Mnjoli Dam – Swaziland

Project overview


  • Purpose: Increase storage capacity
  • Performance requirements: Non electro-mechanical operation; Automatic to open to pass floods and close to retain FSL
  • Type: TOPS automatic spillway gates
  • Size: 16 m x 1,5 m high for emergency spillway
  • 12 m x 1,5 m high for service spillway
  • № off: 6 to emergency spillway and 1 to service spillway
  • Storage increase: 22 x 106 m3 (16%)
  • Maximum design discharge: 4000 m3/ sec
  • Manual override: yes
  • Material: mild steel with polyamine coating

Location: Mnjoli Dam, Mbuluzi River, Swaziland

Client and Consultant: Royal Swaziland Sugar Corporation (RSSC)

Contractor (Civil): Construction Associates (Pty) Ltd

Contractor (Mechanical): Iron Engineering (Pty) Ltd

Scope of services: (Turnkey Project) Design of civil works and gates, Project Management, Civil Construction, Fabrication, Installation, Commissioning

Completion: 2008



The Mnjoli Dam is to be raised by 1,5 m to increase capacity by 15 % for the extensive sugar estates at RSSC as well as offset siltation losses and to supply nearby communities.  The first phase was to replace existing fuse embankments on a 100 m wide emergency spillway with automatically opening and closing gates.  The second phase is to install one gate  on the service spillway once environmental processes are completed.


The project was put out to tender by international suppliers of specialist automatic gate systems and it was awarded to Flowgate Projects, Swaziland for the installation of the TOPS gates.

 The gates are designed to pass a PMF of 4000 m3/sec which resulted in support piers being 7 m high to give 6 m of waterway under the gates.

 This was a turnkey project which included the design of the civil works as well as the steel gates.