Technical Performance Assessment of Urban Sewer Systems

Performance assessment in urban water infrastructures is an increasingly important field of knowledge. Performance has traditionally been expressed in a variety of ways relating mostly to local design practice, with hardly any consensus on how it should be measured or compared. The efficient technical management of these systems deserves a specific approach, suited to the methodologies regularly employed while planning, designing, constructing, operating, and maintaining the systems. At the engineering level, decisions are based on operational, physical, and resources data and on analyses deploying simulation models, geographic information systems, or other information systems. However, such tools tend to produce vast amounts of insufficiently aggregated or performance-oriented information. This paper presents a performance assessment system that is based on the decisional concept of utility functions and designed as a technical analysis tool with the purpose of shifting the focus of technical management of urban drainage systems to a performance-oriented view.     

Financial Outlay Modeling for a Local Sewer Rehabilitation Strategy

Modern infrastructure systems are highly developed, with considerable capital funding invested in them. While capital is spent on new infrastructure initiatives, the maintenance of the present infrastructure must not be neglected. Increasingly, public agencies are being urged to develop improved systematic methodology for allotting their period budgets more appropriately so that the capacity of the installed infrastructure is more fully utilized and sustained. When planning the allocation of investment funds, multiple objectives may exist that are dependent on the constraints, resources available for construction, and the interrelationships and dependencies among all of the alternatives. This makes the task of planning, prioritizing, and allocating funds a complex exercise. This paper presents a financial outlay model called PRISM, Proactive Rehabilitative Sewer Infrastructure Management, which uses linear programming to optimize allocation of funding for the local sewer network maintained by the City of Edmonton, Canada. By grouping sewer pipes into categories based on parameters of age, diameter, material type, waste types, and average depth of cover, the model provides a mechanism for determining the most appropriate allocation or appropriation of funding given a planning horizon and budgetary constraints.     

Influence of Wastewater Constituents on Hydrogen Sulfide Emission in Sewer Networks

Transport of wastewater in sewer networks causes potential problems associated with hydrogen sulfide in regard to odor nuisance, health risk, and microbially induced corrosion. To what extent these problems occur depends not only on the rate of sulfide formation but also on the rate of hydrogen sulfide emission into the sewer atmosphere. To gain understanding of the influence of wastewater constituents on the emission process, a number of batch experiments were conducted on domestic wastewater collected from sewer networks. The emission rate of hydrogen sulfide in the wastewater investigated was found to be approximately 60% of that in de-ionized water in terms of the overall mass-transfer coefficient, resulting in a correction factor (alpha) of 0.6. The alpha factor did not change significantly within the turbulence range studied (Froude numbers of 0.04–0.23). The Henry’s law constant for hydrogen sulfide in wastewater was observed to be close to that in de-ionized water, reflecting a correction factor (beta) of 1.0. By taking these results into account, modeling aspects of hydrogen sulfide emission in sewer networks are presented in this paper.     

Hydraulic Characteristics of Gabion-Stepped Weirs

Experimental studies on the hydraulics of flow through and over gabion-stepped weirs are presented. Two flow components were observed, i.e., base flow through the void between filled stones and overflow on the gabions. The energy loss ratios in the gabion-stepped weirs are greater than those in the corresponding horizontal stepped weirs by approximately 7, 10, and 14% for weir slopes of 30, 45, and 60°, respectively. As a result, the velocity at the outlet is lower. Stone size and shape have little influence on the energy loss and flow velocity as compared to the increasing effect of the weir slope. The pressure acting on the step face for the gabion-stepped weirs is less than that of the horizontal steps owing to the cushioning effect generated by filled stones. To reduce pressure on a step face at a fixed discharge for different weir slopes, the void ratio of the filled stones should be low to allow a small amount of base flow. The pressure distribution pattern on the horizontal face of a step is provided.     

Experimental Study of Surcharged Flow at Combining Sewer Junctions

The results of a laboratory investigation on surcharged flow in combining sewer junctions are presented in this paper. Experiments were conducted in a 90° model junction and the 25.8° Edworthy model junction. The study confirmed the existence of three flow regimes in sewer junctions with a steep outgoing pipe: Regime I denotes the open-channel flow through the junction chamber; Regime II flow is partially surcharged flow featured by orifice flow into the outlet pipe; and Regime III flow is fully surcharged flow with all connecting pipes running full. The transition flow from Regimes II to III was investigated, and it may be related to the inlet waves at the entrance of the outlet pipe. Criteria for the transition were provided. Theoretical analyses were conducted based on one-dimensional momentum equation. The derived equations are able to estimate the water depth in the junction chamber. Energy loss in Regime III flow was studied and predictions based on the momentum equation were evaluated.     

