Water count

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Ruth Beran discovers that public interest in the state of fresh waterways has driven a dramatic change in the tools used by scientists.

Dr Doug Booker using a Flow Tracker ADV (Acoustic Doppler Velocity) meter. This instrument gives us water velocity at the point where we set it in the water column. [Photo: Dave Allen]

A survey of 5000 people by Water New Zealand late in 2017 found that the majority of New Zealanders are concerned about pollution and the impacts of climate change and intensive agriculture on water quality.

It found that most people are very concerned about drinking water quality and poor water quality in waterways, particularly litter and floating plastics.

Water New Zealand CEO John Pfahlert said that the survey showed that “people understand how extraction, climate issues and pollution are impacting on our water resources and the quality of waterways”.

The strength of public concern is being reflected in demand by authorities for new and better ways of measuring the changing state of fresh water.

This has driven changes in the measuring tools and techniques, such as the rise of automated machines to replace manual collection, ‘always on’ tools that record data constantly or at regular intervals, and devices that can send information from remote locations.

Stream of numbers

NIWA Principal Technician Evan Baddock and his team are running a pilot scheme in Southland to monitor water quality continuously.

ADCP [Acoustic Doppler Current Profiler] equipment is mounted underneath this small boat. To calculate water current velocities the equipment sends out sound waves and measures the reflected signal or echo from particles within the water column and also the river bed for depth. [Photo: Dave Allen]

“For the past nearly 30 years, we’ve done manual samples,” says Baddock. “But that’s only monthly, so we’re now following the US and other countries around the world, and doing continuous water quality monitoring.”

Every five minutes, sensors in the Mataura River measure different aspects of the water, such as dissolved oxygen, nitrates, temperature, salinity and turbidity.

“Instead of getting a snapshot, we’re now getting recordings continuously.”

The results are stored in a logging device and sent telemetered by cellphone or satellite phone back to the NIWA office every hour.

By monitoring continuously, the sensors measure floods or other events, or pollution that might be released into the river. These are things that could be missed with only monthly monitoring.

Installing permanent monitoring equipment is never easy in New Zealand’s waterways, among the shortest, most changeable and most remote in the world.

 

Baddock says it all comes down to picking the right location.

“You want measurements to be representative of the waterway, but you also want the location of your equipment to be sheltered from major logs coming down during floods,” he says.

To avoid wrecking very expensive sensors in the water (one sensor can cost between $5,000 and $15,000), a system can be installed that also pumps water out via a tube. “That pumps water out to our housing or shed,” says Baddock. “The sensor sits at the top end, so all the expensive parts are up out of the flood zone.”

The biggest challenge for installing this type of monitoring in waterways is false readings from algae that tends to grow on sensors. One way to stop this algal growth is to have automatic wipers for the sensors, like those on cars but much smaller.

Another challenge is power. The sensors can work on low power, but if the site is running pumps then it will usually be connected to mains power or, in a remote area, to solar panels.

Go with the flow

For NIWA Principal Technician Wayne McGrath, probably 90 per cent of the work his team does is measuring water flow.

Previously, water flow was measured with “old fashioned current meters which were either propeller- or bucket- driven”. It meant that scientists had to wade into the streams or put lines across the waterways to retain boats. This method was slow and only gave specific points in the river — where the scientists were standing with a current meter attached to a rod.

According to McGrath, ADCPs (Acoustic Doppler Current Profilers) have revolutionised measuring flows in rivers and made it a lot safer.

ADCP (Acoustic Doppler Current Profiler) equipment is mounted alongside this small jet boat. To calculate water current velocities the equipment sends out sound waves and measures the reflected signal or echo from particles within the water column and also the river bed for depth. [Photo: Dave Allen]

These devices (worth about $40,000 to $50,000) send out a "ping like a depth sounder, and get a reflection off particles in the water, or bubbles in the water", says McGrath.

“From that reflection it can tell how fast the velocity underneath it is.” By traversing across the stream, the ADCP calculates the amount of water going down a particular waterway.

 

The ADCPs are installed in remote-controlled boats called Q-boats, which weigh about 30 kilograms, and are about two metres long. They need two people to lift them.

This new method collects a vast amount of velocity points throughout the profile. So instead of 25 points across the stream, you get something like 250.

“It increases the amount of data that you’ve got, and from that you get a truer picture of what the flow is,” says McGrath.

Software is also being developed so that the ADCP can be lowered into the river and then provide a sediment concentration reading instantaneously, rather than having to collect a bottle of water and send it away to a lab. “Sediment had been a hassle to measure in the past. You need great weights and great volumes of water,” says McGrath.

Stunning tool

What lives in the water is as important to waterway health as the water itself. NIWA has invented its own electric fishing machine to catch and measure fish health and populations.

“It really is the most effective way of sampling a fish community, if it’s in shallow water,” Phil Jellyman on electric fishing. [Photo: Dave Allen]

NIWA Freshwater Fish Ecologist Philip Jellyman uses these electric fishing machines to temporarily stun fish and then measure things like their length, weight, numbers, and whether they’re about to spawn.

“It really is the most effective way of sampling a fish community, if it’s in shallow water,” says Jellyman.

The electric fishing machine looks a little like a large gold detector, powered by batteries housed in a day pack.

The device puts an electrical current from 0 to 600 volts through the water. “You can alter the size of the field,” says Jellyman. “You’re trying to alter the current so the amount of amps that you’re putting through the water is safe for the operator and for the fish.”

Electric fishing stuns some fish better than others. “Some species will swim towards you and will sort of roll over and then you can quickly pick them up,” says Jellyman. Electric fishing doesn’t work so well on smaller fish either, like larval fish.

“I have no doubts that it will affect the behaviour of some for the rest of the day, but there’s no sort of long-term consequences.”

Electric fishing is more efficient and effective than netting, which is more physically harmful to fish, and usually requires two trips to set and recover a net.

Jellyman says, “Electric fishing is a standard sampling technique and it’s really safe when done well. It’s the best non-selective fishing method we have.”

Research subject: Water Quality