Lenthals Dam – Queensland, Australia

Project overview


  • Purpose: Increase storage capacity to give an additional 5 yrs water supply
  • Performance requirements: More electro-mechanical operation, Fully automatic to open and close to pass floods and retain FSL, Limit upstream flooding
  • Type: FDS Automatic Crest gates
  • Height of raising : 2 m
  • Size: 4 № 15,8 m long & 1 № 9,8 m long
  • Manual override: yes
  • Material: Gates — mild steel with polyamine coating, Structural frames — Stainless Steel Gr 304L

Location: Hervey Bay, Queensland, Australia

Client: Wide Bay Water Corporation

Consultant: GHD (Brisbane)

Fabricator: Stewart and Sons (Pty) Ltd

Scope of services: Design, Assistance with Fabrication, Installation and Commissioning.

Completion: 2009



Wide Bay Water Corporation required additional water supply to meet the expansion of Hervey Bay and surrounds.  Tenders were called from design consultants and GHD Consulting Engineers were awarded the design based on an innovative design using FDS spillway crest gates.  A further requirement was to limit the backwater rise for more frequent floods in order not to inundate sensitive areas upstream of the dam.  Electrically operated gates were not considered because of the remote location.  The FDS crest gates were selected because they are totally automatic to open and close and could meet the water level rise requirements.


The raised water level height is 2 m and 4 № 14.8 m long and 1№ 9.8 m long gates were fitted to a slightly curved spillway.  Stainless steel support frames were fitted to concrete piers to support the crest gates.

The inlet weirs are clustered in a protected frame on the R.H. flank of the spillway and are specially designed to exclude debris.  The connecting pipework is built into the spillway.  The inlet weirs are set at different levels to ensure the gates open sequentially as the water level rises.

The crest gates have additional inlets for redundancy and all the gates can be opened manually.

Stop logs are provided to isolate a gate against a full head of water. The gates can be floated out if necessary. 

The gates have operated under high flow conditions to open and close automatically.