Undular Hydraulic Jumps in Circular Conduits

Undular hydraulic jumps in circular conduits are considered with an experimental approach. Based on previous findings in rectangular channels, this research indicates differences in terms of shape effects. All present results depend on the filling ratio of the upstream conduit flow in addition to the upstream Froude number. The results include information on the wave crests and troughs, wave lengths, and generalized axial surface profiles. The wall surface profile is shown to be similar to the axial wave profile, but with smaller wave extrema and a wave shift. The design of conduits containing undular jumps should be avoided because of unstable flow. It is also demonstrated that conduits may choke in the presence of undular jumps, with a previously established choking number relating to a design limit. For flows with choking numbers in excess of 1, choking occurs associated with a transition from the free surface to the pressurized conduit flow.     

Dimensionless Method to Characterize the Mixing Effects of Surcharged Manholes

Solute transport processes affect the performance of a wide range of water engineering structures. In the context of urban drainage, the effects of dispersion may act to reduce peak concentrations associated with intermittent discharges or cause pollutants to be retained for longer or shorter durations than mean travel times would predict. With respect to surcharged manholes, previous research employed laboratory experiments to identify best-fit parameter values for the first-order advection-dispersion equation (ADE) and aggregated dead zone (ADZ) routing models. This paper presents data from a new set of smaller-scale laboratory measurements and demonstrates that the threshold depth separating two distinct hydraulic regimes can be identified independently of scale. However, the fitted ADE and ADZ routing model parameters are not generally amenable to conventional hydraulic scaling, because the models do not provide good fits to the observed data. An alternative approach is proposed based on the cumulative residence time distribution (CRTD). This approach is shown to be scalable and practical. The solute transport characteristics of a specific configuration of a surcharged manhole are shown to be characterized by just two dimensionless CRTDs corresponding to prethreshold and postthreshold surcharge depths.     

Optimal Layout of Sewer Systems: A Deterministic versus a Stochastic Model

The optimization of a new or partially existing urban drainage system may be modeled as a subproblems sequence of layout and optimal design within the discrete search space. The design optimization, incorporating the optimal selection of the pumping stations, intermediate manholes, pipe sections, and installation depths, for a general system fixed layout in plan, is a high level sequential decision problem which may be efficiently solved deterministically through a multilevel dynamic programming model. The optimal general layout may be selected in a deterministic way by means of a simple economical comparison of all plan solutions having optimized designs, for small to medium sized systems (if the specific restrictions of the applications are appropriately exploited) in practicable computer time. For larger dimension networks, where it is clearly impossible to achieve plan optimization with full enumeration (which is a NP complete), stochastic search models can be used. For the subproblem layout, an effective enumeration model is presented; the results of a stochastic model proposed previously, using simulated annealing for an application example, are compared and discussed in detail.     

Estimation of Uncertainty in Long-Term Sewer Sediment Predictions Using a Response Database

Regulations require U.K. water companies to reduce the number of properties at risk of sewer flooding. One of the potential causes of sewer flooding is the presence of persistent sediment deposits in sewers, such deposits are a common problem in many combined sewers. Although the regulations are risk based, there is a gap in the current knowledge on how the risk assessment is affected by the uncertainty in sewer sediment transport prediction. This paper describes the development of a methodology for estimating uncertainty in sewer sediment deposit depth predictions using existing empirically calibrated sediment load equations and Monte Carlo simulations combined with a response database. This methodology has been used to estimate the range of uncertainty of in-pipe deposit build-up predictions for a U.K. combined sewer system that suffered persistent deposition problems.     

