Webb surveyed further waterways and came across an area where a farmer had laid concrete posts across a waterway to allow for irrigator pivot wheels to cross the stream.
A little further along the same drain he found some large boulders that had washed down into the stream from an area of stream bank that had been reinforced to manage erosion.
"It was really interesting to see that fish numbers appeared to be thriving in both these locations. It looked like the structures and rocks had created a little bit of instream habitat diversity by changing the water depths and bed gradients."
This gave Webb the idea to purposefully put structures in streams to create instream habitat diversity and a bit of excitement for fish.
In June 2015, 22 weirs were created in Windermere Drain and 19 Weirs in Taylors Drain by placing boulders into the stream bed thanks to the help of local farmers.
The boulders were mechanically deposited in the drains and then moved by hand to create the preferred water conditions.
Webb says three years on the weirs have settled into the stream environment and have created some exciting habitat for fish.
"The working party is excited about the changes that have been seen in the drains and we think there could be an opportunity for this technique to be used in other waterways in the Hinds Drains and potentially further afield," he said.
One of the concerns when the weirs were installed was that they might impede drainage during high flows. Mark says it was pleasing to see that they held up during the floods in July 2017, which were 30-50-year events.
"The floods also produced a significant redistribution of habitat around the weirs and in effect reset the drain environment to incorporate the boulders and weirs as natural features of the drain.
"Immediately downstream of each weir small pools were also formed from scouring gravel from below each weir, creating additional habitat for in-stream species," said Webb.
The sites are now being monitored to assess the impact of the boulder induced habitat on fish populations.
An ongoing monitoring programme is being undertaken by the HDWP to monitor and access water quality data at 13 sites in the drains.
The HDWP was formed by the Ashburton Water Zone Committee to ensure the drains are managed in a way that provides for multiple needs while protecting water quality and in-stream biodiversity.
The party is made up of a mix of zone committee members and elected farming community members and receives support from its partners FAR, DairyNZ, Beef & Lamb, the Department of Conservation, Fish & Game, the zone committee and Environment Canterbury.
- Environment Canterbury Regional Council
