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The prosperity of urban life is dependent on its infrastructure. Urban underground infrastructure components (assets) are aging and need regular monitoring, maintenance and rehabilitation. These assets are often placed under pavements and in close vicinity to each other. Managing them in a coordinated way is rational considering costs and disruption of services and communities caused by each intervention on the different assets. Recently, interest in practice as well as in research has grown to manage urban infrastructures in a coordinated way. This article reviews journal articles and grey literature to evaluate managing these infrastructures in an integrated way (i.e. the highest level of coordination) and describe possible obstacles for doing so. This article identifies seven main challenges of integrated multi-infrastructure asset management (IMAM) that need to be addressed by practitioners and researchers. These challenges are related to: (i) dependencies and interdependencies, (ii) data quality, availability and interoperability, (iii) uncertainties in modelling and decision-making, (iv) comparability, (v) problems of scale, (vi) problems of fit and (vii) problems of interplay. This article provides details on these challenges and discusses future research and practical directions. [ABSTRACT FROM AUTHOR]

Urban water systems worldwide need integrated, cross-sectoral innovations to anticipate developments like climate change and population growth. Development and implementation of such innovations is challenging due to the operational and sectoral mindset of organizations in which these innovations take place. This study uses the concept of ambidexterity to get a better understanding of how organizations responsible for urban water management deal with the tension between operation and the need for innovation. We focused on Amsterdam and Rotterdam, two Dutch cities that are global frontrunners in urban water management. Combining a desk study with 25 semi-structured interviews, we found four mechanisms to manage innovation and operation tensions: network, hierarchical, process and human-resource mechnanisms. Different from the literature on ambidexterity, our empirical findings show that the connection between operation and innovation is dominated by networks rather than by executives. Hierarchical mechanisms could be used to complement this, catalyzing innovation or formalizing it. [ABSTRACT FROM AUTHOR]

Polyvinyl chloride (PVC) sewer pipes have operated for decades in a hostile environment, raising concern among sewer managers over the longevity of their drainage systems. Inspection data (CCTV and Panoramo®) reveals that severe defects have already surfaced, yet it is unknown if the material properties of PVC sewers have been affected. In order to address this issue, extensive testing (among others flexural and tensile tests, FT-IR, X-ray, viscosity measurements) was conducted on eight exhumed PVC sewer pipes (16–43 years old) with known defects and one brand-new for reference purposes. Visual examination during excavation revealed various failure causes, including uncontrolled handling of the pipes during construction or due to digging activities in the direct vicinity of the pipes. The test results indicate that physical ageing is extensively detected while other degradation mechanisms had minimal or no effect on the investigated pipes. However, mechanical testing on exhumed 3-layer pipes show that the incorporation of layered wall constructions is potentially a critical factor for the structural status of the pipe. [ABSTRACT FROM AUTHOR]

An outbreak of SARS-CoV-2 Alpha variant (Pango lineage B.1.1.7) was detected at a primary school (School X) in Lansingerland, the Netherlands, in December 2020. The outbreak was studied retrospectively, and population-based screening was used to assess the extent of virus circulation and decelerate transmission. Cases were SARS-CoV-2 laboratory confirmed and were residents of Lansingerland (November 16th 2020 until February 22th 2021), or had an epidemiological link with School X or neighbouring schools. The SARS-CoV-2 variant was determined using variant PCR or whole genome sequencing. A questionnaire primarily assessed clinical symptoms. A total of 77 Alpha variant cases were found with an epidemiological link to School X, 16 Alpha variant cases linked to the neighbouring schools, and 146 Alpha variant cases among residents of Lansingerland without a link to the schools. The mean number of self-reported symptoms was not significantly different among Alpha variant infected individuals compared to non-Alpha infected individuals. The secondary attack rate (SAR) among Alpha variant exposed individuals in households was 52% higher compared to non-Alpha variant exposed individuals (p = 0.010), with the mean household age, and mean number of children and adults per household as confounders. Sequence analysis of 60 Alpha variant sequences obtained from cases confirmed virus transmission between School X and neighbouring schools, and showed that multiple introductions of the Alpha variant had already taken place in Lansingerland at the time of the study. The alpha variant caused a large outbreak at both locations of School X, and subsequently spread to neighbouring schools, and households. Population-based screening (together with other public health measures) nearly stopped transmission of the outbreak strain, but did not prevent variant replacement in the Lansingerland municipality. [ABSTRACT FROM AUTHOR]

