M. Hanif Chaudhry

• Assoc Dean (International Programs) at University of South Carolina

Laboratory experiments were conducted to investigate the reduction of flood depth in a channel due to an engineered levee breach. Different combinations of inflow hydrographs, breach openings, and floodplain storage areas were considered. Inflow hydrographs with various peak discharges, hydrograph shapes, and flood durations were generated by a com...

The steady flow in open channels was addressed in the previous chapters. However, in real-world systems, flow conditions change with time, resulting in unstable flows. Natural processes, human acts, and accidents and incidents may all contribute to the unsteadiness. The analysis of unsteady flows is usually more complex than that of steady flows be...

Since the unsteady flow in open channels is described by a set of hyperbolic partial differential equations as discussed in the previous chapters, the dependent variables need to be integrated to know their values. And as there is no closed-form solution of these equations, except for very simplified cases, the governing equations (continuity and m...

The flow depth at which the specific energy is minimum for a given discharge is termed the critical depth and its corresponding flow as the critical flow. In this chapter, several properties of critical flow that can be utilized in different engineering applications are discussed and a number of expressions are derived for a rectangular cross secti...

Water-surface elevations are necessary for engineering applications, such as planning, design, and operation of open channels in order to assess the consequences of various engineering works and channel variations. A dam, for example, raises water levels upstream of the dam, and determining the flow depths in the upstream area is required to calcul...

Liquids are transported from one location to another using natural or constructed conveyance structures. The cross section of these structures may be open or closed at the top. The structures with closed tops are referred to as closed conduits like tunnels and pipes, while those with the top open are called open channels like rivers, streams, estua...

The pressure distribution in the flows in the previous chapters was assumed as hydrostatic. However, if the streamlines have abrupt curvatures, assuming the pressure distribution as hydrostatic becomes invalid. In addition, if the flow depth changes rapidly, the surface profile may break and flow surface may be discontinuous. Such flows are called...

The alignment, shape, size, and bottom slope of a channel, as well as whether the channel should be lined to limit seepage and/or prevent erosion of the channel sides and bottom, are considered in its design. There are currently no procedures for selecting optimal channel dimensions directly. Each site has its own set of characteristics that must b...

Three conservation laws – conservation of mass, conservation of momentum, and conservation of energy – describe steady, free-surface flows. In this chapter, these three conservation laws are derived for one-dimensional steady, free-surface flows using the basic principles of mechanics and using Reynolds Transport Theorem. One-dimensional analysis i...

In free-surface flow, the component of the weight of water in the downstream direction causes acceleration of flow, whereas the shear stress at the channel bottom and sides offers resistance to flow. Depending upon the relative magnitude of the accelerating and decelerating forces, the flow may accelerate or decelerate. Flow in which the flow depth...

In this chapter, a number of special topics are discussed. First, the analysis of flow in a channel connecting two reservoirs is presented. The reservoir water level may vary in either the upstream, downstream, or both reservoirs and the channel bottom slope may be mild or steep. Salient features of air entrainment in high velocity flow are outline...

Uniform flow occurs only in long and prismatic channels. However, in real-life projects, channel cross sections and bottom slopes are not constant with distance in natural channels and these are varied in constructed channels to suit the existing topographical conditions for economic reasons. In addition, hydraulic structures are provided for flow...

Mountain streams, rivers during high floods, spillway chutes, conveyance channels, sewer systems, and outlet works are all examples of natural and man-made open channels with rapidly varied flows. In contrast to gradually varying flows, the analysis of these flows encounters a number of challenges, including the formation of roll waves, air entrain...

Three conservation laws - mass, momentum, and energy - are used to describe open-channel flows. Two flow variables, such as the flow depth and velocity, or the flow depth and rate of discharge, are sufficient to define the flow conditions at a channel cross section. Therefore, two governing equations may be used to analyze a typical ow situation. T...

