Integrated Catchment Management

Flood gate design and management

 Research Status: Ongoing
Double tidal gate

Double tidal gate


Concerns from a number of councils around the country over the potential effects of floodgates (or more correctly tidegates) restricting fish passage and altering lowland/coastal habitat have been expressed. There are probably thousands of floodgates around the coastline of New Zealand that were constructed in conjunction with reclamation/development of low lying coastal land. Their primary function is to allow water to flow out to sea during low tides and stop water flowing back upstream during high tides. Most tidegates consist of a solid 'gate' that is hinged at the top and opens up when water pressure builds behind the gate and is closed at other times.

A wide variety of fish species move between freshwater and saltwater areas and the majority of New Zealand's native freshwater fish require access to and from the sea to complete their lifecycle. Coastal margins are also important juvenile rearing areas for some marine fish species. Tidegates represent a significant potential barrier to fish movement since they are closed for much of the time and when open have water velocities that are too fast for fish to negotiate.

The other issue with tidegates is that they facilitate a sudden change from a freshwater habitat to a salt water habitat. This is a problem because key species like inanga spawn in very localised areas near what's called the top of the 'salt water wedge'. At this location tidal fluctuations change the water level, but don't actually make it very salty. Installation of tidegates stops the tidal fluctuation in traditional inanga spawning grounds upstream and other areas downstream of the gates are not suitable because they are too salty.

Research Approach

During the 2006 whitebaiting season we monitored fish movement for 24 hours at two tidegates - one on the western side of the Motueka Rivermouth and one at the outlet of Pearl Creek. The monitoring was done using a DIDSON acoustic camera, which enables you to 'see' through turbid water and/or at night.

Research Results

Some interesting observations were made:

More details »

A single tidal gate Scan from DIDSON scanner

A single tidal gate

Scan from DIDSON scanner

Recent Publications

Year Title File Size
2012 A Summary of Outcomes and selected formal publications from the Integrated Catchment Management (ICM)research programme:2000 – 2011
pdf       1.08MB
2011 Integrated Catchment Management – Special Issue of the NZ Journal of Marine & Freshwater Research  
2007 Assessment of affects on fish passage at tide gates using DIDSON technology pdf       4.27MB
2006 Fish passage in the Tasman District pdf       1.85MB
More publications on this topic »
All ICM Publications »

Primary Contacts:

Image - Trevor James Trevor James  EmailSend email to trevor.james
Tasman District Council
Water Quality and Aquatic Ecology
Image - Rowan Strickland Rowan Strickland  EmailSend email to trevor.james
Cawthron Institute
Coastal and Freshwater Group Manager, Freshwater scientist
Image - Roger Young Roger Young  EmailSend email to roger.young
Phone: (03) 548 2319
Fax: (03) 546 9464
Cawthron Institute
Land/water interactions, water quality, fisheries, river health
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Page last updated Thursday, 4 October 2007

Related areas

Stream health – fish Stream health – invertebrates

Related Website(S)

Flood gates – NIWA Te Ara – The encyclopedia of New Zealand. Freshwater habitats.