Spreading of Nearshore Effluent Discharges on Eroded Sloping Sandy Beaches

A far field modeling study is presented to evaluate the effect of erosion of a sloping sandy beach upon the mixing and dispersion of the effluent discharges from a multiport diffuser. The two-dimensional advection-diffusion equation with multiple point sources is analytically solved and illustrated graphically by plotting contours of solution to replicate the interaction and merging of the nearshore effluent discharged plumes in coastal waters. The compounded shoreline concentration is asymptotically approximated and used as an environmental impact measure to assess how well the effluent plumes are diluted downstream. It is found that the significant increase in maximum concentration value due to erosion can be reduced by adding more ports and extending the diffuser pipe. The result demonstrates that a modern marine outfall system equipped with multiport diffusers does produce lower potential environmental impacts.