Dimensionless Approach for the Design of Flushing Gates in Sewer Channels

The various hydraulic and environmental problems related to the accumulation of solids have recently drawn increasingly attention to deposits in the management of sewer systems. Among the mechanical and hydraulic devices used for deposit removal, hydraulic flushing gates have proved to be a cost-effective solution and have been adopted in several sewer networks. This paper reports the results of an investigation on the scouring performance of flushing waves produced by hydraulic flushing gates. A numerical model based on the De Saint Venant–Exner equations in dimensionless form was validated by using data derived from laboratory experiments and was then utilized in this investigation. Simulations were carried out considering various values of the dimensionless parameters involved in the analysis, in order to obtain indications for the design and positioning of flushing devices in sewer channels. The problem of optimal flushing frequency was also investigated.     

Prediction of Sewer Condition Grade Using Support Vector Machines

Assessing the condition of sewer networks is an important asset management approach. However, because of high inspection costs and limited budget, only a small proportion of sewer systems may be inspected. Tools are therefore required to help target inspection efforts and to extract maximum value from the condition data collected. Owing to the difficulty in modeling the complexities of sewer condition deterioration, there has been interest in the application of artificial intelligence-based techniques such as artificial neural networks to develop models that can infer an unknown structural condition based on data from sewers that have been inspected. To this end, this study investigates the use of support vector machine (SVM) models to predict the condition of sewers. The results of model testing showed that the SVM achieves good predictive performance. With access to a representative set of training data, the SVM modeling approach can therefore be used to allocate a condition grade to sewer assets with reasonable confidence and thus identify high risk sewer assets for subsequent inspection.     

Installed Geometry of Cast-in-Place Polymer Sewer Liners

Polymer liners cast within damaged sewer pipes are commonly used in rehabilitation without the disruption associated with conventional trench excavation and pipe replacement. Linear stability depends on both the thickness of the liner, and any out-of-roundness (ovality or other shape imperfections). Field trials of four cast-in-place liner systems permitted samples to be exhumed and inspected. Measurements of liner thickness and out-of-roundness are presented, for use by researchers and others seeking to establish the stability of these pipe repairs. Significant variations in thickness were observed. These took the form of wavelike increases in local thickness. For all four types of lining systems, the maximum thickness was more than double the average thickness, and up to three times thicker than the minimum thickness values. Higher frequency thickness variations were also superimposed on those wavelike changes in wall dimension. Liner ovality of up to 10% was also observed due to ovality in the clay sewer pipes being repaired, even though those pipes were not fractured longitudinally. Postconstruction inspection of liners ideally includes assessment of liner thickness. Wavelike increases in liner thickness might be estimated, where these lead to intrusions into the waterway. However, irregularities on the external surface of the liner or long wavelength thickness variations would be impossible to detect from video inspection alone, and new inspection techniques are likely need to be developed to ensure the installed liner performs successfully over its design life.     

Effects of Iron on Chemical Sulfide Oxidation in Wastewater from Sewer Networks

Effects of iron on the kinetics and stoichiometry of aerobic chemical sulfide oxidation in wastewater from two different sites were studied at pH 8 and 20°C. Iron(III) chloride was added to the wastewater in concentrations of up to 20?g?Fe?m?3. The rate of aerobic chemical sulfide oxidation increased linearly with the iron(III) additions resulting in equal effects with wastewater from the two sites. Despite the significant effect of the iron(III) additions, the background concentrations of iron cannot explain the significant temporal and spatial variability of aerobic chemical sulfide oxidation kinetics reported in this study and in the literature. In this respect, other metals are probably also important. In addition to the impacts on the oxidation kinetics, the iron(III) additions resulted in a change of the oxidation stoichiometry. With increasing amounts of iron(III) added to the wastewater, less dissolved oxygen was required for the sulfide oxidation.     

Dynamics of Air Flow in Sewer Conduit Headspace

Pressurization in sanitary sewer conduit atmosphere is modeled using computational fluid dynamics techniques. The modeling approach considers both turbulent and laminar flow regimes. The turbulent model takes into consideration the turbulence-driven secondary currents associated with the sewer headspace and hence the Reynolds equations governing the air flow field are closed with an anisotropic closure model which comprises the use of the eddy viscosity concept for the turbulent shear stresses and semiempirical relations for the turbulent normal stresses. The resulting formulations are numerically integrated. The turbulent model outputs are verified with experimental data reported in the literature. Satisfactory agreement is obtained between numerical simulations and experimental data. Mathematical formulas and curves as functions of longitudinal pressure gradient, wastewater velocity, and sewer headspace geometry are developed for the cross-sectional average streamwise velocity.     

