Design Optimisation of Marine Wastewater Outfalls

This work presents a method that optimises the manifold pipe of a marine wastewater outfall under various hydraulic principles and cost considerations. Costing data from 37 international pipe supply companies providing pipes of various diameters for HDPE, steel and concrete were used to develop hybrid design equations for these three main materials used for outfall construction. These equations optimise the trade-off between pumping head and pipe size as well as the compromise between cost of material and favourable hydraulic characteristics. Various grades for each material were considered if relevant to marine outfalls. The resulting equations are very useful for outfall design, as oversizing of a project can incur unnecessary cost and under-sizing will not fulfil an outfall’s intended hydraulic purpose and will increase the operational cost in terms of energy.