title: Lost in calibration: why people still do not calibrate their models, and why they still should - a case study from urban drainage modelling.
abstract: From a scientific point of view, it is unquestioned that numerical models for technical systems need to be calibrated. However, in sufficiently calibrated models are still used in engineering practice. Case studies in the scientific literature that deal with urban water management are mostly large cities, while little attention is paid to the differing boundary conditions of smaller municipalities. Consequently, the aim of this paper is to discuss the calibration of a hydrodynamic model of a small municipality (15,000 inhabitants). To represent the spatial distribution of precipitation, three distributed rain gauges were used for model calibration. To show the uncertainties imminent to the calibration process, 17 scenarios, differing in assumptions for calibration, were distinguished. To compare the impact of the different calibration scenarios on actual design values, design rainfall events were applied. The comparison of the model results using the different typical design storm events from all the surrounding data points showed substantial differences for the assessment of the sewers regarding urban flooding, emphasizing the necessity of uncertainty analysis for hydrodynamic models. Furthermore, model calibration is of the utmost importance, because uncalibrated models tend to overestimate flooding volume and therefore result in larger diameters and retention volumes.
authors.affiliation: Unit of Environmental Engineering, University of Innsbruck, Technikerstrasse 13, Innsbruck 6020, Austria E-mail: franz.tscheikner-gratl@uibk.ac.at.
authors.forename: Franz
authors.initials: F
authors.lastname: Tscheikner-Gratl
authors.affiliation: Unit of Environmental Engineering, University of Innsbruck, Technikerstrasse 13, Innsbruck 6020, Austria E-mail: franz.tscheikner-gratl@uibk.ac.at.
authors.forename: Peter
authors.initials: P
authors.lastname: Zeisl
authors.affiliation: Unit of Environmental Engineering, University of Innsbruck, Technikerstrasse 13, Innsbruck 6020, Austria E-mail: franz.tscheikner-gratl@uibk.ac.at.
authors.forename: Carolina
authors.initials: C
authors.lastname: Kinzel
authors.affiliation: Institute of Urban Water Management and Landscape Water Engineering, Graz University of Technology, Stremayrgasse 10/I, Graz 8010, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Leimgruber
authors.affiliation: Institute of Sanitary Engineering and Water Pollution Control (SIG), University of Natural Resources and Life Sciences, Muthgasse 18, Vienna 1190, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ertl
authors.affiliation: Unit of Environmental Engineering, University of Innsbruck, Technikerstrasse 13, Innsbruck 6020, Austria E-mail: franz.tscheikner-gratl@uibk.ac.at.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Rauch
authors.affiliation: Unit of Environmental Engineering, University of Innsbruck, Technikerstrasse 13, Innsbruck 6020, Austria E-mail: franz.tscheikner-gratl@uibk.ac.at.
authors.forename: Manfred
authors.initials: M
authors.lastname: Kleidorfer
mesh_terms: D002138:Calibration; D002947:Cities; D055868:Floods; D057446:Hydrodynamics; D008962:Models, Theoretical; D011891:Rain; D035501:Uncertainty