“The results of the calculations are only as good as the input data on which they are based,” explains Tobias Knödlseder. ‘That's why we decided to have a precipitation-discharge-pollution load measurement campaign carried out, which primarily serves to calibrate the sewer network model. This allows us to adjust the calculation results to the measurement data and thus obtain calculation results that are as realistic as possible.’ The measurement campaign allows important input data to be validated, e.g. the degree of sealing and connection, the hydraulic function of the precipitation discharge systems as well as dirt and extraneous water parameters.

Before the measurement campaign was carried out, MSE worked with Prof Dieter Sitzmann (Scientific Consultancy for Water and Environment) to develop a measurement concept that took into account the size and complexity of Munich's sewer network. “The city of Munich's sewer network is largely designed as a combined system,” says Knödlseder. “It covers a channelled area of around 18,000 hectares and has a total length of around 2,400 km. It is very complex and meshed due to a large number of network-internal transfers, special structures and culverts.” Despite this complexity, the aim of the concept was to create a very high-quality sewer network model and to obtain the most accurate knowledge possible about the catchment areas. This project could only be achieved with a monitoring network with around 180 additional mobile flow measurement points, around 50 additional water level measurement points and around ten temporary precipitation measurement points. They were intended to supplement the many measuring points already permanently operated by the MSE.

MSE decided in favour of NIVUS GmbH as part of a Europe-wide tendering process for the precipitation-discharge-pollution load measurement campaign. The company had applied in a bidding consortium with the engineering firm IGM Messen GmbH.

The key factors in the decision were

• the expertise of the personnel deployed,
• the quality and availability of the measuring devices (high-quality precipitation, discharge and water level measuring devices in sufficient quantities),
• the analysis of the task (e.g. with regard to practical implementation and the division of project roles),
• the processing and quality assurance concept (handling of installation and removal as well as operation, maintenance and validation of the measuring devices, preliminary checking of the data for completeness, data transmission, preparation of reports) and 
• quality assurance and further processing of the data by the engineering office.

After being commissioned, the NIVUS Urban Drainage Monitoring team first carried out an above-ground and underground site inspection. The measuring locations were checked for hydraulic suitability and the optimum sensor technology was selected for the measuring points.

NIVUS also provided the following key services:

• Drawing up a detailed schedule for the measurement campaign, with a target/actual comparison accompanying the entire campaign in collaboration with the engineering firm IGM Messen
• Installation and operation of the measuring points
• Quality assurance during the installation of the measuring points and during the execution of the measurements (through extensive verification and validation measurements)
• Daily data transmission by radio to quickly recognise any errors
• Daily preliminary check of the data for completeness and plausibility before handover to the engineering service provider
• Intermediate documentation (especially on data availability) and final report

NIVUS installed NivuFlow Mobile 750 flow transmitters for self-sufficient flow measurement in part filled sewers. “For fully filled pipes, we used NivuFlow Mobile 600 transmitters for contactless measurement,” explains Holger Hansen, who was responsible for carrying out the measurement campaign at NIVUS. “The sensors are clamped onto the pipe from the outside.”

Also used were:

• NivuLevel Mobile, a gateway for data transmission for contactless and hydrostatic level measurements
• Precipitation recorder including data monitoring

In addition to the measurement services, NIVUS was also responsible for traffic safety. For this purpose, the service provider used fully equipped emergency vehicles including safety technology for traffic and occupational safety. All sensors and data were monitored around the clock via the Nivus WebPortal and NIVUS provided detailed reports, the data of which was previously verified by its own data analysts.

A major challenge for NIVUS in this project was to install the measuring devices in the sewer network in accordance with the measurement concept and then to ensure the operation of the measuring points and the continuous transmission of the measurement data in high quality. Due to the size and complexity of the sewer network and the very ambitious schedule, these tasks were particularly challenging. “However, we were able to benefit from our large inventory of devices - and from our highly experienced team with many years of experience in measurement services,” says Thorsten Bayer, Head of the Urban Drainage Monitorimg department at NIVUS. The automatic data transfer and remote access to the measurement technology were also an advantage for the NIVUS team.

“The sometimes difficult conditions in the sewer network not only required NIVUS to have a high level of expertise among the specialist staff on site, but also to establish a very good external communication structure. This particularly affected the operating staff of Munich's municipal drainage system, but also other municipal departments, such as the district administration department,” adds Tobias Knödlseder from MSE. It was necessary to react promptly to disruptions and unforeseen circumstances in order to minimise measurement downtimes. This required a high degree of flexibility combined with short response times. NIVUS also mastered these challenges thanks to the combination of experienced specialists and flexible web solutions.

The measurement campaign provided precise results for the additional flow, water level and precipitation measuring points. Some of the measuring points were also operated for the entire duration of the campaign to obtain external water parameters. In addition, wastewater samples were taken by Blasy + Mader GmbH at selected measuring points in the sewer network and the sewage treatment plant inlets during dry weather to calculate pollution loads. The sub-project precipitation-discharge-pollution load measurement campaign was thus successfully completed.

The measurement results obtained provided MSE with the required more precise information on flow rates, water levels and precipitation in the urban area. They form the main basis for the upcoming calibration of the new sewer network model.