It’s not every day an adult jumps in the river before the children, but for Downer Construction’s Environmental Co-ordinator David Maucor, it’s all in a day’s work.
David is helping maintain the Avon River/Otakaro’s water quality while his Downer colleagues place a pipeline under the river bed. That means he regularly wears waders to work and thinks nothing of getting in the river to show a group of visiting school pupils what happens on the riverbed.
The old wastewater pipe or syphon under the river on Park Terrace, bordering Hagley Park, sheared apart during the February 2011 earthquake. Downer, part of SCIRT, has the job of replacing the syphon with a new 180mm diameter PVC (plastic) pipe, protected inside a bigger steel pipe. But it has to do this without releasing mud or silt into the river. This would be disastrous for the trout which spawn near the loop around Christ’s College on a shingly area of riverbed.
Cathedral Grammar year eight pupils, who go to school nearby, visited the site in early June to find out how SCIRT and Downer is managing the project to protect the water quality and the fish life.
David explains that the Downer team are three weeks into the work with at least another three weeks to go. Work involves installing sheet piles to create a trench to work within and dewatering the trench area by pumping out water. The pumped water is allowed to settle in in a sediment tank before it is returned to the river. The site is also double-fenced using geotextile fabric to contain any muddy water, and downstream there is a containment boom as a backstop.
David regularly samples the river water upstream and downstream of the syphon site in keeping with the resource consent from Environment Canterbury, which has been involved from the start. To date the downstream water samples have matched the upstream samples, good for fish life.
The students are particularly interested in the macro-invertebrates – tiny insects and snails - living under the river’s rocks. They quickly work out why a layer of silt would prevent any hatching trout find invertebrate food.
The new syphon will take all the wastewater generated by the Botanic Gardens, public toilets and from events in the Hagley Park dome, to the main pipe on Park Terrace for disposal at the Treatment Plant.
What is a syphon?
A syphon (also spelled siphon) is a tube which moves water from a reservoir to another place. Syphons can raise water over a barrier, which is what makes them so useful. There is evidence that ancient cultures were familiar with the basic principle of the syphon. Typically, a syphon is a flexible tube, bent into a u-shape, although a rigid pipe can also be used. One end is inserted into a reservoir or water-filled container, and the other end is inserted into a container to catch the liquid, or left hanging to drain away. Once the syphon has been started with a priming pump, it will pull liquid out of the reservoir until it is removed or the reservoir is drained.
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David Maucor, Downer Construction’s Environmental Co-ordinator, shows students why the Avon riverbed contains important habitat for trout and other aquatic species.
The Hagley Park work site for the new syphon taking wastewater from the Botanic Gardens and events area to the main wastewater pipe on Park Terrace. Note geotextile sediment fencing in the foreground around the sheet piling area.
Stuart McCarron, Downer Site Engineer, demonstrates a model of a syphon to visiting school pupils to the Hagley Park work site.