轧机液压故障智能诊断技术探讨与展望

专家系统与神经网络是轧机液压故障智能诊断的主要途径,智能诊断的发展方向是系统的不断完善和提高学习能力。组合化,开发容错智能系统,以及进一步实用化等人工智能技术将与先进的信息技术紧密组合,并使智能诊断系统性能更佳。     

Ferrous Salt Demand for Sulfide Control in Rising Main Sewers: Tests on a Laboratory-Scale Sewer System

The addition of ferrous salts is a commonly used strategy for sulfide control in sewer networks. The Fe2+ dosing requirement in rising main sewers which takes into account of the effect of anaerobic sewer biofilms on the dosing demand is investigated. A laboratory-scale rising main sewer, consisting of four biofilm reactors in series and fed with real sewage, was operated for over 12 months, during which FeCl2 was dosed at several locations and at various dosing rates. The experimental results consistently revealed that approximately 0.7 mol of Fe2+ was required to precipitate sulfide formed from the reduction of 1 mol of sulfate by anaerobic sewer biofilms. This ratio is significantly lower than the ratio expected from reaction stoichiometry (molar ratio of 1:1), and also the Fe2+ to sulfide ratio (1.07–1.10 mol:1 mol) observed in batch tests conducted with real wastewater in the absence of sewer biofilms. Biofilms adapted to Fe2+ addition were found to contain a substantially higher amount of elemental sulfur than biofilms not receiving Fe2+ dosage. This suggests Fe2+ addition might have altered the final product of sulfate reduction by anaerobic sewer biofilms. The study also showed that the addition of ferrous salts at the inlet of a rising main sewer can effectively control sulfide throughout the whole system despite of the presence of competing anions in wastewater. Phosphate precipitation with ferrous iron in anaerobic rising main sewers is negligible.     

Integrated Decision Support System for Optimal Renewal Planning of Sewer Networks

Municipalities are under increasing pressure to adopt proactive and optimized renewal strategies to reduce the risks, life-cycle costs, and resources needed to maintain acceptable performance and service levels of their infrastructure assets. A new integrated approach for optimal renewal planning of municipal infrastructure systems has been developed. This paper discusses the application of the proposed approach to implement a GIS-based decision support system (DSS) to support the renewal planning of sewer networks. Condition rating, risk assessment, and prioritization techniques are described. A procedure for identifying and selecting the most suitable renewal technologies is also presented. A genetic algorithm-based multiobjective optimization technique is used to find a Pareto front of feasible solutions, each comprising a set of sewers to be renewed each year, along with the associated costs and expected benefits in terms of condition improvement and risk reduction. The paper also presents an example application of the prototype DSS on the sewer network in Regina, Canada.     

Case Study on Hydraulic Performance of Brent Reservoir Siphon Spillway

The Brent Reservoir was constructed in the mid-1830s and its siphon spillways were completed in 1936 to protect the dam from overtopping in the event of an extreme flood. Since completion, there have been problems with the hydraulic performance of the siphons, some of which primed simultaneously, causing flooding downstream. A physical hydraulic model study has been conducted to investigate the hydraulic performance of the siphons in order to establish reliable stage discharge relationships. The existing bellmouth siphon system was found to be unsuitable, causing the siphons to prime suddenly at discharges of around 3 m3/s. This was due to the sudden removal of an air pocket from the siphon’s crown. The model tests were carried out in two stages. In the first stage, the existing geometry was examined. Based on the results from stage 1 of the experiments, it was concluded that the air inlet requires redesign and various options to improve the air regulation should be considered. In the second stage, various options to regulate the inlet of air and establish stable siphon performance over the entire range of discharges were considered. It was found that the most stable conditions are provided by an air slot being cut into the spillway hood at an appropriate level. This geometry provides excellent air-regulated stability, unimpaired spillway capacity, and is insensitive to tail water level and wave conditions in the reservoir.     

连铸机液压翻转冷床故障分析

针对邢钢炼钢厂液压翻转冷床在连铸生产过程中经常出现的故障、故障产生的原因及设备本身的设计缺陷做了系统的技术分析 ,并提出了相应的技术改造方案。实践证明取得了良好效果。