Impacts of climate change on urban drainage systems – a case study in Fredrikstad,Norway

Norway has frequently encountered flood damage in urban areas during recent years. In this paper the authors, taking Veumdalen catchment in Fredrikstad as an example, simulated the possible consequences in the sewer system, in the present, predicted and artificial climate scenarios. Indicators that describe (1) surface flooding, (2) surcharging sewers, (3) basement flooding and (4) combined sewer overflow (CSO) are defined to represent the adverse effects of climate change. It is concluded from the annual-based simulation that the total volume of water spilling from the flooding manholes will increase 2–4-times the increase in precipitation, and the total CSO will increase 1.5–3-times as much as the increase in precipitation. The simulation results also show that the number of flooding manholes and number of surcharging sewers may change dramatically and irregularly with a slight change of precipitation, and vary with events and durations.     

The relevance of sewer deterioration modelling to support asset management strategies

Deterioration modelling can be a powerful tool to support utilities in planning efficient sewer rehabilitation strategies. However, the benefits of using deterioration models are still to be demonstrated to increase the confidence of utilities toward simulation results. This study aims at assessing the performance of a statistical deterioration model to estimate the current condition and predict the future deterioration of a sewer network. The prediction quality of the deterioration model GompitZ has been assessed using the extensive data-set of 35,826 inspections performed in the city of Braunschweig, Germany. The performance of the statistical model has been compared with the performance of a simple model based only on the condition of observed sewers. Results show that the statistical model performs much better than the simple model for simulating the deterioration of the network. The findings highlight the relevance of using modelling tools to simulate sewer deterioration and support strategic asset management.     

Non-deposition design criteria for sewers with part-full flow

In this study, the existing self-cleansing design criteria for sewers based on minimum velocity and minimum bed shear stress have been reviewed. Based on several laboratory experiments, the study then develops non-deposition criteria for non-cohesive sediment in uniform flow. The developed criteria take into account geometry of flow sections, hydraulic and sediment properties based upon three dimensionless parameters, namely, the densimetric Froude number, the volumetric sediment concentration and the relative grain size. The proposed criteria provide improved estimates of self-cleansing minimum velocities compared to the traditional one-parameter design criteria and agree well with the well-known existing design criteria, namely, Macke's formula for suspended load and May's formula for bed load. The present study therefore contributes new non-deposition design criteria for sewers with part-full flow in the range of the experiment conducted and yet which are simple for practical applications. Further research work is required to substantiate the preliminary character of the results presented for wider application of the proposed self-cleansing design criteria.     

埋地燃气管网泄漏规律及其次生灾害预防研究

分析了城市埋地燃气管道泄漏规律、泄漏的燃气在土壤中扩散范围的关键影响因素。对城市排水管道产生的沼气和燃气管道泄漏,在市政地下密闭空间（管廊、排水管道、各类井室等）累积所引发的爆炸和中毒特性进行了研究,提出了避免这些次生灾害的具体措施。     

Gross Solids' Movement in Sewers: Laboratory Studies as a Basis for a Model

A simple model of gross solids' movement in sewers is proposed, based upon the results of studies of part-full pipe flow in two laboratory installations, under steady and unsteady flow conditions. The model covers advection and deposition, and is intended as one component in a comprehensive model of the behaviour of gross solids in sewers. Such a model is needed because gross solids are not included in the currently available sewer-flow quality models, even though they can cause pollution which is of particular concern to the public
The paper describes the laboratory studies and their results. It sets out the principles of the proposed model and explains why these differ from existing models of dissolved and fine suspended pollutants.     

Enhanced air flow modelling for AccuRate – A nationwide house energy rating tool in Australia

In this study, an improved multi-zone air flow model has been developed and implemented to replace the existing large opening air flow model MIX2 used in AccuRate's simulation engine. Good agreements have been obtained between the results predicted by the new air flow model and those predicted by analytical solutions for single opening and two-opening cases. A cross-check between MIX2 and the new model has also been carried out. It is shown that the new AccuRate engine converges much better compared to the existing engine with MIX2. In addition to the improved modelling results due to better convergence, the implementation of mass balance with variable density further enhances the performance of the new AccuRate engine which improves the calculation accuracy in modelling natural ventilation and its cooling potential.     

