River Siphons

Johnston Civil have constructed two siphons in both the Avon and Heathcote Rivers.

Both of these projects faced the same environmental challenges, and Johnston Civil worked closely with both Downer NZ and Fletcher Construction to construct the necessary silt and spill barriers around the job site, including running all machines on bio oil.

The siphons were constructed with sheet-piled cells, dewatered then the new wastewater pipes installed.

For each halt, the centre was joined by overlapping the ends of the pipe, and then dewatering the centre pit. After this was completed the total siphon was tested then handed over to the respective contractors to complete the works.


The Hagley Park Siphon

Downer subcontracted JCL to install a 150 pe water water siphon under the Avon River at the end of Kilmore & Park Terrace.  The project required JCL to install a temporary working platform to support a 25 tonne excavator, JCL was then able to drive in sheet piles via a trench system. Once the sheet piles were installed in the trench, JCL dewatered the site using 2 Sykes 150 QS pumps. The water was passed through two silt traps via a concrete spill chamber and back in the Avon River. Both Downer and the CCC were pleased with the result, particularly due to JCL’s care to ensure there was no environmental harm to the Avon River.