The main application of the mobile geo-electrical measurement is the detection of the presence and determining the location of leakage in sewer systems. To do so, this method relies on the increase in the measured electrical current between an electrode inside and an electrode outside the sewer system. To use this technique for the quantification of leakages further assumptions on the measured current are required. In this study, a model to simulate the geo-electrical measurement system is developed. Laboratory experiments are conducted to investigate the influence and contribution of the model components on the measured current and the validity of the assumptions. The experimental results demonstrate that multiple components significantly contribute to the measured current apart from the leakage in the pipe. As a consequence, the properties of the leakage in the pipe are likely to be significantly under- or overestimated in most measuring systems currently applied in practice. [ABSTRACT FROM AUTHOR]

Urban runoff remobilises solids and their associated pollutants from urban-built environments and transports them to drainage systems via gully pots. This study presents an extensive monitoring campaign on the solids loading to drainage systems, including 104 gully pots as sampling locations and lasting 2 years. The solids loading is modelled with Build-Up and Wash-Off (BUWO) models and a Regression Tree (RT). The performance of the RT is substantially better than the performance of the BUWO models, such that it is not recommended to use a single BUWO model to predict the loading of a set of gully pots/catchments. It is discussed whether the generally observed mismatch between monitoring data and wash-off models, both in this study and in literature, points to a fundamental misunderstanding of the underlying processes. Finally, the results show that an increased street sweeping frequency does not significantly reduce the solids loading to drainage systems. [ABSTRACT FROM AUTHOR]

To evaluate the performance of Real Time Control (RTC) of urban drainage systems (UDS) a comparison is made with the pre-RTC situation, making the RTC performance dependent on the functioning of the UDS prior to implementation. To standardise things, a generalised baseline is formulated here as the operation with optimal static settings of the UDS. Two maximum theoretical potential performances are then calculated, one including and one excluding system limitations. These are combined with the generalised baseline to form Realised Potential Indicators (RPIs), objective values which indicate the proximity of the RTC strategy to its maximum potential. The proposed methodology was demonstrated on the case study of Eindhoven, the Netherlands. The results obtained show that using RPIs allows for a more objective assessment and improved understanding of the efficacy of different RTC procedures. Additionally, the RPIs can provide an indication if RTC is sufficient to achieve the desired UDS performance. [ABSTRACT FROM AUTHOR]

Runoff (re)mobilises solids and their associated pollutants from streets and transports them via gully pots to the drainage system. As the solids negatively impact the performance of the drainage systems, knowledge on the solids loading in terms of mass and composition is essential. However, monitoring data on the solids loading, in particular, covering all seasons and a number of sites, is scarce. This article presents the results of a monitoring campaign on the solids loading to a drainage system via 52 gully pots over a period of 2 years at a sampling rate of once per 3–4 weeks. The loading shows a maximum during the tree phases 'leaf growth' and 'full capacity' and is correlated with the rain intensity during these phases. The organic fraction and D50 of the solids are correlated with leaf abscission. The settling velocity of the particles <1800 µm is strongly correlated with their organic fraction. [ABSTRACT FROM AUTHOR]

