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# Adopting metrology best practices in urban hydrology with the UDMT (Urban Drainage Metrology Toolbox)

Jean-Luc Bertrand-Krajewski, Mathieu Lepot, Nicolas Invernon

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Jean-Luc Bertrand-Krajewski, Mathieu Lepot, Nicolas Invernon. Adopting metrology best practices in urban hydrology with the UDMT (Urban Drainage Metrology Toolbox). 4th International Symposium on Sustainable Urban Drainage, Ningbo University, Dec 2025, Jiashan, China. hal-05417008

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Submitted on 15 Dec 2025

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# Adopting metrology best practices in urban hydrology with the UDMT (Urban Drainage Metrology Toolbox)

Jean-Luc BERTRAND-KRAJEWSKI *¹, Mathieu LEPOT¹, and Nicolas INVERNON ²

¹ Laboratory DEEP UR 7429, INSA Lyon, France

² Alison, France

(*Presenting Author, e-mail: <mailto:jean-luc.bertrand-krajewski@insa-lyon.fr>)

**Keywords:** monitoring, sensor calibration, uncertainty assessment, data validation, free software.

## Abstract

In the context of global challenges (climate change, continuous urbanisation and densification of cities, ageing and deteriorating infrastructures, emerging contaminants, water quality and ecology issues...), knowledge on urban drainage systems (UDS), including both traditional grey and more recent blue-green infrastructures (swales, bioretention filters, green roofs, etc.), and on their functioning must be based on high quality monitoring data, to improve understanding, modelling, planning, adaptation, and decision making. Unfortunately, it appears that metrology applied to UDS is frequently of insufficient quality [1-3]. Several reasons may explain these observations: i) lack of staff with advanced skills in metrology in general and applied to UDS in particular, ii) lack of sufficient financial resources devoted to UDS metrology and monitoring, iii) lack of incentives to generate and share high quality data on UDS, and iv) habit to accept poor quality information and to devote insufficient resources to monitoring of UDS.

In the H2020 INFRAIA European Project Co-UDlabs (Building Collaborative Urban Drainage research labs communities), the UDMT – Urban Drainage Metrology Toolbox free software tool was developed as both an online web app and downloadable executable versions for Windows and macOS operating systems. The UDMT aims to promote and implement best practices in metrology and standard methods inspired by quality assurance [4], to facilitate their real application by UDS operators/utilities.

**UDMT description.** The UDMT is an integrated tool, offering five blocks of functionalities (Figure 1) which can be used successively to transform raw measured values into final corrected and validated data given with systematic uncertainty assessment. Raw data from sensors are imported from data loggers, Scada systems, etc. They are corrected according to calibration functions established from calibration experiments and their uncertainties are systematically evaluated by combing uncertainties from the sensor, the calibration function, and the monitoring site conditions. The same block of functions also allows to transform raw data from a surrogate sensor into usual parameters, for example to convert turbidity measurements into TSS (total suspended solids) or COD (chemical oxygen demand) concentrations estimated with their uncertainties. A set of predefined parametric tests can be used to automatically pre-validate the data and identify problematic values, which can then be substituted or replaced by the user before the final data set is exported for further analyses and processing.

The five blocks of functions are the following ones:
<figure><img src="image_3.png" /><figcaption>**Figure 1:** UDMT main user interface window with five blocks of functions.</figcaption></figure>

**Sensor calibration / Correlation:** This block provides methods to determine i) calibration functions (based on a data set of outputs of a sensor submitted to standards or certified values), and ii) correlation functions (based on a data set of values given by a sensor and corresponding values obtained e.g. with laboratory analyses of samples). Various methods are available: i) ordinary least squares, ii) weighed ordinary least squares, iii) Williamson regression to account to uncertainties in both coordinates, iv) partial least squares for processing spectral data sets (e.g. UV-visible spectrophotometer data), and v) power function.

**Calibration / Correlation correction:** This block allows to convert automatically single, or time series of raw values provided by a sensor into corrected values according to previously determined calibration or correlation functions. In addition, uncertainties in corrected values are estimated from uncertainties in the sensor raw data, the calibration / correlation function, and the monitoring site conditions.

**Uncertainty assessment:** This block allows to apply standard methods for uncertainty assessment (type A, type B, and Monte Carlo) to various data sets and to any combination of data. In addition, the variograph method is proposed to estimate uncertainties in integrated values (e.g. sums, means, event, daily or annual pollutant loads, etc.).

**Data validation:** This block provides a set of automated pre-validation parametric tests to help the user to validate data according to eight criteria: i) sensor range, ii) measuring range, iii) expert range, iv) gradient of the time series, v) absolute uncertainty, vi) relative uncertainty, vii) redundancy of data, and viii) outlier detection.

**Tracing experiments:** This block allows to calculate a discharge from experimental data collected during salt or dye tracing experiments. Tracing experiments are useful to qualify flowmeters in urban drainage systems and may be used for example to establish correction functions.

