Introduction to Hydrology PDF
Preview Introduction to Hydrology
Contents PREFACE xiii PART ONE THE HYDROLOGIC CYCLE CHAPTER 1 lntroduction 1 . 1 t.2 r.3 t.4 1.5 1.6 I.7 1.8 CHAPTER 2 Precipitation 2.1 2.2 2.3 2,4 2.5 2.6 2.7 Hydrology Defined 3 A Brief History 3 The Hydrologic Cycle 5 The Hydrologic Budget 5 Hydrologic Models 11 Hydrologic Data 11 Common Units of Measurement 12 Application of Hydrology to Environmental Problems t2 1 5 Water Vapor 15 Precipitation 17 Distribution of the Precipitation Input Point Precipitation 27 Areal Precipitation 29 Probable Maximum Precipitation 34 Gross and Net PreciPitation 36 vi coNTENTS CHAPTER 3 Interception and Depression Storage 40 3.1 Interception 40 3.2 Throughfall 44 3.3 Depression Storage 45 CHAPTER 4 Infiltration 52 4.I Measuring Infiltration 53 4.2 Calculation of Infiltration 53 4.3 Horton's Infiltration Model 57 4.4 Green-AMPT Model 64 4.5 Huggins-Monke Model 67 4.6 Holtan Model 68 4.7 Recovery of Infiltration Capacity 69 4.8 Temporal and Spatial Variability of Infiltration Capacity 70 4.9 SCS Runoff Curve Number Procedure 73 4.10 @ Index 76 CHAPTER 5 Evaporation and Transportation 82 " 5.1 Evaporation 86 5.2 Estimating Evaporation 86 5.3 Evaporation Control 95 5.4 Transpiration 95 5.5 Transpiration Control 100 5.6 Evapotranspiration 100 5.7 Estimating Evapotranspiration 103 CHAPTER 6 Streamflow 11 1 6.1 Drainage Basin Effects 111 6.2 The Hydrograph 11,2 6.3 Units of Measurement for Streamflow 113 6.4 Measuring and Recording Streamflow 113 6.5 Measurements of Depth and Cross-Sectional Area II4 6.6 Measurement of Velocity lI4 6.7 Relating Point Velocity to Cross-Sectional Flow Velocity 115 6.8 The Slope-Area Method for Determining Discharge II7 oONTENTS Vii PART TWO HYDROLOGIG fT'IEASUREMENTS AND MONITORING CHAPTER 7 Hydrologic Data Sources 123 7.1 General Climatological Data I23 7.2 Precipitation Data 123 7.3 Streamflow Data 124 7.4 Evaporation and Transpiration Data I24 CHAPTER 8 f nstrumentation 126 8.1 Introduction 126 8.2 HYdrologic Instruments 127 8.3 Telemetry SYstems 135 8.4 Remote Sensing 135 CHAPTER 9 Monitoring Networks 144 121 9.r 9.2 9.3 9.4 The Purpose of Monitorin g 144 Special Considerations I45 Uie of ComPuters in Monitoring I47 Hydrological-Meteorlogical Networks 147 PART THREE SURFACE WATER HYDROLOGY 151 CHAPTER 1O Runoff and the Catchnient 153 10.1 Catchments, Watersheds, and Drainage Basins tO.2 Basin Characteristics Affecting Runoff 155 10.3 RudimentaryPrecipitation-RunoffRelationships IO.4 Streamflow Frequency Analysis 166 10.5 StreamflQw Forecasting 168 CHAPTER 1 1 Hydrographs 171 11.1 Streamflow HYdrograPhs 171 Il.2 Factors Affecting Hydrograph Shape 172 11.3 HydrograPh ComPonents 174 153 164 viii ooNTENTS lI.4 Base Flow Separation I77 11.5 Hydrograph Time Relationships 181 11.6 Time of Concentration I82 Il.7 Basin Lae Time I82 CHAPTER 12 Unit Hydrographs 188 l2.I Unit Hydrograph Definition 188 12.2 Derivation of Unit Hydrographs from Streamflow Data 190 12.3 Unit Hydrograph Applications by Lagging Methods I94 12.4 S-Hydrograph Method 198 12.5 The Instantaneous Unit Hydrograph 201 12.6 Synthetic Unit Hydrographs 205 CHAPTER 13 Hydrograph Routing 234 13.1 Hydrologic River Routing 235 13.2 Hydrologic Reservoir Routing 245 13.3 Hydraulic River Routing 248 CHAPTER 14 Snow Hydrology 265 I4.l Introduction 265 I4.2 Snow Accumulation and Runoff 267 I4.3 Snow Measurements and Surveys 268 I4.4 Point and Areal Snow Characteristics 269 14.5 The Snowmelt Process 271. 14.6 Snowmelt Runoff Determinations 284 CHAPTER 15 Urban and Small Watershed Hydrology 309 15.1 Introduction 309 15.2 Peak Flow Formulas for Urban Watersheds 311 i5.3 Peak Flow Formulas for Small Rural Watersheds 33I 15.4 Runoff Effects of Urbanization 344 CHAPTER 16 Hydrologic Design 359 16.l Hydrologic Design Procedures 360 16.2 Data for Hydrologic Design 363 CONTENTS IX 16.3 16.4 16.5 t6.6 16.7 16.8 1 8 . 1 t8.2 18.3 18.4 18.5 18.6 r8.7 18.8 18.9 1 8 . 1 0 1 8 . 