Seasonal Behaviour of Mar Chiquita Tidal Inlet in Relation to Adjacent Beaches, Argentina

Abstract

Mar Chiquita microtidal inlet is subject to seasonal periods of summer sand availability and winter scarcity. In the long-term trend the coast is erosive although the se environments were deposited in the last 5,000 years due to a sea-level fluctuation of 2 m. In the past, the inlet used to migrate northwards and episodically to obstruct.

There are sediment interchanges between the inlet and adjacent beaches. During the summer, sand is stored as a flood-tidal delta covered by flood-oriented megaripples. The ebb channel is narrow, shallow and oriented to the southeast. It's bottom is floored by dunes composed of fine sand and oriented seawards. During the autum and caused by an increase in precipitation, sand is transferred offshore to form an assymetric tidal inlet. The channel bottom becomes floored by lag beach-rock gravels lying over cohesive muds related to the former and extended coastal lagoon. During winter, this ebb-tidal delta bypasses sand to the northern beach. The ebb channel is then oriented to the north east increasing the discharge along the longshore troughs of the northern beach. Sand is therefore transported northwards along this beach and diminishing wave-induced losses downdrift of the hydraulic jetty. Averaging Spring (October), drift reversed and sand is trasported southwards shoaling the inlet, progressively oriented to the southeast again.

Although Mar Chiquita is a typical coastal lagoon, its degree of sediment infill prevents tidal effects within the entire basin. Tidal amplitude diminishes in a short distance along the channel. The inlet flow area is in a first approach in relation to the potential tidal prism, but its main changes are in relation to precipitations within the basin. The minimum flow area can vary 10 times in relation to rainfall within the catchment basin.