BUOYANT SPREADING PROCESSES IN POLLUTANT TRANSPORT AND MIXING .2. UPSTREAM SPREADING IN WEAK AMBIENT CURRENT

Buoyant upstream spreading forms part of the more or less radial spreading motion that occurs when a continuous buoyancy source exists within a weak ambient flow. Such buoyancy source may be located at the water surface, or bottom, or at a terminal level within an ambient density stratification, and follows the initial mixing phase of a pollutant discharge, The upstream spreading flow stagnates against the oncoming ambient flow, and is ultimately diverted in the downstream direction, The numerical solutions by Jones, Jirka and Caughey (1983) for the buoyant spreading flow with a drag-like arresting mechanism at the density front is used to predict the overall properties of the spreading motion for different ambient conditions. Data from laboratory experiments and from field observations are in good agreement with the model predictions.