1 1 18.t2 Hydrologic Design-Frequency Criteria Design Storms 373 Critical Event Methods 391 Airport Drainage Design 400 Design of Urban Storm Drain Systems Floodplain Analysis 409 Hydrostatics 435 Groundwater Flow 436 Darcy's Law 436 Permeability 438 Velocity Potential 440 Hydrodynamic Equations 441 ' Flowlines and Equipotential Lines Boundary Conditions 447 Flow Nets 449 Variable Hydraulic Conductivity Anisotropy 452 Dupuit's Theory 453 365 402 PART FOUR GROUNDWATER HYDROLOGY 425 CHAPTER 17 Groundwater, Soils, and Geology 427 l7.l Introduction 427 I7.2 Groundwater Flow-General Properties 429 I7.3 Subsurface Distribution of Water 429 I7.4 Geologic Considerations 430 I7.5 Fluctuations in Groundwater Level 433 I7.6 Groundwater-Surface Water Relations 433 CHAPTER 18 Mechanics of Flow 435 444 451 CHAPTER 19 Wells and Collection Devices 19.1 19.2 19.3 19.4 19.5 460 Flow to Wells 460 Steady Unconfined Radial Flow Toward a Well 461 Steady Confined Radial Flow Toward a Well 462 Well in A Uniform Flow Field 463 Well Fields 465 X CONTENTS 19.6 The Method of Images 466 I9.7 Unsteady Flow 467 19.8 Leaky Aquifers 4'13 I9.9 Partially Penetrating Wells 473 19.10 Flow to an Infiltration Gallery 473 19.ll Saltwater Intrusion 474 19.12 Groundwater Basin Development 475 CHAPTER 20 Modeling Regional Groundwater Systems 481 20.I Regional Groundwater Models 481 20.2 Finite-Difference Methods 484 20.3 Finite-Element Methods 493 20.4 Model Applications 494 20.5 Groundwater Quality Models 500 PART FIVE HYDROLOGIC MODELING 505 CHAPTER 21 Introduction to Hydrologic Modeling 5O7 2l.I Hydrologic Simulation 508 2t.2 Groundwater Simulation 509 21.3 Hydrologic Simulation Protocol 524 21.4 Corps of Engineers Simulation Models 526 CHAPTER 22 Synthetic Streamflows 535 22.I Synthetic Hydrology 536 22.2 Serially Dependent Time Series Analysis 539 CHAPTER 23 Continuous Simulation Models 548 23.1 Continuous Streamflow Simulation Models 549 23.2 Continuous Simulation Model Studies 570 CHAPTER 24 Single-Event Simulation Models 594 24.1 Storm Event Simulation 594 24.2 Federal Agency Single-Event Models 597 24.3 Storm Surge Modeling 625 CHAPTER 25 Urban Runotf Simulation Models CONTENTS Xi 25.1 25.2 25.3 PART SIX STATISTICAL METHODS 630 Urban Stormwater System Models 63I Urban Runoff Models Compared 659 Vendor-DevelopedUrbanStormwaterSoftware 663 669 CHAPTER 26 Probability and Statistics CHAPTER 27 Frequency Analysis APPENDICES INDEX 757 751 671 Random Variables and Statistical Analysis 672 Concepts of Probability 673 ProbabilityDistributions 676 Moments of Distributions 681 Distribution Characteristics 682 Types of Probability Distribution Functions 685 ContinuousProbabilityDistributionFunctions 685 Bivariate Linear Regression and Correlation 690 Fitting Regression Equations 692 Regression and Correlation Applications 697 26.1 26.2 26.3 26.4 26.5 26.6 26.7 26.8 26.9 26.r0 27.1 27.2 27.3 27.4 27.5 27.6 27.7 708 Frequency Analysis 708 Graphical Frequency Analysis 709 Frequency Analysis Using Frequency Factors 7Il Regional Frequency Analysis 7I9 Reliability of Frequency Studies 730 Frequency Analysis of Partial Duration Series 734 Flow Duration Analysis 737 Preface Water management is taking on new dimensions. New federal thrusts, the grow- ing list of global iisues, and strong public sentiment regarding environmental protec- tion have been the principal driving forces. In the early years of the 20th century, water resources development and manage- ment were focuied almost exclusivd on water supply and flood control' Today, these issues are still important, but protecting the environment, ensuring safe drinking water, and providing aesthetic -and recriatioinal experiences compete equally for attention and funds. Furthermore, an environmentally conscious public is pressing for greater reliance on improved management practices, with fewer structural compo- ients, to solve this nuiion'. water problems. The notion of continually striving to provide more water has been replaced by one of husbanding this precious natural resource. There is a growing constituency for allocating water for the-benefit of fish and wildlife, for protection-of marshes and estuary areas' and for other natural system uses. But estimating the quantities of water needed for environmental protection and for maintaining and/or restoring natural systems is difficult, and there are still many unknowns. Scilntific data are ,putt", and our understanding of the complex interac- tions inherent in ecosystems of an scales is rudimentary. Indeed, this is a critical issue' since the quantities of water involved in environmental protection can be substantial and competition for these waters from traditional water users is keen' The nations of the world are facing major decisions regarding natural systems-decisions that are laden with significant ectnomic and social impacts. Thus there is_an urgency associ- ated with developing a better understanding of ecologic systems and of their