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Benchmarking Against Traditional Methods

There will always be a place for traditional high end environmental monitoring stations however their cost and cumbersome installation requirements makes them unsuitable for wide scale projects. Waterwatch solves this issue by providing a cost effective and easy to install remote water level monitoring solution.

The Waterwatch LS1 provides more than sufficient accuracy for supplementing an existing monitoring network to provide comprehensive catchment coverage, especially for civil defence purposes.

To demonstrate this, we installed one of our all-in-one telemetered ultrasonic water level sensors along side a sophisticated traditional water level monitoring station.

About the site

Owhiro Creek is a tributary of the Taieri River and part of the Taieri plains flood protection scheme near Dunedin, New Zealand. The outfall of the creek has flap gates installed which can be closed when the Taieri river floods to prevent backflow into the low lying area protected by stop banks. This site is also affected by tidal change in the Taieri river. 

 

Monitoring at this site provides real time awareness of the situation at the flap gates during weather events. Both sides of the gates are monitored to ensure they are functioning correctly. Monitoring at this site also provides the Regional Council with updates on where the water level sits relative to the top of the stop banks.

The Benchmarking Method

A Waterwatch LS1 was installed along side an existing environmental monitoring station consisting of a high end pressure transducer in a stilling well. This monitoring station was serviced at the start of the trial. 

The LS1 was mounted on a concrete face, directly above the inlet to the stilling chamber. A surveyed staff gauge is present at the site and this was used to calibrate the sensor offset height along with survey equipment.

At the time of installation, the staff gauge was read, and an instantaneous distance measurement was taken from the LS1 using the mobile application. A difference of 6mm was noted.

The LS1 is configured to measure every 5 minutes and transmit those measurements every 30 minutes. In this configuration predicted battery life is 3 years. Measurement is synchronised with the monitoring station to within 30s.

The Results

Here we have published analysis of data collected over 3 days from the LS1, and from the monitoring station. A longer time frame analysis will be published in the near future.

From the chart below, it is clear that although the monitoring station benefits from natural smoothing provided from the stilling well, the LS1 tracks very closely with the high end monitoring equipment.

By analysing the absolute value of the difference between sensors in each measurement, we can see in the histogram below that the greatest variation between sensors during the trial period was 8mm, and the most common difference was 2mm. One could argue that the consistent 2mm difference is within the error of the calibration survey

In Conclusion

This benchmarking project has shown that the Waterwatch LS1 has acceptable accuracy when compared to a traditional monitoring station.

Waterwatch provides an adequate and cost effective solution for comprehensive  monitoring of rivers and streams. Practical applications include: flood protection scheme monitoring and warnings for civil defence.