Journal of Hydraulic Engineering

In this paper, a stochastic method of characteristics (MOC) solver is developed based on polynomial chaos expansion (PCE) to quantify the uncertainty in water-hammer equations describing transient flow in a simple reservoir-pipeline-valve system. The randomness is considered due to boundary and initial conditions. The Galerkin scheme is used for the projection of equations onto the stochastic dimension, and the governing equations are solved for the expansion coefficients. These coefficients are then used to reconstruct the mean solution of pressure wave perturbation as a result of valve closure, in addition to the calculation of other higher-order statistical moments. The computed results are in excellent agreement with those calculated by using the traditional MOC over a wide range of system parameters including steady and unsteady friction. The stochastic solution has the advantage of being robust and more efficient than other nonintrusive methods, such as Monte Carlo simulations (MCS).

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.

Strategies for managing leakage from water distribution systems require the ability to effectively evaluate such real losses through the understanding of the behavior of individual leaks, including their response to changes in pressure regime due to demand or management strategies. This paper presents the results from an innovative experimental investigation aimed at understanding the response of longitudinal slits in pressurized viscoelastic pipes, specifically considering the interaction between the structural and leakage dynamics. For the first time, leakage flow rate, pressure, leak area, and material strain were recorded simultaneously, providing new knowledge of the complex interaction of these factors. The paper shows that strain and area are directly related, hence it is possible to employ strain as a predictor of leak area, calculated using a calibrated viscoelastic model. Using such an approach, the leakage flow rates under a range of quasi-static pressures were accurately predicted and validated. Overall the paper demonstrates that the orifice equation, with a constant coefficient of discharge, is suitable for accurately estimating dynamic leakage flow rates from longitudinal slits, provided that the leak area is suitably incorporated.

In this study, an improved two-dimensional (2D) model is proposed for simulating shallow water flows over complex bathymetry through their subgrid modeling. The proposed model delineates the detailed unevenness in the topography of selected 2D elements that are usually ignored in other common 2D hydrodynamic models by specifying the bed elevation at more than one point in an element. The relationship between submerged area and water stage and the relationship between water volume and water stage can then be preprocessed for every specified element. The process is similar to how cross sections are handled in standard one-dimensional models. Thus, the 2D model can simulate the open channel flow accurately and efficiently, with only one element been applied over the channel width. The proposed model was tested using a hypothetical channel flow with an analytical solution and a real river-coast system with measured data. The simulations showed that the model could achieve the same level of accuracy using a coarse mesh as that obtained by previous 2D models with a refined mesh. The proposed 2D model performs well at predicting shallow flows over complex terrain, which is usually handled by coupled models.

Air valves are normally installed at high points along undulating pipelines to allow for air discharge or intake during filling or dewatering. Initial filling of a newly constructed pipeline, or refilling a portion of an existing pipeline after a shut-down for maintenance purposes, can produce destructive pressure surges caused by air-valve closure. Methodologies for determining safe filling rates for the pipeline, taking into account factors such as air-valve characteristics, riser dimensions, driving head, and allowable working pressure, are proposed in this paper. An optimal filling method can be achieved either by a two-stage filling procedure, which comprises a fast filling rate during the first stage and a slower filling rate during the second stage when the water level approaches the highest air valve, or by using an antislam air valve. The comparison of computed transient pressures with test data indicates that the analytical models produce reasonable predictions of pressure surges caused by air-valve closure.

Elevated high points along a pipeline profile are the most common places where air vacuum valves (AVVs) are installed. This paper uses basic water hammer theory to semianalytically explore the effects of such AVVs. A simple frictionless reservoir-pipe-reservoir system with an exaggerated intermediate high point is considered with a sudden flow curtailment assumed upstream. Key design parameters such as the maximum air pocket volume, the duration of air pocket growth and collapse, and the maximum magnitude of the pressure spike resulting from water column rejoinder are semianalytically developed for various high point locations. The magnitude of the reduced pressure wave created by the refraction at the high point, and both its vertical and horizontal position, are demonstrated to crucially determine system performance. Numerical examples are compared with the semianalytical expressions to highlight the accuracy of the derived expressions. The effect of friction is later introduced to help reveal friction’s influence on air valve performance.

