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Title: Effluent dispersion studies and measurement techniques, with particular reference to the Swansea Bay area
Author: Borthwick, I.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1982
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A series of physical oceanographic investigations were carried out in Swansea Bay to assess the hydrodynamics, circulation processes and the diffusion and dispersion characteristics of the area. The study was designed to describe effluent dispersion in the embayment using various measurement techniques. Current-meter stations were established using either long or short period observations, and existing data from various sources was reanalysed. Vertical current and density fields were measured at various locations, and current shear and stratification parameters, and the related Richardson Number were described. A series of surface salinity surveys were conducted over varying environmental conditions. 18 instantaneous point sources of Rhodamine W.T. dye were released in the Bay, to determine the diffusion characteristics prevalent in the area. These experiments were designed specifically to examine two-dimensional horizontal diffusion processes at two levels in the water column, over relatively short time intervals (maximum 6 h). All releases except the Rivers Neath and Tawe utilized a neutrally buoyant source, the exceptions used a buoyant source. The concentration distributions were measured using continuous recording fluorometric instrumentation. Swansea Bay may be divided into 6 regions, each exhibiting distinct flow regimes. Diagrams are presented depicting the generalized circulation patterns at varying stages of the tidal cycle. Residual current analyses indicate a variable residual system. Logarithmic linear velocity profiles are observed throughout the Bay. The embayment is stratified throughout with values of the mean stratification parameter, ranging between 0.26 x 10'3 to 2.36 x 10-1 (S-2 ). The mean vertical current-shear parameter ranges between 9.5 x 10"3 and 2.11 x 10-t (S -1 ). Computed Richardson Numbers are in excess of the critical value, suggesting that vertical turbulence is surpressed by the density structure observed in the region. The dye experiments were analysed using rotationally symmetrical and two-dimensional techniques. Diffusion diagrams were constructed and diffusion relationships computed such that the behaviour of variance with time, and diffusion coefficient with length scale is described. Horizontal variances in the range 105 to 1010 cm2, and horizontal diffusion coefficients in the range 102 to 109 cm2 are observed for time periods of 103 to 104 s. Vertical diffusion coefficients, determined from dye distributions, are in the range 2 to 20 cm s-) and are comparable with those estimated from vertical current data. The experiments carried out in the western and north-eastern sections of the embayment can be characterised by the Joseph and Sender (1958) P-class solution, diffusion velocities in the range 0.42 to 1.14 cm s'( and 0.22 to 0.51 cm s-( were observed in each area respectively. Shear diffusion characteristics are described by a series of relationships between the longitudinal diffusion coefficients and various current velocity parameters.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available