Dispersion of a pollutant in an estuarine environment

Iain Cameron

Under license, the Swan Wool Scouring Company discharges a waste effluent into an estuarine environment via a submerged outfall an an ebbing tidal flow. It has been the primary objective of the present thesis to carry out an investigation into the dispersion of this waste effluent by detailed laboratory simulation modelling and field study techniques. The objectives associated with laboratory simulation were to provide details which would enable a more profound understanding of the buoyant jet trajectory and dilution characteristics ascertained from both theoretical and practical determinations. Objectives of the field study were directed at describing what parameters caused major changes in the dynamics of the estuarine environment associated with the Swan River and then using this knowledge to calculate dispersion and dilution coefficients for the discharging waste effluent. The laboratory objectives were achieved through developing a simulated model which used Henderson's (1966) concepts of dynamic similarity and secondary scaling ratios to provide relationships between protype and model. In this laboratory investigation new techniques were developed. to assess trajectory positions and dilution characteristics of a simulated buoyant jet through microdensitometer scanning of photographic negatives and use of an insitu light probe respectively. The buoyant jet's theoretical trajectory position was determined by application of Bosanquet's (1961) theory and when this was compared with laboratory experiments an almost identical trajectory was formed by the simulated buoyant jet. Field study objectives were achieved through measurement of salinity and tidal velocity profiles at various sampling stations in the field location. These parameters were measured over several months of a summer regime as well as throughout tidal oscillations that prevail within the Swan River Estuary. The major results of this investigation were that buoyant jet trajectories have been accurately predicted from application of Bosanquet's theoretical concepts in both laboratory and field environments. Also through this study a more detailed understanding of a buoyant jet's characteristics has been obtained together with new assessment techniques for laboratory modelling and an estimation of the waste effluent's dispersion and dilution coefficients. As a conclusion the present investigation offers that the introduction of a waste effluent to the Swan River Estuary as now licensed does not place any extra environmental stress upon that system, however, before the licensing agreement is renewed further investigation should be conducted into the avenues of long term pollution from BOD and suspended solids content of the waste effluent.

Dispersion of a pollutant in an estuarine environment

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