Quick Dips

High-Tech Ingenuity

A little ingenuity and back-to-front use of some off-the-shelf technology has seen Landcare Research scientists answer the tricky problem of monitoring a slowly moving landslide.

To monitor a slip threatening houses at Akaroa, the researchers needed a method of automatically determining the water pressure build-up in the landslide. There was no such equipment to do the job, so they decided to build their own.

The system uses tensiometers, normally employed in agriculture to check how dry soil is. Chris Phillips of Landcare Research says that they are using the tensiometers "the other way round, to measure how saturated the soil is".

That information, and data from an instrument detecting small movements in the landslip, is sent by radio to the Banks Peninsula District Council offices. Scientists back in Christchurch can phone the machine for the latest readings.

Since the system has been in place, 13 centimetres of movement has been recorded as the slip settles and consolidates. Clearing tonnes of earth from the top of the slip has reduced stresses considerably, but Phillips says that if the soil reservoir gets filled up "you can get to the point where slope failure is imminent".

If all works as planned, the team may be able to predict the action an hour or more before it moves when the next big rain comes.

The team is applying to the Earthquake Commission for funding to develop computer software for a landslide monitoring system that can be used in other landslip areas, such as Gisborne.

Phillips credits geotechnical engineer Jagath Ekanayake with seeing how to adapt equipment for the new purpose, and Ekanayake has also been behind the development of another home-made monitoring system.

A bicycle chain, an upturned plastic compost bin and some specially made valves are the heart of an automatic suction lysimeter being field trialled on the Heretaunga Plains in the Hawkes Bay. With input from Phillips and Richard Nicholson, Ekanayake has turned existing automatic water sampler technology into a machine which will take the soil water samples needed to monitor the rate at which contaminants are leached through the soil to ground water.

It means scientists won't have to get their feet wet, or even leave the office, to take samples. When it rains, or when the paddock is irrigated, the machine is triggered to start sucking up samples at uniform pressure into 32 tiny sterile bottles to be tested back in the laboratory.

Phillips says the machinery is not the sort of thing that can be bought off the shelf. By adapting existing technology to suit their own needs, samples can be collected in a shorter time, giving better and more accurate information.

"For what we want it serves our purpose. Our research is field based and we need to be able to develop appropriate technology to do the job. It also has to be rugged and reliable and user-friendly, so it can be used by a non-technical person at the flick of a switch."

The machine will also be used to look at isotopes involved in soil water hydrological processes, as well as gathering the samples needed to determine what pesticides, microbes and other effluent residues turn up in ground water.