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About this book

Covering all the fundamental topics in hydraulics and hydrology, this textbook is an accessible, thorough and trusted introduction to the subject. The text builds confidence by encouraging readers to work through examples, try simple experiments and continually test their own understanding as the book progresses. This hands-on approach aims to show students just how interesting hydraulics and hydrology is, as well as providing an invaluable reference resource for practising engineers. There are numerous worked examples, self-test and revision questions to help students solve problems and avoid mistakes, and a question and answer feature to keep students thinking and engaging with the text.

The text is essential reading for undergraduates from pre-degree through all undergraduate level courses and for practising engineers around the world.

Table of Contents

Chapter 1. Introduction

Abstract
This chapter introduces some of the fundamental quantities involved in hydraulics, such as pressure, weight, force, mass density and relative density. It then considers the variation of pressure intensity with depth below the surface of a static liquid, and shows how the force on a submerged surface or body can be calculated. The principles outlined are used to calculate the hydrostatic forces on dams and lock gates, for example. These same principles are applied in Chapter 2 in connection with pressure measurement using piezometers and manometers, and in Chapter 3 to the analysis of floating bodies. Thus the sort of questions that are answered in this chapter are:
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Chapter 2. Pressure measurement

Abstract
It may be necessary to measure the pressure of a liquid for operational reasons, such as to monitor the distribution and supply of water, or to enable the discharge in a pipeline to be calculated. Whatever the reason, piezometers and manometers can be used for this purpose. The basis of these devices is the pressure–depth relationship that exists in a static liquid, and the principles described in the last chapter. The type of questions that are answered in this chapter include:
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Chapter 3. Stability of a floating body

Abstract
There are many situations where civil engineers have to work from barges and pontoons floating on water, rather than from dry land. A typical example could be building a bridge across a wide river or estuary, where the girders forming the structure have to be floated out on barges and then lifted into position using floating cranes. Another example could be the construction of a marina or jetty in the sea. In these situations all of the construction activity may have to take place from floating barges and pontoons. Therefore it is essential that an engineer has an understanding of whether or not a pontoon will float or sink, and whether or not it is stable. The alternative to it being stable is being unstable, so that if a piece of construction plant moves across the deck the whole pontoon capsizes, tipping everything and everyone into the water. This would be extremely dangerous and very expensive and, of course, must be avoided at all costs. Hence the need to know something about how and why bodies float, and what makes them stable or unstable. The latter involves the position of the metacentre with respect to the centre of gravity of the floating body. Thus the sort of questions that are raised in this chapter are:
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Chapter 4. Fluids in motion

Abstract
It is a gross oversimplification, but it is often said that there are only three equations in hydraulics: the continuity equation, the momentum equation and the energy equation. However, it is true that an awful lot of problems can be solved using only these equations, and they hold the key to many of the topics that follow later in the book. Therefore it is important to have a sound understanding of what they represent and how they are used. This chapter introduces the three equations and the basic principles required to understand and analyse what is happening in a system involving a moving liquid. The sort of questions that are answered include:
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Chapter 5. Flow measurement

Abstract
This chapter describes how the flow or discharge of a stream of liquid in a pipe or open channel can be measured using a variety of devices such as a Venturi meter, Pitot tube, orifice, sharp crested weir and velocity meter. The characteristics of each device, its advantages and disadvantages, and situations where it may be used are described. The theoretical discharge equations are derived, but because they ignore effects like viscosity, friction and turbulence, they have to be used with experimentally determined coefficients of discharge in order to obtain an accurate estimate of the flow rate. The definition and evaluation of these coefficients is fully described. The information presented enables questions like those below to be answered:
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Chapter 6. Flow through pipelines

Abstract
Much of Britain’s water supply is obtained from rainfall that has been collected in upland reservoirs and then piped to the consumer via a treatment works. Thus flow through pipelines is an important part of hydraulics. These pipelines flow full under pressure, and are analysed by applying the energy equation. This is a totally different approach from the analysis of gravity flow in open channels, such as rivers and partially full sewers where there is a free water surface at atmospheric pressure (see Chapter 8). This chapter begins by revising the concept of head and the application of the energy equation to situations involving a significant loss of energy. The energy equation is then used to calculate the flow rate when, for example, a reservoir discharges to the atmosphere through a long pipeline. The analysis of the flow between two reservoirs, flow in branching pipelines and flow in two or more parallel pipelines is then outlined.
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Chapter 7. Flow under a varying head – time required to empty a reservoir

Abstract
A problem sometimes faced by engineers is calculating the time required to empty a reservoir. This may be a purpose-built flood storage reservoir located upstream of a town or city to store excess riverflow during a storm, and then discharge it safely back to the river channel after the flood has subsided. It is important that the reservoir empties as quickly as possible, because if another flood occurs while the reservoir is still full the flow cannot be stored and flooding will occur downstream. So, when designing the dam it is important to know how long it takes for the reservoir to empty; if it is too long the spillway or outlet must be made larger. Alternatively, the problem may involve a water supply reservoir that has been damaged by either natural causes or terrorist action, as happened in the former Yugoslavia in 1993. Whether or not the dam will collapse may depend upon how quickly the hydrostatic force on it can be reduced, that is the time to empty the reservoir. On a more modest scale, the problem could involve the time taken to empty an oil storage tank or a water distribution reservoir. In the laboratory, by measuring the time required to empty a tank it is possible to calculate the coefficient of discharge of, say, an orifice. Therefore the sort of questions answered in this chapter include:
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Chapter 8. Flow in open channels