Drinking water distribution networks (WDNs) are a crucial infrastructure for life in cities. Deterioration of this ageing, and partly hidden from view, infrastructure can result in losses due to leakage and an increased contamination risk. To counteract this, maintenance strategies are required to maintain the service level. Information on the most critical elements of a WDN, with respect to the functioning of the system as a whole, is essential for prioritising maintenance or rehabilitation activities. In this study a Graph theory based method is developed and applied for efficiently identifying the most critical elements. The main advantage of this method is that it avoids the need to perform elaborate hydrodynamic model calculations. Instead, the structure of the network is the main starting point. The results show that the structure of the network is more decisive than the hydraulics with respect to the criticality of the system's performance as a whole. Results depict that the suggested approach is applicable not only to the main (primary) network, but also to the capillaries which are normally beyond the scope of the traditional methods applied so-far because of the complexity of the networks and the required calculation time. [ABSTRACT FROM AUTHOR]

Runoff entering urban drainage systems contains suspended solids, which carry pollutants and may cause blockages in downstream parts of the system (for example infiltration facilities). Suspended solids inflow should, therefore, preferably be controlled by solids removal at gully pots. This paper presents the results of lab experiments on the solids accumulation in gully pots in a scale 1:1 setup. The accumulation process is initially dominated by settling in the gully pot. When a substantial sediment bed is created, the bed starts to interact with the flow, the removal efficiency of solids decreases, and the bed eventually reaches an equilibrium level. The effects of the discharge, sediment size, and geometry on these processes are assessed. The accumulation rate and equilibrium bed level are strongly affected by the flow pattern which is influenced by the combination of the position the jets impinge on the water and the gully pot's outlet position. [ABSTRACT FROM AUTHOR]

Polyvinyl chloride (PVC) has become one of the dominant construction materials for sewer systems over the past decades, as a result of its reputed merits. However, since PVC sewer pipes have operated for decades in a hostile environment, concern over their longevity has been lately raised by sewer managers in the Netherlands. Towards that direction, the main factors and mechanisms that affect a PVC pipe's lifetime are discussed in this article, along with the current lifetime prediction methods and their limitations. The review of relevant case studies indicates that material degradation, if any, occurs slowly. However, inspection (CCTV) data of three Dutch municipalities reveals that severe defects have already surfaced and degradation evolves at an unexpected fast rate. A main reason of this gap between literature and practice is the fact that comprehensive material testing of PVC sewer pipes is rarely found in the literature although it proves to be essential in order to trustfully assess the level of degradation and its origins. [ABSTRACT FROM AUTHOR]

Sewer asset management gained momentum and importance in recent years due to economic considerations, since infrastructure maintenance and rehabilitation directly represent major investments. Because physical urban water infrastructure has life expectancies of up to 100 years or more, contemporary urban drainage systems are strongly influenced by historical decisions and implementations. The current decisions taken in sewer asset management will, therefore, have a long-lasting impact on the functionality and quality of future services provided by these networks. These decisions can be supported by different approaches ranging from various inspection techniques, deterioration models to assess the probability of failure or the technical service life, to sophisticated decision support systems crossing boundaries to other urban infrastructure. This paper presents the state of the art in sewer asset management in its manifold facets spanning a wide field of research and highlights existing research gaps while giving an outlook on future developments and research areas. [ABSTRACT FROM AUTHOR]

Fat, oil and grease (FOG) deposits are an important contributor to blockages in building drainage systems. Such blockages bring undesirable financial, health and environmental costs, and thereby burden society. It is unclear to what extent the behavior of inhabitants, and more precisely domestic FOG disposal, affects the occurrence of FOG blockages. For this study, samples of FOG blockages were collected from building drainage systems (kitchen drains and lateral house connections) and analyzed. The results showed that the deposits were calcium salts of fatty acids. Dissimilarities between the network locations demonstrate that, even at short distance, in-sewer transformation processes occur. Surveys were conducted to reveal information about FOG disposal patterns. Three households showed a clear link between the type of cooking oils used and the type of deposits collected. [ABSTRACT FROM AUTHOR]

