Journal of Hydraulic Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

The analytical solution of the steady-state seepage field of a circular cofferdam in nonhomogeneous layered soil of finite depth is derived, including the head function, exit hydraulic gradient formula, and seepage flow formula. The head function is obtained by dividing the circular cofferdam seepage field into regions and then using the separated variable method combined with the Sturm–Liouville theory, and the unknown coefficients in the head function are determined by constructing a system of equations through the integral transformation of the Bessel function. Based on the head function, an analytical equation is also given for the exit hydraulic gradient and seepage flow. The accuracy of the proposed analytical solution is verified by a comparison with numerical results as well as with the results of other methods. The proposed analytical solution is a display analytical solution without singularities and can be used as an effective tool for the analysis of circular cofferdam seepage problems.

The existing one-dimensional model is inadequate in predicting the dynamic interactions between hydraulic transients and inline air pockets in water pipelines, leading to underestimated pressure dissipation in the modeling results. In this study, a one-dimensional (1D)–three-dimensional (3D) coupling model was applied to analyze and explain the interactions between the hydraulic transients and inline air pockets observed in systematic laboratory experiments. In this model, the method of characteristics provides 1D modeling of hydraulic transients in the regions without the inline air pocket and the finite-volume method with volume of fluid approach provides 3D modeling of hydraulic transient interactions at the air pocket. The coupling between 1D and 3D models is achieved using the partly overlapped coupling method. The analysis of the transient velocity profile unveils unique velocity distributions on both sides of the air pocket due to reflection and transmission processes, which contribute to the compression and movement of the air pocket. The investigations of variation in the internal energy of the air pocket using the 1D–3D model demonstrate that the internal energy reduces in the slow compression process due to greater energy fluctuations and more rapid energy transfer between air and water, especially at the front of the air–water interface directly impacted by the incident wave. This explains why the existing 1D model underestimates the pressure damping.

Abstract

Flooding in urban communities is an increasingly prevalent issue that causes significant financial loss, property damage, and long-term adverse health effects. Backwater valves can reduce the risk of basement flooding during sewer surcharge events at the lot-level scale. However, guidelines for installation and maintenance can be limited or inconsistent, with little underlying literature or research. Without proper installation and ongoing maintenance, solids can accumulate, resulting in the valve failing to close or being unable to form a watertight seal during a sewer surcharge event. This research provides insights to inform future design iterations or updates to best practices guidelines by characterizing flow patterns and velocities within the Mainline Fullport backwater valve. A series of laboratory experiments are described at two common flow rates (0.1 and $0.3\mathrm{L}/\mathrm{s}$) and various slopes ($-2\%$, 0%, 2%, 5%, and 10%) using fluorescent particle tracers as a novel replacement for more traditional laser-based particle image velocimetry. Results revealed a complex flow environment influenced by slope, flow rate, initial water level conditions, and the fluid properties of water. Regions for potential solids accumulation leading to mechanisms of potential failure occurred near the inlet, at the downstream edge of the closing gate, and along the side channels. Increased slopes generally improved flow conditions, with least favorable outcomes below a 2% slope and diminishing returns above a 5% slope. Between 2% and 5% slope, conditions were the most complex but improved with increased flow rates. Fluorescent particle velocimetry shows promise as a powerful, affordable, and reliable tool to visualize flow and measure velocities in complex, shallow flow environments where other methods are unsuitable.

Practical Applications

Floods are an increasingly common and highly damaging problem, during which wastewater can back up in sewage pipes into basements. A backwater valve reduces the risk of sewer back-up and basement flooding. The valve closes when sewage flows backward and seals shut until the event ends. A backwater valve must be properly installed and maintained to ensure intended performance, but the associated guidelines can be unclear. To help improve those guidelines, this paper clarifies performance for various flow patterns and slopes in a backwater valve at different flow rates using laboratory experiments. Faster-moving water flushes debris and helps keep the valve clean, but raising slopes to achieve that may be difficult or expensive. Experiments used particles glowing under a black light to visualize water movement. Results reveal complicated flow patterns, with the worst conditions for flushing debris developing below 2% slope (2-cm drop per 100-cm of length) and the best conditions at 5% or above. Between 2% and 5% slope, the benefits of increasing slope were complex and depended on other factors. Methods used in these experiments can be adapted for different applications because they are relatively inexpensive and can work in shallow-water environments.

