Quantifying Culvert Exit Loss

According to the Federal Highway Administration’s Hydraulic Design of Highway Culverts (HDS-5) Manual and the Hydrologic Engineering Center River Analysis System (HEC-RAS) Reference Manual, the exit loss associated with a culvert discharging into a downstream channel is equal to the change in culvert and channel velocity heads or a loss coefficient multiplied by the culvert velocity head. For a short culvert, the calculated exit loss often represents the largest single system energy loss component. To investigate the apparent dominance of exit loss in outlet control culvert hydraulics, a laboratory culvert exit loss study was conducted using prototype-scale culverts, with projecting end treatments, discharging into a downstream channel where all of the channel discharge was supplied by the culvert. The experimentally determined exit losses were compared with predicted exit loss values using traditional exit loss equations and the Borda–Carnot minor loss expression, which is traditionally used to quantify energy loss at sudden expansions in pressurized pipe flow. The Borda–Carnot expression proved to be significantly more accurate, relative to traditional methods, for the conditions tested.     

Generalized Study of Hydraulics of Culvert Fishways

This study presents a comprehensive analysis of the experimental observations, collected previously in an extended project on culvert fishways with offset baffle, slotted weir baffle, weir baffle, spoiler baffle, Alberta fishweir, and fishbaffle systems. It has been found that a general correlation exists between the dimensionless discharge Q? = Q/ and the relative depth of flow (y0/D) for each value of the relative baffle height (h/D). Furthermore, for relative baffle heights in the practical range of 0.1–0.15, longitudinal baffle spacing should be limited to a maximum of D. The velocity field in the centerplane of each of these culvert fishways was analyzed and was found to be similar with the similarity profiles having different shapes for different baffle systems. A general correlation was also found for the normalized velocity scale. Even though most of the baffle systems worked reasonably well in the range of parameters recommended, the weir and slotted weir baffle systems are simpler yet equally effective. The results presented in this paper will hopefully facilitate the design and building of successful culvert fishways.     

Experimental Study of a Right-Angled End Junction between a Pipe and an Open Channel

This paper presents an experimental study of a junction between a closed conduit and an open channel. This study was undertaken to explore hydraulic properties of outlets of subsurface drainage or sewage networks into an open air stream during flood events. Experiments were conducted in a laboratory flume, with a main rectangular channel joined at right angle to a lateral circular pipe. Both branches were supplied with independent flow rates and downstream water level was controlled by an adjustable weir. Several flow patterns were identified, combining free-surface and pressurized flows. Transitions between these flow patterns, as well as changes in water level or energy, in response to the modifications of experimental variables, were studied and could be linked to known properties of single channels, single pipes, and homogeneous junctions. Transitions between free-surface and pressurized pipe flow appeared to be strongly dependent on the whole set of experimental variables and the pipe longitudinal slope. This work contributes to a better knowledge of hydraulic and hydrologic key processes for point source discharging.     

Hydraulics of Multibarrel Culverts under Inlet Control

The hydraulic characteristics of multi- and single-barrel circular culverts were compared in this study. One-, two-, and three-barrel culverts configurations, operating under inlet control, were tested in the laboratory with various approach conditions and barrel spacing (horizontal and vertical). The single-barrel head-discharge relationship was consistent with the average head-discharge relationship of the individual barrels in a multibarrel culvert configuration with a uniform upstream approach flow and uniform invert elevations. For the nonuniform approach flow condition, the single-barrel model overpredicted the average-barrel flow by up to 10%. With the middle barrel installed at a lower elevation than the outside barrels, in submerged flow the single-barrel head discharge relationship was consistent with the outside barrels, but the middle barrel was up to 7% more efficient than the single-barrel discharge. The flow rate variations are attributed, in part, to a reduction in approach flow contraction entering the center culvert in the three-culvert configuration and a nonuniform distribution of intermittently forming surface vortices at the culvert inlets. The results of a state (United States) Department of Transportation survey regarding multiple culvert use are also presented.     

Hydraulics of Large Culvert beneath Roman Aqueduct of N?mes

The Romans built ancient culverts beneath roads and aqueducts. The hydraulic operation of a large culvert, built around the 1st century A.D. beneath the N?mes aqueduct, is described. The investigation shows the advanced design of an ancient multicell structure with a large discharge capacity equivalent to about 12 times the aqueduct maximum discharge capacity.     

