Detection and abundance of SARS-CoV-2 in wastewater in Liechtenstein, and the estimation of prevalence and impact of the B.1.1.7 variant.

The new coronavirus 2 (SARS-CoV-2) is known to be also shed through feces, which makes wastewater-based surveillance possible, independent of symptomatic cases and unbiased by any testing strategies and frequencies. We investigated the entire population of the Principality of Liechtenstein with samples from the wastewater treatment plant Bendern (serving all 39,000 inhabitants). Twenty-four-hour composite samples were taken once or twice a week over a period of 6 months from September 2020 to March 2021. Viral RNA was concentrated using the PEG centrifugation method followed by reverse transcription quantitative PCR. The aim of this research was to assess the suitability of SARS-CoV-2 fragments to relate the viral wastewater signal to the incidences and assess the impact of the emerging B.1.1.7. variant. The viral load in the wastewater peaked at almost 9 × 108 viral fragments per person equivalent (PE) and day on October 25, and showed a second peak on December 22 reaching a viral load of approximately 2 × 108 PE-1d-1. Individual testing showed a lag of 4 days and a distinct underestimation of cases at the first peak when testing frequency was low. The wastewater signal showed an immediate response to the implementation of non-pharmaceutical interventions. The new virus variant B.1.1.7. was first detected in wastewater on December 23, while it was first observed with individual testing on January 13, 2021. Further, our data indicate that the emergence of new virus variant may change the wastewater signal, probably due to different shedding patterns, which should be considered in future models.

Modelling transitions in urban water systems.

Long term planning of urban water infrastructure requires acknowledgement that transitions in the water system are driven by changes in the urban environment, as well as societal dynamics. Inherent to the complexity of these underlying processes is that the dynamics of a system's evolution cannot be explained by linear cause-effect relationships and cannot be predicted under narrow sets of assumptions. Planning therefore needs to consider the functional behaviour and performance of integrated flexible infrastructure systems under a wide range of future conditions. This paper presents the first step towards a new generation of integrated planning tools that take such an exploratory planning approach. The spatially explicit model, denoted DAnCE4Water, integrates urban development patterns, water infrastructure changes and the dynamics of socio-institutional changes. While the individual components of the DAnCE4Water model (i.e. modules for simulation of urban development, societal dynamics and evolution/performance of water infrastructure) have been developed elsewhere, this paper presents their integration into a single model. We explain the modelling framework of DAnCE4Water, its potential utility and its software implementation. The integrated model is validated for the case study of an urban catchment located in Melbourne, Australia.

Integrated hydraulic modelling of water supply and urban drainage networks for assessment of decentralized options.

The impact of climate change, water scarcity, land use change, population growth and also population shrinking can only be predicted with uncertainties. Especially for assets with a long planning horizon this is a critical part for planning and design. One solution is to make centralized organized water infrastructure with a long-planning horizon resilient and adaptive. For existing centralized infrastructure such a transition would be to increasingly implement decentralized measures. But such a transition can cause severe impacts on existing centralized infrastructure. Low flow conditions in urban drainage systems can cause sediment deposition, and for water supply systems water age problems may occur. This work focuses on city-scale analysis for assessing the impact of such measures. For that a coupled model for integrated city-scale analysis is applied and further developed. In addition, a geographic information system (GIS)-based approach for sensitivity analysis is enhanced and also implemented in that model. The developed approach is applied to assess the water infrastructure of an alpine case study. With the obtained results it is demonstrated how the planning process is enhanced by indicating where and where not to implement decentralized measures in an existing water infrastructure.

The application of a Web-geographic information system for improving urban water cycle modelling.

