Showing papers by "Francois Clemens published in 2016"

Decision-making for sewer asset management: Theory and practice

Abstract: Operational decision-making for sewer asset management has hardly been empirically analysed, hampering the current challenge for cost-effectiveness in the urban drainage sector. This paper analyses how decisions for sewer replacement are actually made and to what extent complexity of the decision-making environment is addressed. Decision argumentation of 150 sewer replacement projects in the Netherlands was obtained by interviews. The decision process was analysed by the rational and streams model. The decision argumentation is a relatively wide variety of information sources, of which the majority is case-specific. Yet, decision-making does not rely purely on data analysis; it also includes negotiations between involved infrastructure managers. Then, replacement planning of a sewer asset manager depends on other public works. Consequently, individual cost-effectiveness as an evaluation criterion should be expanded to include group utility.

Statistical analysis of lateral house connection failure mechanisms

Abstract: The performance of lateral house connections can have a substantial impact on the overall level of service provided by sewer systems. However, knowledge on the failure probability of these components remains scarce. This paper analyses field data to determine failure rates. A distinction is made between different mechanisms that contribute to the overall failure probability of lateral house connections. Root causes that promote the occurrence of these failure mechanisms are derived from a literature review. Results of a trend analysis shows a time constant failure rate, which exceeds blockage rates reported for main sewers. Fat, oil, and grease deposits are the dominant failure mechanism for both a specific case study in Rotterdam and the Netherlands. Literature suggests misuse and the structural condition as main root causes for this failure mechanism. The sheer number of failures associated with lateral house connections suggests that these components should be taken into account in sewer asset ...

Special Issue on ‘Sewer asset management’

Abstract: Sewer systems are vital urban infrastructures, requiring appropriate asset management to safeguard serviceability and to balance service life versus costs for rehabilitation. In Europe, the total value of the sewer assets amounts to e 2000 billion. Assuming a replacement rate of once per 100 years, the annual rehabilitation costs amount to e 20 billion The shear height of these investments along with the recognition that the available knowledge on processes driving the ageing of these systems is still rather limited, should stimulate innovation on a vast scale. However, current sewer asset management has, unpurposely, been trapped in a deadlock since the 1980swithCCTV inspection as the ‘one size fits all’ source of information for sewer rehabilitation. All sewer operators throughout the EU and worldwide rely on this same source of information, which has been widely used as a basis for sewer deterioration models, decision support systems and sewer asset management approaches. Recently, however, CCTV inspection has been demonstrated not to be fully reliable and an insufficient source of information for sewer rehabilitation. The limited reliability is closely related to human errors in the assessment of CCTV footage and, in addition, CCTV cannot account for sewer conditions and failure mechanisms that cannot be observed form inside a sewer, such as exfiltration. The recognition of the limitations of using CCTV as a ‘one size fits all’ information source has opened up a newwindow of opportunity for research on sewer asset management. The papers of this Special Issue on Sewer Asset Management in the Urban Water Journal explore new directions for Sewer Asset Management by introducing inspection techniques to the ‘one size fits all’ approach, decision support systems with a broad and integrated approach, and interesting new material on lateral house connections, typically a forgotten part of the sewer system in sewer asset management. Plihal et al. developed a new method for the rapid inspection of sewer networks comprising a combination of acoustic sensors and the latest generation of manhole zoom cameras. The acoustic sensor is very powerful in detecting anomalies in the cross section of the sewer and locating these along the sewer length. Combined with a manhole zoom camera, this method is capable of providing information on the condition of the sewer comparable with traditional CCTV inspections for most type of conditions. The relative low costs of the new method will allow sewer asset managers to develop new inspection techniques for obtaining information on the hydraulic and/or structural condition. Cardoso et al. describe the application of the AWAREP procedure for planning sewer infrastructure asset management at fourteen wastewater utilities. Advanced sewer infrastructure asset management is key to achieve and ensure adequate future levels of service, in issues such as urban flooding, CSO discharges, and balancing performance, risk and costs. One of the key features in AWARE-P is to balance decision planning at three levels: strategic, tactical and operational. In order to facilitate decision making, data and information from various sources apart from the basic CCTV inspection is integrated in one system. Tscheikner-Gratl et al., describe the development of an tool for integrated rehabilitation planning of urban infrastructure systems using a street section priority model. Per street section, the condition and importance of sewers, drinking water pipes and rod construction are assessed in the street section priority model. Based on a weighed combination of condition and importance indicators, an integrated priority is given for the rehabilitation of urban infrastructures, exemplified by a case study. Ahmadi et al. describe the impact of the sample size on the calibration results of a decision-making multivariate model. They conclude that the calibration results rely heavily on the characteristics of the selected sample. As such, the reliability of the model supported decisionmaking relies strongly on the quality of its calibration, which is typically unknown to practitioners. Van Riel et al. have studied decision making for sewer asset management. Based on a survey of 150 sewer rehabilitation projects, they concluded that information on the condition of the assets is only dominant in 50% of the projects, whereas in 50% other factors play a dominant role. The other factors may range from implementing a policy to convert combined sewer systems into separate sewer systems to urban redevelopment, with a planning horizon that strongly depends on the economic development. This limits the general applicability of rational decision support models based on sewer asset information only, which might challenge further development of the decision support systems described in the preceding papers of Tscheikner-Gratl et al. and Cardoso et al.

