prelims engg hydro - mcgraw hill...

Introduction to the CourseHydrology is the science dealing with the occurrence and movement of water on, above, and below the surface of the earth. The movement of water is conveniently described through a hydrologic cycle, involving evaporation of water from water bodies, return of this water to the earth in form of rain, snow, etc., transfer of rain water as runoff to surface streams and infiltration to underground water, and finally, the movement of water from surface streams and underground water to the water bodies. This book deals with basic understanding of various processes of the hydrologic cycle, with emphasis on the engineering aspect, i.e., the application for management of water resources.

Target AudienceThe book is primarily designed for a first course in hydrology at the undergraduate level. However, the treatment of the subject matter is such that it may also be useful in a graduate level course. Scientists and engineers dealing with water resources may use this book to get a broader perspective and learn about recent developments, particularly in the areas of statistical analysis and measurement of hydrologic variables.

Objective of this BookSeveral books are already available on the subject with some emphasising the basic concepts, while others concentrating on problem-solving. Following the principle of science based engineering, we believe that the students should not only know how to apply a technique, but should also know how it has been arrived at, in order to better understand its limitations. The presentation of material in this book is made with emphasis on engineering applications of hydrology, with enough fundamental concepts interwoven in between for better understanding of the basic principles.

Salient Features ∑ Comprehensive coverage of the science of hydrology, incorporating the recent developments and

techniques ∑ Exclusive coverage on topics like statistical methods in hydrology, estimation of evaporation and

runoff, infiltration capacity models, and transient flow of groundwater, to help students develop a deeper understanding of the subject

∑ A dedicated chapter on measurement of hydrologic and climatic variables explaining the conventional and advanced methodologies, which has not been paid much attention in the existing books on hydrology

Preface

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xvi Preface

∑ Summary of important concepts for a quick review before exams∑ Over 680 chapter-end exercises and 76 solved examples to illustrate the underlying concepts and

help the students prepare for fi rst course in hydrology of their engineering degrees/diplomas and competitive examinations

∑ Online links to hydrological and meteorological databases to help students understand hydrological concepts and instructors to develop additional examples/questions

Learning Tools in the First Edition

3.1 INTRODUCTION

Although precipitation is an important part of the hydrologic cycle, as mentioned earlier, the topic of greater interest for engineers and hydrologists is the amount of water � owing in the rivers. If we could estimate how and how much water is being abstracted from the precipitation before it runs-off to the streams, we will have a tool to estimate the runoff from the precipitation records.

In this chapter, we will describe some of these abstractions in terms of their basic mechanism, factors affecting these, and their methods of estimation. The measurement techniques are described in greater details in Chapter 10.

3.2 ABSTRACTION PROCESSES

Let us consider a stream for which we want to study the � ow at asection O, as shown in Figure 3.1.

LO 1 Know about the various abstraction processes

and initial abstraction

Abstractions from Precipitation�

LO 1 Know about the various abstraction processes and initial abstraction

LO 2 Defi ne evaporation, factors affecting it, and the methods of estimation

LO 3 Estimate potential and actual evapotranspiration

LO 4 Discuss the infi ltration process and the infl uence of various factors on the rate of infi ltration

LO 5 Summarize empirical and theoretical methods for the estimation of infi ltration

L E A R N I N G O B J E C T I V E S

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Introduction 5

We hope that this book will either help the reader in answering these and many more similar questions, or will provide the background which would help in searching for the answers. The �rst step towards this goal is to understand the occurrence and movement of water, which is achieved through a simple but powerful concept of “Hydrologic Cycle.”