Research in urban water management has experienced a transition from traditional model applications to modelling water cycles as an integrated part of urban areas. This includes the interlinking of models of many research areas (e.g. urban development, socio-economy, urban water management). The integration and simulation is realized in newly developed frameworks (e.g. DynaMind and OpenMI) and often assumes a high knowledge in programming. This work presents a Web based urban water management modelling platform which simplifies the setup and usage of complex integrated models. The platform is demonstrated with a small application example on a case study within the Alpine region. The used model is a DynaMind model benchmarking the impact of newly connected catchments on the flooding behaviour of an existing combined sewer system. As a result the workflow of the user within a Web browser is demonstrated and benchmark results are shown. The presented platform hides implementation specific aspects behind Web services based technologies such that the user can focus on his main aim, which is urban water management modelling and benchmarking. Moreover, this platform offers a centralized data management, automatic software updates and access to high performance computers accessible with desktop computers and mobile devices.

Estimating inflow to a combined sewer overflow structure with storage tank in real time: evaluation of different approaches.

The performance assessment of storage tanks and combined sewer overflow (CSO) structures in sewer systems requires knowledge of the total inflow from the catchment during rainfall events. Many structures are, however, only equipped with sensors to measure water level and/or outflows. Based on the geometry of the tank, expressed as a level-storage relationship, inflow can be calculated from these data using a simple conceptual storage model. This paper compares a deterministic and a Bayesian approach for estimating the inflow to a CSO structure from measurements of outflows and water level. The Bayesian approach clearly outperforms the deterministic estimation which is very sensitive to measurement errors. Although computationally more demanding, the use of a simple linear storage model allows the online application of the Bayesian approach to repeatedly estimate inflow in short time intervals of a few minutes. The method could thus be used as an online software sensor for inflow to storage structures in sewer systems.

Assessing the efficiency of different CSO positions based on network graph characteristics.

The technical design of urban drainage systems comprises two major aspects: first, the spatial layout of the sewer system and second, the pipe-sizing process. Usually, engineers determine the spatial layout of the sewer network manually, taking into account physical features and future planning scenarios. Before the pipe-sizing process starts, it is important to determine locations of possible weirs and combined sewer overflows (CSOs) based on, e.g. distance to receiving water bodies or to a wastewater treatment plant and available space for storage units. However, positions of CSOs are also determined by topological characteristics of the sewer networks. In order to better understand the impact of placement choices for CSOs and storage units in new systems, this work aims to determine case unspecific, general rules. Therefore, based on numerous, stochastically generated virtual alpine sewer systems of different sizes it is investigated how choices for placement of CSOs and storage units have an impact on the pipe-sizing process (hence, also on investment costs) and on technical performance (CSO efficiency and flooding). To describe the impact of the topological positions of these elements in the sewer networks, graph characteristics are used. With an evaluation of 2,000 different alpine combined sewer systems, it was found that, as expected, with CSOs at more downstream positions in the network, greater construction costs and better performance regarding CSO efficiency result. At a specific point (i.e. topological network position), no significant difference (further increase) in construction costs can be identified. Contrarily, the flooding efficiency increases with more upstream positions of the CSOs. Therefore, CSO and flooding efficiency are in a trade-off conflict and a compromise is required.

Identifiability analysis in conceptual sewer modelling.

For a sufficient calibration of an environmental model not only parameter sensitivity but also parameter identifiability is an important issue. In identifiability analysis it is possible to analyse whether changes in one parameter can be compensated by appropriate changes of the other ones within a given uncertainty range. Parameter identifiability is conditional to the information content of the calibration data and consequently conditional to a certain measurement layout (i.e. types of measurements, number and location of measurement sites, temporal resolution of measurements etc.). Hence the influence of number and location of measurement sites on the number of identifiable parameters can be investigated. In the present study identifiability analysis is applied to a conceptual model of a combined sewer system aiming to predict the combined sewer overflow emissions. Different measurement layouts are tested and it can be shown that only 13 of the most sensitive catchment areas (represented by the model parameter 'effective impervious area') can be identified when overflow measurements of the 20 highest overflows and the runoff to the waste water treatment plant are used for calibration. The main advantage of this method is very low computational costs as the number of required model runs equals the total number of model parameters. Hence, this method is a valuable tool when analysing large models with a long runtime and many parameters.

A software-based sensor for combined sewer overflows.

