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Blockage detection in circular open channels (partially filled pipes, e.g., gravity sewer pipes) has gained increasing interest in the water industry. While there have been significant advancements in monitoring technologies for such systems (e.g., smart sewer systems), there is a lack of quantification of the hydraulic impact of partial blockages in circular pipes, which is a limiting factor for cost-effective detection. This study presents and validates a numerical framework to quantify the changes in water depth caused by extended bottom blockages in circular open channels. The analysis is based primarily on continuity and energy conservation with the assumption of a lossless transition at the blockage. The proposed approach can determine the critical blockage height that would induce choking, therefore a change in the upstream depth. It can also calculate the changed upstream water depth for various bottom blockage height values (above the critical height) for both subcritical and supercritical conditions. The proposed approach is numerically implemented and then validated through a series of laboratory experiments under the subcritical flow condition (which is the most common condition for gravity sewer systems). The numerically determined water depth results are consistent with the experimental results, which confirms that the proposed approach can accurately estimate the new upstream depth under the choking condition induced by a bottom blockage in circular open channels. The results contribute to advancing the hydraulic understanding in circular open channels with extended partial blockages, which is useful in the development of smart sewer technologies. Practical Applications: Spills and overflows out of the gravity sewer system damage the environment and bring risks to public health. The problem is typically caused by partial blockages, which can reduce the flow capacity of the sewer pipe and induce higher-than-designed flow depth on the upstream of the blockage (known as choked flow condition). This study helps water engineers and operators to understand how an extended bottom blockage affects the flow condition just upstream of the blockage in a circular gravity sewer pipe. Charts have been presented to enable the determination of (1) the critical height of an extended bottom blockage that would induce choking; (2) the expected upstream flow depth for blockages with various heights, with a given flow rate under choked flow condition; and (3) the expected upstream flow depth for various flow rates, with a given blockage height under choked flow condition. The results can be used to evaluate the risk of bottom blockage-induced spill for sewer pipes with various sizes, slopes and flow rates (e.g., some may be more tolerant to bottom blockages while some may be more sensitive). This information can then be used to prioritize preventative measures such as sewer depth monitoring or regular cleaning. [ABSTRACT FROM AUTHOR]

Air in the headspace of sewer laterals can be driven by the flowing sewage as well as air pressure. In this study, the openings on manholes for air flow are approximated as a thin continuous slot at the laterals. In this way, the governing equations can be solved analytically for infinitely long laterals without water flow. For cases with water flow, a numerical solution is developed. It is found that the air flow pattern in a long lateral can be categorized into three zones. The zone closest to the trunk is defined as the "zone of influence," where the air flow in the lateral is dominated by air pressure, and the air pressure and air velocity decay exponentially in the lateral. The second zone is named as "zone of equilibrium" where the air pressure gradient is zero and the air flow is only driven by the drag of water and can be calculated analytically. The air flow zone farthest from the trunk is defined as the "zone of induction" where the air is inducted into the system for mass balance in the system. An explicit fitting expression on the air velocity and water velocity in a long lateral is provided. A graphic solution for air velocity and zone of influence is also developed for a quick estimation on the air movement in sewer laterals. [ABSTRACT FROM AUTHOR]

This study conducted experiments to investigate the impact of bottom obstacles, specifically broad-crest weir-type and cylindrical obstacles, on the flow within a sewer pipe. It was observed that these two types of obstacles, when possessing the same cross-sectional area and length, exhibited nearly equivalent hydraulic responses for both supercritical and subcritical flows. The obstacle height was found to be the primary factor responsible for choking and the transition between different flow regimes. The results of the one-dimensional analysis show that the threshold value of obstacle height depends on the approaching flow conditions, including the Froude number and the filling ratio that is defined as the flow depth to the pipe diameter. In the context of a partially blocked sewer, the relationships established by using the one-dimensional model between the size of the bottom obstacle and the inflow characteristics enable the identification of flow regimes, assessment of reduced hydraulic capacity, and evaluation of local energy loss. The findings of this study elucidate the hydraulic behavior of obstructed sewers, contributing to the development of more effective strategies for the identification of obstructions through monitoring data. [ABSTRACT FROM AUTHOR]

During the discharge of floodwater from a hydropower station, a significant number of water droplets in motion are created in the downstream space. These droplets vary in size and velocity, causing challenges in determining the particle size and velocity distribution of the flood discharge atomized droplets. Currently, the particle-size distribution and velocity distribution of atomized droplets are considered to be independent, and the gamma function is used to describe the particle-size distribution and velocity distribution of droplets separately. However, a joint distribution of atomized droplet size and velocity is lacking. This paper uses the basic theory of maximum entropy to study the combined distribution of droplet size and velocity in the atomized flow caused by jet overflow. The present model was in a good agreement with experimental data, providing a method for the theoretical study of droplet size and velocity distribution in flood discharge atomization. [ABSTRACT FROM AUTHOR]

