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Analyses of case studies are used to evaluate new or existing technologies, measures or strategies with regard to their impact on the overall process. However, data availability is limited and hence, new technologies, measures or strategies can only be tested on a limited number of case studies. Owing to the specific boundary conditions and system properties of each single case study, results can hardly be generalized or transferred to other boundary conditions. virtual infrastructure benchmarking (VIBe) is a software tool which algorithmically generates virtual case studies (VCSs) for urban water systems. System descriptions needed for evaluation are extracted from VIBe whose parameters are based on real world case studies and literature. As a result VIBe writes Input files for water simulation software as EPANET and EPA SWMM. With such input files numerous simulations can be performed and the results can be benchmarked and analysed stochastically at a city scale. In this work the approach of VIBe is applied with parameters according to a section of the Inn valley and therewith 1,000 VCSs are generated and evaluated. A comparison of the VCSs with data of real world case studies shows that the real world case studies fit within the parameter ranges of the VCSs. Consequently, VIBe tackles the problem of limited availability of case study data.

To simulate hydrological models of combined sewer systems an accurate calibration is indispensable. In addition to all sources of uncertainties in data collection due to the measurement methods itself, it is a key question which data has to be collected to calibrate a hydrological model, how long measurement campaigns should last and where that data has to be collected in a spatial distributed system as it is neither possible nor sensible to measure the complete system characteristics. In this paper we address this question by means of stochastic modelling. Using Monte Carlo Simulation different calibration strategies (selection of measurement sites, selection of rainfall-events) and different calibration parameters (overflow volume, number of overflows) are tested, in order to evaluate the influence on predicting the total overflow volume of the entire system. This methodology is applied in a case study with the aim to calculate the combined sewer overflow (CSO) efficiency. It can be shown that a distributed hydrological model can be calibrated sufficiently when calibration is done on 30% of all existing CSOs based on long-term observation. Event based calibration is limited possible to a limited extend when calibration events are selected carefully as wrong selection of calibration events can result in a complete failure of the calibration exercise.

In cold climate regions winter conditions significantly influence the performance of stormwater infiltration devices. Frozen soil and water storage by snow changes their operation. In this paper winter operation of a grassed infiltration swale was investigated using on-site and laboratory measurements. The field investigation of a grassed swale at a parking place in an Alpine region showed that the swale fulfilled its function properly. Although the top layer was frozen for some time, the storage capacity of the swale was sufficient to store the precipitation until the conditions improved. The soil attenuated the air temperature, at 20 cm below ground surface the soil was only frozen for one week. winter maintenance proved to be a problem, together with the snow from the parking place a lot of gravel and fine particles were deposited at one end of the swale. This decreased the hydraulic conductivity at that point significantly. The laboratory tests with soil columns showed an increase of flow time through the soil column with decreasing soil moisture content. For soil temperatures below 0 degrees C the hydraulic conductivity was reduced for increasing initial soil moisture contents. All in all the hydraulic conductivity was best around 0 degrees C for all soil water contents. However, also at minus 5 degrees C the coefficient of hydraulic conductivity was always at least above 10(-6) m/s, thus within the range of tolerated hydraulic conductivity specified in the national guidelines. Nevertheless, the handling of the soil was found to have high influence on the results. The results indicate that in the Alpine region infiltration swales operate sufficiently under winter conditions although with decreased performance.