Due to a variety of contaminants in floodwater, exposure to urban pluvial flooding may pose a health risk to humans. In-sewer defects may cause increased pluvial flooding, possibly increasing health risks. This paper addresses the impact of in-sewer defects on urban pluvial flooding and, subsequently, on infection probabilities for humans. As such, it provides a necessary input for risk-informed sewer maintenance strategies in order to preserve the hydraulic performance of a sewer system. Critical locations in sewer networks can be safeguarded through detecting changes in hydraulic properties of the sewer system, by using monitoring equipment or alternative inspection methods. Two combined sewer systems in The Netherlands with different characteristics are studied. The catchment-wide average infection probability was calculated using Quantitative Microbial Risk Assessment (QMRA) and flooding frequencies from Monte Carlo simulations with a hydrodynamic model. For the studied catchments, it is concluded that the occurrence of flooding is significantly affected by sediment deposits and, consequently, the infection probability as well. The impact of sediment deposits on infection probabilities depends on sewer systems characteristics and varies within the catchment. The results in this paper also demonstrate that further research on the relationship between flood duration and infection probabilities is required. [ABSTRACT FROM AUTHOR]

Underground water infrastructure is essential for life in cities. The aging of these infrastructures requires maintenance strategies to maintain a minimum service level. Not all elements are equally important for the functioning of the infrastructure as a whole. Identifying the most critical elements in a network is crucial for formulating asset management strategies. The graph theory is presented as a means to identify the most critical elements in a network with respect to malfunctioning of the system as a whole. As opposed to conventional methods, the proposed method does not rely on iterative hydraulic calculations; instead, the structure of the network is taken as a starting point. In contrast to methods applied in practise, the results are independent on the chosen test-load. Because of the limited calculation effort, the method allows the analysis of large networks that are now, for practical reasons, beyond the scope of methods applied so-far. [ABSTRACT FROM AUTHOR]

Integrated Catchment Modelling aims to simulate jointly urban drainage systems, wastewater treatment plant and rivers. The effect of rainfall input uncertainties in the modelling of individual urban drainage systems has been discussed in several studies already. However, this influence changes when simultaneously simulating several urban drainage subsystems and their impact on receiving water quality. This study investigates the effect of the characteristics of rainfall inputs on a large-scale integrated catchment simulator for dissolved oxygen predictions in the River Dommel (The Netherlands). Rainfall products were generated with varying time-aggregation (10, 30 and 60 min) deriving from different sources of data with increasing spatial information: (1) Homogeneous rainfall from a single rain gauge; (2) block kriging from 13 rain gauges; (3) averaged C-Band radar estimation and (4) kriging with external drift combining radar and rain gauge data with change of spatial support. The influence of the different rainfall inputs was observed at combined sewer overflows (CSO) and dissolved oxygen (DO) dynamics in the river. Comparison of the simulations with river monitoring data showed a low sensitivity to temporal aggregation of rainfall inputs and a relevant impact of the spatial scale with a link to the storm characteristics to CSO and DO concentration in the receiving water. [ABSTRACT FROM AUTHOR]

Gully pots and lateral connections represent the anterior part of the sewer infrastructure responsible for the majority of flooding events in public areas. This study provides a statistical procedure to quantify the effectiveness of proactive management strategies to improve their performance. The first part consists of non-parametric methods to determine the evolution of gully pot blockages. The second part presents a Bayesian approach to quantify the development of reported flooding events when lateral connections are subject to proactive strategies. To this end, call data were collected from areas that were maintained proactively instead of reactively. Application of the procedure revealed a significant call decrease in one area. In addition, an increasing blockage likelihood over time indicated cyclic cleaning to be effective to improve sewer serviceability. By linking management strategies to performance, this flexible procedure can support sewer managers to balance the merits of proactive and reactive management strategies. [ABSTRACT FROM PUBLISHER]

