What is a Piezometer?

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If you travel through Bothamley Park you may have seen a few of these red steel boxes like this one (there’s 22 scattered around the park), so we wanted to provide you with some more information of what they do:

These red steel boxes are part of our piezometers (pahy-uh-zom-i-ter), which help us monitor groundwater levels. We’ve temporarily installed piezometers along the proposed Bothamley Park wastewater pipe route to help us to measure groundwater levels and understand by how much, and how quickly, they change when it rains (and when it doesn’t).

The piezometers are made up of a borehole filled with concrete, a sensor (‘transducer’) at the base, a logger at the top, and wires connecting the sensor to the logger. The red steel upstands are key to protecting the piezometers and recording the data.

Piezometers work by the sensor measuring the groundwater pressure on the diaphragm in the sensor, and the logging unit converting that pressure to a groundwater depth. This information is reviewed by Te Aranga’s technical experts to inform the design and construction methodology for the wastewater pipe. During construction, measurements from the piezometers will also allow us to check if construction is affecting the groundwater levels.

To be able to do this work we need to monitor groundwater levels before, during and after construction. We’ve included a sample output from one of the piezometers in Bothamley Park, below. It shows how the groundwater level (in metres below ground level) has changed over the course of a month (between late November and late December 2021:

 Example output of groundwater levels from one of the piezometers in Bothamley Park

Since their installation, some of our piezometers have been significantly damaged.
It’s important that they remain upright and working to help us to inform the pipe design and construction which will help to improve our our taiao and waterways.

We really appreciate your help in looking after our piezometers, and reporting any damage to us. If you have any questions or concerns regarding piezometers or the upgrade of the wastewater pipes through Bothamley Park please reach out!

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