Greater Wellington is trialling a new floodgate device to allow native fish and their juveniles (whitebait) more time to migrate between the sea and freshwater upstream.

Biodiversity Restoration Adviser Anna Burrows says a new fish friendly attachment consisting of a cantilever and counterweight will be fitted to the Otaki River floodgate in early April so that it closes more slowly, allowing fish more time to move upstream on the incoming tide.

"Many of our whitebait need to migrate upstream where they spend their adult lives in our rivers before swimming back downstream to breeding grounds to lay their eggs.

"Floodgates play a critical part in protecting our communities from floods but they can also keep out whitebait as they swim upstream on the incoming tide because they close too quickly.

"This device is designed to help keep the floodgate open long enough for whitebait to move upstream, while not impeding the operation of the floodgate in any way - it won't prevent flow to the sea during flood events." Because the floodgate closes more slowly, more salt water will flow upstream above the gate increasing the length of the stream where whitebait can breed. Increasing the periods when flows occur will encourage a more natural habitat for our native fish and some of our aquatic invertebrates, Anna says. "It's still early days but if the device is successful we will look at installing it on floodgates in other parts of the region."

Fish-friendly rivers - talk

When: Tuesday 5 April at 3pm
Where: Otaki Memorial Hall (Main Hall)

Environmental engineer and conservationist Kelly Hughes, of ATS Environmental, will give a talk about obstacles in rivers, how they affect fish and new innovations that can be used to help our native species negotiate them. Anyone is welcome, tea and coffee and biscuits to be provided.

How does the fish friendly gate work?

* At low tide counter-weights keep the flap open

* As the water rises the fish friendly gate delays the closing moment

* The rising water continues to push and hold the flap closed as usual

* During up-stream flood events a secondary hinge-point allows the gate to over-ride the closing mechanism and open fully to expel the flood waters

ENDS

© Scoop Media