The performance of lateral house connections has a direct impact on sewer serviceability. Despite the potential consequences of a blockage, these components are generally maintained with a reactive approach. As inspection data on the condition of lateral house connections are scarce, this study adopts a statistical procedure to support proactive strategies by analysing spatial blockage patterns to identify system parts with higher blockage incidences. First, a Monte Carlo simulation test provides insight into whether the spatial variation of the blockage likelihood is significant. This justifies the identification of explanatory factors by means of a bootstrapped generalised additive model. Application of the procedure to two databases containing 10 years of lateral house connection blockage data, revealed factors such as building age, sewer system type and ground settlement rate to explain spatial differences in the blockage likelihood. Furthermore, a likelihood ratio test demonstrated that the addition of a spatial smoother improved model performance. This smoother was able to account for additional spatial variation caused by explaining factors for which no data were available. The procedure provides key information for inspection and rehabilitation strategies by taking into account the model performance in assessing the trade-off between costs and benefits in terms of serviceability. [ABSTRACT FROM PUBLISHER]

Sewer performance is typically assessed using hydrodynamic models assuming the absence of in-sewer defects. As a consequence, hydraulic performance calculated by models is likely to be overestimated, while the real hydraulic performance of the sewer system remains unknown. This article introduces the concept of ‘hydraulic fingerprinting’ based on model calibration to identify in-sewer defects affecting hydraulic performance. Model calibration enables detection of changes in hydraulic properties of the sewer system. Each model calibration results in a set of model parameter values, their uncertainties and residuals. The model parameter values also incorporate the antecedent condition of the catchment of the event calibrated and are therefore less suitable to identify in-sewer defects. The residuals on the other hand, and more specifically their absolute values, statistical properties and the correlation between residuals at different monitoring locations are suitable as indicators of the occurrence of in-sewer defects. This allows the application of ‘hydraulic fingerprinting’ based on model calibration, where the ‘fingerprint’ is defined by the model parameters and the residuals. The concept of ‘fingerprinting’ is demonstrated for the combined sewer system ‘Tuindorp’ (Utrecht, the Netherlands). The results show that ‘hydraulic fingerprinting’ can be a powerful tool for directing sewer asset management actions. [ABSTRACT FROM PUBLISHER]

Wastewater treatment plants (WWTP) typically have a service life of several decades. During this service life, external factors, such as changes in the effluent standards or the loading of the WWTP may change, requiring WWTP performance to be optimized. WWTP modelling is widely accepted as a means to assess and optimize WWTP performance. One of the challenges for WWTP modelling remains the prediction of water quality at the inlet of a WWTP. Recent applications of water quality sensors have resulted in long time series of WWTP influent quality, containing valuable information on the response of influent quality to e.g., storm events. This allows the development of empirical models to predict influent quality. This paper proposes a new approach for water quality modelling, which uses the measured hydraulic dynamics of the WWTP influent to derive the influent water quality. The model can also be based on simulated influent hydraulics as input. Possible applications of the model are filling gaps in time series used as input for WWTP models or to assess the impact of measures such as real time control (RTC) on the performance of wastewater systems. [ABSTRACT FROM AUTHOR]

Operational decision-making processes for networked infrastructure management often occur as a multi-actor planning problem, implying these are based on negotiations between different stakeholders in addition to available system quality information. As such, does more accurate data about actual structural condition lead to other or better decision-making? A serious game is introduced, Maintenance in Motion, aiming at investigating the influence of information quality on rehabilitation decisions, for single- and multi-actor decision-making. Players manage drinking water, gas, sewer and street infrastructures. They are to balance their individual goal, cost-effectiveness, with their team utility, increasing overall infrastructure quality to minimise failure while minimising overall public costs. The game design, calibration and solution space are presented. [ABSTRACT FROM AUTHOR]

Operational decision processes for networked infrastructure management often occur as a multi-actor planning problem, implying these are partly based on negotiations between different stakeholders. The starting point for negation for each stakeholder is the available information about the structural condition of his infrastructure. In this respect, this leads to the question: ‘does more accurate data about actual structural condition lead to other or better decision-making?’ A serious game is introduced, ‘Maintenance in Motion’, aiming at investigating the influence of information quality about structural condition on replacement decisions, for single and multi-actor decision-making. Players are challenged to balance their individual goal, cost-effectiveness, with their team utility, increasing overall infrastructure quality to minimise failure while minimising overall public costs. Results show that if players are presented with perfect instead of imperfect information, in a single player environment, they played more cost-effectively. The availability of perfect instead of imperfect information about object state hardly changes game outcome in terms of team utility. It means collaborative choices for team utility are primarily based on negotiations that lead to compromises, instead of analytical reasoning as a group. This indicates that efforts in improving decision-making by improving information quality are only partly effective. [ABSTRACT FROM AUTHOR]

