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Roman water distribution and inverted siphons - until our days
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178805.pdf (Publisher’s version ) (Open Access)Radboud University, 21 november 2017Promotores : Moormann, E.M., Clemens, F.H.L.R.404 p
Quantitative risk analysis of urban flooding in lowland areas
No full textUrban flood risk analyses suffer from a lack of quantitative historical data on flooding incidents. Data collection takes place on an ad hoc basis and is usually restricted to severe events. The resulting data deficiency renders quantitative assessment of urban flood risks uncertain. The study reported in this thesis reviews existing approaches to quantitative flood risk analysis and evaluation of urban flooding guidelines. It proceeds to explore historical data on flooding incidents from municipal call centres in two cities in the Netherlands with the final aim to quantitatively assess urban flood risk. The data from municipal call centres consist of texts describing citizens’ observations of urban drainage problems. The texts provide information about causes, locations and consequences of flooding incidents. Call information on flooding causes is used to identify causes of urban flooding through application of probabilistic fault tree analysis. Urban flooding probabilities are quantified as well as contributions of a range of causes to the overall flood probability. Call information on flooding consequences is used to draw risk curves for a range of consequence classes: separate risk curves are drawn for consequences associated with human health, damage to private property and damage related to traffic disturbance. The curves depict a combination of flood consequences of increasing severity and associated probabilities of occurrence. Health risk associated with urban flooding is evaluated additionally in a screening-level quantitative microbial risk assessment. The assessment is based on analyses of samples from flooding incidents and from combined sewers. Risk values from call data analysis are translated into monetary values and into numbers of people affected by flooding in order to obtain risk outcomes that can be weighed against investments to reduce flood risk. It is discussed how outcomes in monetary terms differ from those based on numbers of affected people affected. The effectiveness of urban flood reduction strategies is assessed based on a comparison of flood risk values associated with three main failure mechanisms causing urban flooding. The effectiveness of existing strategies for flood risk control is discussed and potential improvements are indicated. Finally the acceptability of flood risk is discussed in view of the quantitative flood risk outcomes of this thesis. It is shown how quantitative risk values based on call data provide a starting point for the development of risk-based standards for urban flooding.WatermanagementCivil Engineering and Geoscience
Co-current air-water flow in downward sloping pipes: Transport of capacity reducing gas pockets in wastewater mains
No full textAir-water flow is an undesired condition in many systems for the transportation of water or wastewater. Air in storm water tunnels may get trapped and negatively affect the system. Air pockets in hydropower tunnels or sewers may cause blow-back events and inadmissible pressure spikes. Water pipes and wastewater pressure mains in particular are subject to air pocket formation in downward-sloping reaches, such as inverted siphons or terrain slopes. Air pocket accumulation causes energy losses and an associated capacity reduction. Whereas in horizontal and in upward inclined pipes all entrained air is transported with the water flow, the air in downward sloping pipes can move in both directions. Knowledge on air pocket motion in downward sloping pipes is essential for the proper venting of pressurized pipes and for the prevention of severe blow-back events. The motion of air pockets in downward sloping pipes, is closely related to liquid slugs in inclined pipes carrying gas with a small fraction of liquids (i.e. water, oil and gas condensate). The bubble-shaped interface and gas entrainment at the slug front are two features that are similar with air pockets in downward sloping pipes. Existing two-phase flow models have been validated mainly on data in horizontal and vertical pipes in which the gas phase drives the liquid phase. The performance of these models in inclined pipes, in which the liquid phase drives the gas phase, is not yet known. Despite its practical relevance in a variety of engineering fields, the literature on air-water flows in downward sloping pipes is scarce. The fundamental momentum balance that predicts when an elongated air pocket becomes stagnant in a downward inclined pipe, is yet to be developed. Lubbers was the first to systematically investigate the co-current flow of air and water in downward sloping pipes over the complete range of possible air accumulations. Like this thesis, Lubbers’ experimental research was part of the CAPWAT project on capacity losses in pressurised wastewater mains. The main research question, addressed in this thesis, is the development and validation of a total air transport model by flowing water, including the influence of pipe angle, length of sloping section, pipe diameter, surface tension, absolute pressure, pipe friction factor and viscosity. Furthermore, the air discharge by flowing water and the gas pocket head loss in wastewater will be compared with those in clean water. In order to quantify scale effects new measurements have been performed in laboratory facilities with internal pipe diameters of 0.08 m and 0.15 m and in a large-scale facility at a wastewater treatment plant with internal pipe diameter D = 0.192 m, a downward sloping length of L = 40 m (L/D = 209) and a downward pipe angle of 10°. Three series of experiments on co-current air-water flow have been conducted in the large-scale facility, each with its own specific objective in addition to the purpose of model validation: 1 Experiments with clean water, which provided quantitative information on the influence of the length of the downward sloping reach on the air pocket head loss and net air discharge. 