1.3 HYDROLOGIC CYCLE

The water present on, above, and below the earth’s surface could be thought of as constituting three big reservoirs: a surface reservoir (oceans and lakes), a subsurface reservoir (groundwater), and an atmospheric reservoir which comprises mainly water vapour. There is a nearly continuous movement of water from one reservoir to the other through various pathways, e.g., evaporation from the oceans transfers water from the surface reservoir to the atmospheric reservoir, precipitation transfers from the atmospheric reservoir to the surface reservoir, seepage from lakes transfers from the surface to the subsurface reservoir, seepage from coastal aquifers transfers from subsurface to surface reservoir, and so on. This cycle of storage and transfer is called Hydrologic Cycle or Water Cycle and can be depicted in several forms with varying degrees of details. One such description is given in Figure 1.1 as shown below:

Figure 1.1 The Hydrologic Cycle

We �rst look at the occurrence of water and then describe its movement. We also describe brie�y the factors affecting the components of the water cycle, so that we are able to make an informed choice about what is important and what is not, when we analyse the hydrologic data.

LO 3 Explain hydrologic cycle and its various

components

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Precipitation 25

2

existingdesired existing

desired

CVN N

CV (2.1)

The following example illustrates the procedure.

EXAMPLE 2.1

The annual precipitation at the four rain gauges is shown in the table below. Determine whether more stations are needed, if the desired CV is 20%.

Station S1 S2 S3 S4Annual Rainfall (mm) 830 1120 1000 650

SolutionThe mean of the station data for annual precipitation is obtained as 900 mm, and the standard deviation,

2 2 2 2

1(70 220 100 250 )

204.78 mm.3n The coef�cient of variation is, therefore, 0.228. Since it

is more than the desired CV of 0.2, we require more stations and the total number of stations, using Eq. (2.1),

is 2

0.2284 5.18.

0.2 We should provide two more stations.

Notes: If there is another station close to the boundary, but outside the catchment area, we may expect it to be climatically similar to other stations and should include it in the analysis, even though it lies in a different catchment. Also, we should keep in mind that this technique should be applied to long-term data, e.g., annual, which tends to average out the temporal and spatial variations in rainfall.

(ii) Based on the allowable error in the estimation of the mean We could view the observed station data as a “sample” drawn from a large “population” of possible stations located in and around the catchment area and then estimate how close is the sample mean to the true value, i.e., the population mean (more details about sample and population characteristics are provided in Section 9.2). In statistical terms, we measure this closeness by the standard error of the mean, defined as the standard deviation of the estimates of the

population mean through sample means, and given by ,SEn

where is the sample standard deviation

and n is the sample size. A relative standard error, RSE, is defined as the ratio of the SE and the mean, and we could stipulate that the station density is adequate if RSE is below, say, 10%. Assuming that addition of stations does not significantly change the standard deviation, the number of stations required to achieve a desired RSE is given by

N =

2

desired

CV

RSE (2.2)

If this number comes out to be less than or equal to the number of existing stations n, the network density is adequate, otherwise we need to add N − n stations (obviously, N − n is rounded up to the next higher

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each chapter is organized into multiple learning objectives (LOs). The topics covered in the chapter closely follow these objectives with each section listing the relevant objective. This feature of tagging each section with respective learning objective will help the instructors to plan the structure of course. The tagged LO brings out the essence of every section before the readers.

Learning Objectives

Illustrations and Diagrams

it is quite essential for a book to present fi gures to keep the interests of the users, and hence liberal use of fi gures is made in the book to aid in understanding of basic concepts.

The book contains 76 solved examples for better understanding and application of concepts. Solved example problems also help in explaining new concepts and illustrate the working of computational procedure.

Worked-Out Examples


Preface xvii

16 Engineering Hydrology

1.5 There are several resources available online for � nding out the precipitation and evaporation at any place (some links are provided in Chapter 10). Obtain the record of daily precipitation and actual or potential evaporation for the previous year at a station near you, plot the data, and compute the total annual precipitation and evaporation.

1.6 Stream� ow data may also available for a river near your area. If so, plot the precipitation versus stream� ow and see whether there is any relationship between these.

