Modelling of stratified flow over topography in semi-deep coastal channels

摘要

Sudden changes of sea bottom topography in coastal channels can be viewed as a source of flow disturbances and turbulent energy transferred into the flow domain causing a series of hydrodynamic phenomena and enhanced mixing between layers of stratified fluid, particularly in regions adjacent to the topography change. As a consequence, resulting gradual destruction of stable density stratification (typically present in coastal channels in summer season) can be accompanied by adverse environmental effects if, for example, large amounts of wastewater is being discharged in the region affected by the obstacle. In such conditions, increased mixing and partial or complete homogenisation of water column in the vicinity of the obstacle can cause submerged field of wastewater mixture to reach the sea surface, causing aesthetic nuisances and water quality problems in wider region around the submarine source of pollution. In such situations, estimate of spatial extent of the zone which is hydrodynamically affected by the obstacle assumes great environmental importance and calls for application of hydraulic and/or 3-D mathematical models, suitable for stratified flow analysis. Faced with lack of field data, modelling approach, supported by modeller's intuition and available literature data, remains very often the only means for qualitative and quantitative analysis of the nature of local hydrodynamic phenomena caused by the obstacle. In addition to presentation of results of a series of 3-D numerical experiments, this paper deals with the application of obtained results to the Split Channel (Southern Croatia) where several important wastewater treatment and discharge facilities will be put in operation in the near future.