Abstract
A significant part of Civil Engineering is that concerned with land drainage, much of which involves flow in open channels. These channels are very common: rivers, canals, pipes flowing partially full and irrigation ditches are all examples. Consequently it is very important that a channel can be designed to carry a particular discharge or, alternatively, that the discharge in a channel can be calculated from measurements of the bed slope, the width and the depth of flow.The flow in open channels can be subcritical or supercritical, with critical depth representing the boundary between the two. The difference between these types of flow must be understood, otherwise an incorrect analysis will be conducted.
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Chapter 9. Hydraulic structures

Abstract
Hydraulic structures include dams, which store water for water supply, and sluice gates which are used to control the discharge in rivers and to alleviate flooding. Bridges and culverts, which carry roads and railways over rivers, are very numerous examples of hydraulic structures; few roads are constructed without them. Knowledge and skill are needed to design a hydraulically efficient bridge or culvert that has a waterway of an appropriate size, does not cause upstream flooding, and is unlikely to be damaged by floods. Concrete weirs are used to measure the discharge of a river. They are designed to operate with critical depth on the crest, and illustrate the use of the principles outlined in Chapter 8. Thus some of the questions answered in this chapter include:
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Chapter 10. Dimensional analysis and hydraulic models

Abstract
This chapter explores the difference between units and dimensions. It then shows how the analysis of dimensions can be used to derive the equations that govern hydraulic phenomena. In some cases it is possible to obtain dimensionless groupings of variables, such as the Reynolds and Froude numbers, that have a particular hydraulic significance. Since such groupings are dimensionless, they do not change with the size or scale of the hydraulic system concerned. This leads to the concept of hydraulic models, where scaled-down versions of a system are used to predict the performance of the real thing. Examples include the analysis of the head-discharge characteristics of unusually shaped weirs, as mentioned in the last chapter, and the determination of the equations and performance characteristics of pumps and turbines, as described in the next chapter. Thus dimensional analysis is a powerful and useful tool that can be used to investigate and obtain solutions to real problems. The questions answered include:
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Chapter 11. Turbines and pumps

Abstract
This chapter starts by considering the difference between positive displacement and rotodynamic machines, the difference between impulse and reaction turbines, and the general definition of efficiency and power. It then uses the momentum equation to obtain the force exerted by a jet of water when it hits a stationary or moving vane, such as the bucket of a Pelton wheel. The Pelton wheel is an impulse turbine suitable for sites with large heads of water. Other types of turbine, such as reaction turbines, are then considered, and their performance discussed. Some pumps can be thought of as turbines operating in reverse, and there are many pumped-storage schemes where water is pumped into storage reservoirs during off-peak periods, then allowed to flow through the same machines (now operating in reverse) to generate electricity when it is required. The performance characteristics of various types of pump are outlined, and what happens when two or more pumps are used in series or in parallel. How to match a pump to a rising main (delivery pipe) is then considered, as well as some common operational problems. This chapter answers such questions as:
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Chapter 12. Introduction to engineering hydrology

Abstract
Hydrology involves the movement of water (in all its forms) over, on and through the Earth. Engineering hydrology encompasses subjects such as rainfall, riverflow, groundwater, water supply, flood estimation and forecasting, flood alleviation, the design of storm water sewers, and a host of other things. Everyone needs a continuous supply of fresh water, and expects adequate protection from flooding. These things can literally be a matter of life and death. This became all too apparent in 2000 when the wettest autumn on record resulted in severe and prolonged flooding over large areas of England, the damage to property and agriculture amounting to around £1 billion. It was estimated that in the UK as many as five million people may be at risk from flooding. Many properties can no longer be insured because they flood too frequently. Some blamed global warming for the extreme weather. It is far too early to be sure, but recent years have been the warmest on record in England and the warmest in the northern hemisphere for a millennium. Global warming could make extreme events more common. By 2025, two-thirds of the world’s population could experience water shortages, often referred to as ‘water stress’ (Head, 2009).
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Chapter 13. Applications of engineering hydrology

Abstract
Chapter 12 presented the basic knowledge and principles required to understand the applications outlined in this chapter. Here we consider how to evaluate and solve some of the problems that are commonly encountered in engineering hydrology. This includes a simple, introductory guide to the Flood Estimation Handbook (FEH), which can be used to obtain the magnitude and frequency of occurrence of flood events. Given the possibility that global warming may result in damaging floods occurring more often, this is an important and very relevant topic. According to the Centre for Ecology and Hydrology, as a result of climate change the cost of providing the present levels of flood protection may increase fourfold over the next 50 years. The measures that can be adopted to try to control or alleviate flooding are also discussed. In urban areas, flooding is prevented by surface water sewers, and a simple design method is introduced.
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Chapter 14. Sustainable Drainage Systems (SUDS)

Abstract
Sustainable drainage aims to avoid problems with flooding and pollution by controlling the quantity and quality of surface runoff at source using ‘soft’ engineered systems that copy nature. Thus interception, infiltration, evapotranspiration and storage at source are encouraged; natural wetlands and floodplains are valued for their amenity and biodiversity potential (Woods-Ballard et al., 2007). Rapidly piping water from ever-expanding artificial, impermeable surfaces straight to rivers becomes a last resort, because it is unsustainable, makes flooding worse and alters the natural state of rivers and groundwater. This became all too apparent in England in 2007 when there was widespread, disruptive surface water and sewer flooding of urban areas (see section 13.4).
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