Flow Measurement Specialists to Supply Sewer Network Monitoring, Maintenance and Flood Prevention in Athens

Detectronic (UK) is working in partnership with its Greek agent, Metrica, to supply sewer monitoring and maintenance in support of flood prevention in the country’s capital, Athens, for the Athens Water Supply and Sewerage Company (EYDAP SA).

EYDAP SA invited Metrica and a number of other suppliers to look at long term monitoring and maintenance of the city’s trunk sewers with a view to appointing a suitable delivery partner. Following initial trials of Detectronic monitoring equipment and a formal tender process, Metrica won the contract.

Explains Dave Walker, commercial director for Detectronic: “This is a particularly complex and challenging project for us and our colleagues at Metrica. First of all, the pipes in the existing sewer network vary from 1000mm to 3500mm in diameter, with invert levels (depth from ground-level to the bottom of the pipe) of up to 9000mm.

“Secondly, the shape of the pipes in the sewage network varies from circular, to egg-shaped and bonnet-shaped pipes which makes flow calculating more difficult.

“However, one of the biggest challenges is that we are not permitted to enter either the existing access chambers or the sewer pipes to install the monitoring equipment.”

Adds Hippokrates Pappas, director at Metrica: “Another issue to be addressed is that during floods measuring at the intersections or the sewer chambers where shapes change and flow is irregular, measurements are not considered reliable.

“Working with EYDAP SA and Detectronic, we have devised a perfect solution to measure flow in the pipes, away from the intersections and access chambers. The engineered solution means we are at a suitable distance from the turbulent flows and therefore measuring laminar flow patterns. After excavating and digging down to the sewer pipe, the engineers drill into the crown of the pipe using a 200mm core-drill. They then insert a vertical shaft and feed the sensor, which is fixed on a special bracket.”

Continues Hippokrates: “For EYDAP SA, following calibration, the engineered solution provides accurate measurement even in surcharged conditions. This is achieved from the unique mounting arrangement of the sensor.

“Special antennae with the ability to withstand more than two tonnes are permanently installed at street level in order to secure a good mobile signal for the upload of the data. The ultrasonic sensor is fitted inside an IP68 barrel- type housing that, if the water level reaches the sensor, will retract via buoyancy to protect the electronics.

“We chose to install the Detectronic non-contact monitor, MSFM Lite and its two main components, the ultrasonic sensor and GSM/GPRS data logger. One of the stations was extra equipped with an MSFM 12 Area velocity flow sensor for validating the Manning theoretical approach of flow calculation.”

Adds Dave: “All installation accessories were manufactured to fit exactly for each different pipe size and shape so that EYDAP SA employees could fit the components without our presence.

“Ten monitoring ‘stations’ have so far been installed and the results look very accurate and consistent. All data monitored directly from EYDAP SA and the oracle database of EYDAP SA will be continuously updated for historical data purposes. Specific attention has been paid to setting up alarm regimes that are sent directly to EYDAP SA. Whenever the thresholds are exceeded, an alarm is activated and the latest data is forwarded to the EYDAP SA Database and the Detectronic Data Centre. In normal conditions, the data is sent daily to optimise power usage.”

Concludes Dave: “Once installed, the network of sensors will facilitate remote monitoring for EYDAP SA and enable the team to predict blockages and improve operational network performance. To achieve this, they will use our specialist, web-based DetecDataPro platform to access and analyse their data. Web access ensures that Network Management data are available to each relevant person within EYDAP SA. We have also developed bespoke level to flow formulas derived from Manning’s Equation so EYDAP SA can monitor levels and calculate theoretical flow rates and volumes of effluent passing through their sewers.”