BUOYANT SPREADING PROCESSES IN POLLUTANT TRANSPORT AND MIXING .1. LATERAL SPREADING WITH AMBIENT CURRENT ADVECTION

Buoyant spreading phenomena are driven by the buoyant horizontal sprea ding force that arises from the density difference between the mixed e ffluent and the surrounding ambient fluid. Such spreading effects, occ urring at either water surface, or bottom, or at terminal levels withi n an ambient density stratification, are significant transport and mix ing processes. A model for the lateral buoyant spreading within a curr ent-advected plume is formulated including several distinct mechanisms : convective spreading with frontal drag effects, interfacial friction , entrainment at the density front, shear flow entrainment, wind-induc ed entrainment, and surface heat exchange. Also, a criterion, based on a flux Richardson number, has been developed that delineates the tran sition between the spreading phase and the subsequent passive ambient diffusion regime. The buoyant spreading model is implemented within th e Cornell Mixing Zone Expert System (CORMIX). Comparisons with availab le laboratory and field data support the accuracy and flexibility of t he model formulation for analyzing complex and diverse plume patterns.