Accurate measurement of bedload is challenging, considering its spatial and temporal variability. Various indirect acoustic techniques are often used for estimating the bedload rate and total bedload mass. Estimating the grain size distribution for a bedload event of relatively short duration, taking the smaller bedload particles into account, is difficult. In the current study, an impact plate with two sensors, namely, an accelerometer and a geophone, is tested in a laboratory flume. Available bedload grains are sorted into different grain size classes, and two sets of experiments are conducted. Single-grain/multigrain particles and mixed-grain particles are considered in the single-class and multiclass experiments, respectively. Three different grain mixtures with variable fineness are fed to the plate in the mixed-grain experiment. The present setup can detect bedload grains from 2.36 to about 150 mm, which is an improvement over other indirect methods. A hybrid analysis methodology to predict the grain size distribution using signals from both sensors is developed. The grain size distributions (GSDs) are estimated with a maximum deviation of 22%, which is expected to improve further with data from longer bedload events.

This paper discusses a full-fledged uncertainty analysis implementation using the Guide to the Expression of Uncertainty in Measurement (GUM) as framework. Currently, there are few examples of rigorous GUM implementations in hydrometry. This work fills this gap by demonstrating the use of the GUM framework to estimate the uncertainty of open-channel discharge measurements conducted with the velocity-area method using acoustic doppler velocimeters. The paper first presents the GUM protocol and the steps leading to discharge measurement followed by evaluations of Type A uncertainty from customized experiments, Type B uncertainty informed by prior experiments and engineering judgment, and the total discharge uncertainty. Finally, the uncertainty analysis (UA) implications and practical usage for data management and improvement of measurement processes are discussed. While the detail of the analysis can be further increased, the main role of this paper is to illustrate a step-by-step implementation of GUM procedures applied to natural-scale measurements using a GUM-compliant software.

Flooding water in extreme hydrometeorological events may be significantly contracted by bridge abutments and superstructures, leading to severe sediment scour and threatening structure stability. A series of large-scale laboratory experiments assessing flood-induced scour processes near bridge abutments are presented, with particular attention paid to the dependence of scour pattern on factors such as deck submergence (vertical contraction), abutment/embankment length (lateral contraction), abutment structure, and general bed mobility, which are analyzed based on post-scour transverse bed profiles and the general bed morphology. It is found that the scour hole’s depth, geometry, location, and corresponding time dependence are intricately affected by the aforementioned factors and demonstrate very complicated behaviors. The current design criterion of HEC-23 is sufficient to prevent disastrous embankment breaching but cannot avoid channel erosion or abutment toe undercutting in severe floods. The location of the greatest scour may migrate with time during floods and is closely related to the abutment structure and length. Furthermore, the existing scour predictors are examined and compared with recent data sets; more improvements are needed to reflect the complex physical mechanism of scour processes. Finally, a new method for estimating sediment loss is proposed.

A filter unit (FU) is a structure installed with the aim of protecting the foundation of an embankment revetment from riverbed scouring, and there are cases in which sediment is deposited in the surrounding area after installation. Vegetation growth in sediment can improve the environment and protect revetments. Hydraulic experiments and numerical calculations were conducted to investigate how suspended sediments are deposited around FUs over a large area within a short period of time. We performed suspended sediment deposition experiments using FU models and confirmed that sediment deposition can be calculated accurately using a two-dimensional planar model. We also analyzed FU placement and its impact on topographical changes in an actual river in which FUs were installed. The results showed that (1) the continuous placement of FUs inhibits sediment deposition on the downstream side; (2) arranging FUs at intervals facilitates sediment deposition even under small-scale floods; and (3) employing an interval of half the FU width for every three or more FUs can effectively promote suspended sediment deposition at intervals.

