Sensors in the drains and above ground record rainfall, gauge levels and drainage in the district of Fehraltorf in Zurich. Low-power wireless technology transmits the measurements to the Internet. The wireless sensor network, built by Eawag and ETH Zurich, is still the world's only observatory for drainage systems.

Frank Blumensaat (r.) and his technical employee Simon Dicht. (Photos: Kellenberger Kaminski Photographie)

Crossing the street in Fehraltorf, you would never know that there is a constant stream of data being recorded and transmitted up underfoot. The water level in the drainage canals, which run under three quarters of all the city's streets, is detected by sensors in that district of Zurich. The ultrasound level sensors under the manhole covers transmit the measured values wirelessly to a base station at five-minute intervals; the base station, in turn, forwards the data to an Internet server.

The sensors in the sewage system are part of a field experiment led by environmental engineer, Frank Blumensaat at Eawag. "Digitisation creates previously untold possibilities," explains the sanitary engineering specialist, who is also a lecturer at ETH Zurich. "Data can increasingly be recorded and transmitted in a resource-efficient manner using geographically distributed sensors." An innovative aspect of the work in Fehraltorf is the combination of robust and energy-efficient sensors and data transmission via low-power wireless technology or LPWAN, which is short for the Low Power Wide Area Network of the Internet of Things (IoT). Despite being used underground, the LoRa® standard has a great range, but requires much less power than wireless technology and is much more cost-efficient.

"Operating independent gauges with long service lives and transmitting data efficiently – they are the innovative features of our Urban Water Observatory," Frank Blumensaat explains. "The data used to be saved on small memory cards, which are limited in terms of their memory capacities, in the gauges. Therefore, you frequently had to log in and export the values."  The low-power wireless technology does away with this hassle. Since launching the project with five rain gauges in February 2016, the Eawag team has installed around 60 sensors over an area of three by three km and, for the first time, has demonstrated that this resource-efficient technology is the perfect solution for detecting the highly dynamic processes that occur in drainage systems.

Frank Blumensaat (l.) and his technical employee Simon Dicht.

Flood warnings

Firstly, Fehraltorf was an obvious choice of location for the observatory – the place is only around 15 km from Eawag in Dübendorf; secondly, there were existing good contacts with local industry. Most of all, however, the community which has around 7,000 inhabitants has a drainage system which is characteristic of those used nationwide. The researchers are seeking to capture the district water regime as accurately and comprehensively as possible in their project; from the rain which runs off the roads and squares into the drainage system, to the water that flows into the sewage treatment plant and into rivers and lakes, or that penetrates into the ground and raises the groundwater table. They are seeking to find out more information about drainage in areas that are not readily accessible, with particular regard to geographical differentiation, and to use these findings in a meaningful way, for instance to give early warnings of floods in the event of heavy rain or of contamination.

The network of sensors can also be used to find out how much sewage is discharged into streams, rivers and lakes and how this pollution can be minimised. Leaks in drains can also be identified and repaired. Up until now, this involved time-consuming and costly measurements. It is Frank Blumensaat's hope that, thanks to digitisation, even local authorities with limited budgets will be able to monitor their drainage systems efficiently and take suitable action to protect the environment. During the five-year term of the project, it will also provide training for students who, as the engineers of tomorrow, will bring that new expertise into planning offices.  For instance, young environmental engineers attending the Master's lecture on "Planning and modelling sewage systems", which was introduced in 2017, learn how to use modern simulation tools directly with high-resolution data from the observatory.

"There may be perfectly sensible reasons for publishing environmental data," explains Frank Blumensaat. "There are still unresolved questions to be clarified here."

However, the expert cautions against exaggerated expectations in the course of the digital transformation. Handling big volumes of data sensibly and the rapid development of the Internet of Things pose challenges.  As does the scientist's objective of placing the data collected in the public domain so as to enable other researchers around the world to work with it. This prompts questions about data privacy. As there is an understanding about the composition of waste water, conclusions can be drawn about consumer behaviour. "There may be perfectly sensible reasons for publishing environmental data," explains Frank Blumensaat. "There are still unresolved questions to be clarified here."