A new methodology for online estimation of excess flow from combined sewer overflow (CSO) structures based on simulation models is presented. If sufficient flow and water level data from the sewer system is available, no rainfall data are needed to run the model. An inverse rainfall-runoff model was developed to simulate net rainfall based on flow and water level data. Excess flow at all CSO structures in a catchment can then be simulated with a rainfall-runoff model. The method is applied to a case study and results show that the inverse rainfall-runoff model can be used instead of missing rain gauges. Online operation is ensured by software providing an interface to the SCADA-system of the operator and controlling the model. A water quality model could be included to simulate also pollutant concentrations in the excess flow.

Influence of characteristics on combined sewer performance.

Elements of combined sewer systems are among others sub-catchments, junctions, conduits and weirs with or without storage units. The spatial distribution and attributes of all these elements influence both system characteristics and sewer performance. Until today, little work has been done to analyse the influence of such characteristics in a case unspecific approach. In this study, 250 virtual combined sewer systems are analysed by defining groups of systems, which are representative for their different characteristics. The set was created with a further development of the case study generator (CSG), a tool for automatic generation of branched sewer systems. Combined sewer overflow and flooding is evaluated using performance indicators based on hydrodynamic simulations. The analysis of system characteristics, like those presented in this paper, helps researchers to understand coherences and aids practitioners in designing combined sewers. For instance, it was found that characteristics that have a positive influence on emission reduction frequently have a negative influence on flooding avoidance and vice versa.

GIS-based applications of sensitivity analysis for sewer models.

Sensitivity analysis (SA) evaluates the impact of changes in model parameters on model predictions. Such an analysis is commonly used when developing or applying environmental models to improve the understanding of underlying system behaviours and the impact and interactions of model parameters. The novelty of this paper is a geo-referenced visualization of sensitivity indices for model parameters in a combined sewer model using geographic information system (GIS) software. The result is a collection of maps for each analysis, where sensitivity indices (calculated for model parameters of interest) are illustrated according to a predefined symbology. In this paper, four types of maps (an uncertainty map, calibration map, vulnerability map, and design map) are created for an example case study. This article highlights the advantages and limitations of GIS-based SA of sewer models. The conclusion shows that for all analyzed applications, GIS-based SA is useful for analyzing, discussing and interpreting the model parameter sensitivity and its spatial dimension. The method can lead to a comprehensive view of the sewer system.

The Cauvery river basin in southern India: major challenges and possible solutions in the 21st century.

India is facing major challenges in its water resources management (WRM) sector. Water shortages are attributed to issues such as an explosion in population, rapid urbanization and industrialization, environmental degradation and inefficient water use, all aggravated by changing climate and its impacts on demand, supply and water quality. This paper focuses on the contemporary and future situation in the Cauvery river basin in Southern India, shared by different states, predominantly Karnataka and Tamil Nadu. As water issues largely fall under the authority of the states, inter-state water disputes have a long tradition in the Cauvery river basin. Future changes in precipitation during the two monsoon seasons will only increase these tensions. Both states depend on the arrival of these monsoon rains to water their crops and to replenish the groundwater. The paper identifies the major challenges and general possible solutions for sustainable WRM within the river basin. It synthesises the relevant literature, describes practices that should be addressed in the scope of integrated WRM--including water availability increase and demand management--and stresses the need for further quantitative analyses.

Cascade vulnerability for risk analysis of water infrastructure.

One of the major tasks in urban water management is failure-free operation for at least most of the time. Accordingly, the reliability of the network systems in urban water management has a crucial role. The failure of a component in these systems impacts potable water distribution and urban drainage. Therefore, water distribution and urban drainage systems are categorized as critical infrastructure. Vulnerability is the degree to which a system is likely to experience harm induced by perturbation or stress. However, for risk assessment, we usually assume that events and failures are singular and independent, i.e. several simultaneous events and cascading events are unconsidered. Although failures can be causally linked, a simultaneous consideration in risk analysis is hardly considered. To close this gap, this work introduces the term cascade vulnerability for water infrastructure. Cascade vulnerability accounts for cascading and simultaneous events. Following this definition, cascade risk maps are a merger of hazard and cascade vulnerability maps. In this work cascade vulnerability maps for water distribution systems and urban drainage systems based on the 'Achilles-Approach' are introduced and discussed. It is shown, that neglecting cascading effects results in significant underestimation of risk scenarios.