The assumption of one-dimensional flow may not be valid in many situations – e.g., flow in a non-prismatic channel, flow downstream of a partially breached dam, or lateral flow from a failed dyke. Although flow in these situations is three-dimensional, we may simplify their analysis by considering them as two-dimensional flows by using vertically a...

In this chapter, a number of special topics regarding unsteady flows in open channels. First, rating curve at a channel cross section during steady and unsteady flow conditions is discussed. Then, different methods for flood routing are described. This is followed by a discussion of the aggradation and degradation of channel bottom due to imbalance...

Sediment transport is basically a two-phase flow problem with air or water as the fluid phase and sediment particles as the solid phase. Sedimentation refers to the erosion, transport, and deposition of sediment, all of which are natural processes that have occurred throughout geologic time. Sedimentation continues to alter the terrain as well as t...

Levees may fail due to overtopping, pipping, or slope stability; overtopping being the most common cause of failures. Levee failure may result in catastrophic property damage and loss of life. An accurate prediction of the development of a breach, breach outflow, and the resulting flow field is needed for emergency preparedness and for flood-damage...

As discussed before, there are several numerical methods that may be used for the integration of de Saint Venant equations. Of these methods, the finite-difference methods have been utilized extensively in the literature and details of some of these methods are outlined in this chapter. Either a conservation or nonconservation form of the governing...

This study investigates the effects of wildlife activities by beavers, muskrats, gophers, and ants on seepage through Barr Lake, Commons Pond, Lake Elizabeth, Village Pond, and Walden Place Dams in South Carolina, USA, using a numerical seepage model. Data was collected from all dam sites for geotechnical testing, and observations were made for ani...

For a channel with a constant discharge, the characteristics of the surge wave entering a junction are obtained from the classical Stoker solution, and then the effect of the junction is analysed by applying the momentum and mass conservation equations. Experimental cases involving different combinations of the tributary lake height and the main ch...

A leak detection technique in liquid pipelines is presented in this paper. The governing equations of continuity and momentum are simplified and solved in the frequency domain using the transfer matrix method (TMM). A relationship between the relative leak location and the amplitude of the pressure oscillations is obtained, which depends on the pip...

The structural integrity of earthen dams in the natural habitat of wildlife is commonly affected by invasive animal burrowed into the embankment. The effects may be observed on the phreatic line, pore water pressures and seepage rate through the dam. This study investigates the effects of previously reported wildlife activities on two failed dams i...

Piping systems are commonly designed to withstand the first transient pressure peak, which is unaffected by dissipation. However, for multiple operations of control equipment, for example, pump start-up following pump shutdown, and load acceptance following load rejection on hydraulic turbines, an accurate prediction of the dissipation of pressure...

The uncertainty of a model to determine the damping of pressure head oscillations following a sudden valve closure in a simple piping system in a pressurized closed conduit is quantified using Bayesian inference. The joint probability density of the model parameter is estimated based on experimental results published in the literature as well as ex...

The transfer matrix method was applied to detect partial blockages in liquid pipelines using the first four harmonics of the pressure oscillations produced by sinusoidal opening and closing of a downstream valve. Unlike most available methods, which use a large number of harmonics to analyze the pattern of the frequency response diagram, this study...

The transfer matrix method was applied to detect partial blockages in liquid pipelines using the first four harmonics of the pressure oscillations produced by sinusoidal opening and closing of a downstream valve. Unlike most available methods, which use a large number of harmonics to analyze the pattern of the frequency response diagram, this study...

The overtopping failure of noncohesive earthen levees was investigated by considering sediment transport by flowing water and including slumping failure due to slope instability. The breach-shape evolution and breach hydrograph were measured during laboratory experiments. The experiments were performed with different inlet discharges and downstream...

The overtopping failure of noncohesive earthen levees was investigated by considering sediment transport by flowing water and including slumping failure due to slope instability. The breach-shape evolution and breach hydrograph were measured during laboratory experiments. The experiments were performed with different inlet discharges and downstream...