**Resources.** All methods implemented in the UDMT are presented in [5]. A comprehensive UDMT user manual [6] is available and allows users to train themselves with examples. The free UDMT software, the user manual and the examples files are available on internet at https://u.pcloud.link/publink/show?code=kZegnQVZM53qyjRJ4cHn7Pi5WzrR9HJ0PL4V.
## Example of application

The example is based on data collected during a storm event dated 30 May 2008 measured in the Chassieu experimental site in Lyon, France. Chassieu is a 185 ha industrial area drained by a separate stormwater system. At the outlet of the catchment, a monitoring station with various sensors (water level, flow velocity, pH, temperature, turbidity, conductivity) is operated since 2003. The data set includes three time series: i) rainfall intensity (mm/h) at 1-minute time step measured with a tipping bucket raingauge, ii) water depth (m) at 2-minute time step measured in the outlet 1600 mm circular sewer with an ultrasonic sensor, and iii) turbidity (NTU) at 2-minute time step measured with a turbidity sensor installed in an off-line measurement flume fed by continuously pumping water from the circular sewer. Raw data are presented in Figure 2 (left).

The UDMT software is used to i) establish the calibration function of the water level ultrasonic sensor, ii) correct the raw data of water level with the calibration function, iii) calculate the discharge in the sewer, the event volume and their uncertainties, iv) calibrate the turbidity sensor and establish a correlation function between turbidity and TSS (total suspended solids) concentration, v) use the calibration and correlation functions to calculate the TSS concentration and its uncertainty, and vi) combine discharge and TSS concentration data to calculate the event TSS load and its uncertainty (Figure 2 right). The TSS event load is equal to $M = 471.6$ kg and its standard uncertainty is $u(M) = 26.5$ kg.

<figure><img src="image_4.png" /><figcaption>**Figure 2:** Left: raw data measured on 30 May 2008 from 14:00 to 21:00 in Chassieu. From top to bottom: rainfall intensity *I* (mm/h), water level *h* (m) and turbidity *Tu* (NTU); right: TSS load time series and its 95% coverage interval calculated with the UDMT.</figcaption></figure>

## Acknowledgments

This work has received funding from the European Union's Horizon 2020 INFRAIA research and innovation programme (Co-UDlabs project. GA No. 101008626). It was performed within the framework of the OTHU (www.othu.org) and the Graduate School H2O'Lyon (ANR-17-EURE-0018).
## References

[1] Dittmer, U., Alber, P., Seller, C., & Lieb, W. (2015) Kenngrössen für die Bewertung des Betriebes von Regenüberlaufbecken [Parameters for evaluating the operation of stormwater overflow basins]. Jahrestagung der Lehrer und Obleute der Kläranlagen- und Kanal-Nachbarschaften des DWA-Landesverbands Baden-Württemberg, Deutschland, 25-26 March.

[2] Pistocchi, A., Dorati, C., Grizzetti, B., Udias, A., Vigiak, O., & Zanni, M. (2019) Water quality in Europe: effects of the Urban Wastewater Treatment Directive - A retrospective and scenario analysis of Dir. 91/271/EEC. EUR 30003 EN, Publications Office of the European Union, Luxembourg. 118 p. doi: https://doi.org/10.2760/303163.

[3] Perales-Momparler, S., Andrés-Doménech, I., Hernández-Crespo, C., Vallés-Morán, F., Martín, M., Escuder-Bueno, I., & Andreu, J. (-2017) The role of monitoring sustainable drainage systems for promoting transition towards regenerative urban built environments: a case study in the Valencian region, Spain. *Journal of Cleaner Production*, 163, Supplement, S113-S124. doi: https://doi.org/10.1016/j.jclepro.2016.05.153.

[4] ISO (2003). ISO 10012:2003 - Measurement management systems - Requirements for measurement processes and measuring equipment. Geneva (Switzerland): International Standards Organisation, 26 p.

[5] Bertrand-Krajewski J.-L., Clemens-Meyer F.H.L.R., & Lepot M. (editors) (2021) Metrology in Urban Drainage and Stormwater Management: Plug & Pray. London (UK): IWA Publishing, August 2021, 517 p. ISBN 9781789060119. Open Access available from https://doi.org/10.2166/9781789060119 (accessed 26 April 2025).

[6] UDMT User Manual (2025). Co-UDlabs Task 6.2, UDMT - Urban Drainage Metrology Toolbox User Manual, version 2025a. Lyon (France): INSA Lyon, 83 p., 10 April 2025. Available at https://u.pcloud.link/publink/show?code=kZegnQVZM53qyjRJ4cHn7Pi5WzrR9HJ0PL4V.

## Biography

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Jean-Luc Bertrand-Krajewski is professor of Urban Hydrology at INSA Lyon, France (National Institute for Applied Sciences) since 1997. He was director of the laboratory DEEP (Laboratory on Wastes, Water, Environment and Pollution) from 2014 to 2020. He is co-president of the OTHU French Research Federation (Field Observatory of Urban Hydrology) since 2023 (www.othu.org). His research topics are related to urban water systems, including modelling and monitoring of water quantity and quality in grey and blue-green infrastructures, with numerous national and international collaborations. He was chair of the IWA Specialist Group on Urban Drainage (2005 to 2008), member of the IWA Strategic Council (2010 to 2018) and member of the IWA Publishing Board of Directors (2018 to 2024), and recently got the IWA Outstanding Service Award (2024). Additional information is available on his website at https://jlbkpro.free.fr.