An agent-based approach for generating virtual sewer systems.

The application of artificial case studies is a well established technique in urban drainage to test measures, approaches or models. However, the preparation of a virtual case study for a sewer system is a tedious task. Several algorithms have been presented in the literature for an automatic generation of virtual sewer systems. Applying the approach of generating virtual cities by means of the software VIBe (Virtual Infrastructure Benchmarking) the urban structure (including elevation map, land use and population distribution) is generated firstly and the infrastructure is designed meeting the requirements of the urban structure. The aim of this paper is the development of an agent based approach for generating virtual sewer systems. This new algorithm functions as module of the software VIBe but can of course also be applied to a real city in order to get information on possible/optimal sewer placement. Here hundred virtual VIBe cities and for each twelve virtual sewer networks are generated and calibrated based on data of an alpine region. It is revealed that with the approach presented virtual sewer networks which are comparable with real world sewer networks can be generated. The agent based method provides data sets for benchmarking and allows case independent testing of new measures.

Stormwater quality models: performance and sensitivity analysis.

The complex nature of pollutant accumulation and washoff, along with high temporal and spatial variations, pose challenges for the development and establishment of accurate and reliable models of the pollution generation process in urban environments. Therefore, the search for reliable stormwater quality models remains an important area of research. Model calibration and sensitivity analysis of such models are essential in order to evaluate model performance; it is very unlikely that non-calibrated models will lead to reasonable results. This paper reports on the testing of three models which aim to represent pollutant generation from urban catchments. Assessment of the models was undertaken using a simplified Monte Carlo Markov Chain (MCMC) method. Results are presented in terms of performance, sensitivity to the parameters and correlation between these parameters. In general, it was suggested that the tested models poorly represent reality and result in a high level of uncertainty. The conclusions provide useful information for the improvement of existing models and insights for the development of new model formulations.

Sediment and pollutant load modelling using an integrated urban drainage modelling toolbox: an application of City Drain.

Numerical and computational modelling of flow and pollutant dynamics in urban drainage systems is becoming more and more integral to planning and design. The main aim of integrated flow and pollutant models is to quantify the efficiency of different measures at reducing the amount of pollutants discharged into receiving water bodies and minimise the consequent negative water quality impact. The open source toolbox CITY DRAIN developed in the Matlab/Simulink environment, which was designed for integrated modelling of urban drainage systems, is used in this work. The goal in this study was to implement and test computational routines for representing sediment and pollutant loads in order to evaluate catchment surface pollution. Tested models estimate the accumulation, erosion and transport of pollutants--aggregately--on urban surfaces and in sewers. The toolbox now includes mathematical formulations for accumulation of pollutants during dry weather period and their wash-off during rainfall events. The experimental data acquired in a previous research project carried out by the Environmental Engineering Research Centre (CIIA) at the Universidad de los Andes in Bogotá (Colombia) was used for the calibration of the models. Different numerical approaches were tested for their ability to calibrate to the sediment transport conditions. Initial results indicate, when there is more than one peak during the rainfall event duration, wash-off processes probably can be better represented using a model based on the flow instead of the rainfall intensity. Additionally, it was observed that using more detailed models (compared with an instantaneous approach) for representing pollutant accumulation do not necessarily lead to better results.

Parallel computing in conceptual sewer simulations.

Integrated urban drainage modelling is used to analyze how existing urban drainage systems respond to particular conditions. Based on these integrated models, researchers and engineers are able to e.g. estimate long-term pollution effects, optimize the behaviour of a system by comparing impacts of different measures on the desired target value or get new insights on systems interactions. Although the use of simplified conceptual models reduces the computational time significantly, searching the enormous vector space that is given by comparing different measures or that the input parameters span, leads to the fact, that computational time is still a limiting factor. Owing to the stagnation of single thread performance in computers and the rising number of cores one needs to adapt algorithms to the parallel nature of the new CPUs to fully utilize the available computing power. In this work a new developed software tool named CD3 for parallel computing in integrated urban drainage systems is introduced. From three investigated parallel strategies two showed promising results and one results in a speedup of up to 4.2 on an eight-way hyperthreaded quad core CPU and shows even for all investigated sewer systems significant run-time reductions.