Hydraulics of Bottom Rack Intake

Bottom racks are a standard hydraulic structure used as intakes in mountainous regions, to divert water to turbines, and to retain sediment and other solid matter larger than rack spacing. These racks are also used for fish ways, and to retain floating matter. The present project was directed to explore the hydraulics of bottom rack intakes, without considering any solids in the fluid. Based on extended laboratory observations, the effect of various parameters were explored, such as the bottom slope, the rack geometry, and the rack porosity. In addition, a novel approach to determine the discharge coefficient of a rack structure was developed. Finally, the intake channel below the bottom rack was investigated and several interesting features were found, including a significant flow instability that may have a strongly adverse effect on the rack performance. Guidelines for successful rack designs are given, and the results of the present study may be readily applied.     

Hydraulics of Rectangular Dropshafts

A dropshaft is an energy dissipator connecting two channels with a drop in invert elevation. The hydraulics of vertical rectangular shafts was systematically investigated in seven configurations. A particular emphasis was on the effects of shaft pool, outflow direction, and drop height, while geometrically similar shafts (scale 3.1:1) were studied using a Froude similitude. The results demonstrate that rectangular dropshafts with 90° outflow are the most efficient energy dissipators. The shaft pool and drop height have little effect on the rate of energy dissipation. Recirculation time results exhibited marked differences between flow regimes and the longest dimensionless residence times were observed at low flow rates. Although basic flow characteristics were similar between model and prototype, observations of dimensionless bubble penetration depths and recirculation times showed some discrepancy, highlighting limitations of the Froude similitude for studies of air entrainment and residence times in dropshafts.     

Experimental Evidence of the Applicability of Colebrook and Borda Carnot-Type Head Loss Formulas in Transient Slug Test Analysis

Radius changes along the flow path inside a well can have a substantial nonlinear impact on head responses to a slug test. The present paper investigates the applicability of head loss formulas rooted in steady-state pipe hydraulics to account for minor and major head losses in transient slug test analysis. Such nonlinear head losses, which frequently occur when using a packer for test initiation, have not systematically been investigated before. Packer-internal turbulence is accounted for based on Colebrook’s formula, while minor head losses originating at the inlet and outlet of the packer are treated by Borda Carnot-type head loss formulas. The analysis of a specifically designed set of 12 slug tests provides extended experimental evidence of the applicability of these nonlinear head loss formulas when accounting for well bore-internal turbulence and minor head losses in transient slug test analysis.     

Hydraulics of 3D Plunge Pool Scour

The main flow features of three-dimensional plunge pool scour are explored in this experimental research for steady flow conditions. These include the maximum depth of the scour hole, its streamwise geometry, and the maximum width, the maximum height of the ridge, its shape in plan view, and its profile. Expressions for all these parameters are presented in terms of the basic scour variables, including the approach flow densimetric Froude number, the jet impact angle, the jet diameter, and the tailwater elevation above the originally horizontal sediment bed. This research is based on a previous work relating to two-dimensional plunge pool scour. Differences between the two phenomena are outlined, and the results are discussed in terms of engineering applications. The results of the two works allow for the prediction of the most salient features of plunge pool scour for both the dynamic and the static scour holes.     

Hydraulics of Circular Drop Manholes

Circular drop manholes are widely employed in steep urban drainage systems. Drop manholes may lead to poor hydraulic conditions if their energy dissipation is inadequate. The dominant hydraulic features of drop manholes depend on the flow regimes, characterized in terms of the dimensionless impact parameter. Depending on the latter parameter, the energy dissipation can vary within large limits, affecting thereby the downstream flow features. Also, the water pool depth inside the manhole and the air entrainment have been studied in terms of both the hydraulic and geometric parameters. Moreover, the conditions for which a drop manhole generates flow choking at its inlet or outlet have been investigated. Empirical equations for practical manhole design are provided. The importance of suitable manhole aeration is highlighted.     