North Tyneside Bathing Waters' Scheme

The North Tyneside bathing waters' scheme reduces the frequency and quality of storm sewage which is discharged inshore from existing interceptor sewers along the coast.
Flow-simulation modelling is applied to the existing system to determine the frequency and volume of interceptor sewer overflow against a range of storm intensity and return periods. The models are extended to an evaluation of new systems of storm-sewage management.
An optimized solution is described in which new storm sewers are utilized for the storage of all storm-sewage overflow discharges prior to screening and pumping of the storm sewage to sea via an outfall.     

Excluding Groundwater Infiltration into New Sewers

Much attention has been focused on the need for sewer renovation and rehabilitation of old sewerage systems, but age is not always the reason for sewer failure. Serious problems of performance have also been encountered on sewerage schemes less than 10 years old. This paper considers the problems of groundwater infiltration into new foul sewers, and suggests that deficiencies might exist in some aspects of modern sewer design and construction.
Infiltration is most frequently observed at sewer joints. Results are presented of laboratory tests which show the ability of flexible fixed-ring joints on clay sewers to withstand both internal and external pressures. Damaged polyester fairings on the spigots of these pipes can act as one-way valves, and massive infiltration may result. The standard site water test is shown to be inadequate in detecting some of these types of defect which may result from damaged pipes or poor workmanship.     

Development of a model for assessing methane formation in rising main sewers

Significant methane formation in sewers has been reported recently, which may contribute significantly to the overall greenhouse gas emission from wastewater systems. The understanding of the biological conversions occurring in sewers, particularly the competition between methanogenic and sulfate-reducing populations for electron donors, is an essential step for minimising methane emissions from sewers. This work proposes an extension to the current state-of-the-art models characterising biological and physicochemical processes in sewers. This extended model includes the competitive interactions of sulfate-reducing bacteria and methanogenic archaea in sewers for various substrates available. The most relevant parameters of the model were calibrated with lab-scale experimental data. The calibrated model described field data reasonably well. The model was then used to investigate the effect of several key sewer design and operational parameters on methane formation. The simulation results showed that methane production was highly correlated with the hydraulic residence time (HRT) and pipe area to volume (A/V) ratio showing higher methane concentrations at a long HRT or a larger A/V ratio.     

Discrete element visco-elastic modelling of a realistic graded asphalt mixture

The Discrete Element Model has been used here to simulate constant strain rate uniaxial compression tests for a realistic asphalt mixture comprising graded aggregates. A numerical sample preparation procedure has been developed to represent the physical specimen. A parallel bond model has been used in the elastic modelling to give moment resistance at the contacts. Uniaxial constant strain rate loading and unloading tests have been simulated. The effects of the normal to shear contact stiffness ratio on the bulk properties, the parallel bond radius, the number of particles and their positions, and the loading speed have been investigated. A modified Burger's model has been used to introduce time-dependent contact stiffness with the ability to transmit moment and torsion. Two-ball clumps have been used to investigate the effect of particle shape. The effect of Burger's model parameters, the ratio of normal to shear Burger's model parameters, the bond radius multiplier, the friction coefficient and the bond strength distribution in the viscoelastic simulations have been investigated. Constant strain rate uniaxial compression tests have been undertaken in the laboratory where the axial stress–strain response has been measured for comparison with the numerical modelling results. The modified Burger's model has proved to be useful and ready for simulating uniaxial constant strain rate and creep tests in the laboratory.     

Modelling sewer discharge via displacement of manhole covers during flood events using 1D/2D SIPSON/P-DWave dual drainage simulations

In urban areas, overloaded sewers may result in surcharge that causes surface flooding. The overflow from sewer systems mainly starts at the inlets until the pressure head in the manhole is high enough to lift up its cover, at which stage the surcharged flow may be discharged via the gap between the bottom of the manhole cover and the ground surface. In this paper, we propose a new approach to simulate such a dynamic between the sewer and the surface flow in coupled surface and sewer flow modelling. Two case studies are employed to demonstrate the differences between the new linking model and the traditional model that simplifies the process. The results show that the new approach is capable of describing the physical phenomena when manhole covers restrict the drainage flow from the surface to the sewer network and reduce the surcharge flow and vice versa.     