1. Maps of average annual precipitation (a) India: commons.wikimedia.org/wiki/File:India_annual_rainfall_map_en.svg,

www.mapsofi ndia.com/maps/india/annualrainfall.htm (b) US: www.wrcc.dri.edu/pcpn/us_precip.gif (c) Global: www.whymap.org/whymap/EN/Downloads/Additional_global_maps/precipitation_pdf,

www.britannica.com/science/climate-meteorology/World-distribution-of-precipitation

2. Maps of evaporation/evapotranspiration (a) India : nihroorkee.gov.in/rbis/india_information/evaporation.htm (b) US: www.extension.purdue.edu/extmedia/nch/nch-40.html, (c) Global: nelson.wisc.edu/sage/data-and-models/atlas/maps/pevapotrans/atl_pevapotrans.jpg,

www.waterandclimatechange.eu/evaporation/average-monthly-1985-1999

3. Map of global surface runoff

atlas.gwsp.org/atlas/img/map/a3_runoffWSAG1_0_wl.png, wwap.cesr.de/results.htm#map1

4. Map of global groundwater recharge

www.whymap.org/whymap/EN/Downloads/Additional_global_maps/gw_recharge_pdf

5. Hydrologic cycle and its components

scied.ucar.edu/longcontent/water-cycle

100-year-� ood: The � ood which is expected to occur, on an average, once in 100 years.

Aquifer: A soil formation which can store enough water and can transmit it at a reasonably fast rate.

Artesian well: A well from which water � ows out without pumping, due to the large pressure under which water is stored in the soil.

Base � ow: The � ow in a stream which comes from the seepage of water from the adjacent soil.

Catchment: The area which catches the rain falling over it and carries it to a stream.

Con� ned aquifer: A completely saturated aquifer bounded by impermeable layers on top and bottom and, therefore, carrying water under pressure.

Depression storage: The capacity of an area to store water in pits and depressions on the land surface.

Evaporation: The process by which liquid water changes into water vapour.

*A very brief and general de� nition is given here. More speci� c descriptions are provided in the relevant chapters.

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(b) US: www.wrcc.dri.edu/pcpn/us_precip.gif (c) Global: www.whymap.org/whymap/EN/Downloads/Additional_global_maps/precipitation_pdf,

www.britannica.com/science/climate-meteorology/World-distribution-of-precipitation

Maps of evaporation/evapotranspiration (a) India : nihroorkee.gov.in/rbis/india_information/evaporation.htm (b) US: www.extension.purdue.edu/extmedia/nch/nch-40.html, (c) Global: nelson.wisc.edu/sage/data-and-models/atlas/maps/pevapotrans/atl_pevapotrans.jpg,

www.waterandclimatechange.eu/evaporation/average-monthly-1985-1999

Map of global surface runoff

atlas.gwsp.org/atlas/img/map/a3_runoffWSAG1_0_wl.png, wwap.cesr.de/results.htm#map1

Map of global groundwater recharge

www.whymap.org/whymap/EN/Downloads/Additional_global_maps/gw_recharge_pdf

Hydrologic cycle and its components

scied.ucar.edu/longcontent/water-cycle

Hydrograph Routing 207

6.5 IUH DEVELOPMENT

In the previous chapter, we learnt the concept of Instantaneous Unit Hydrographs (IUHs). An IUH is a hypothetical concept describing the DRH response from a catchment when it is subjected to 1 cm of effective rainfall (ER) instantaneously and uniformly over the catchment. There are several catchment simulation models that have been developed to model this complex rainfall-runoff process. These catchment simulation models employ the concepts of hydrograph routing that we learnt in this chapter. In this section, we will learn about the two important conceptual models for IUH development using routing methods.

The transformation of rainfall into runoff is an extremely complex, nonlinear, and dynamic process that is dif�cult to understand and model. The two major steps involved in the transformation of rainfall into runoff are: (i) calculation of in�ltration and other losses and estimation of the effective rainfall, and (ii) subsequent transformation of the effective rainfall into runoff hydrograph through an operator, which simulates the behavior of the catchment. As rain falls on the catchment, some of it gets trapped in depressions

LO 5 Summarize instan-taneous unit hydrograph

development using routing concepts

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where, P is the average depth of precipitation (usually in mm) over an area A (usually in km2) for a d-hour storm (d is not directly included in the equation, but the parameters K and n are functions of d, in addition to being dependent on the general climate of the area under consideration. As an example, for North India, for a 48-hour storm, K is about 0.001 and n is about 0.63). Clearly, P0 in this equation signi� es the precipitation depth for a zero area, implying that it corresponds to the storm centre. We could use the rainfall depth at the station with maximum precipitation as P0. However, since the storm centre does not normally coincide with a station, it is customary to obtain P0 by assuming that the station value, Ps, corresponds to an area of25 km2, and then using the exponential equation with known values of P (=Ps), A (=25) and the given values of K and n.

