Waimanu Lagoons: Automated Ecological and Flood Protection Control Gate

The ecologically important Waimanu Lagoon system is situated in the tidal zone near to the Waikanae River mouth and is surrounded by residential development. Since around 1983 the pond level has been artificially maintained by a manually operated weir gate that has deteriorated in the coastal environment causing maintenance problems and potential upstream flood risk. The weir gate effectively prevents upstream migration of fish into an area that is ideal for spawning.

Kapiti Coast District Council has undertaken to replace the control gate so that the health of the ponds can be better managed, the upstream flood risk can be reduced and fish passage can be restored.

Our presentation will outline the key considerations in designing and implementing the control gate upgrade including:

• Manual, actuated and passive weir concepts
• The types of packaged weir available off the shelf and the features of these
• Risks involved with weirs including failure, malfunction, human interference
• Environmental benefits to lagoon management
• Aesthetics and safety considerations in a recreation environment
• Integration with fish passage
• Design, procurement and implementation