Quantifying turbulent friction holds significant importance, not only for understanding the fundamental flow physics but also for enriching system performance across a wide range of engineering applications. This vision article presents the state of the science of the turbulent friction in canonical flows, shedding light on its current status through a combination of theoretical developments and experimental observations. First, the article discusses the law of the wall, including the scaling behavior, the possible origin of the logarithmic law, and the effects of wall roughness. Then, it provides an overview of roughness height and its connection with the wall topography. The scaling behaviors of the logarithmic and power laws of turbulent friction are thoroughly appraised, offering insights into their implications. Additionally, the phenomenological models of turbulent friction based on the spectral and co-spectral budget theories are furnished. The behavior of turbulent friction for extremely large Reynolds number flows is examined, based on theoretical models and experimental data. The semiempirical finite Reynolds number model for turbulent friction is reviewed, emphasizing the pertinent scaling laws in various forms. The scaling laws of turbulent friction in curved-pipe and axisymmetric boundary layer flows are discussed. Finally, future research directions are outlined, highlighting the key challenges to be addressed.

Abstract

This work proposes the use of an array of yawed porous vanes to control the lateral bedload transport by locally steering bedform migration and maximize the amount of sediments redirected toward a potential sediment extraction system or bypass channel. A laboratory experiment was conducted in a quasifield-scale channel with an array of permeable vanes installed on one side, in live-bed conditions under bedload dominant regime, i.e., negligible suspended load. A baseline experiment without vanes was also performed for comparison. The evolution of migrating bedforms of different scales was tracked in space and time using a high-resolution, state-of-the-art laser scanning device. The bedload transport rate in the streamwise direction was first calculated using bedforms’ geometry and migration velocity, and then spatially distributed over the entire monitored area using a new Eulerian-averaged grid-mapping method. This allowed us to introduce a new methodology to estimate the lateral bedload transport using control volume theory and applying mass conservation. Quantitative assessments of lateral bedload transport along the channel yield consistent results, suggesting that the vanes effectively move sediments laterally as intended. Under the investigated setup, the maximum lateral sediment transport rate ranges from 9% to 18% of the whole domain-averaged streamwise transport rate. The developed methodology also allowed to identify the location where sediment capture could be maximized for the given vane spatial distribution.

Practical Applications

In river engineering, in-stream structures are used to control flow and sediment movement to prevent erosion, intake clogging, and habitat disruption. Submerged vanes are small, angled structures that are installed to redirect sediments toward a preferred direction by creating secondary flow circulations. This study tests experimentally an array of porous vanes in an open channel to measure and quantify the lateral displacement of sediment. Porous plates were selected to minimize local scour and anchoring requirements while directing flow, bedforms, and sediment laterally. The amount of sand moved laterally is measured by comparing the streamwise bedform transport within and outside of the vane array. The proposed vane array is part of a modular hydrosuction sediment bypass system being developed for low-head dams, which features inlets to collect coarse sediments and siphon them over the dam via a slurry conduit. The vane array is meant to be installed upstream of the collector to increase the lateral transport of coarse sediment toward the intake structures. Porous elements can potentially be replaced by vegetation and log structures for nature-based alternatives.

Rockfill dams are a common dam type, but breach development in these dams is not very well understood, particularly rockfill dams with placed or dumped riprap protections on the crest and downstream slope. In this paper, we look at several experimental setups investigating the overtopping of rockfill dam models with and without riprap protections and how these experimental results compare with existing empirical models for breach development in embankment dams. We describe the model setups, data acquisition, and data analysis as well as the comparison with existing empirical equations for breach development, focusing on the following parameters: breach width, breach formation time, and peak outflow. The discussion brings to light how the parametric breach models can predict breach development in rockfill dam models. It also highlights how the existing models are wholly unsuited to predict breach development in protected dam models. Breach initiation and development in protected dams differs so much from unprotected dams that new models are needed. Such models could integrate new parameters that describe the resistance against erosion the crest and slope protection provides, as well as the sudden breach development that ensues once the protection fails.

