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uMgeni Water Desalination Plants – East Coast, South Africa

In an effort to address water shortage issues in the country, uMgeni Water has proposed desalination plants in Tongaat and Illovu.

 

Overview

Desalination is the process of removing minerals, particularly salt, in sea water to make it consumable.

Two sites, north and south of the Durban metropolitan area, were selected for desalination plants, with capacity of 150 million ℓ/d. Each plant will require 4.5m3/s of seawater. It will return 2.8m3/s of brine to the sea.

Challenges

A key concern was dispersion and impact of the brine waste discharge. The plants would be the largest in southern Africa. They will need to be cost-competitive against the alternative of constructing a large dam.

Our Approach / Services

WSP | Parsons Brinckerhoff was appointed as specialist marine consultant on a detailed feasibility study for the seawater intake and brine outfall works at two large desalination plants proposed for the South African east coast. Due to increasing potable water demand, our client needed to investigate the feasibility of implementing largescale seawater reverse osmosis.

We undertook engineering design services, including cost estimates, and numerical modelling:

  • Modelling of waves and currents, using Delft3D modelling suite, to determine design wave conditions and far-field dispersion of the brine effluent
  • Near-field dilution modelling, to optimise design of brine diffusers, and provide initial dilutions for far-field models

Outcomes

These study outcomes were used in the Environmental Impact Assessment process. There was some

uncertainty about geotechnical conditions at the two sites. We were requested to provide additional investigations.

The results were used to customise the marine works for each site:

  • A sandy beach and seabed at the southern site was suitable for trenching of the intake and outfall pipelines through the surfzone
  • At the northern site, micro-tunnelling with pipejacking was proposed for both intake and outfall conduits. This method takes advantage of shallow bedrock conditions, and avoids construction work in the surfzone. It would be the first application of micro-tunnelling for intakes or outfalls in South Africa.

Facts and Figures

Client: uMgeni Water

Project Date: June 2012 – February 2015

Project Fee: ZAR 1.8 million