromorphologic setting of the Samborombon Bay. In particular, the outcomes of the first step of the research, i.e., the remote sensing analysis, are illustrated. Satellite images acquired with the same tidal levels were selected and compared to perform the morphological analysis. The available dataset considers the period between 1972 to 2011. In the northern sector, along the coastline no significant morphological modifications in the marshland occurred over the last three decades. However, since the ?990 the ancient shell ridges have been seriously damaged by excavation for mining.  In the central sector, the construction of the Ancillary canal of the Salado River in 1987 accelerated the water and sediment discharges into the bay leading to morphologic changes along the coastline. In the southern coastal plain tidal creek network maintained its shape and extension, whereas a small retreat of the coastline was detected along the southern bay margin (Ajo River mouth). Significant morphologic changes occurred in the Punta Rasa spit. Strong occasional south-eastern wind). The former is related to the long-term water level rise, yielding progressive permanent coastline retreat, lowland flooding, groundwater and soil salinizations. The latter is triggered by anomalous 3-4 m storm surges due to 3-5 day long meteo-marine events whose effects seriously impacts on built-up areas and human activities. Taking into account SLR scenarios of 12, 50, and 300 cm resulting from the past sea level rise in Buenos Aires, the IPCC mid-term scenario, and the 5-year return period of ?sudestadas?, respectively, the flooding extent during an astronomic mean high tide at the end of the 2100 has been simulated. To do this, the digital elevation model (DEM) obtained by the Shuttle Radar Topography Mission (SRTM), ad hoc calibrated/validated for the study area, has been used. Results clearly show that the tidal flats and marshes are expected to be permanently submerged. The extent of the affected areas significantly varies according to the latitude, with the worst situation expected in the southern zones, where the sea could encroach up to 30 km inland. According to this prediction, a serious reduction in the volume of freshwater reserves is expected with a significant decrease of the thickness or freshwater lenses. In the southern sector, SLR will be able to contaminate the whole fresh groundwater lens located in the sandy ridges.