Understanding solute transport in pipe flows is essential for ensuring consistent water quality throughout the entire drinking water supply network. This study used four planar laser-induced fluorescence (PLIF) units for the first time to quantify the cross-sectional concentration distribution resulting from a single pulse of tracer injected at an upstream location under both steady and accelerating flow conditions. Compared with conventional fluorometers, PLIF provides a better measure of the cross-sectional mean concentrations because it allows the cross-sectional distribution of the tracer to be quantified. Under steady turbulent flow conditions, the tracer was cross-sectionally well-mixed, and the concentration uniformity increased with increasing Reynolds number. In laminar flows, as a result of minimal radial mixing, the tracer exhibited a spatial distribution created by the longitudinal differential advection, transforming from a central core to an annulus, which expanded toward the pipe boundary. Under accelerating flows, the temporal concentration profiles displayed two peaks and the tracer close to the source was not cross-sectionally well-mixed. With increasing discharge, the tracer became cross-sectionally well-mixed while retaining the two peak profiles. These results have implications for water quality modeling in unsteady conditions, especially in domestic plumbing, when boundary and biofilm interactions control important processes.

Abstract

This work presents nonlinear and linear controls ensuring the global stability of a pressure-reducing valve. The global property using both nonlinear and linear controls is very important to guarantee stability even though the pressure-reducing valve operates far from its nominal working point. To this goal, this work develops the mathematical description of a pressure-reducing valve. It is a second-order model, nonlinear, and nonaffine in control implemented with two secondary (solenoid) valves. Due to the nonlinear nature of the system, the Lyapunov theory allows developing the control, which ensures the global stability of the system using one input. In addition, the second control input is modified to enlarge the operating range of the pressure-reducing valve. To implement the control in (nowadays) industrial controllers, a linear proportional-integral (PI) control, ensuring all the stabilizing properties of the nonlinear control, is included as a subset of the nonlinear law. Experimental results demonstrate the good performance of the proposed PI.

Practical Applications

The importance of controlling pressures in water distribution systems is widely recognized. This study delves into the analysis of a pressure-reducing valve, beginning with its mathematical model and culminating in its control mechanism. Two secondary (solenoid) valves serve to operate the pressure-reducing valve, acting as the system’s control inputs. The research showcases that the achieved control operates effectively across a broader range of operating conditions, a notable distinction from other pressure-reducing valve controls. Furthermore, it demonstrates the feasibility of utilizing only one control input while keeping the other fixed. Additionally, a strategy is proposed to maximize the operational range of the pressure-reducing valve within the constraints of the inputs. Finally, considering implementation in the field using validated hardware, and acknowledging the complexity of the obtained control, this study substitutes the original control with a well-established (PI) control, ensuring the desired properties. Experimental results validate the effectiveness of the proposed control strategy.

Abstract

Desanding facilities (DFs) limit particle sizes and reduce the suspended sediment load in hydropower plants. Multiple successive tranquilizing racks (TRs) at settling chamber inlets are a cost-efficient structural measure to homogenize the flow and reduce local velocities and turbulence in the chambers. We summarized the state of the art of TRs and conducted detailed flow velocity measurements in the settling chambers of a DF with TRs. In the first campaign, a pronounced flow concentration beneath the vertical bars of the TRs was found, resulting in flow velocities along the invert of up to 3.5 times the average cross-sectional velocity. Because this impairs the trapping efficiency, the TR bars were extended downward to achieve a more even distribution of the flow resistance over the entire flow section. A subsequent measurement campaign confirmed a more homogeneous flow field and a considerable reduction of the turbulence intensities and turbulent kinetic energy, which were the lowest compared to six other DFs. The results highlight the potential to modify existing TRs at other DFs with inhomogeneous flow fields and the practical importance of TR design for new DFs.