This document provides a discussion of the article "Design Considerations for High-Speed Flow in Sewer Systems" by Yu Qian, David Z. Zhu, and Bert van Duin. The authors emphasize the importance of addressing issues such as air pulsation, abrasion, and abrupt pressurization in sewer structures with fast flows. They propose design criteria and structural solutions, including specific manholes as drop structures, to mitigate these problems. The document also includes equations and empirical solutions for predicting the discharge capacity of bend manholes. It references the experimental and numerical observations of Gisonni and Hager and Crispino et al. regarding the capacity of supercritical flow in bend manholes. The authors suggest equations to predict the capacity of supercritical junction manholes based on previous experimental data. The text briefly mentions the topic of cavitation in sewer flows, stating that it is less likely to occur in fast sewer flows due to the absence of incipient velocities. The authors note that most codes limit sewer flow velocity to prevent wastewater outflow, but cavitation is unlikely to occur. The document concludes by mentioning the availability of data supporting the findings in the cited references. [Extracted from the article]

An innovative numerical model called the Modified Two-Component Pressure Approach (MTPA) is proposed to better capture the physics of column separation in conduit systems. Based on the Two-Component Pressure Approach (TPA), the MTPA calculates both cavitating and pressurized flow using a single set of equations that governs unsteady flow in open channel flow. As opposed to shock-fitting-based models, in which a complex algorithm is needed to keep track of the interfaces separating the cavitating and liquid zones, the proposed model can capture both flow phases automatically. The first-order Godunov type finite volume method is utilized to numerically solve the equations. A customized Harten, Lax and Van Leer (HLL) Riemann solver is employed to calculate the fluxes at the computational cell boundaries and to dissipate potential post-shock oscillations generated when the cavity is collapsed and the open channel flow beneath the cavity is switched back to pressurized flow. The numerical results are shown to be in good agreement with both experimental data and the results obtained from the Discrete Gas Cavity Model (DGCM). A hypothetical test case is also presented to demonstrate the unique feature of the proposed model, which is the ability to simultaneously account for waterhammer, cavitation, and open channel flow regimes, a feature making the model even superior to the DGCM. Several numerical approaches are available to successfully calculate the induced waterhammer pressures following column separation. Existing 1D models based on these numerical approaches can help engineers quantify the impacts of column separation and design measures to protect the pipe system against this phenomenon. Nevertheless, most of the existing models used in the industry exclusive work with pipe systems that remain fully pressurized during transient flow. However, column separation may occur in pipe systems carrying concurrent open channel and pressurized flows. Examples of such systems and operating conditions are sewer conveyance and pipe system collection, intermittent water distribution systems, pump power failure in self-draining pumped pipelines, and pipeline filling and draining. To fill part of this gap, this paper presents a numerical open channel-based 1D model that can treat concurrent transient open channel, pressurized flow, and column separation. The model is validated using experimental data, numerical results from other models, and a hypothetical example. The results reveal that the model is accurate enough to be used in practical applications. The model can also calculate the shape and spread of vapor cavities across the pipe system, a feature that makes the proposed model superior to counterpart models. [ABSTRACT FROM AUTHOR]

The numerical study in this paper aims at obtaining exact well-balance and improving the computational accuracy, efficiency, and the performance at wet–dry fronts, especially for the flows in ventilated sewer pipes. To this end, a novel numerical model for mixed flows in a circular-shaped sewer is proposed. The major contributions of this study are: (1) a MUSCL scheme (monotonic upstream-centered scheme for conservation laws) is designed so that second-order accuracy is achieved, which leads to accurate solutions even over coarse meshes; (2) a special reconstruction technique and novel source term discretization are proposed for pipe flows to guarantee the exact well-balance in the framework of a MUSCL scheme, thus numerical oscillations at stationary steady states are avoided; (3) the proposed new scheme produces reasonable solutions for kinetic flows in underresolved finite-volume grids with very low water volumes; and (4) it guarantees the positivity of the computed water volume without forcing a minimum wetted area value or reducing the global time step size. The performance and superiorities of the proposed new scheme for sewer flows are verified against previously reported well-balanced numerical models on a number of experiments. [ABSTRACT FROM AUTHOR]