Drill core samples are taken in practice for an analysis of the material characteristics of concrete pipes in order to improve the quality of the decision-making on rehabilitation actions. Earlier research has demonstrated that core sampling is associated with a significant uncertainty. In this paper, the results of core samples are compared with the results of full-scale pipe cracking lab experiments. It is shown that the concrete of deteriorated sewer pipes shows a significant variability in material characteristics. Further it is shown that the formation of ettringite due to biochemical sulphuric corrosion is not necessarily limited to the crown of the pipe and also degradation of pipe material, measured by the carbonation depth, is occurring at the inside and outside of the pipe. It is concluded that tensile splitting strength and the carbonation depth are the two material property parameters of core sampling with a sufficiently high correlation (R2 > .90) with the structural strength of the pipe. The thickness of the remaining ‘healthy’ concrete material is the optimal parameter, as this requires the smallest sampling size. [ABSTRACT FROM AUTHOR]

In sewer asset management, decision making on rehabilitation or replacement should preferably be based on the actual functionality of a sewer system. In order to judge the ability of a sewer system to transport wastewater, hydrodynamic models are used; in these, hydraulic roughness is one of the key parameters. For new pipes, this is well known, but for aged pipes with uneven deterioration along the cross section, information on the hydraulic roughness is lacking. In this article, the potential of laser scanning methods for accurate, noninvasive, and nonintrusive assessment of the hydraulic roughness of concrete sewer pipes is described, demonstrated, and discussed. Processing of raw scanned data consists of two steps: (1) spatial interpolation with uncertainty analysis, and (2) statistical analysis for estimating the hydraulic roughness. Moreover, a statistical analysis was carried out to determine the minimal scanning resolution required in order to yield results accurate enough for subsequent modeling uses. The results show a promising potential of the laser scanning approach for a simple and fast quantification of the hydraulic roughness in a sewer system. [ABSTRACT FROM AUTHOR]

• In fingerprinting method sampling from only the influent of a WWTP is required. • Fingerprinting method is based on the rain proportion in a sample and a mass balance. • Drugs like painkillers are suitable tracers for estimating the rain proportion. The ecological state of receiving water bodies can be significantly influenced by organic micropollutants that are emitted via stormwater runoff. Reported efforts to quantify the emission of micropollutants mainly focus on sampling at combined sewer overflows and storm sewer outfalls, which can be challenging. An alternative method, called fingerprinting, was developed and tested in this study. The fingerprinting method utilizes wastewater treatment plant (WWTP) influent samples and derives the proportion of stormwater in a sample. This is achieved by comparing the wet weather vs dry weather concentrations of substances-tracers which are present only in wastewater. It is then possible to estimate the concentration of organic micropollutants in stormwater runoff from measurements in the influent of a WWTP based on a mass balance. In this research, the fingerprinting method was applied in influent samples obtained in five WWTPs in the Netherlands. In total, 28 DWF and 22 WWF samples were used. The chosen tracers were ibuprofen, 2-hydroxyibuprofen, naproxen and diclofenac. Subsequently, the concentration in stormwater runoff of 403 organic micropollutants was estimated via the WWF samples. The substances that were present and analyzed included glyphosate and AMPA, 24 out of 254 pesticides, 6 out of 28 organochlorine pesticides, 45 out of 63 pharmaceuticals, 15 out of 15 PAHs, 2 of the 7 PCBs, and 20 of 33 other substances (e.g. bisphenol-A). A comparison with findings from other studies suggested that the fingerprinting method yields trustworthy results. It was also noted that a representative and stable dry weather flow reference concentration is a strict requirement for the successful application of the proposed method. [Display omitted] [ABSTRACT FROM AUTHOR]