Precipitation is the driving force behind the run-off and, in general, higher precipitation would lead to larger run-off. However, it is not always true since the abstractions from precipitation, in the form of in� ltration, evaporation, etc., may be different for the same amount of precipitation, depending on the atmospheric and soil conditions. Therefore, in the next chapter we describe various processes which abstract water from the precipitation and look at their measurement, estimation, and analysis.

SUMMARYPresence of water and condensation nuclei in the atmosphere is required for the formation of clouds and, for precipitation to take place, a cooling mechanism is needed. The cooling may occur due to orographic, convective, frontal, or cyclonic mechanisms, and results in precipitation in any of its various forms, such as rain, snow, or hail. The severity of precipitation is expressed either in terms of its intensity, generally in mm/h, or the depth, generally over the period of a day. The variation of intensity with time is shown by a hyetograph and the variation of the depth with time is shown either through a histogram (showing daily precipitation depths) or a mass curve (showing cumulative depths). The measurement of precipitation is done by recording rain gauges, which maintain a continuous record, or non-recording gauges, which provide only the daily precipitation depths. Any missing values in a precipitation record may be estimated by utilizing the precipitation records at nearby stations. The normal ratio method, inverse distance method, quadrant method, or more advanced techniques like Kriging, may be used for this purpose. To check if the data is consistent with the general climatic conditions, a double mass curve analysis is performed. This technique also provides a method to correct the data, if found to be inconsistent. The point rainfall data measured at a rain gauge is processed to obtain meaningful quantities related to catchment area, by using the arithmetic mean method, the Thiessen polygon method, or the isohyetal method. The isohyetal method is likely to be the most accurate method of estimating the average rainfall over an area, but the arithmetic mean method is the simplest and may provide reasonably accurate estimates for some catchments. The temporal variation of precipitation during an event could be analyzed using the intensity-duration curve (or the depth-duration curve), which shows the variation of the maximum intensity (or depth) observed over different durations of the precipitation event. The spatial variation of precipitation for an event is represented by a depth-area-duration curve, which shows the relation between the area analyzed and the corresponding average precipitation depth for various storm durations. Most of the depth-area-duration curves could be represented by an exponential relationship, with empirical coeffi cients varying from one region to the other.

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There are several conceptual methods for developing an instantaneous unit hydrograph from a catchment using the concept of attenuation and delay in a catchment. In Clarks’ method for conceptual IUH development, unit effective rainfall is applied to a time area diagram of the catchment fi rst to impart pure translation effects using a linear channel element. Then the translated output from the linear channel element is routed through a linear reservoir element to impart attenuation effects and calculate the IUH. On the other hand, the Nash’s method of IUH development is based on simulating the catchment using n identical linear reservoirs and passing the input through this series of reservoirs to calculate the output from the last reservoir as the IUH.

OBJECTIVE-TYPE QUESTIONS

6.1 The factors affecting the size, shape, and other characteristics of an in� ow hydrograph while traveling through a channel reach include

(a) Storage in the river reach (b) Resistance to fl ow due to friction from sides and bed (c) Lateral addition or subtraction of fl ow within the reach (d) All of the above

6.2 Hydrograph routing is important in (a) Flood forecasting and fl ood control (b) Design of reservoirs and spillways (c) Catchment simulation studies (d) All of the above

6.3 Which of the following statements is/are true for hydrograph routing? I. Hydraulic routing uses law of conservation of mass only. II. Hydrologic routing uses both law of conservation of mass and momentum. III. Spatio-temporal variations in an infl ow hydrograph are non-existent as it travels through a river reach or

a reservoir. (a) I only (b) II only (c) III only (d) I and II (e) I and III (f) II and III (g) I, II, and III (h) All three statements are false

