25 Jul 2022
25 Jul 2022
Status: this preprint is open for discussion.

All models are wrong, but are they useful? Assessing reliability across multiple sites to build trust in urban drainage modelling

Agnethe Nedergaard Pedersen1,2, Annette Brink-Kjær1, and Peter Steen Mikkelsen2 Agnethe Nedergaard Pedersen et al.
  • 1VCS Denmark, Vandværksvej 7, 5000 Odense C, Denmark
  • 2DTU Sustain, Technical University of Denmark, Bygningstorvet, Bygning 115, 2800 Kgs. Lyngby, Denmark

Abstract. Simulation models are widely used in urban drainage engineering and research, but they are known to include errors and uncertainties that are not yet fully realised. Within the herein developed framework, we investigate model adequacy across multiple sites by comparing model results with measurements for three model objectives: ‘surcharges’ (water level rises above defined critical levels related to basement flooding), ‘overflows’ (water levels rise above a crest level), and ‘everyday events’ (water levels stay below the top of pipes). We use multi-event hydrological signatures, i.e. metrics that extract specific characteristics of time series events in order to compare model results with the observations for the mentioned objectives through categorical and statistical data analyses. Furthermore, we assess the events with respect to sufficient or insufficient categorical performance, and good, acceptable, or poor statistical performance. We also develop a method to reduce the weighting of individual events in the analyses, in order to acknowledge uncertainty in model and/or measurements in cases where the model is not expected to fully replicate the measurements. A case study including several years of water level measurements from 23 sites in two different areas shows that only few sites score as “sufficient categorical performance” in relation to the objective ‘overflow’, and that sites do not necessarily obtain good performance scores for all the analysed objectives. The developed framework however highlights that it is possible to identify objectives and sites for which the model is reliable, and we also suggest methods for assessing where the model is less reliable and needs further improvement, which may be further refined in the future.

Agnethe Nedergaard Pedersen et al.

Status: open (until 19 Sep 2022)

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  • RC1: 'Comment on egusphere-2022-615', Anonymous Referee #1, 02 Aug 2022 reply

Agnethe Nedergaard Pedersen et al.

Agnethe Nedergaard Pedersen et al.


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Short summary
A framework for assessing the reliability of urban drainage models is developed in this paper. The method applies observation data from water level sensors, and model results for up to 10 years of data for 23 sites in two case areas in Odense, Denmark. With the use of signatures as a method to extract information from the timeseries, it is possible to differentiate the performance for different model objectives.