Design of Straight Expansive Pipe Transitions

Pipe transitions frequently occur in piping networks such as a water distribution system, or piping in a chemical engineering plant. Whereas the contraction transitions involve less head loss, the expansion transitions involve a sizable head loss. Considerable energy savings can be achieved if the transitions are designed by minimizing the head loss. The conservation of energy will be significant if the transition is meant for a steel-lined power tunnel where the flow velocities are high. Similarly, in a system having frequent occurrence of transitions, such as a high-rise building or plan of a city, the optimum transition profile can be used most effectively. This paper uses optimal control theory to develop a methodology for optimal design of expansion pipe transitions. Analyzing a large number of designed optimal transitions; empirical design equations for the pipe diameter profile are obtained.     

Total Friction Loss along Multiple Outlets Pipes with Open End

This paper describes the derivation of the total direct and relative reduction factors for both discrete and continuous outflow along mixed service sections of close end multiple outlets pipes. Discrete outflow factors depend on the numbers of outlets along the section and the entire pipeline, while for continuous distribution there is no such dependence. Solutions for close end pipes are also derived. The total relative factors are related to those previously calculated total factors for close end pipes. The concept of “effectiveness” is presented here for close and open end pipes by taking into account the friction loss occurred downstream of the first outlet, resulting in both head and flow variation between that upstream outlet and the remaining outlets along the line. The dependence upon the extremity spacing is also considered. There are also proposed formulations for mixed factors for intermediate sections between two locations along a close end pipe.     

Computing Inlet Pressure Head of Multioutlet Pipeline

Expressions for the factor K to relate the total frictional head loss, average outlet operating pressure head, and the inlet pressure head of a multioutlet pipeline are developed. In the developed expressions, the factor K is a function of the number of outlets on different pipe diameters, combination of diameters, and position of the first outlet from the inlet. Values of the factor K obtained from the developed expressions are compared with constant values being taken as per existing practice. The comparison suggests using the developed expressions for accurate computation of the factor K for multioutlet pipelines especially comprising of two or more diameters. An example is presented to compute the inlet pressure head of a multioutlet pipeline using the factor K.     

Analytical Relationships for Designing Multiple Outlets Pipelines

In this paper an analytical procedure taking into account the nonuniform outflow profile for hydraulic analysis and design of multiple outlets pipelines, is presented. Energy relations are improved based on the average friction drop approach with a simple exponential function, to express the nonuniform outflow concept. To determine friction head losses, the Darcy-Weisbach formula is used here; and the kinetic head change is considered whereas minor head losses are neglected. Several mathematical relationships are also derived for computing extreme pressure heads and their locations of occurrence along the pipeline. The presented method also provides specific lengths of the segments in which the different flow regimes occur along its length. This method simulates pressure and outflow profiles along trickle and sprinkler irrigation laterals and manifolds, as well as gated pipes. The presented technique was applied to several computational examples to clarify its precision for trickle and sprinkler lateral design and the analytical results were compared with those obtained using the numerical step-by-step method. The comparison test for the various design combinations indicated that, the proposed method is found to be sufficiently accurate in all design cases for both trickle and sprinkler lateral design. The analytical development is simple, direct, and easily adaptable to solve hydraulic design problems of various types of single-diameter mutiple-outlet pipelines in different flow regimes and uniform line slope cases. It is preferred to the numerical techniques which need large amounts of execution time and complex computer operations.     

Using CFD Modeling to Improve the Inlet Hydraulics and Performance of a Storm-Water Clarifier

The feasibility of high-rate treatment of storm water achieving total suspended solids (TSS) removals in the range from 60 to 80% was studied using an available clarifier. The clarifier (3?m long, 1.4?m wide, and 2?m deep) was fitted with a removable lamella pack and had a limited flow capacity (surface load rate of 35?m/h). To achieve the desired removals of TSS, the clarifier required polymer feed (4?mg/L), which caused maintenance problems during intermittent storm-water treatment—laborious and costly cleaning of lamella plates after individual storm events. This problem posed the following challenge: was it feasible to avoid costly maintenance by removing the lamella pack and at the same time to retain the high TSS removals by improving the clarifier hydraulics by internal structural changes? The purpose of the paper is to evaluate such changes by focusing on different inlet configurations designed using computational fluid dynamics (CFD) simulations. This analysis resulted in adopting a U-tube duct inlet (inserted into the outer box of the original clarifier) with two special features: (1) three horizontal slot openings (width = 0.1?m) releasing flow into the clarifier and (2) a narrow slot opening in the bottom U bend allowing removal of grit. The flow release slots in the rising leg of the U tube were fitted, along the upper edge, with horizontal trailing plates protruding 0.15?m into the clarifier and forcing the flow to move horizontally. This clarifier design performed well, but storm-water grit accumulated at the bottom of the U tube, which had to be cleaned out after individual storms to avoid plugging. This issue was resolved by allowing grit to move into the sludge storage compartment of the clarifier through a narrow tilted slot opening in the U-tube bottom. The final clarifier design with polymer feed, without lamellas, produced TSS removals comparable to those in the original lamella clarifier (almost 80%), but at a higher surface loading rate (43?m/h, which was limited by the feed pump capacity). CFD modeling, in comparison to conventional methods of hydraulic design, served as a flexible and powerful tool providing distinct advantages with respect to the speed, efficiency and reduced cost of analysis, and a better understanding of the clarifier operation.     

