Detecting inflow and infiltration within a wastewater sewer network


Detectronic was commissioned by a UK Water company to help investigate inflow and infiltration (I&I), entering the wastewater sewer network.

Das untersuchte Einzugsgebiet befindet sich an der Küste und unterliegt dem Einfluß der Gezeiten. Von besonderer Bedeutung für den Kunden und ein Schwerpunkt des Projekts war es, den Eintrag von Meerwasser in das Abwassernetz zu lokalisieren.

Detectronic wurde beauftragt, festzustellen, wo Meerwasser aus dem Gezeitenfluss in die Kanalisation gelangt.


Identenifizierung und Lokalisierung des Salzwassereintrages innerhalb des Abwasserkanalnetzes.


Owing to the fast rate of rise from the expected tidal influence within the sewer network, it was not possible to use conventional monitoring technology. The fast rate of rise and high tide limits the use of non-contact ultrasonic level sensors, and compression sealed manholes prevent the use of vented pressure sensors.

The chosen technology used to gather seamless level data throughout the sealed part of the wastewater network under both normal and surcharged conditions, was the LIDoTT level sensor.

The LIDoTT has patented technology which integrates level, depth and temperature sensors into one compact device. As such it is proficient in delivering reliable data during normal and surcharged conditions. For conventional surface water runoff I&I reporting, a raingauge was used.

The horizontal or detailed point of entry is calculated by evaluating the varying crest height of the transient pressure between the four monitoring nodes and the time of transition between the crest travelling along the sewer network.

The above data shows the crest height and time taken for it to be present at MH8709. Time of travel = 9.402m/min. Using this information together with the known height above chart Datum (750mm), it is possible to estimate where the entry point of the river is.

Der LIDoTT® ermöglicht einen nahtlosen Mess- bzw. Datenübergang zwischen Normalzustand und Einstau, so dass der gesamte Einstaubereich abgebildet werden kann.


Mit Hilfe der Wasserstandsaufzeichnung des LIDoTT® Sensors, der Skalierung der Gezeitenströmung und einem einfachen Timing gegen den Abstandsalgorithmus war es möglich, mit einem ein hohes Maß an Sicherheit, den Ort zu bestimmen, an dem das Meerwasser in das Kanalnetz eindringt.

As a result of the steep catchment, I&I from rainfall precipitation is present throughout the entire wastewater network. Although there has only been a few significant rainfall events, it can be concluded that rainfall has a major impact on the available capacity within the waste water network when coupled with a spring tide.