Design considerations for tunnelled seawater intakes

Abstract

As a result of prolonged drought conditions and declining raw water storages, six large capacity seawater reverse osmosis (SWRO) desalination plants were constructed to secure the water supplies of the five major Australian state capital cities. For a variety of reasons including capacity, local geology, site topography, environmental concerns as well as the construction programme and construction risk mitigation considerations associated with hostile marine conditions, tunnels were adopted for five of the SWRO plants, connecting the desalination plants with their open intakes and brine concentrate outfall systems. The tunnel system is a relatively new concept for SWRO intake and outfall design. The design of marine intake and outfall works is very complex because of the wide range of constraints that must be accommodated as well as the hydraulic interactions among the intake system, pretreatment facilities, desalination plant, and outfall system over a wide range of possible climatic, physical, and operational conditions. The challenges posed in the design and construction of tunnel and marine structures in high-energy open ocean environments are presented. These challenges include those associated with waves and currents, short- and long-term hydraulic considerations, durability and corrosion, biofouling control, and ongoing operation and maintenance. Different intake design approaches at two of the Australian SWRO plants are discussed.