The collection of time-sensitive data on real-life embankment failures and their analysis are essential steps to model breach processes and the consequential flood, which are of great importance for preparing emergency action plans. In this paper, data on 14 earthen embankments that failed or were damaged in the Midlands of South Carolina resulting...

Despite many embankment failures worldwide, data on such failures are limited. An understanding of the embankment failure and the dominant parameters affecting the failure are crucial for predicting and modelling the breach process. Laboratory experiments are conducted on overtopping of embankments consisting of uniform homogenous sand and construc...

Although the modeling of transient conditions in closed conduit has advanced significantly during the last four decades, the dissipation of transient oscillations with time is not completely understood at present, and usually, dissipation in computed results is slower than that in the actual systems. Since the first transient state peak pressure th...

This paper presents experimental results on partial-breach dam-break flows. Three-dimensional (3D) flood waves resulting from an instantaneous breach of a dam are experimentally investigated by combining different measurement techniques. The dam-break flow is initiated by quickly lifting a gate separating a reservoir and a downstream dry basin. Thr...

Experimental results on the piping erosion process in an earthen embankment emplaced in a laboratory flume are reported in this paper along with the details of the experimental set-up and procedures. A mixture of sand, silt, and clay with different compaction rates is used for constructing the embankment. An image processing technique is successful...

Internal erosion processes due to piping in an earthen levee built in a laboratory flume are reported in this paper. Different sand, silt and clay mixtures are used for constructing the levee. An image processing technique using an edge-detection algorithm is successfully applied to track the erosion process from the recordings of both side and bot...

Levee failure due to overtopping during floods is a common phenomena. An experimental study was conducted in the hydraulics laboratory, University of South Carolina, to develop an understanding of the effects of soil properties on the breaching process of earthen levees. A total of eight experiments were conducted. A new methodology to measure the...

Levees are constructed along rivers and channels for flood protection. Failure of these levees can cause loss of life and property damage. A better understanding of the flow fi eld from a levee breach allows the decision maker to assess risks and to prepare emergency plans. For this purpose, a two-dimensional numerical model is developed to simulat...

Although, natural channels are rarely rectangular or trapezoidal in cross section, these cross sections are assumed for the computation of steady, gradually varied flow in open channel networks. The accuracy of the computed results, therefore, becomes questionable due to differences in the hydraulic and geometric characteristics of the main channel...

Equations for the conservation of mass and momentum describe the transient flow in closed conduits. These equations are usually referred to as the continuity and momentum equations. Some authors call a simplified form of the latter, the equation of motion or the dynamic equation. These equations are a set of partial differential equations since the...

Cross-country pipelines transporting crude oil or refined products are usually hundreds of kilometers long with several pumping stations located along their length (Fig. 7-1). The pumping head of these stations mainly covers the friction losses in the pipeline. In a mountainous terrain, however, gravity lift may be required in addition to the frict...

Cooling-water systems are utilized in thermal and nuclear power plants to condense steam after it leaves the turbine. The condensed water is then used in the steam generators. For this purpose, steam is passed around a large number of small-diameter tubes through which cooling water, or coolant, is pumped. These tubes are contained in a large chamb...

The starting or stopping of pump produces transient flows in pumping systems. These flows may be analyzed by using the method of characteristics presented in Chapter 3. Since the pumping head, discharge and pump speed for a centrifugal pump, are inter-dependent, transient-state speed needs to be included in the analysis. This requires special bound...

In Chapters 1 through 7, we considered transient flows that represented the intermediate flow conditions when the flow is changed from one steady state to another. However, depending upon the characteristics of the system and of the excitation, a disturbance in a piping system may be amplified with time instead of decaying and may result in severe...