Practical Applications

In hydropower plants (HPPs) with water intakes located at sediment-laden rivers, DFs are crucial for reducing the sediment load in the turbine water, consequently minimizing wear on the turbines. A DF usually consists of one or several chambers through which the water flows slowly, allowing sand particles to settle. However, for geometrical, hydraulic, and economic reasons, the flow at the chamber inlet is often not favorable for settling. In such situations, TRs can be installed to slow down and distribute the inflow more evenly. Because no general design guidelines for TRs are available, we reviewed the state of the art based on literature and present the field investigation of flow fields in a DF with TRs. We found an unfavorable flow concentration and modified the TRs to cover the whole flow section. This resulted in more favorable conditions for settling, also in comparison with other DFs. In DFs with inhomogeneous inflow conditions, suitably designed TRs enhance the trapping efficiency and contribute hence to the cost- and energy-efficient use of the hydropower potential at sediment-laden rivers.

Abstract

This paper experimentally studied water jets issued vertically downward from rectangular nozzles into still ambient air. Two rectangular nozzles having the same aspect ratio but different cross-sectional areas were tested under different water flow rates. The water jet surface characteristics while falling were explored using a high-speed camera. The phenomenon of axis switching was observed under both rectangular nozzles. The magnitude of the jet surface fluctuation with falling distance was found to follow an exponential growth. The breakup length was found linearly increasing with the square root of the liquid Weber number. The diameters of the droplets released from jet breakup were analyzed and were mostly around 2 cm.

Practical Applications

This investigation studied the characteristics of water jets issued from two rectangular nozzles, including the axis-switching phenomenon, surface wave disturbance, jet breakup length, and diameter of droplets. The outcomes of this study contribute to a better understanding of rectangular jet flows in practical applications. For example, the water flow discharged from spillway gates can be approximated as a large rectangular water jet, the breakup features of such water flows can be estimated, which are closely related to the total dissolved gas level downstream of the dam. Also, the flow inside a dropshaft can be approximated as a rectangular water jet. The results of jet breakup length in this study can provide design reference for noncircular jets.

Shallow reservoirs are ubiquitous in hydraulic engineering. Predicting the properties of the flow field in such reservoirs is instrumental to inform their design, operation, and maintenance. In previous research, oscillating jets were experimentally observed in rectangular shallow reservoirs, and we assess here the performance of a simple analytical model to predict the frequency of the dominating jet oscillation mode(s). The model couples the evaluation of the reservoir natural frequencies with the Rossiter feedback loop formula. The analytical predictions are compared against experimental observations by reanalyzing an existing data set. In many cases, the model predictions match the observations. Remaining discrepancies may result from experimental uncertainties, which could be reduced in future tailored laboratory tests, or from the dimensionless vortex celerity value used by the feedback loop model, which was not assessed experimentally.

Abstract

An air-entraining vortex begins to form when the submergence of an intake is not adequate and less than the critical value known as critical submergence. In the present study, critical submergence for a laterally placed single rectangular intake under a uniform approach flow in an open channel was investigated experimentally. Analysis of the data collected in the present study reveals that critical submergence is significantly influenced by intake size, intake aspect ratios, approach Froude number, intake Froude number, intake Reynolds number, and Weber number. However, intake Froude number and intake aspect ratio were found to be the most sensitive parameters that affect critical submergence. An empirical relationship for critical submergence has been developed using collected data used to compute the critical submergence within an error of $\pm 20\%$. The findings of this investigation is advantageous for hydraulic engineers when designing lateral rectangular intakes to prevent the formation of an air-entraining vortex.

Practical Applications

Insufficient water cover over the hydraulic intakes causes an air-entraining vortex formation in the vicinity of the intake. The formation of such an air-entraining vortex results in significant hydraulic issues, structural damages, etc. Ensuring enough submergence for the intake during its operational period is necessary to evade such problems. The submergence at which the air-core tail of the surface vortex reaches the intake initiating air-entrainment is called critical submergence. Critical submergence is an important parameter for the design of intakes and is widely used as a parameter to determine an incipient state for which no air is entrained by intake vortices. This paper discusses the experimental investigation of critical submergence for single lateral rectangular intakes concerning significant geometrical parameters, such as intake aspect ratio, approach Froude number, intake Froude number, etc. The proposed empirical equations in this study are helpful to hydraulic engineers when computing critical submergence to fix the invert level of a lateral rectangular intake.