With the development of urban areas, many municipalities are facing issues where the flow velocity in their sewer systems is relatively high at various locations. This is because of either geographical or local hydraulic conditions. Existing design guidelines generally include a velocity limit of 3 m/s. However, the rationale for this limit is not presented in these guidelines. This study explores the feasibility of higher allowable sewer velocities on municipal infrastructure. Potential issues that may be considered when increasing the velocity to a higher value of 6 m/s or even around 10 m/s are discussed, including capacity, air demand, and transient flow. Considerations as to system protection are then reviewed including the forces exerted on structures, cavitation, and presence of sediments. Design alternatives are also discussed including drop shafts and energy dissipators. Increasing the existing maximum allowable velocity of 3 m/s to a higher value may result in a decrease in pipe diameter and depth of cover, which would yield financial savings. A value for the maximum allowable velocity in sewer system design is not proposed in this paper given the complicated hydraulic features of high-speed flow and the significant gaps between research and actual engineering requirements. [ABSTRACT FROM AUTHOR]

Understanding the air demand of a hydraulic jump in a closed conduit is important in hydropower operations and urban sewer designs. In this study, physical experiments are described to study flow regimes and the air demand of a hydraulic jump in a closed conduit with various submerged outlet depths. Flow regimes with a submerged outlet were defined following previous studies based on outlet depth. Free-surface supercritical flow with a hydraulic jump can induce a relative air demand (air flow rate to water flow rate) of approximately 3%–14%. If the hydraulic jump is followed by pressurized pipe flow, the air demand decreases with increasing outlet depth until the return roller is fully developed in the pipe. For the partially submerged hydraulic jump, the relative air demand is significantly reduced to less than 1%. Field measurements of the air demand at the Hugh Keenleyside Dam, British Columbia, were consistent with the experimental measurements for the partially submerged hydraulic jump. The dynamics of the air pocket upstream of the hydraulic jump was studied. If the air supply was constrained by nozzles of various sizes placed on the top of the air vent, the air pressure in the closed conduit decreased and the hydraulic jump was pushed upstream. The energy loss coefficient in the air vent was also studied. [ABSTRACT FROM AUTHOR]

Manholes in combined sewers may become surcharged during storm events, resulting in complex mixing conditions. Although manhole hydrodynamics are reasonably well understood, predicting mixing across a surcharged manhole remains a challenge. An analytical compartmental mixing model for manholes, based on jet theory, has been further developed and applied to generate cumulative residence time distributions (CRTDs), which describe mixing. The modeled CRTDs were compared with the experimentally derived CRTDs of over 850 manhole configurations to evaluate how well the new compartmental model represents physical processes. The model underpredicts short-circuiting in manholes with manhole diameter to pipe diameter ratios greater than 4.4 and consequently overestimates mixing. Otherwise, the modeled CRTDs show good agreement with the experimental CRTDs. The new compartmental model represents key manhole hydrodynamics that are not represented in current software modeling packages, which assume manholes are instantaneously well-mixed. The compartmental model provides good predictions of the experimental downstream concentration profiles, although with reduced peak concentrations in those manhole configurations where short-circuiting is not well-predicted. Despite this, the compartmental model still predicts concentrations downstream of a manhole in closer agreement with the recorded data than the complete instantaneously well-mixed assumption. As an analytical model requiring no inputs other than manhole geometry, the new compartmental model applies to a wide range of manhole configurations, is robust, and is useful for predicting manhole mixing in practical applications. [ABSTRACT FROM AUTHOR]

This document is a closure to a study on the design considerations for high-speed flow in sewer systems. The authors appreciate the comments and interest from discussers regarding the hydraulic characteristics of high-speed flow in sewers. The paper discusses the maximum allowed flow velocity as an important design criterion, but the rationale for the limits is still unclear. Municipalities are seeking ways to increase the velocity limit, but this can lead to unfavorable flow conditions and damage to infrastructure. The document also addresses the Froude number calculation, the possibility of cavitation in sewers, the occurrence of roll waves, and the need for further study on damage mechanisms and specific criteria for bend and junction manholes in sewer systems. [Extracted from the article]

This paper presents experimental and numerical results of air movement in sewer pipes. Both the airflow in a straight pipe and pipes with changing slopes were studied. The result from the straight-pipe model suggests that the air pressure gradient is built up in the pipe even when it is kept at atmospheric pressure at both ends. The combined effects of water drag and the pressure gradient were analyzed. A general method for estimating the airflow rate was proposed. Further, physical and numerical experiments were performed on air movement induced by water flow with a hydraulic jump in pipes with a changing slope. The ratios of air and water flow rates were found to be substantially higher than published values because of different air transportation mechanisms. The rough surface and air/water bubbly flow in the roller of the hydraulic jump can affect the momentum flux of the air phase, and this additional momentum needs to be incorporated in airflow modeling. [ABSTRACT FROM AUTHOR]

