Integral modelling of brine discharge in coastal waters

Freshwater is produced from seawater by desalination plants. The by-product of this process is brine which is twice the salinity of the original seawater. There is a need to dilute the brine in order not to affect the ambient environment. This is achieved by discharging at an angle and establishing a mixing zone. The brine discharge is considered a negatively buoyant jet compared to the ambient water because it is heavier and thus will sink to the sea bed. There had been numerous researches on positively buoyant jet in history but only few on negatively buoyant jet. This project is set to apply the integral model, originally for the positive jet, on the negative jet. The integral model is based on several physical principles including the conservation of mass, conservation of total momentum fluxes and conservation of total buoyancy flux. The integral model was applied to the negative jet by closing an equation for Reynolds shear stress by conducting experiments. Experimental results were then extracted and analysed on MATLAB to fit the Reynolds shear stress curve characterised by dual Gaussian. Wang & Law (2002) second-order integral model was modified in order to incorporate the curve-fitting coefficients. This was done by adopting Fox (1970) approach of utilizing the conservation equation of kinetic energy. Subsequently, predictions were made to model real-life inclined discharge trajectory based on the experimental results by Shao (2008). The key alternatives of predictions were Wang & Law second-order integral model, Fox approach using jet coefficients from Wang & Law, Fox approach using plume coefficients from Wang & Law and Fox approach using coefficients obtained from the experiments from this study. It was found that the coefficients from this research produced the closest match to the initial rising stage of the inclined jet. However, the falling stage of the buoyant jet was significantly different from the experimental data by Shao (2008). Several modifications were made to the MATLAB programs in the process. The various modifications and comparisons are elaborated in this report.Bachelor of Engineering (Environmental Engineering