2 Experiments with surfactant-added water for the assessment of the influence of surface tension on the air pocket head loss and net air discharge. 3 Experiments with untreated wastewater in order to determine the air pocket head loss and net air discharge in pipelines carrying wastewater. Obviously, these results have been compared with the first experimental series on clean water. The following main conclusions are drawn from this thesis: 1 A physically-based predictive model has been developed for the net air discharge by flowing water in downward sloping pipes. The model parameters include the length of the downward sloping reach and total length of the air pockets, pipe angle, pipe diameter, water (or liquid) discharge, viscosity, surface tension and pipe friction factor. 2 The model has been calibrated to a unique dataset of co-current air-water flows in downward sloping pipes. 3 The composition of wastewater, i.e. lower surface tension and solids content, does not enhance the air transport in comparison with the air transport in clean water. 4 A new velocity criterion for the occurrence of multiple air pockets in a downward sloping reach has been developed. This criterion defines whether the maximum gas pocket head loss may occur in practice. 5 A new momentum balance for elongated air pockets in downward sloping pipes has been developed. This momentum balance defines the clearing flow number. It is useful in practice to predict the direction and velocity of an elongated air pocket in a downward sloping pipe. The momentum balance and velocity criterion support the design of storm water storage tunnels and bottom outlets of hydropower stations for the proper venting of pipes and tunnels and for the prevention of severe blow-back events. Furthermore, two-phase flow models for the prediction of the transition to slug flow and its properties may benefit from these developments. 6 The required water velocity to start the transport of an elongated gas pocket to the bottom of a downward sloping pipe reach is 0.9?(gD)^1/2 (or Fw = 0.9) over a wide range of pipe angles (5° – 20°). This statement has been substantiated with experimental data at D > 0.19 m and the derived momentum balance. 7 A gas pocket detection method for the prediction of a gas pocket location has been extended with a total gas volume prediction. The detection method has been tested successfully in a field experiment.Sanitary EngineeringCivil Engineering and Geoscience
Monitoring ground settlement to guide sewer asset management
No full textThe study into the influence of (differential) settlement on the functioning of sewer systems was initiated to search for additional criteria to make sewer pipe replacement decisions more sensible. For this Amsterdam was used as a case study. Like many megacities (e.g. Jakarta, Bangkok, Tokyo, Shanghai), Amsterdam is situated in a delta area. As delta areas are characterized by soft soil conditions, it is to be expected that (differential) settlement is an important cause for dysfunctioning of sewer systems. Because the influence of settlement on sewer system performance has not yet been studied using empirical data, a large part of the study was focused on the assessment of the potential and accuracy of methods to study (differential) settlement. Application of the assessed monitoring techniques (sewer invert measurements, sewer profile measurements, visual sewer inspection) showed that even within an area with a limited settlement rate (5 mm/year), the influence of settlement on sewer system performance is significant (blockages, fouling and FOG deposits) and to a large extent predictable. Ultimately, understanding of the failure mechanisms related to settlement can be used to improve decision-making for sewer asset management.Water ManagementCivil Engineering and Geoscience
Assessment Methods for Structural and Hydraulic Properties of Concrete Sewer Pipes
No full textAsset management is a tool for maintaining the required level of serviceability of urban drainage systems, which are costly to construct and in some cases even more costly to replace. The required asset management effort to achieve a certain level of service is unclear due to a limited knowledge on sewer failure mechanisms and due to scarcity of information on the functioning and conditions of urban drainage systems. An important question is: what information of what quality is necessary for cost-effective sewer asset management? In The Netherlands the majority of urban drainage systems are made of concrete elements (about 72%), including nearly all main sewers > 500 mm, thus making the information on the concrete sewer pipes of significant importance. This research aims at (i) identifying the required information on the structural and hydraulic performance of the sewer pipes, (ii) quantifying the uncertainties of information and (iii) improving the quality of this information in order to further understand the changes in processes/status. Sewer failure mechanisms explain the structural and/or operational failures of sewer elements. In order to be able to identify the main processes and defects responsible for the structural and/or operational failures of sewer elements, as well as the possibility of obtaining the information about them, a HAZard and Operability (HAZOP) approach was applied. This technique was demonstrated to be applicable for analysing the information needed for sewer asset management. Structural strength and hydraulic capacity are two essential parameters in the assessment of the need for sewer rehabilitation. In sewer systems where corrosion is the dominant failure mechanism, visual inspection by closed circuit television (CCTV) and core sampling are among the methods mostly applied to assess sewer pipe condition. A study was carried out on visual inspection and drill core analysis in order to enhance a further understanding of the limitations and potentials of both methods and the added value of combining the information from both sources. Both methods have been applied on a selected sewer reach in the city of The Hague, which was reportedly