A multi-layer cellular automata approach for algorithmic generation of virtual case studies: VIBe.

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.

Determining the spill flow discharge of combined sewer overflows using rating curves based on computational fluid dynamics instead of the standard weir equation.

It is state of the art to evaluate and optimise sewer systems with urban drainage models. Since spill flow data is essential in the calibration process of conceptual models it is important to enhance the quality of such data. A wide spread approach is to calculate the spill flow volume by using standard weir equations together with measured water levels. However, these equations are only applicable to combined sewer overflow (CSO) structures, whose weir constructions correspond with the standard weir layout. The objective of this work is to outline an alternative approach to obtain spill flow discharge data based on measurements with a sonic depth finder. The idea is to determine the relation between water level and rate of spill flow by running a detailed 3D computational fluid dynamics (CFD) model. Two real world CSO structures have been chosen due to their complex structure, especially with respect to the weir construction. In a first step the simulation results were analysed to identify flow conditions for discrete steady states. It will be shown that the flow conditions in the CSO structure change after the spill flow pipe acts as a controlled outflow and therefore the spill flow discharge cannot be described with a standard weir equation. In a second step the CFD results will be used to derive rating curves which can be easily applied in everyday practice. Therefore the rating curves are developed on basis of the standard weir equation and the equation for orifice-type outlets. Because the intersection of both equations is not known, the coefficients of discharge are regressed from CFD simulation results. Furthermore, the regression of the CFD simulation results are compared with the one of the standard weir equation by using historic water levels and hydrographs generated with a hydrodynamic model. The uncertainties resulting of the wide spread use of the standard weir equation are demonstrated.

Identifying weak points of urban drainage systems by means of VulNetUD.

This article presents the development and application of the software tool VulNetUD. VulNetUD is a tool for GIS-based identification of vulnerable sites of urban drainage systems (UDS) using hydrodynamic simulations undertaken using EPA SWMM. The benefit of the tool is the output of different vulnerability maps rating sewer surcharging, sewer flooding, combined sewer overflow (CSO) efficiency and CSO emissions. For this, seven predefined performance indicators are used to evaluate urban drainage systems under abnormal, critical and future conditions. The application on a case study highlights the capability of the tool to identify weak points of the urban drainage systems. Thereby it is possible to identify urban drainage system components which cause the highest performance decrease across the entire system. The application of the method on a real world case study shows for instance that a reduction of catchment areas which are located upstream of CSOs with relatively less capacity in the downstream sewers achieves the highest increases efficiency of the system. Finally, the application of VulNetUD is seen as a valuable tool for managers and operators of waste water utilities to improve the efficiency of their systems. Additionally vulnerability maps generated by VulNetUD support risk management e.g. decision making in urban development planning or the development of rehabilitation strategies.

Impact of input data uncertainties on urban stormwater model parameters.

The use of urban drainage models requires careful calibration, where model parameters are selected in order to minimize the difference between measured and simulated results. It has been recognized that often more than one set of calibration parameters can achieve similar model accuracy. A probability distribution of model parameters should therefore be constructed to examine the model's sensitivity to its parameters. With increasing complexity of models, it also becomes important to analyze the model parameter sensitivity while taking into account uncertainties in input and calibration data. In this study a Bayesian approach was used to develop a framework for quantification of impacts of uncertainties in the model inputs on the parameters of a simple integrated stormwater model for calculating runoff, total suspended solids and total nitrogen loads. The framework was applied to two catchments in Australia. It was found that only systematic rainfall errors have a significant impact on flow model parameters. The most sensitive flow parameter was the effective impervious area, which can be calibrated to completely compensate for the input data uncertainties. The pollution model parameters were influenced by both systematic and random rainfall errors. Additionally an impact of circumstances (e.g. catchment type, data availability) has been recognized.