Intelligent SUBsurface Quality: Intelligent use of subsurface infrastructure for surface quality

Abstract: This project focuses on the urban renewal of (delta) metropolises and concentrates on the question how to design resilient, durable (subsurface) infrastructure in urban renewal projects using parameters of the natural system – linking in an efficient way (a) water cycle, (b) soil and subsurface conditions, (c) soil improvement technology, and (d) opportunities in urban renewal (e.g. urban growth or shrinkage). The subsurface is the technical space, the engine room of a city, housing the vital functions of water, electricity, sewers and drainage, but also housing the natural system that is crucial for a stable, green, healthy and livable city. Especially the effects of climate change, the boosts for an energy transition and the fact that there are less financial mean makes the intelligent use of the subsurface more important. This prublication reprots on the explorative method to get insight and design methods for the urban renewal of (delta) metropolises where resilient, durable (subsurface) infrastructure is carefully balanced out with parameters of the natural system. The question “how can the different technological artefacts in the subsurface be synchronized offering more space and adding to a better urban quality?” is answered by taking procedural steps from the technology (the knowledge of) to the design of public space and urban main structures. In each step the translation from the engineering language to the language of the urban designer (and vice-versa) is done producing an informative and useful overview in how to relate technological artefacts to urban quality. In order to reach interdisciplinary design, explorative research is used for creating a shared language. Explorative research has been useful because the problems at hand are wicked problems that has not been clearly defined. The exploration was framed by co-creation in workshops and later a more precise elaboration of these results in the working group.

Integrated real time control of influent pumping station and primary settling tanks at WWTP Eindhoven

Abstract: This research deals with the design and implementation of an integrated control for the WWTP of Eindhoven. The control influences the operation of the primary settling tanks and influent pumping station to reduce reduce ammonia peaks in the WWTP effluent. The control takes into account the treatment capacity of the biological tanks, the influent flows and the available storage capacity in the individual catchments. It was implemented in winter 2016 and has been operational since April 2016. Model results and preliminary measurements show that the WWTP can be operated with a reduced number of PCs for over 90% of the time

Experimental research on free-surface vortices as transport mechanism in wastewater sumps

Abstract: Sumps of wastewater pumping station can experience problems due the formation of (solid) floating layers of fat and scum as a result of insufficient current guidelines for sump design with respect to transport of floating debris. To complimentary the guidelines, the use of free-surface vortices is defined as a potential transport mechanism for floating debris. The transport ability and capacity of vortices is investigated in an experimental set-up and experimental data will be used to design and validate a theoretical vortex transport model describing the transport ability and capacity of a free-surface vortex. Two theoretical vortex models describing the vortex flow field are used as a base for the transport model. Experimental results show that both models needs adaptation to match experimental results. Furthermore, the experiments show that the ability to transport buoyant material is highly sensitive on the flow field in the vortex (core) and on the particle density. Particles can either get stuck in the vortex core with no or less transport or either translated around the core with efficient transport. Before designing and validating the vortex transport model, extensive future research is needed to capture the observed phenomena’s.

Effect of spatiotemporal variation of rainfall on dissolved oxygen depletion in integrated catchment studies

Abstract: This study addresses the effect of spatial and temporal resolution of rainfall fields on the performance of a simplified integrated catchment model for predicting dissolved oxygen concentrations in a river. For that purpose we propose a procedure to generate rainfall products with increasing spatial information at different time step accumulations (10’, 30’ and 60’) at the spatial support of lumped urban catchment systems. Using a rain gauge network and single-polarization C-Band Radar data we generate 4 rainfall products; 1) Homogeneous rainfall from a single rain gauge, 2) Block kriging interpolation from a network of 13 rain gauges, 3) Averaged Radar estimation and 4) Universal block kriging from a rain gauge network and using Radar as an external covariate. Comparison of the model predictions with monitoring data in the river showed a low sensitivity to the temporal scales proposed and a relative improvement with increasing spatial information linked to the climatological characteristics of the storm period.