Environment Waikato is to trial an innovative approach to flood management that involves removing gravel to fix one problem, and then using the same material to fix another.
Gravel building up in streams on the western side of the Coromandel Ranges, south of Thames, can make nearby farmland prone to flooding.
Meanwhile, the flood protection system guarding the nearby Hauraki Plains town of Ngatea from the Piako River is in need of strengthening.
So Environment Waikato is to begin trials within the next few months which involves removing Coromandel stream gravel to lessen flood risk, and then using it to help bolster Ngatea’s flood defences.
Environment Waikato’s river and catchment services operations manager Guy Russell stressed the need for improvements at Ngatea did not mean the town or nearby farmland was at imminent risk of flooding.
“The stopbank protecting the town is currently performing to design standards and we expect it to keep providing protection for the long-term.”
But Mr Russell noted that a stopbank north of the town had slumped four years ago and had required costly repairs.
And recent investigations have confirmed a 3.3 kilometre stretch of berm between the Piako River, and Ngatea and farmland, had deteriorated. Berms are the strip of land between stopbanks and the river channel - they provide protection to the stopbank and a spillover area where a flooding river can flow before it starts encroaching on to a stopbank itself.
“The stopbanks in the area are slowly consolidating into the ground because of the soft nature of the clay berms they are built on, and we want to provide stable berms before we top any of the stopbanks up,” Mr Russell said.
“So what we’re doing is taking a proactive approach to look at ways of ensuring that, over the longer term, the berm areas along the Piako River and the stopbanks are maintained. We hope the Coromandel gravel will give the Piako River berms much greater stability.”
Mr Russell said the most recent trials are part of a three-year project looking at what is the best solution to the berm and stopbank issues in the area. The investigation stage of the project is due to be completed by June 2009.