Various turbine operations, such as start-up, shut-down, load acceptance and rejection, produce transients in hydroelectric power plants. This chapter deals with the analysis of these transients. In this analysis, the conduits and related boundaries may be simulated utilizing the computational procedures and boundary conditions presented in Chapter...

A piping system may be designed with a liberal factor of safety to withstand possible maximum and minimum pressures. Such a design, however, is uneconomical. Therefore, to develop an economical project, various devices and/or control procedures are considered to eliminate or to mitigate the effects of undesirable transients, such as excessive press...

A surge tank, also referred to as a surge shaft, surge chamber, etc. is an open standpipe or a shaft connected to the conduits of a hydroelectric power plant or to the pipeline of a pumping system. The top of the tank is usually open to the atmosphere.

In this chapter, a number of common terms related to hydraulic transients are defined, and a brief history of the developments in hydraulic transients is presented. The basic waterhammer equations relating the change in pressure due to an instantaneous change in flow velocity and an expression for the velocity of pressure waves in a pipe are derive...

The governing equations and the analysis procedures presented in the previous chapters are based on the assumption that the transient-state pressures throughout the system remain above the vapor pressure of the liquid. However, the transient pressure may be reduced to the vapor pressure of the liquid in low-head systems, systems having high peaks,...

We demonstrated in Chapter 2 that the equations describing the transient flow in closed conduits are hyperbolic, partial differential equations, and discussed a number of numerical methods available for their solution. The details of the method of characteristics [Lister, 1960; Streeter and Lai, 1962; Perkins et al. 1964; Abbott, 1966, Evangelisti,...

Leak and partial blockage are common in pipelines, typically at junctions, joints and connections. Huge losses of drinking water due to leaks in pipelines are well documented [AWWA 1990; Weil 1993]. In addition to reduced flows, there may be economical losses and environmental issues. A pipeline, on the other hand, may be partially blocked due to c...

In the previous chapters, we considered transient flows in the closed conduits. In this chapter, we discuss transient flows in open channels. A flow having a free surface is considered open-channel flow even though the channel may be closed at the top, e.g., a tunnel flowing partially full. A number of common terms are defined, and the examples of...

Breached levees often cause extensive flood damage to urban and residential areas; there has been considerable interest in the numerical modeling of flooding of urban areas in recent years. However, comprehensive data that describe the complex flow field in residential areas are not available for validating the numerical models or for determining t...

This paper presents measurements of velocity profiles obtained from idealized dam-break experiments and results from numerical simulations of these experiments. Dam-break flows were generated in the laboratory by suddenly lifting a gate inside a flume for three different upstream heads with a dry-bed downstream condition. Ultrasonic Doppler velocit...

The shallow water equations, also known as the Saint Venant equations, are commonly used to simulate transient free-surface flows including dam-break and levee-breach flows. However, these solutions give inaccurate results in the near-field of dam-break flow. In this paper, 3D numerical simulations of dam-break flow are done using the large eddy si...

Investigations undertaken to understand the mechanics of the motion of large sandbags and to compute their trajectories are reported in this paper, along with the details of the experimental setup and procedures. The motion of sandbags is recorded from the side of a flume by a high-definition charge-coupled device (CCD) camera, and the digital part...

In this paper, the results of a benchmark test launched within the framework of the NSF–PIRE project “Modelling of Flood Hazards and Geomorphic Impacts of Levee Breach and Dam Failure” are presented. Experiments of two-dimensional dam-break flows over a sand bed were conducted at Université catholique de Louvain, Belgium. The water level evolution...

This paper presents equations developed by using genetic algorithms (GA) to estimate decay coefficients for instantaneous acceleration–based (IAB) unsteady friction models in order to predict energy dissipation following sudden valve closures in simple elastic pipe systems. The GA searched for the optimum combination of IAB coefficients to reproduc...

