Lincoln researchers study braided rivers

Press, 2 November 1984, Page 26

Lincoln researchers study braided rivers

Hydraulic engineers at Lincoln College researching ways of controlling Canterbury’s braided rivers can call up a flood at any time they want — right there in the laboratory. In a quarter-metre deep tank, 20 metres long by three metres wide, they have constructed a model of a braided river.

Called a modelling basin, the tank holds about 7.5 cubic metres of sand and a small-scale river channel has been formed through this.

This channel is allowed to form other small channels, as happens in Canterbury’s big rivers. Lincoln College is researching control of braided rivers under contract to the Ministry of Works and Development Behind the project is senior agricultural engineering lecturer, Dr Tim Davies. “Braided rivers don’t flow in single well-defined channels, but in lots of smaller channels, diverging and joining again,” he said.

“And a braided river is very, very difficult to controt for use as a water resource.

“This modelling basin allows us to test on a small scale, very quickly and cheaply, various methods of controlling braided rivers.” Recirculated by pump, the water in the tank has formed channels • through the sand, and small-scale river control works have been positioned. These are barriers of metal and sand, and the effecgL of these on the minia-

ture river is being examined. •

“We are watching the effects of these river control works, and they have a rapid effect on a small model like this,” said Dr Davies.

“This is much more rapid than in a real river, and if we want a flood we can call one up. “This allows us to test river flows very cheaply, and make predictions about real rivers.”

If research was being done on proper rivers there could be a wait of two or three years for a major flood, he said. A post-graduate agricultural engineering student, Mr Ah Let Lee, from Kuala Lumpur in < Malaysia, designed the tank under Dr Davies’ supervision. Staff and technicians of the hydraulic laboratory built the tank, taking about nine months to complete the job. All the work was done within Lincoln College agricultural engineering department.

Materials for the tank — steel for the framing, plywood for the base, black polythene for the lining and Butynol rubber for leakproofing — cost about $5OOO in all. . ; . Steelwork for the tank was fabricated in three sections in the workshop and then assembled in the laboratory.

As soon as the tank was put together, about seven tonnes of water was pumped in for leakproofing tests. i

' Celebrating construction of the tank, scientists and technicians floated a dinghy in the tank for a short trip along the mini-river.

Work on the M.O.W.D. contract will take about two more years, and then the tank, now a fixture in the laboratory, will be used for further research on braided rivers.