Deep storage tunnels are an alternative to mitigate combined sewer overflows, but they may develop transient flow problems during rapid filling conditions. Such issues include excessive surges, formation of pipe-filling bores, entrapped air pockets, and uncontrolled releases of air. Initial decisions on storm water tunnel designs are generally based on steady-flow considerations but can have a significant impact on the transient hydraulic performance. However, tunnel designers rarely have an opportunity to systematically assess the interplay between geometric characteristics (e.g., tunnel diameter, alignment, and junction areas) and inflow hydro graphs. This work aims to provide an examination of the relationship between key design parameters and the performance of storm water tunnels undergoing rapid filling. A flow regime transition model was used to simulate 216 different scenarios of rapid filling of tunnels, considering air--water interactions such as air pocket entrapment, compression, and expansion. Results indicate that peak surges and air outflows though vertical shafts correlated well with design parameters such as junction shaft plan areas and inflows at the time of tunnel pressurization. Other variables, such as entrapped air pocket volume, did not correlate well with geometric or inflow parameters selected in this study.While these results are not directly applicable to any existing stormwater tunnel geometry, the findings should help designers to understand potential transient flow issues and the input conditions that may lead to the most severe transient conditions. [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]

Stormwater infiltration and inflow are major contributors to sewer flow, and thus they can be significant triggers for combined and sanitary sewer overflows, both of which introduce contaminants to surface waters. There are few estimates of private residential rainfall-dependent inflow and infiltration (RDII), and this paper proposes that a rapid and cost-effective means to locate points of significant stormwater entry into the sewer system would be advantageous for combined and sanitary sewer management. The authors studied the collection system in the Barthman-Parsons area of Columbus, Ohio, performing detailed drainage and connectivity investigations on 116 private houses located in areas served by separated sanitary sewers. Sources of inflow and infiltration (I/I) were identified for private residential properties, which could include sump pumps, foundation drains, downspouts, cleanouts, yard drains, and defective service laterals. The authors then developed estimates of I/I contributions from residential properties in different neighborhood clusters, and these estimates were extrapolated to the entire Barthman-Parsons area. Field results found that 68% of tested properties contribute to I/I. Of the tested sample, 25% had at least one downspout that tested positive for I/I, and 59% had a lateral that tested positive. The results also showed that downspouts and laterals contributed approximately 98% of the total I/I volume generated by the tested properties in response to testing. These residential I/I sources were estimated to make up approximately 35% of total I/I for short, intense storms with dry antecedent conditions, and approximately 7% of total I/I under low-intensity, long-duration storms with wet antecedent conditions. An internally validated logistic model developed for the downspout data set was fairly accurate at predicting whether a property would test positive. It correctly classifies the downspouts of 17 of 27 houses as contributing I/I, and incorrectly predicts 14 as contributing. Had this model been available prior to testing, a majority of the houses' downspouts contributing to I/I could be eliminated without testing the entire population, offering significant savings in assessment and testing costs, and leading to an overall faster turnaround in system improvement. [ABSTRACT FROM AUTHOR]

Vortex drop shafts are used in urban drainage systems to connect two sewers located at considerably different elevations. After their introduction in 1947, these were studied with particular reference to subcritical approach flow. Vortex shafts for supercritical approach flow can also be used, but the intake structure may have relatively high cost due to the complex geometry. The present study includes experimental results of a specific investigation on the changes to be made in the supercritical approach channel if a subcritical vortex intake is used. The experimental investigation analyzes the effect of a hydraulic jump on the performance of vortex intake structure to define appropriate technical solutions, essentially consisting in a negative step to be located along the supercritical approach channel. Design criteria are finally presented for the evaluation of the step height and its distance from the vortex intake structure. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article focuses on Daryl B. Simons, a researcher, educator, and hydraulic engineer, is presented. He graduated from Utah State University, in 1947, where he received a Bachelor of Science in civil engineering.He continued his master's degree in civil engineering at Utah State University, specializing in hydraulics and structures. He served as a consultant for Banner and Associates and worked on the design of airports, flood control, sewage systems, drainage, water supply networks, and other civil engineering infrastructure works.

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. [ABSTRACT FROM AUTHOR]

Sewage pumping stations represent an element of the sewer system, which is directly responsible for affecting serviceability; i.e., failing pumps may result in combined sewer overflows or flooding. However, failures of sewage pumps are not yet incorporated in sewer assessments due to lack of data. This paper presents the analysis of pump failure data provided by two sewer management authorities in The Netherlands. Pump failures have been studied accounting for the nature of the failures, the operation and maintenance procedures of the management authority, the aging of the pumps, and the changes in the environment of pumps. The analysis shows that sewage pumps fail relatively often due to the composition of sewage and the discontinuous operation of the pumps. The interarrival time and the duration of failures are highly variable and independent of the specific function of the pump. Resulting pump failure characteristics are applied in a Monte Carlo simulation to calculate the impact of failures on combined sewer overflow volumes. The results indicate that the serviceability of sewer systems is significantly affected by failing pumps. Therefore, including pump availability in sewer system assessments should be considered. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Municipal wastewater collection systems, due to the nature of their functions, carry varying concentrations of odorous gases. The production rate and transport of these gases within and out of sewer systems depend on air flow rate in the system piping. However, municipal sewers are generally designed to only transport sewage flow without giving consideration to the air flow field. As a consequence, the movement of air into, along, and out of collection systems is for the most part uncontrolled. The purpose of this paper therefore is to provide a new design protocol based on system theoretic techniques to be used by municipal engineers and environmentalists involved in odor control and sewer foul air transport studies. The modeling formulation accounts for combined wastewater drag and pressure-induced air flows, and manhole pressurization. The developed framework is applied to both hypothetical and real sewer systems to only illustrate the applicability of the modeling formulation. [ABSTRACT FROM AUTHOR]