The City of New Orleans is surrounded by an intricate network of floodwalls and dikes built to protect it from flooding from the Mississippi River and Lake Pontchartrain. In 2005, following Hurricane Katrina, New Orleans experienced one of the most devastating urban floods in recent history caused by several dike breaches. This work presents an ide...

Experimental investigations to understand the mechanics of motion of large sandbags and to simulate their settling behaviors are reported in this paper along with the details of experimental setup and procedures. Two high-definition charge-coupled device (CCD) cameras recorded the motion of the sandbags from the side of a glass water tank and a dig...

A lake tap is the submerged piercing of a tunnel at the intake to connect the reservoir to the tunnel system. It is referred to as a dry lake tap if the tunnel is dry before the blasting of the last rock plug at the tunnel entrance. Transient state conditions in the tunnel following a dry lake tap are modeled using the lumped and distributed-system...

The discrete Fourier transform (FT) of the peak pressure frequency response (PPFR) at a downstream valve generated by the transfer matrix method is used to detect a partial pipeline blockage. The location of this blockage is detected by locating the peak in the FT of the PPFR. This is also valid if multiple partial blockages are present. A methodol...

To compute the water-surface profiles in steady-state, gradually varied flows in open channels, an algorithm is presented that allows calculation of the flow depths and discharges at all sections of a parallel-channels system simultaneously instead of by the presently used trial-and-error computations. This algorithm is accurate, efficient, and sui...

This paper presents experimental results on surface erodibility tests performed with undisturbed and remolded samples of cohesive soils. When subjected to shear stress caused by flowing water, erosion occurs in two distinctive modes: particle erosion and mass erosion. Erosion resistance is defined as the applied bed shear stress at which incipient...

A new technique for the detection of leaks in a pipeline is presented utilizing its frequency response. In the system frequency response, a leak increases the amplitude of pressure oscillations at the even harmonics. Such an increase in amplitude has an oscillatory pattern; the frequency and amplitude of this pattern may be utilized to predict the...

The transfer function method is presented to model periodic flows in water pipelines. Laplace transforms are used to transform the governing equations for transient flows and then converted into the time domain by applying the convolution theorem. The accuracy and computational efficiency of the proposed method are evaluated by comparing the comput...

Critical flows may occur at more than one depth in channels having compound cross-sections (cross-sections with flood plains). The possibility of multiple critical depths affects the water-surface-profile calculations. Presently available algorithms determine only one of the critical depths which may lead to large errors. In this paper, computation...

The supercritical flow near an abrupt wall deflection is investigated experimentally and by computer simulations. An extensive series of tests were conducted on a 500 mm wide flume with Froude number up to 8 and wall deflection angle up to 11.3°. A special inlet box was installed to provide smooth flow conditions at the flume entrance. By analyzing...

The utilization of mathematical models in hydraulic engineering for the analysis of one-dimensional, unsteady free-surface, and pressurized flows is discussed, with an emphasis when the models performed well as well as when they did not. For illustration purposes, the applications to a number of real-life projects are presented, outlining limitatio...

In this paper, a wavelet-Galerkin method is utilized to solve the hyperbolic partial differential equations describing transient flow in a simple pipeline. Two wavelets (Haar and Daubechies) are utilized as bases for the Galerkin scheme. The governing equations are solved for the expansion coefficients, which are then used to reconstruct the signal...

On August 29, 2005 Hurricane Katrina resulted in several breaches in the levees and flood walls protecting New Orleans. Of the 20 breaches, the 17th Street Canal breach caused much of the city flooding. In this paper, the results of studies on a 1:50 scale hydraulic model of this breach based on the Froude similitude relationships are presented. It...

We discussed in Chapter 12 that de Saint Venant equations are nonlinear partial differential equations for which a closed form solution is not available except for very simplified cases. In Chapter 13, we briefly presented several numerical methods that may be used for their integration. Of these methods, the finite-difference methods have been uti...

