Abstract

  A three-dimensional numerical circulation model of Lake Tanganyika, developed within the Lake Tanganyika Research Project (LTR-FAO/FINNIDA) is described. The model is based on full non- linear hydrodynamics equations, modified according to hydrostatic and Boussinesq approximations. A space-splitting scheme is used for numerical approximation of governing equations. Numerical experiments with different wind loading revealed the rather complicated flow structure in Lake Tanganyika.
   Data for model validation have been collected since May 1993. Main hydrological and meteorological parameters, such as water level, wind speed and direction, air temperature, humidity and water temperature are recorded with automatic devices. A simple Lagrangian approach with floating buoys and GPS system is used for current measurements.
   The obtained surface velocities in different locations lake-wide were compared with the calculated surface currents. Agreement between measured and simulated velocities was satisfactory. Accuracy of the simulations depends on the accuracy of the wind forcing reconstruction. Regular strong winds are observed over Lake Tanganyika during the dry season, a period of trade winds which starts at the end of May and lasts until late August or early September. Numerical experiments with a mesoscale meteorological model (Savijärvi, 1995) showed that the lake-land breeze system is intensified during this period.
   The collected data and the numerical experiments with the circulation model provide a solid base for understanding the main hydrophysical processes on a lake-wide scale. Important knowledge has also been obtained on the spatial and temporal dynamics of currents.

Keywords: Hydrodynamic model; Currents; Particle tracking