This work is part of a long term project which aims at developing a hydraulic model for real-time simulation of unsteady flows in sewers ranging from gravity flows, to partly gravity–partly surcharged flows to fully surcharged flows. The success of this project hinges on the ability of the hydraulic model to handle a wide range of complex boundaries and to provide accurate solutions with the least central processing unit time. This first paper focuses on the development and assessment of two second-order explicit finite-volume Godunov-type schemes (GTS) for unsteady gravity flows in sewers, but with no surcharging. Traditionally, hydraulic transients have been modeled using the method of characteristics (MOC), which is noted for its ability to handle complex boundary conditions (BCs). The two GTS described herein incorporate BCs in a similar manner to the MOC. The accuracy and efficiency of these GTS schemes are investigated using problems whose solution contains features that are relevant to transient flows in sewers such as shock, expansion, and roll waves. The results show that these GTS schemes are significantly faster to execute than the fixed-grid MOC scheme with space-line interpolation, and in some cases, the accuracy produced by the two GTS schemes cannot be matched by the accuracy of the MOC scheme, even when a Courant number close to one and a large number of grids is used. Furthermore, unlike the MOC solutions, which exhibit increasing numerical dissipation with decreasing Courant numbers, the resolution of the shock fronts was maintained by the GTS schemes even for very low Courant numbers (0.001). [ABSTRACT FROM AUTHOR]

Operational problems and system damage have been linked to the flow regime transition between free surface and pressurized flow in rapidly filling stormwater and combined sewer systems. In response, emphasis has been placed on the development of numerical models to describe hydraulic bores and other flow phenomena that may occur in these systems. Current numerical models are based on rigid column analyses, shock-fitting techniques, or shock-capturing procedures employing the Preissmann slot concept. The latter approach is appealing due to the comparative simplicity, but suffers from the inability to realistically describe subatmospheric full-pipe flows. A new modeling framework is proposed for describing the flow regime transition utilizing a shock-capturing technique that decouples the hydrostatic pressure from surcharged pressures occurring only in pressurized conditions, effectively overcoming the cited Preissmann slot limitation. This new approach exploits the identity between the unsteady incompressible flow equations for elastic pipe walls and the unsteady open-channel flow equations, and the resulting numerical implementation is straightforward with only minor modifications to standard free surface flow models required. A comparison is made between the model predictions and experimental data; good agreement is achieved. [ABSTRACT FROM AUTHOR]

Spreading of a buoyant jet into a counterflowing ambient flow stream is investigated in the laboratory with the laser-induced fluorescence (LIF) technique. The jet behaviors are found to depend on two flow parameters. The densimetric Froude number (F) characterizes the ratio between the initial buoyant force on the jet effluent and the initial jet momentum. The jet-to-current velocity ratio (R) compares the initial jet exit velocity to the speed of the counterflow. Experiments are carried out at Froude numbers F=3–11 and velocity ratios R between 2.5 and 18. Time-averaged patterns of the jet are revealed by the mean LIF concentration field of jet effluent. Global features of the jet including its trajectory, spreading, and dilution are analyzed from the mean LIF images. The buoyant jet penetrates forward into the counterflow for some distance before it is turned backwards by the counterflow. Buoyancy in the effluent results in some vertical rise of the jet in this first region of forward flow, especially at a high velocity ratio. The flow then transits into the second region of backward flow. Buoyant jet effluent is advected backwards by the counterflow and at the same time continuing to rise in a plume-like manner. Radial profiles of mean effluent concentration at successive stations along the jet centerline are found to follow reasonably well the Gaussian distribution. The predictions of the Lagrangian model JETLAG are compared with the experimental data for this complex situation of buoyant jet in counterflow. The jet trajectory data are also interpreted using a length scale analysis. [ABSTRACT FROM AUTHOR]