6.4 Which of the following statements is true for hydrograph routing? (a) Hydrologic routing is more complex than hydraulic routing (b) Hydraulic routing is more complex than hydrologic routing (c) Both are of same diffi culty (d) Insuffi cient information to comment

6.5 Which of the following statements is/are true for hydrograph routing? I. Hydraulic routing is more accurate than hydrologic routing. II. Hydraulic routing is very useful in developing conceptual unit hydrographs in an ungauged catchment. III. Hydrologic routing is employed by NOAA in their fl ood warning system. (b) I only (b) II only (c) III only (d) I and II (e) I and III (f) II and III (g) I, II, and III (h) All three statements are false

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(a) 1 cm/h (b) 10,000 m3/h (c) 2.78 m3/s (d) All of the above (e) None of the (a), (b), and (c) (f) Insuffi cient data

6.72 The out� ow from the � rst linear reservoir in Nash’s method is

(a) /1

1 t KQ e

K (b) /

1t KQ Ke

(c) /1

1 t KQ e

K(d) /

1t KQ Ke

6.73 The number of linear reservoirs for modeling the rainfall-runoff relationship in a catchment was found to be 3.56. The value of (n) is

(a) 0.88964 (b) 2.2778 (c) 3.5529 (d) Insuffi cient data

6.74 If (1.2) = 0.9182, what is the value of (2.2)? (a) 1.2/0.9182 (b) 1.2 × 0.9182 (c) 2.2 × 0.9182 (d) 2.2/0.9182

DESCRIPTIVE QUESTIONS

6.1 Why do the size, shape, and characteristics of an in� ow hydrograph change when it travels through a channel reach?

6.2 Explain the hydraulic and hydrologic methods for hydrograph routing with the help of equations.

6.3 Explain the Modi� ed Puls method of hydrologic routing.

6.4 Explain the Goodrich’s method of hydrologic routing.

6.5 Explain the fourth order SRK method of hydrologic routing.

6.6 For hydrograph routing through a reservoir, prove that the peak of the out� ow hydrograph intersects in� ow hydrograph. (Hint: use continuity equation).

6.7 Discuss the importance of hydrograph routing in � ood management with special emphasis on attenuationand lag effects.

6.8 Search through the internet and prepare a summary of the capabilities and applications of following computer software for hydrograph routing: HEC-RAS, MIKE FLOOD, FLDWAV, FLOW-2D, TUFLOW, and DWOPER.

6.9 Describe the concepts of prism and wedge storages in a channel when a � ood wave passes through it. Use neat sketches to answer.

6.10 What do you understand by a time-area diagram? Explain with the help of sketches. How is it useful in hydrology?

6.11 Describe the Clark’s method for IUH development in a catchment.

6.12 Describe the Nash’s method for IUH development in a catchment.

NUMERICAL QUESTIONS

6.1 The storage, out� ow discharge, and elevation data for a reservoir are given in the following table. The spillway crest of the outlet structure is at an elevation of 180.2 m.

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effects.

Search through the internet and prepare a summary of the capabilities and applications of following computer software for hydrograph routing: HEC-RAS, MIKE FLOOD, FLDWAV, FLOW-2D, TUFLOW, and DWOPER.

Describe the concepts of prism and wedge storages in a channel when a � ood wave passes through it. Use neat sketches to answer.

What do you understand by a time-area diagram? Explain with the help of sketches. How is it useful in

Groundwater 285

7.6 Describe the con� ned and uncon� ned aquifers. Under what conditions will a well tapping a con� ned aquifer � ow by itself, i.e., without any pumping?

7.7 When would you expect upward leakage in a leaky aquifer?

7.8 What are the Dupuit’s assumptions? How are they useful in analyzing groundwater � ow?

7.9 Differentiate between storage coef� cient and speci� c storage. What is meant by diffusivity of a con� ned aquifer?

7.10 For a con� ned aquifer, which � uid/formation properties affect the storage coef� cient? What is the typical value of water compressibility?