新型固流耦合相似材料的研制及其应用

 在固体模型材料研究的基础上,应用固流耦合相似理论,通过大量的配比试验,研制出一种新型的固流耦合相似材料(PSTO),这种材料用砂和滑石粉作为骨料,石蜡作为胶结剂,并配以适量调节剂混合而成。通过大量的室内试验,系统研究不同相似材料配比和装模温度对试件性能的影响规律,得到影响相似材料性质的若干因素。该材料的力学特性与岩石性质相似,且在水的作用下不发生软化,非亲水性良好,可模拟不同渗透性的低强度和中等强度的岩体材料,是一种非常理想的固流耦合相似模拟材料。将该材料应用于隧道涌水模型试验,可有效地揭示了位移、应力、渗压等多场信息的变化规律。     

地下工程流–固耦合模型试验新型相似材料的研制及应用

 依托青岛胶州湾海底隧道的现场勘探资料,应用地质力学模型试验的流–固耦合相似理论,通过大量的配比试验,研制出一种由砂、重晶石粉、滑石粉、水泥、凡士林、硅油和适量拌合水组成的新型流–固耦合相似材料(SCVO)。通过大量的室内试验,系统地研究不同配比对材料参数的影响规律,确定控制相似材料各性能的主要组分。试验表明,材料的强度和弹性模量主要由水泥和凡士林控制;黏聚力受凡士林影响明显;渗透系数可以通过凡士林和硅油的比例调节;硅油还可以起到保水、提高材料密实度的作用。材料的变形特性和水理特性由不同的成分控制,且相互间影响很小,实现材料性质的全面调控。该材料可以模拟不同渗透性的低强度和中等强度的岩体材料,是一种非常理想的流–固耦合相似模拟材料。并已成功应用于青岛胶州湾海底隧道的地质力学模型试验研究中,力学性能和水理特性均达到试验要求,为试验取得良好结果提供材料保证。     

Computational modelling of large aerated lagoon hydraulics

A good understanding of the hydraulic performance of aerated lagoons is required for their design and operation. A comprehensive numerical procedure has been developed for the three-dimensional computational modelling of the flow in large lagoons including high-speed floating mechanical surface aerators. This paper describes the procedure that consists of separate aerator modelling, then applying the obtained results as boundary data for a full lagoon model. A model application to an industrial aerated lagoon serves as an example of flow analysis. Post processing of the results by calculating the local average residence time (age of fluid) provides a powerful and intuitive technique to visualize and analyse the lagoon performance. The model has been verified by comparing the local average residence time predictions with measurements from a dye study. It is shown that the numerical modelling proposed is feasible and constitutes an effective new tool in improving the performance and design of industrial lagoons.     

Renovation of brick interceptor sewers

Brick interceptor sewers began to be built in Europe (London, Paris, Hamburg) in the 18th century. The sewers were built from solid ceramic brick (so called sewer brick) or clinker brick. This paper presents a study of damage to brick interceptor sewers built in the 19th century and at beginning of the 20th century in Poland. Damage to the sewer structure and to the surrounding ground and its causes are identified. On the basis of results of in situ investigations, laboratory tests and structural and strength analyses, the condition of sewer structures in Poland was assessed as a pre-failure one. Underground infrastructure pipes of urban areas can be repaired in trenches or using trenchless techniques. Although trenchless technologies have been known in Poland for more than 25 years, there is still the lack of knowledge and imagination on the part of designers – so different problems in renovating process of brick interceptor sewers are described.     