Experiments on the near-field mixing of wastewater discharged from multiport diffusers into a stationary density-stratified environment are reported for conditions typical of ocean sewage outfalls. Dilutions were measured with a microconductivity probe in which the test tank was stratified with a nonconducting solution; geometrical characteristics such as rise height and layer thickness were measured by planar laser-induced fluorescence in which the test tank was stratified with refractive-index matched fluids. The port spacing was varied over a wide range encompassing rapidly merging to nonmerging plumes. The end of the near-field occurs at a distance of order one plume rise height from the diffuser. At this point the turbulence and mixing induced by the discharge is effectively damped by the ambient stratification, and little near-field mixing occurs beyond it. The results were analyzed in terms of line and point-source parameters to deduce the ranges of port spacings for which line and point plume solutions apply. Equations to predict the near-field characteristics are presented. [ABSTRACT FROM AUTHOR]

Experiments on the near-field mixing of wastewater discharged from multiport diffusers into stratified flowing waters are reported for conditions typical of actual ocean sewage outfalls. Dilutions were measured by a newly developed three-dimensional laser-induced fluorescence system combined with refractive-index matching and by a microconductivity probe. The plume dynamics are complex. Depending on port spacing, plumes discharged from the upstream diffuser side may merge first with themselves, and then with the plumes discharged from the downstream side. Or the plumes that are horizontally opposed may first merge, followed by lateral merging. In all cases, however, the wastefield eventually becomes laterally homogeneous. The results are analyzed in terms of line or point-source parameters and it is found that they can be predicted by assuming the discharge to be a line plume when s/lb<1.0 and as point plumes for s/lb>=6.0. Semiempirical equations to predict the near-field dilution, near-field length, and plume rise height are presented. [ABSTRACT FROM AUTHOR]

The article focuses on gate and vacuum fluxing of sewer sediment. Hydrodynamic and sediment transport processes were determined by flushing operations in sewer channels. Depending on the characteristics of the flush of the sediment, the use of a fixed weir can affect both the hydraulic and sediment transport processes.

In urban areas, when heavy rains occur, the discharge capacity of sewers is usually unable to transport the effective rainfall reaching the streets. When the runoff flow rate exceeds the capacity of the storm sewer system, the excess flow is conveyed through the street network as overland flow. A dual model is proposed for modeling the system as a double network, formed by an upper network of open channels (street gutters) and a lower network of closed conduits (sewer pipes). What is new in this model is its capacity to take into account the hydrodynamic relationship between the flows in the upper and lower networks. The model is applied to computing the response of a real monitored basin; the historical flow rates measured during a first rainfall event are used to calibrate the model, which is then validated using the simulation of two other measured events. [ABSTRACT FROM AUTHOR]

Focuses on the removal of cohesionless sediments deposited over fixed beds. Evaluation of the transport capacity of cohesionless sediments deposited over fixed beds; Analysis of flow characteristics and transport capacities of cohesionless sediments over fixed beds.

The objective of this study was to test the performance of a traditional gate-flushing device and a newly designed vacuumflushing device in removing sediment from combined sewers and CSO storage tanks. A laboratory hydraulic flume was used to simulate a reach of sewer or storage tank. The flushing device was fabricated and installed at upstream end of the flume. The removed sediment was collected at downstream end of the flume and weighed. The test results indicate that the weight of flushed sediment increases with increasing initial water depth in the flushing device; the weight of flushed sediment decreases with increasing initial water depth in the flume; the weight of flushed sediment only changes slightly with changing height of flushing device opening for water release and does not necessarily increase with increasing opening height. Water is held up by vacuum and is released upon dissipation of the vacuum in the vacuum-flushing device rather than through closing and opening of a mechanical gate in the gate-flushing device. The test results indicate that sediment removal efficiency of the vacuum-flushing device is practically the same as the gate-flushing device. [ABSTRACT FROM AUTHOR]

Laboratory experiments were carried out to determine minimum self-cleansing velocities for preventing deposition of sediment in upward sloping and vertical pipes of inverted siphons. Tests were made using sediment sizes of 0.78 and 4.3 mm in a pipe of 150 mm diameter for eight angles of inclination between 0 and 90°. The criterion for self-cleansing conditions was defined as the minimum velocity needed to prevent the formation of deposits on the invert of the pipe. For a given sediment concentration the self-cleansing velocity was found to be a maximum at pipe slopes between about 22.5 and 45°. Analysis of the forces acting on sediment particles in inclined pipes led to the development of a formula for predicting self-cleansing velocities taking account of pipe size, sediment size, sediment concentration, and pipe slope. [ABSTRACT FROM AUTHOR]