7.11 In steady � ow towards a pumping well in a con� ned aquifer, why is the hydraulic gradient inversely proportional to the radial distance from the well?

7.12 Write the integral expression for the well function and obtain the series expression for it using term-by-term integration.

7.13 What is meant by the recovery of a drawdown? How will you obtain a drawdown at any time after the stoppage of pumping?

7.14 Derive an expression for the critical recharge rate which would cause a water divide for a steady one-dimensional � ow in an uncon� ned aquifer between two water bodies.

7.15 What is meant by formation loss and well loss? How does the speci� c capacity of a well change with time and with pumping rate?

7.16 Describe the method of obtaining the groundwater � ow direction using the data from three piezometers in an uncon� ned aquifer.

7.17 Explain the Theis type curve matching technique for obtaining aquifer parameters.

NUMERICAL QUESTIONS

7.1 Water � ows through a 2 m long horizontal soil column at a constant velocity. At a section of the tube, a red dye was inserted and it was observed that it travelled a distance of 1 m in 235 seconds and the dispersion was negligible. The soil is sandy with a porosity of 0.42 and hydraulic conductivity of 1 cm/s. What would be the drop in piezometric head across the column length?

7.2 A 50 m thick con� ned aquifer has a porosity of 0.35. The formation compressibility is 5 × 10−8 Pa–1 and water compressibility is 1 × 10−10 Pa–1. Estimate the storage coef� cient and the speci� c storage of the aquifer.

7.3 Two large lakes are connected by a 200 m long con� ned aquifer in such a way that one-dimensional � ow assumption is valid. The difference in water level of the lakes is 2.5 m and it is estimated that water is being conveyed through the aquifer at a rate of 1 m3/min per meter width. Estimate the transmissivity of the aquifer.

7.4 A fully-screened well is pumping a con� ned aquifer at a constant rate of 1 m3/s. A prior pump test on the aquifer has provided an estimate of the transmissivity as 0.05 m2/s. Two observation wells are located at a distance of 50 m and 100 m, respectively, from the pumping well. After a long time of pumping, the water levels in the observation wells achieve a nearly constant value. If the piezometric level in the � rst well (at 50 m) is 120 m above mean sea level, what would be the level in the other well?

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More than 680 chapter-end exercises have been carefully constructed to enhance knowledge. These are categorized into Objective-Type Questions, Descriptive Questions, and numerical Questions, to enable the students evaluate their understanding of different concepts after end of each chapter. answers to the Objective-type Questions are provided at the end of the book.

Chapter-End Exercises

Use of Technologyin bringing out this book, we have taken advantage of recent technological developments to create a wealth of useful information to be supplemented with the physical book. Considering the ease of internet access at most engineering institutes, useful links to literature and datasets have been provided throughout the book. Moreover, excel based solutions are incorporated in the book.

a detailed chapter-end summary is provided for a quick review of the important concepts. it helps in recapitulating the ideas initiated with the outcomes achieved.

Summary


xviii Preface

Approach Adopted in this Book The presentation of material in this book is made with an emphasis on engineering applications of hydrology with just enough fundamental concepts interwoven in between for better understanding of the basic principles. From an engineering viewpoint, it is the runoff component of the hydrologic cycle which is the most important and, therefore, it is only natural that this component is discussed in greater details than other components. In fact, the objective of nearly all hydrological exercises by engineers boils down to the prediction of peak flows or low flows in a stream or the amount of water available as groundwater. One could then question the utility of studying other parts of the hydrologic cycle, such as evaporation and infiltration. Due to the rapidly changing stream characteristics, in order to draw some logical conclusions about its behavior, one must have data about the streamflow covering a long period. However, the length of record of streamflow and the reliability of this data is generally not adequate. On the other hand, rainfall and other climatic data are available to us for a much longer period and are more reliable, partly because of their direct effect on our daily lives and partly because their measurement requires very little skill or training. Therefore, it is quite common to develop a relationship between rainfall and runoff for the area under consideration and then estimate the runoff on the basis of longer duration and more reliable rainfall record. The rainfall-runoff relationship will be affected by several factors which influence the evaporation, infiltration, and other losses from the precipitation.