Analysis of open-channel flow is essential for the planning, design, and operation of water-resource projects. The use of computers and the availability of efficient computational procedures has simplified such analysis, and made it possible to handle increasingly complex systems. In Open-Channel Flow, Second Edition, author Hanif Chaudhry draws up...

In Section 12-3, we showed that the unsteady flow in open channels is described by a set of hyperbolic partial differential equations. These equations describe the conservation of mass and momentum in terms of the partial derivatives of dependent variables: flow velocity, V, and flow depth, y. However, for practical applications, we need to know th...

In free-surface flow, the component of the weight of water in the downstream direction causes accelerationof flow (it causes deceleration if the bottom slope is negative), whereas the shear stressat the channel bottom and sides offers resistance to flow. Depending upon the relative magnitude of these accelerating and decelerating forces, the flow m...

In this chapter, we discuss a number of special topics, to which we apply concepts presented in the previous chapters. First, we discuss rating curve at a channel cross section during steady and unsteady flow conditions. Then, we describe different methods for flood routing. This is followed by a discussion of the aggradation and degradation of cha...

In the previous chapters, we discussed steady flow in open channels. However, the flow conditions in the real-life systems usually vary with time and thus the flows are unsteady. The unsteadiness may be due to natural processes, due to human actions, or due to accidents and incidents. The analysis of unsteady flows is usually more complex than that...

Liquids are transported from one location to another using natural or constructed conveyance structures. The cross section of these structures may be open or closed at the top. The structures with closed tops are referred to as closed conduits and those with the top open are called open channels. For example, tunnels and pipes are closed conduits w...

In Chapter 2, we called the depth at which the specific energy was minimum for a given discharge as the critical depth and the corresponding flow as the critical flow. In this chapter, we show that there may be more than one critical depth for a specified discharge in a compound channel. Critical flow has a number of special properties. We discuss...

In the previous chapters, we considered one-dimensional flows. However, the assumption of one-dimensional flow may not be valid in many situations — e.g., flow in a non-prismatic channel (i.e., channel with varying cross section and alignment), flow downstream of a partially breached dam, or lateral flow from a failed dyke. Although flow in these s...

In the last chapter, we discussed how to qualitatively sketch water-surface profiles in channels having gradually varied flows. For engineering applications, however, it is necessary to compute the flow conditions in these flows. These computations, generally referred to as water-surface profile calculations, determine the water-surface elevations...

In this chapter, we present a brief discussion on the flows in a channel connecting two reservoirs, air entrainment, flow through culverts, and flow measurement. Most of this discussion involves application of the material presented in the previous chapters.

Three conservation laws – conservation of mass, conservation of momentum, and conservation of energy– describe steady, free-surface flows. In this chapter, equations describing these laws are derived and their application for the analysis of these flows is demonstrated. For simplicity, only one-dimensional flows are considered in this chapter. In t...

Typical examples of natural and man-made open channels having rapidly varied flows are mountainous streams, rivers during periods of high floods, spillway chutes, conveyance channels, sewer systems, and outlet works. Unlike the case of gradually varied flows, a number of difficulties, such as the formation of roll waves, air entrainment, and cavita...

The streamlines in the uniform and gradually varied flows we considered in the previous chapters are either parallel or may be assumed as parallel. Therefore, the accelerations in these flows is negligible and the pressure distribution may be assumed as hydrostatic. The analyses in which the pressure distribution is hydrostatic is referred to as th...

In Chapter 4, we discussed uniform flowin which the flow depth remains constant with distance. Such flows occur only in long and prismatic channels(i.e., the channel cross section and bottom slope do not change with distance). In real-life projects, however, channel cross sections and bottom slopes are not constant with distance in natural channels...

Three conservation laws – mass, momentum, and energy – are used to describe open-channel flows. Two flow variables, such as the flow depth and velocity, or the flow depth and rate of discharge, are sufficient to define the flow conditions at a channel cross section. Therefore, two governing equations may be used to analyze a typical flow situation....