Remote Monitoring to Reduce Wastewater Overflows in Out-of-Sight Places

Heather Kikkert (Hamilton City Council)

Wastewater overflows in heavily vegetated gullies can be out of sight and may therefore go unnoticed. As part of protecting Hamilton’s waterways, Hamilton City Council wished to monitor the wastewater network in remote locations to respond before overflows occurred, preventing wastewater from manholes entering gully streams.

A six-month trial was initiated in Ranfurly Gully using Hynds Smarterwater sensors. Success factors of the trial included: prompt, accurate data in a variety of weather conditions; consistent identification of overflow risk; alert notifications to allow response before an overflow occurred; the sensors needed to be robust to withstand tampering/vandalism; and a monitoring dashboard. The trial period would allow time to test performance in different weather conditions and possibly capture either a blockage or partial blockage.

Four monitoring locations were selected along the main pipeline in Ranfurly Gully based on known previous overflows due to network blockages. The sensors were retrofitted to existing manhole lids rather than swapping out the existing lid and
frame to use special Hynds lids with pre-fitted sensors. This decision was largely made due to the access difficulties that required manual handling of all materials down the steep bank, though reduced costs was also a factor. 

A monitoring dashboard was created by Hamilton City Council’s Information Services Team using the PowerBI online platform to pick up the cleaned data from Hynds API (Application Programming Interface). The dashboard showed a timeline of all four sensors, with the maximum level reached within the time period selected. A second page allows the sensors to be overlapped to see their interrelationships. Developing the dashboard in-house allows greater flexibility to make additions at minimal cost, plus has the flexibility to add specialized pages for interrelated sites. Emailed alert notifications were also created from the dashboard to notify the Operations Team to monitor the dashboard more closely
when pre-set trigger levels were reached. 

During the first rain event of the season, all the sensors responded with alerts. The level data showed two peaks that coincided with two peaks in rainfall intensity. The sensor levels and alerts provided visibility of the situation in Ranfurly Gully, without risking staff safety to visit the sites, though the wet weather reduced options to act to prevent an overflow. Throughout the trial, rainfall intensity correlated well with the level sensor data and indicated that the sensors were providing prompt, accurate readings.

During the trial, data coming back from one of the manhole sensors started to read consistently above zero, though lower than the alert levels, suggesting that a block may have been forming. Investigation discovered that this manhole had been accessed and the lid not put back in the same orientation, thus the sensor was sending false level readings. The sensors are very sensitive to orientation, which must be communicated to maintenance staff and contractors.

A blockage has yet to be detected in the line during dry weather, but the sensors have shown that they respond during high levels and alerts are sent out. The trial was considered a success.