The Cahuil Lagoon, an example of a seasonal estuary in central Chile

Abstract

The hydrological and sedimentological characteristics of the mouth of the Nilahue creek, a body of water known as the Cahuil lagoon, on the coast of the Region VI in Central Chile, are presented. The marked seasonal variability of the mediterranean climatic conditions is demonstrated in the variations of the creek’s runoff, which, upon flowing into the ocean along a wave dominated coast with a high sedimentary transport by the littoral drift, is closed by a sand bar during the summer months. During winter rains the flow increases and the estuary breaks through the bar, connecting it to the ocean, allowing the entrance of the dynamic and salinity tide. During the period with the estuary open to the sea, the salinity distribution behaves like a highly stratified estuary. During the period with low seasonal flow, the lagoon is formed which presents a homogenous salinity with brackish water. The distribution of the sediments during the winter season presents three different depositional environments, one at the mouth of the estuary with a predominance of sandy marine sediments, another in the middle with a predominance of pelitic sediments, and, finally in the upper part, deposits with fluvial characteristics, thereby allowing it to be catalogued as a tidedominated estuary.