Organization of the BookKeeping in mind these points, this book is divided into ten chapters. The chapters are organized as follows:

• Chapter 1 introduces the subject and the motivations for studying it. Chapter 2 deals with precipitation of atmospheric water onto the earth surface with emphasis on various aspects of data collection, presentation, and analysis. The measurement techniques are described very briefly since we find it more convenient to describe the measurement of all hydrologic variables together in the final chapter.

• Chapter 3 describes various abstractions from precipitation before it runs off to the surface streams. These abstractions include interception, depression storage, evaporation and infiltration. Stress is placed on discussion of various factors affecting these abstractions and their estimation, so as to enable an engineer to derive a logical rainfall-runoff relationship.

• Chapters 4, 5, and 6 deal with the runoff component, with Chapter 4 introducing the processes of its generation, its measurement and estimation, and the analysis of data for use in the design and operation of water systems. Chapter 5 emphasizes hydrograph analysis for estimation of runoff. It introduces the concepts of unit hydrograph, its components and estimation, S-hydrograph, instantaneous unit hydrograph, inter-relationships among them, and their application in design and operation of water systems. Chapter 6 discusses the movement of runoff water through a stream or a reservoir and how the concepts of hydrograph routing can be useful in the hydrologic design and flood control studies.

• The subsurface reservoir of groundwater, movement of water within it, and its recharge andwithdrawals are described in Chapter 7, which effectively ends with the discussion of hydrologic cycle and water supply.


Preface xix

• Chapter 8 then describes an aspect of water demand, related to irrigation, and application of the hydrological principles for better management of water resources of an area. Since hydrological variables vary widely in space and time, there is always an inherent uncertainty in the analysis of these variables. Any prediction we make, based on the available data and our understanding of the hydrological principles, will, therefore, not be precise.

• Chapter 9 describes several statistical techniques to not only estimate the desired quantities but to also assign a degree of uncertainty to those. Estimation of flood magnitudes and their probability is an important component of this analysis.

• Finally, asmentioned before, since the issues involvedwithmeasurement ofmost hydrologicalvariables are similar, we have clubbed all measurement techniques in Chapter 10. Particular attention is given to more recent techniques based on remote-sensing of the data, as it is expected to become more common in future.

• References have been provided at the end of the book and an effort has been made to include freely accessible online references, wherever possible, rather than printed books or research papers.

Online Learning Center SupplementsThere are a number of supplementary resources available on the book’s website:http://www.mhhe.com/srivastava_jain/eh

For Instructors � • Solutions Manual

For Students � • Web links for further readings

AcknowledgementsRajesh Srivastava thanks his parents, Mrs. G. K. Srivastava and Late Dr. A. C. Srivastava, for their encouragement, wife, Jayshree, for her understanding and support, and children, Soumya and Tanu, for their delightful presence. Ashu Jain would like to express his deep sense of appreciation to his father, Late Dr. P. C. Jain, for being a constant source of inspiration not only for writing this book but for pursuing academics throughout his life. He is grateful to his mother, Mrs. Swarn Lata Jain, wife, Savita, and children, Ateendriya and Tarushi, for their support, tolerance, and understanding throughout the time spent on writing this book. He would also like to thank all other friends, relatives, and colleagues, who have helped in some form or the other. One learns so much while teaching and the acknowledgement cannot be complete without thanking all the students, teaching whom we learn the nuances of the subject matter, and for their inquisitiveness urging a teacher to delve deep into the subject matter.

The authors would also like to thank the team members of McGraw Hill Education (India), especially Vibha Mahajan, Shalini Jha, Hemant Jha, Vaishali Thapliyal, Sachin Kumar, Satinder Singh Baveja, Anuj Kr. Shriwastava and Taranpreet Kaur who handled various responsibilities related to the book very patiently and effectively.


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