Laboratory study to quantify lower boundary influences on desalination discharges

Brine discharges from desalination facilities represent an important environmental consideration surrounding the use of desalination technologies. These discharges are typically released through a series of subsurface discharge ports, and the ability to quantify their flow behaviour is critical to mitigating adverse environmental effects. Previous experimental studies on desalination discharges or Inclined Negatively Buoyant Jets have highlighted discrepancies in the dilution measurements reported in the literature. These discrepancies are potentially due to the inconsistent treatment of the lower boundary in the experimental setup, which in practice represents the seabed. This issue is investigated through a series of experiments using the Laser Induced Fluorescence method. Three discharge angles (300, 450 and 600) are tested and the non-dimensional source height above the boundary (H/F0d) is varied between 0.06 and 1.84 (termed the bed proximity parameter). The results illustrate a relationship between dilutions measured at common reference points near the boundary and the bed proximity parameter. Dilutions are also shown to decrease by up to 30% compared to experiments without lower boundary influence. The outcomes from this study provide valuable insight into the previously reported discrepancies and enable the lower boundary to be incorporated into the design of desalination discharge systems. •An experimental program was developed to investigate the influence of a lower boundary on desalination discharges.•Experiments were carried out using the Laser Induced Fluorescence (LIF) method.•Geometric and dilution results were extracted from the experiments and used to characterise the flow behaviour.•Empirical equations were developed to predict flow dilutions at key reference locations along the flow path.•Empirical equations were developed to determine whether the lower boundary will impact the flow behaviour.