Observations of the Zambezi River coastal current
Date
2023
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
The Zambezi River is one of the largest outflows along the Sofala Bank of Mozambique on the east coast of Africa. The interactions between the Zambezi River coastal current and adjacent oceanic waters influence fisheries and ecological processes in the region. This thesis investigates the response of the Zambezi River coastal current to oceanographic forcings using remote observation and in-situ measurements from existing field data. ☐ Daily, high-resolution satellite images of the Zambezi River coastal current were obtained from Aqua-MODIS and composited to generate false-color images. Zambezi River flows through a main channel and tributary onto the shelf waters. The coastal current comprises two dynamic elements: recirculating bulges at the estuary's mouth and a downshelf propagating coastal current extending 330 km equatorward. Relevant non-dimensional numbers such as fractional depth, Richardson, Kelvin, Rossby and Ekman numbers were evaluated to provide insight into underlying dynamics and facilitate comparison with other estuary/river outflows. ☐ Interaction between the bulges occurs when the ratio of the distance between the channels (Dx) to the internal deformation radius (Rd) is less than two. The evolution of bulges also varies over a tidal cycle. The dynamics of Zambezi coastal current are characterized as being between intermediate and bottom advected. The coastal current is typically confined within the Ekman layer. South-westerly winds augment the propagation of downshelf coastal current and Ekman transport advects buoyant waters offshore for easterly and northeasterly (upwelling) winds. Strong upwelling winds can reverse the direction of downshelf propagating coastal currents. Upshelf and downshelf (i.e., bi-directional) flows are observed to occur for moderate wind and low/intermediate flow discharge. When large eddies in the Mozambique channel are sufficiently close to the coast, they perturb the dynamics of bulges and coastal currents. ☐ Keywords: Zambezi River, coastal current, Aqua-MODIS, Scaling Analysis
Description
Keywords
Bulge, Coastal current, River plume, Scaling analysis, Zambezi river