Researcher Cheri van Schravendijk-Goodman discusses the problem with culverts that disconnect habitats of fish from the main river. She describes the use of fish ramps and baffles and how they help to improve connectivity between the river and tributaries – particularly for whitebait species of fish.
CHERI VAN SCHRAVENDIJK-GOODMAN
The problem with culverts in tributaries are that they disconnect habitat from the main stem of the river. A culvert is a big pipe, often used for helping with drainage of land, but the problem with the culverts is they tend to sit kind of this high off the surface of the water or maybe a bit closer depending on what the river’s doing. Now our whitebait – species like kōkopu and that – they can climb but they can’t jump. They’re not superfish.
Fish ramps and baffles are infrastructure that we’re going to hopefully retrofit to these culverts and floodgates to improve connectivity between the river and the tributary, because kōkopu and kōaro like to get up into those tributaries, probably inanga as well, and they perhaps could be where they’re spawning, so we want to make the passage as smooth as possible without impacting on the actual adjacent land use, you know, because the culverts and that do perform a function. Often it could be related to human safety, particularly the floodgates. We don’t want to make it difficult for humans and nature to co-exist.
Rock ramps or a fish ramp is a way for reconnecting those tributaries that have these barriers like these culverts and floodgates.
The techniques that have been applied by NIWA is using rocks embedded into concrete ramps. Our fish are really good climbers, our galaxiids, and so you try and create a way to help them get up to that culvert. It also provides a rest spot for the fish.
A baffle is a rocky substrate or a brick or something inside the culvert, and again that’s about giving the fish something to climb up on to and to rest.
Culverts create a really unnatural system. Normally, when these tributaries come down, their flow would be slowed down by twists and turns and rocks and stuff. Culverts are just one straight smooth system, so the water velocity can get really, really fast and hard. By putting baffles in there, you’re not only giving an opportunity for these fish to be able to climb up the incline of those culverts but also giving them a bit of a place to rest and be protected sometimes when they’re tired.
Cheri van Schravendijk-Goodman
Dr Bruno David, Waikato Regional Council
Dr Cindy Baker, NIWA, Taihoro Nukurangi
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The Waikato Tainui College for Research and Development acknowledges the financial support given by the Waikato River Cleanup Trust Fund which is administered by the Waikato River Authority.
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