Influencia antrópica en la evolución del paisaje hidrológico de la planicie costera de Ajó (Argentina)

The coastal plain of the Ajó River is part of the Samborombón Bay wetlands. Because of the morphologic setting and the clay soils, the Ajó wetland is frequently inundated during rainy periods. Since 1900, several canals were dug for improving the drainage of surficial water into the bay. Moreover, in recent decades, road embankments were built to facilitate the connection with isolated areas. Satellites images pointed out a "ghost channel", i.e. the potential occurrence of an ancient channel, and its path is evident only in conditions of high soil moisture. Unfortunately, no historical map was found to prove its occurrence. This study is aimed at the reconstruction of paleo-hydrologic setting of the area and at understanding how the engineering works caused the disappearance of the ancient channel influencing the present hydrologic landscape. The investigation was performed through the analysis of topographic maps, satellite images and field surveys. Results highlight that hydraulic works altered the natural hydrology of the Ajó area, because channelization and embanking intersected the path of the ancient natural channel. The distal part of the former channel is silted up while the inner sector has evolved in lowlands because the sediment supply through the tidal flow has ceased.