Abstract
The calibration of models for urban drainage systems has become more and more important as especially the usage of detailed models has increased considerably over the last years as the basis for planning and design. Still the effects originating from the choice of data used for model calibration are little known and advice on planning measurement campaigns for model calibration is limited, especially for small and medium-sized municipalities. The choice of measurement sites (number and location) within a sewer system is affecting the robustness of the calibration and in consequence the assessment of the modelled system behaviour. This paper discusses the calibration of a hydrologic-hydrodynamic model using the representative example of a small municipality. Different calibration scenarios were created using a model-based approach, focusing on varying availability of in-sewer measurement data. To assess the performance of different scenarios and validate the respective models, different model outputs were compared. The different calibration scenarios resulted in high variations in the model performances. The number and location of used calibration points influence model performance significantly. Predicted CSO volumes deviate from a set of given reference values in ranges between 1% and 253% for one, −21% to −5% for two and 1% to 237% for five used calibration points, depending on the rainfall data input. Consequently, the design of measurement campaigns for calibration data is a very sensitive decision in the modelling process. The model performance further influences design and decision-making processes, which are then perceptible in economic and functional aspects.
Highlights
The usage of hydrodynamic models, for flood forecasting and as a planning tool in urban drainage has increased considerably over the last decades and with it the importance of understanding a model’s ability to reproduce the system behaviour
Even for different rainfall inputs and neglecting spatial distributions of occurring intensities, their validations resulted in very good agreements and low deviations from the used reference scenario when looking at the combined sewer overflows (CSO) volumes
For design storms with return periods of 5 and 10 years, it shows higher possible deviation ranges for flooding than for CSO volumes
Summary
The usage of hydrodynamic models, for flood forecasting and as a planning tool in urban drainage has increased considerably over the last decades and with it the importance of understanding a model’s ability to reproduce the system behaviour. They stem of measurement errors for both input and calibration data, the selection of appropriate calibration and validation datasets, the applied calibration algorithms and the objective functions used during the calibration process (Deletic et al 2012) Another possible deficit of urban water management studies is that the case studies in scientific literature are often the same, usually larger cities which have the financial and human resources to participate in research projects and to provide an appropriate data-background (i.e. Los Angeles in Barco et al (2008), Melbourne in Bach et al (2013) or Shenzen in Gong et al (2017)). The influence of data availability on calibration performance is investigated for the hydrodynamic drainage model of a small Austrian municipality For this purpose, different scenarios of data availability for calibration are simulated. This paper describes three scenarios (scenario I, II and III – varying in amount and distribution of measurement sites) to highlight the influences originating from the design of in-sewer measurement campaigns
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