Circulation and Suspended Sediment Concentrations in a Highly Stratified Estuary in the Caribbean Sea

Liliana Velasquez Montoya, United States Naval Academy, Naval Architecture and Ocean Engineering Department, Annapolis, MD, United States and Carlos A Escobar, Universidad EAFIT, Departamento de Ingenieria Civil, Medellin, Colombia
The Gulf of Uraba is a microtidal estuary in the southernmost corner of the Colombian Caribbean Sea. As in most developing countries where estuaries are drivers of economic development, the gulf of Uraba is undergoing rapid marine and terrestrial infrastructural advances. Thus, creating an increasing need to understand the circulation and sediment dynamics of the system. Here, field observations during different climatic seasons and a validated three-dimensional numerical model are used to identify flow and sediment concentration patterns in the region. Spatiotemporal analysis of observations and model results reveal a two-layer circulation typical of highly stratified estuaries in the center of the gulf. Such pattern is caused by the freshwater discharge of the Atrato River that typically exceeds 4,000 m3/s. The river’s advection and intensified trade winds during the dry season, can create a three-layer flow in the inner portion of the gulf, while a one-layer outflow with a right-directed rotation occurs in the outer opening to the Caribbean Sea. Comparison of model results with satellite images suggest a strong effect of the migration of the Intertropical Convergence Zone (ITCZ) on the seasonal suspended sediment concentrations. In the rainy season, when the ITCZ is located over the gulf and the winds are slow, the Atrato River turbid plume extends northward and dominates the sediment dynamics. During the dry season when the strong trade winds blow over the gulf, bed transport is enhanced and the river's plume and the litoral drift shift southwards. In addition to identifying patterns and the processes driving estuarine dynamics in the tropics, this study highlights strategies to combine observations and global and local models for regions lacking systematic monitoring efforts of atmospheric, hydrologic, and oceanographic variables.