This paper presents a historical overview of the sewer sediment control projects conducted by the Wet-Weather Flow Research Program of the United States Environmental Protection Agency. The research presented includes studies of the causes of sewer solids deposition and development/evaluation of control methods that can prevent sewer-sediment accumulation. Discussions focus on the relationship of wastewater characteristics to flow-carrying velocity, abatement of solids deposition and solids resuspension in sewers, and sewerline flushing systems for removal of sewer sediment. Methods for abating sewer sedimentation include steeper sewer slope, pipe bottom shapes that maintain high velocity during low-flow conditions, and periodic sewer flushing. The future research program plan for sewer-sediment control is also presented. [ABSTRACT FROM AUTHOR]

This paper summarizes the design of passive automatic flushing systems installed in the City of Cambridge's storm and sanitary sewer system tributary to the Alewife Brook as part of a $75 million sewer separation program. Grit and debris deposition is severe in the existing combined sewers, storm drains, and sanitary trunk sewers due to the flat topography of the area. This condition is exacerbated by hydraulic constraints imposed on the system's outlet by the Alewife Brook (shallow stream) and downstream sanitary siphons (again because of the Alewife Brook). The use of pumps to lift flows from sewers and drains to permit self-scouring velocities is prohibitively expensive. To overcome this problem, five automated flushing systems using quick opening (hydraulic operated) gates discharging collected stormwater were constructed in conjunction with downstream collector grit pits covering a distance of 1,604 m for storm drain pipes ranging from 1.4 m circular to 1.2 m by 1.8 m rectangular. New 450 and 600 mm sanitary trunk sewers, 561 m long, will be flushed daily by two flushing systems using spent filtrate water from Cambridge's water treatment plant recently constructed nearby. The flushing systems are sized to achieve wave velocity of 1 m/s at the end of the flushing segment. The flush vault volumes range from 11 to 40 m[SUP3] for the storm drain systems and 6 m[SUP3] for the sanitary system. Construction was completed in May 2002 and functional testing of the flushing systems is in progress. Partial test results are reported. [ABSTRACT FROM AUTHOR]

The need for sewers to carry sediment has been recognized for many years. Traditionally, a minimum "self-cleansing" velocity was specified and, although this approach had been successful in many cases, it was appreciated that a minimum velocity--unrelated to the characteristics and concentration of the sediment or to other aspects of the hydraulic behavior of the sewer--could not properly represent the ability of sewer flows to transport sediments. During the 1980's, sediment transport theory had been increasingly applied to the design of sewers, particularly in major interceptor sewer schemes. But, in the absence of any universally recognized guidance, the design methodologies and criteria adopted were developed on a project-by-project basis, building on the increasing experience and understanding of the subject of the designer. In recognition of this, a research project was initiated by the U.K.'s Construction Industry Research and Information Association to develop a new design methodology for sewers, which would take advantage of the available knowledge (mostly laboratory derived) on sediment mobility and the effects of sediment deposition on the hydraulic performance of sewers. This paper describes the main findings of the project and summarizes the recommended design guidance. [ABSTRACT FROM AUTHOR]

The release of fine-grained organic sediments from sediment deposits can have a detrimental impact on water quality in a number of situations. This paper examines the release of such sediment in the context of the erosion of mixed organic/granular sediment in-sewer deposits. In the European Union, sewer flow quality modeling software uses equations derived from uniform granular sediment studies. Actual sewer sediments are mixtures of organic and granular material and interactions between these fractions may account for the poor performance of current models. Laboratory experiments were carried out using surrogate sewer sediment mixtures. Impaction of the bed surface by saltating granular particles increased the erosion of fine-grained organic sediments. Changes in the composition of the bed surface over the duration of a test resulted in change in the availability of fine-grained sediment. A model that attempted to simulate these mechanisms, using an empirically based correction factor to account for the impaction mechanism and an active bed layer to account for changes in the bed surface composition was developed. The limited success of the simulations indicated that such simple modeling approaches may not be appropriate for organic/granular deposits in which grain sorting occurs. [ABSTRACT FROM AUTHOR]

High levels of suspended solids are typically observed during the initial part of storms. Field evidence suggests that these suspended solids derive from the erosion of in-sewer sediment beds accumulated during dry and previous wet weather periods. Suspended sediment transport rate models within existing sewer network modeling tools have utilized inappropriate transport rate relationships developed mainly in fluvial environments. A process model that can account for the erosion of fine-grained highly organic in-sewer sediment deposits has been formulated. Values of parameters describing the increase in deposit strength with depth are required. These values are obtained using a genetic algorithm based calibration routine that ensures model simulations of suspended sediment concentrations that correspond to field data collected in a discrete length of sewer in Paris under known hydraulic event conditions. These results demonstrate the applicability of this modeling approach in simulating the magnitude and temporal distribution of suspended in-sewer sediment eroded by time varying flow. Further work is developing techniques to enable the application of this type of model at the network level. [ABSTRACT FROM AUTHOR]