CFD modelling of naturally ventilated double-skin facades with Venetian blinds

This study describes computational fluid dynamics (CFD) modelling of naturally ventilated double-skin facades (DSFs) with Venetian blinds inside the facade cavity. The 2D modelling work investigates the coupled convective, conductive and radiative heat transfer through the DSF system. The angles of the Venetian blind can be adjusted and a series of angles (0°, 30°, 45°, 60° and 80°) have been modelled. The modelling results are compared with the measurements from a section of a prototype-facade testing facility and with predictions from a component-based nodal model. Agreement between the three methods is generally good. It is thought that discrepancies in the results are caused by the simplification of the CFD model resulting in less turbulence mixing within the facade cavity. The CFD simulation output suggests that the presence of the Venetian blinds is able to enhance the natural ventilation flow within the facade cavity and significantly reduce the heat gains to the internal environment. It was also found that the convective heat transfer coefficients on the glazing surfaces are insensitive to the blind angles. The work demonstrated the capability of CFD for modelling complicated heat transfer processes through the DSF system and offered some guidance for CFD practitioners who wish to model similar type of flow.     

Measurement of sewer sediments with acoustic technology: from laboratory to field experiments

Monitoring sewer sediments is necessary to better understand sedimentation and erosion processes. Sonar is one of the available techniques to proceed to sewer sediment measurements. Extraction of numerical data, implementation of a new algorithm to identify the water-sediment interface, laboratory and field experiments have been done to evaluate the device, to quantify uncertainties and to test the sonar under various conditions. Results demonstrate that: 1) uncertainties in repeatability are less than 4%, 2) the sonar delivers accurate results under various conditions (small to large sewers and grit chambers), and 3) in situ measurements are affected by uncertainties, mainly due to the fact that the sensor is not in a fixed position but is floating on the free surface in the sewer. This device is useful and accurate for semi-automatic measurement but further research and improvements should be done to better know the position of the device in the section.     

Uplift of Sewage Manholes and Pipes During the 2004 Niigataken-Chuetsu Earthquake

About 1,400 sewage manholes were uplifted during the 2004 Niigataken-chuetsu earthquake in Japan. Many buried sewage pipes were also uplifted. Before the restoration work, detailed soil investigations were carried out to reveal the mechanism of the uplift. Based on the investigations, it was clarified that uplift occurred in mainly clayey grounds. No sand boils were observed on the clayey ground. However, boiled sands were observed just beside the uplifted manholes and above the buried pipes. During the construction of buried pipes and manholes, the ground was excavated first, the pipes and manholes were placed in the ditches, then the ditches were filled with sand. The soil investigation of the sand fill after the earthquake revealed that the sands were very loose and easy to liquefy. It was concluded that the uplift of the manholes and pipes occurred due to the liquefaction of the sand fill. In preparation for the restoration work, appropriate countermeasures for future earthquakes were discussed, and finally, the cement mixing method was selected.     

Methane formation in sewer systems

Methane formation and emission in sewer systems has not received as much attention as hydrogen sulphide formation. Through field measurements from two rising mains, with an average sewage temperature of 28.4 and 26.6 degrees C, respectively, at the time of sampling, this study shows that a significant amount of methane can be produced in sewer systems, and that this production is positively correlated with the hydraulic retention time of wastewater in these systems. The experimental results from a laboratory-scale sewer system fed with real sewage with a temperature of approximately 21 degrees C confirmed these field observations and further revealed that methanogenesis and sulphate reduction occur simultaneously in sewers, with methane production contributing considerably more to the loss of soluble COD in sewers than sulphate reduction. The production of methane in sewers at levels revealed by this study is a serious environmental concern as it potentially results in greenhouse emissions that is comparable to that caused by the energy consumption for the treatment of the same wastewater. Further, methane production in sewers influences sulphide production and its management due to the competition between methanogens and sulphate-reducing bacteria for potentially the same electron donors. The potential interactions between sulphate-reducing and methanogenic bacteria in sewer networks are discussed.     

Mathematical modeling of sewers under surcharge for real time control of combined sewer overflows

The efficiency of real time control (RTC) to decrease storm overflows from combined sewers to receiving waters was demonstrated in several case studies. Global predictive control (GPC), an effective strategy to perform real time management of sewers, requires simulation models to anticipate the future state of the system (flow rates and water levels). To compute these predictions, a hydraulic model using an implicit discretization scheme to solve simplified continuity and momentum equations was developed. The performance of the model is evaluated by comparison with the USEPA EXTRAN model results. This comparison shows that the model gives results similar to those of the EXTRAN model, with the advantage of producing faster and more stable results regardless of space and time steps used. Additional validation with the SUPERLINK model is also presented.