In the present study, two bed-load transport models are introduced in an existing idealized dune model. These allow for the modeling of the spatial lag between the sediment transport rate and bed shear stress along dune surfaces. This lag is an important factor in determining transitions between bedform regimes. Results of the original dune model (using an equilibrium transport formula) are compared with (1) a new model version that directly models spatial lag with a relaxation equation and (2) a new model version including pick-up and deposition processes. Both bed-load models use mean particle step length as an important parameter, which is varied to assess which value is appropriate for the dune regime. Laboratory experiments are simulated with the model. This shows that the results are best with the pick-up and deposition model version, combined with a step length of 25 times the particle diameter. It is furthermore shown that in principle the model is also able to wash out fully grown dunes, by increasing the step length parameter.

Field studies, modeling, and the design of two major outfalls to discharge domestic wastewater from Buenos Aires, Argentina, into the Río de la Plata are described. Extensive data were gathered from current profilers, Lagrangian drifters, meteorological stations, and water column profiling. The river is essentially freshwater and is the main water source for the city; it is tidally dominated, shallow, and well-mixed vertically. The data were used to develop a two-dimensional hydrodynamic model of the river that closely simulated its major features. The wastewater disposal strategy and special design and modeling considerations of the outfalls and diffusers are discussed. The tidal currents will recirculate the wastewater back and forth over the diffuser several times before it is flushed away by the mean river flow. Because of the shallow water and low flushing currents, it is not possible to achieve the high near-field dilutions typical of deep-water marine outfalls, and other design constraints include the proximity to water intakes. Lagrangian particle-tracking modeling approaches were used to predict the fate and transport of the effluent and its dilution. The models reproduce near-field mixing at moderate to high current speeds and also reentrainment due to the reversing tide without the need for special model coupling. However, dilutions at low current speeds were corrected to account for the jet momentum and reentrainment. The near-field jet modeling to determine the riser and port designs is discussed. Bacterial impacts decreased rapidly with distance from the diffuser and no impacts on the shoreline or water intakes were predicted. The effects of sudestadas were also modeled and it was concluded that they will not significantly affect water quality for the proposed outfalls.

In this paper, the flow and bed shear stresses downstream of a tidal barrage, with open ducts and with swirl created by stators and rotors, are investigated experimentally. The wake created by open ducts is significantly three-dimensional within 20-duct diameters ($20D$) from the barrage. Within $20D$ of the barrage, the duct blockage and swirl also affect flow patterns and bed shear stress. Swirl affects jet mixing and local downstream circulation within 5-duct diameters ($5D$), resulting in large-scale cross-stream circulation further downstream. After $20D$, the flow becomes predominantly parallel and depth averaging would be appropriate. Bed shear stress just downstream of the barrage is magnified by up to 3, 7, and 12 times, respectively, for open ducts, stators alone, and rotors plus stators. This has major implications for sediment motion and scour.

The processes involved in bed-load sediment transport are complex and difficult to quantify. Field measurements provide insight and a chance to improve predictive methods. A comprehensive database is described that contains more than 15,000 observations from nearly 500 data sets of bed-load sediment transport. Observations are compiled from published sources, author responses to queries, and personal visits to offices. Each entry has been checked twice for accuracy against the original data and converted to a common set of units. The database contains sections for sample descriptions, discharge and transport data, channel and bankfull characteristics, surface and subsurface grain size distributions, and, where possible, stream classification descriptors. Discharges range from far below to several times bankfull values. The database is freely available to the public and may be accessed via direct download and through WaterML based web services from the BYU World Water Data Sediment Transport Database portal at http://worldwater.byu.edu/app/index.php/sediment. The intent of this database is to provide useful data to researchers as they continue to investigate bed-load transport processes. Data can be added to the database by contacting the authors.