Processes affecting horizontal mixing and dispersion in Winam Gulf, Lake Victoria

Okely, Patricia, Jörg Imberger, and Jason P. Antenucci

Limnol. Oceanogr., 55(5), 2010, 1865-1880 | DOI: 10.4319/lo.2010.55.5.1865

ABSTRACT: Several large rivers enter Winam Gulf, a large shallow semi-enclosed embayment of Lake Victoria. Given the vast spatial scale of this embayment (1400 km2), horizontal transport of waterborne material plays a major role in determining its biochemical properties. To identify the dominant hydrodynamic characteristics of this horizontal transport, a combination of field data and three-dimensional numerical modeling were employed to investigate effects due to variable wind forcing, riverine inflows, and interactions with the rest of Lake Victoria including astronomical tides and a complex bathymetry. Currents in the Gulf were oscillatory due to periodic wind and tidal forcing leading to surface seiching, with a residual circulation component. In the western region of the Gulf near the connection with Lake Victoria, substantial vertical and horizontal shear in the currents resulted in efficient horizontal dispersion with rates of up to 160 m2 s-1 simulated using numerical tracers. In the eastern region, however, rates of horizontal dispersion were reduced to around 12 m2 s-1. This spatial variability in hydrodynamic conditions underpins regional differences in ecological properties of Winam Gulf.

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