Granular sediment in pipe inverts has been reported in a number of sewer systems in Europe. Given the range of flow conditions and particle characteristics of inorganic sewer sediments the mode of transport may normally be considered as bed load. Current commercial software for modeling the erosion and transport of sediments in sewer pipes still utilizes well-known, or modified versions of transport equations that were derived for transport of noncohesive sediment in alluvial streams. In this paper the performances of the equations of Ackers and White (originally developed for the transport of river sediments) and of May (derived from laboratory pipe experiments) are examined against two separate data sets. One set is from laboratory erosion experiments on sewer sediment obtained in Paris. A second data set has bed load transport rate measurements recorded in a sewer inlet pipe. The formulas were selected because of their widespread use in the prediction of in-sewer sediment transport both in commercial software and in the latest United Kingdom design guidance for new sewers. The results indicated that both the relationships performed poorly, even in such well-controlled conditions. These formulas have significant difficulties in predicting the erosion thresholds and fractional transport rates for non-uniformly sized in-sewer sediments. An empirical formula to adjust the threshold of motion for individual grain size fractions was developed which significantly improved predictions. Although such techniques have been used in gravel bed rivers, the threshold adjustment function for in-sewer deposits was significantly different from these previously published for fluvial gravels, indicating that a direct transfer of fluvial relationships to sewers may be inappropriate without further research. [ABSTRACT FROM AUTHOR]

The hydraulics of supercritical flow across manholes in sewers is explored using systematic experimentation. Due to the expansion at the manhole entrance an in-manhole wave is generated. Further, at the downstream manhole end, flows with a sufficiently large filling ratio impinge on the wall and lead to a so-called swell. In addition, due to shock wave generation in the downstream sewer, a sewer wave is generated. The heights and locations of these three waves were determined in terms of basic hydraulic quantities. More importantly, the capacity of the manhole and the downstream sewer under wave action was quantified. It was found that in order for free surface flow to be maintained the common design standard for sewers with a supercritical approach flow have to be revised. These implications have to be accounted for in future designs. [ABSTRACT FROM AUTHOR]

This paper presents the results of an observational study related to the behavior of drainage sewers under conditions of hydraulic overloading. Specifically, the investigation focuses on the interaction of water and trapped air in surcharging drainage and pressurized pipeline systems, by studying the air–water flow behavior in a rapidly filling horizontal pipe. Air–water interface patterns, air entrainment, and air release through an orifice at the pipe end are documented photographically. Synchronously recorded pressure traces are also presented to illustrate the relation between the air–water phase evolution and the pressure oscillation patterns. Depending on the air release rate of the orifice, there are three types of pressure oscillation behavior, each corresponding to a particular behavior of the air–water interface in the rapidly filling horizontal pipe. [ABSTRACT FROM AUTHOR]

Presents the Double ORder Approximation (DORA) algorithm for the solution of shallow water equations to compute the unsteady-state flow in an urban drainage network. Role of numerical models in designing and improving drainage networks; Components of DORA; Performance of the model in some selected cases; Application of DORA in an experimental sewer system in Pavia, Italy.

Examines the condition of choke-free flow in ovoidal sewers subject to a rise in bed elevations. Review of related literature; Description of geometric properties; Equations and computation.

Provides information on a study which examined the dynamics of a storage tunnel using a model based on on-line measured data and a combination of simple deterministic and black-box stochastic elements. Description of the sewer system of the city of Copenhagen, Denmark; Description of the gray box model; Conclusions.

The article focuses on the theoretic approach for modeling ventilation phenomenon in sanitary sewer systems. It is stated that ventilation events in sewers are complex phenomena because of the unpredictable nature of the air exerting forces and the complex interaction between the system air space and the ambient surroundings. It mentioned several pressure-inducing events which include siphon, barometric and wind pressure, downstream air capacity reduction and drop-structure turbulence. It is revealed that temperature difference is important in a cold climate where ambient temperature is different from sewer air temperature.

The article presents the authors' comments on the study "Hydraulic Efficiency of Grate and Curb Inlets for Urban Storm Drainage," by Brendan C. Comport and Christopher I. Thornton. The authors appreciated the study Comport and Thornton, saying that the results could be extremely useful for engineers to analyze street flow during rain events and determine the optimum inlet spacing.

The article focuses on analytical solutions for estimating effective discharge which is a critical issue in stream restoration projects. The goodness of fit between the observed flow record and the assumed frequency distribution affects the accuracy of the estimation of effective discharge. Urban stream restoration project usually produces a very small drainage area.

The article focuses on gate and vacuum flushing of sewer sediments. Research work on effects of the downstream weir on hydrodynamics and sediment transport is valuable and appreciated. The use of artificial, fixed weir enabled the creation and maintenance of initial water depth in the flume, but had a minimal effect on the amount of flushed sediment.