subject to pipe corrosion. The results show that both methods, visual inspection and core sampling, are associated with large uncertainties and that there is no obvious correlation between the results of visual inspection and the results of drill core analysis. The conclusion is that information of a certain quality (depending on the circumstances) on the actual status of the assets is a prerequisite for adequate sewer asset management. For instance, especially concrete pipes suffer from loss of wall thickness due to biochemical corrosion and, consequently, a decreasing structural strength along with an increase in hydraulic roughness. Unfortunately, routinely used visual inspection methods do not allow a quantification of the internal pipe geometry, which would enable not only detection but also the quantification of the progress of biochemical corrosion. Advances in laser technology and digital cameras theoretically allow a cost-effective application of laser profilers to measure the interior geometry of sewer pipes. An analysis of associated uncertainties revealed that the position and alignment of the laser in commonly used laser profiling techniques are the main sources of measurement errors. A full-scale laboratory set-up demonstrated, based on tests on a new and an 89 year old corroded sewer pipe, that laser profiling is indeed capable of measuring the interior geometry accurately enough to determine wall thickness losses for corroded pipes, provided that the position and alignment of the laser and camera are accounted for. Further, drill core samples are taken for an analysis of the material characteristics of concrete pipes in order to improve the quality of decision making on rehabilitation actions. It was shown in this study that core sampling is associated with a significant uncertainty. 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 that 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 carbonation depth (i.e. loss of 'healthy' wall thickness) are material property parameters of core sampling with a sufficiently high correlation (R^2 > 0.90) with the constructive strength of the pipe. The thickness of the remaining healthy concrete material is the optimal parameter in terms of correlation with collapse strength, as this requires the smallest sampling size. Furthermore, 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 sewage, hydrodynamic models are used: hydraulic roughness is one of the key parameters. For new pipes, the hydraulic properties are well known, but for aged pipes, with uneven deterioration along the cross section, information on the hydraulic roughness is lacking. The potential of laser profiling methods for accurate, non-invasive and non-intrusive assessment of the hydraulic roughness of concrete sewer pipes is described, demonstrated and discussed. Processing of raw scanned data consists of two steps: (i) spatial interpolation with uncertainty analysis and (ii) 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 modelling 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. A Prototype v1.0 (in this study) of an unbiased laser profiler was developed to improve the accuracy of collected information. However, there is a need for more accurate apparatus. The new design of the Prototype v2.0 presented provides accurate measurements (sigma < 2 mm) of the cross section and, from frame to frame, an accurate 3D image of a pipe. The potential applications of the improved laser profiling technique are comprehensive e.g. enhancement of inaccurate visual inspection, deposit measurements, roughness measurements. The combination of the two methods, i.e. to use the laser profiler to determine the pipe interior geometry as well as to identify representative patches where roughness should be measured, is an opportunity to strengthen laser profiling as a method that may partially replace a CCTV inspection as a dominantly applied sewer investigation technique. Additionally to achieve a higher accuracy, there are several improvements that can be applied to a potential third version of the prototype. Currently the amount of raw data that is generated during the experiment over 1 m of pipe length is around 4.86 GB: the data flow is too high for an embedded application but this can be significantly reduced. There are still some improvements to be done with the presented hardware to make the data acquisition faster and easier. Future work will concentrate on the development and improvement of the laser profiling technique accuracy and possibilities for its use - Prototype v3.0. The results of this research will be used for future development of inspection strategies using core sampling. For sewer rehabilitation decisions, it is necessary to be able to calculate the remaining strength of the soil-pipe construction environment for deteriorated pipes. Further research will concentrate on simulations with a Finite Element Method (FEM), with the pipe geometry information provided by laser profiling and material properties by core sampling. The model will be used to determine the remaining load-bearing capacity of a sewer pipe and to determine the type of information needed to further enhance the decision making process.Water ManagementCivil Engineering and Geoscience
Probabilistic assessment of the performance of combined sewer systems
No full textCivil Engineering and Geoscience
Laser profiling of sewer pipes
No full textThe goal of the research is to determine the potential of laser scanning methods for accurate, non-invasive assessment of the changes in the inner pipe profile of concrete sewer pipes. The main research question is: ‘How accurate is the laser profiler when measuring deteriorated sewer pipes?’ In the research egg shaped concrete sewer pipes were measured under laboratory conditions. The used experimental setup consists of an old concrete, egg shaped sewer pipe. At the front and back of the pipe a ramp is placed to ensure a smooth entrance and exit of the inspection camera. The recordings from the laser profiler are analyzed with Matlab to determine the accuracy.Sanitary EngineeringWater ManagementCivil Engineering and Geoscience
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