*6.3.2 Discharge through a unidirectional diffuser creating a surfacing plume*

An optimum design with multiple ports (which has lower cost than a single port design) can be found for all cases when the effluent plume is allowed to hit the surface. **Figure 6** shows the variation of *Hsh*, ð Þ *D*<sup>0</sup> *sh*, ð Þ *u*<sup>0</sup> *sh* and *Nsh* as functions of *RB* and *RC*. The discharge velocity needs to be adjusted to ensure uniform flow for *RB* >4*:*2 when brine is blended with SW and CW and for *RB* >9*:*6 when brine is blended with TWE. For other cases, all variables can be adjusted to minimize cost. The required water depth can be seen to reduce as *RB* increases for pre-dilution with SW and CW. This is similar to the case of a single jet with surfacing plume.

For the multiport diffuser designs calculated here, the ratio of offshore distance of the diffuser (*X*) to its length (*L*) is more than 3 for the pre-dilution cases and more than 1.2 for the pre-concentration cases. For these values of *X=L*, the presence

#### **Figure 6.**

*Variation of H, N, D*<sup>0</sup> *and u*<sup>0</sup> *with RB and RC for discharge using a unidirectional diffuser with surfacing plume for Qb* <sup>¼</sup> <sup>1</sup> *<sup>m</sup>*<sup>3</sup>*=s,* <sup>Γ</sup> <sup>¼</sup> <sup>0</sup>*:*<sup>01</sup> *and a desired excess salinity of* <sup>2</sup> *ppt. (variables are scaled differently for the pre-dilution and pre-concentration cases as indicated in the legend).*

of the shoreline is not expected to have a significant effect on outfall dilution (dilution reduction of less than 15% in stagnant receiving water) [21, 22].