Hydraulic Performances of Minimum Energy Loss Culverts in Australia

Culverts are among the most common hydraulic structures. Modern designs do not differ from ancient structures and are often characterized by significant afflux at the design flows. A significant advance was the development of the minimum energy loss (MEL) culverts in the late 1950s. The design technique allows a drastic reduction in the upstream flooding associated with lower costs. The development and operational performances of this type of structure is presented. The successful operation of MEL culverts for more than 40 years is documented with first-hand records during and after floods. The experiences demonstrate the design soundness, while highlighting the importance of the hydraulic expertise of the design engineers.     

Calibration of On-Demand Irrigation Network Models

In this study, a new procedure for calibrating on-demand irrigation network models was developed. This procedure used a new objective function called maximum data with a reasonable error (MDRE) for calibrating the network. It was compared with the two more commonly used objective functions in calibration procedures that are the simple least squares (SLS) and the maximum likelihood estimator for the heteroscedastic error case (HMLE). In order to carry out the calibration, a quasi-Newton optimization method was used having as variable the Hazen-Williams head losses coefficient (C). This procedure was applied to an on-demand irrigation network located in Tarazona de La Mancha (Albacete, Spain) where flow and pressure at hydrant level was measured. The calibration procedure using the MDRE objective function was applied considering all the pressure control points simultaneously and the obtained results were compared with the results of considering the pressure control points independently. Therefore, the effect of the location of the pressure control point was studied. Results showed that, when the proposed objective function was used, the root mean squared error (RMSE) comparing the measured and simulated data after calibration was lower than when the SLS or HMLE objective functions were used. The location of the pressure control points throughout the irrigation network could affect the results; therefore, it was more accurate to use all the control points simultaneously than independently in the calibration process.     

Determining Operating Inlet Pressure Head Incorporating Uniformity Parameters for Multioutlet Plastic Pipelines

An important objective of a microirrigation system is to determine the proper operating inlet pressure head, ensuring the desired level of water application uniformity as well as the allowable pressure head variation along the multioutlet pipeline. This paper offers, simple, direct, but sufficiently accurate, relationships incorporating different microirrigation uniformity parameters, such as Christiansen uniformity coefficient, coefficient of variation of emitter discharge, and allowable pressure head variation, to determine the operating inlet pressure head (i.e., pressure head and outflow profiles) for multioutlet plastic pipelines. In this analysis some mathematical expressions were deduced to relate three uniformity parameters; then the operating inlet pressure head is simply reformulated by taking into account a multiplying factor α to the required average outlet pressure head, in terms of three uniformity parameters. Resulting, the influence of different uniform pipe slopes on the water application uniformity and the operating inlet pressure head for various emitter discharge exponents, was evaluated. In addition, to cover various design combinations an extensive comparison between the proposed equations and those of the previous studies was also presented. Examination of the results from this research indicated that, the performance of the proposed technique is sufficient in comparison to those of the recent analytical and numerical procedures.     

Fluid–Solid Interaction in Particle-Laden Flows

Using a laser-Doppler split-phase measuring technique, the rates of fluctuation in horizontal and vertical directions of pipe flow containing solid particles were observed. Employing these observations the effect of particles on flow turbulence was analyzed and a formula for determining the initial condition of particles restraining the flow turbulence in the mainstream region was developed. The mechanisms affecting the energy loss of flow were then analyzed.