Investigations and Design of the Hew Pltmooth Sewerage Scheme Ocean Outfall

The paper describes investigations undertaken for the design of an ocean outfall for disposal of treated effluent from the City of New Plymouth's wastewater treatment plant. The outfall is 575 metres long. 950mm diameter and constructed of mild steel pipe. Wind and tidal currents were investigated using current drogues and dye releases. Bathymetric sidescan sonar and subsurface profile surveys were used to select the optimal outfall route. Structural design required research of suitable pipeline materials, corrosion protection systems and an appraisal of potential launching techniques.