hydrologic components. Water policies of the future must therefore take on broader dimensions' More emphasis must be placed on regional planning and management, and regional institu- tions to accommodate this muJt be devised. Water management must be practiced at, and between, all levels of government. Land use and water use planning must be more tightly coordinated as well' XIV PREFACE Water scientists and engineers of tomorrow must be equipped to address a diversity of issues such as: the design and operation of data retrieval and storage systems; forecasting; developing alternative water use futures; estimating water re- quirements for natural systems; exploring the impacts of climate change; developing more efficient systems for applying water in all water-using sectors; and analyzing and designing water management systems incorporating technical, economic, environ- mental, social, legal, and political elements. A knowledge of hydrologic principles is a requisite for dealing with such ibsues. This fourth edition has been designed to meet the contemporary needs of water scientists and engineers. It is organized to accommodate students and practitioners who are concerned with the development, management, and protection of water resources. The format of the book follows that of its predecessor, providing material for both an introductory and a more advanced course. Parts One through Four provide the basics for a beginning level course, while Parts Five and Six may be used for a more advanced course on hydrologic model- ing. This fourth edition has been updated throughout, and many solved examples have been added. In addition, new computer approaches have been introduced and problem-solving techniques include the use of spreadsheets as appropriate. New fea- tures of each chapter include an introductory statement of contents and, at the conclu- sion of the chapter, a summary of key points. Many sources have been drawn upon to provide subject matter for this book, and the authors hope that suitable acknowledgment has been given to them. Colleagues and students are recognized for their helpful comments and reviews, par- ticularly the following reviewers. Gert Aron, The Pennsylvania State University John W. Bird, University of Nevada-Reno Istvan Bogardi, University of Nebraska Ronald A. Chadderton, Villanova University Richard N. Downer, University of Vermont Bruce E. Larock, University of Califurnia-Davis Frank D. Masch, University of Texas-San Antonio Philip L. Thompson, Federal Highway Administration A special note of thanks is due to Dr. John W. Knapp, President of the Virginia Military Institute, coauthor of previous editions of this book, for his past contributions and valuable guidance. Warren Viessman. Jr. Gary L. Lewis PART ONE THE HYDROLOGIC CYCLE L. Chapter 1 lntroduction I Prologue The purPose of this chaPter is to: . Define hydrology. . -,.1L , Give a brief niJiory of the evolution of this important earth science' . State the fundamental equation ofhydrology' . Demonstrate trow ffiofogic principle, "urib" applied to supplement decision support systems for water and environmental management' 1.1 HYDROLOGY DEFINED Hydrologyisanearthscience'Itencompassestheoccuffence'distribution,move- menr, and properties of the waters of the earth. A knowledge of hydrology is funda- mentaltodecisionmutingp,o.",,e,*he,ewaterisu"ompon"nto.f.th.esystemof concern. water and environmental issues are inextricably linked' and it is important toclear$understandhowwaterisaffectedbyandhowwateraffectsecosystem maniPulations' 1.2 A BRIEF HISTORY Ancient philosophers focused their i Production of surface water flows oc"ur."n"e of water in various stag from the sea to the atmosPhere to t early speculation was often faulty'l of large subterranean reservoirs th is interesting to note, however' tha *suoeriornumbersindicatereferencesattheendofthechapter. CHAPTER 1 INTRODUCTION Greek aqueducts on both conveyance cross section and velocity. This knowledge was lost to the Romans, and the proper relation between area, velocity, and rate of flow remained unknown until Leonardo da Vinci rediscovered it duringihe Italian Renais- sance. During the first century s.c. Marcus Vitruvius, in Volume 8 of his treatise De Architectura Libri Decem (the engineer's chief handbook during the Middle Ages), set forth a theory generally considered to be the predecessor of modern notions of the hydrologic cycle. He hypothesized that rain und ,no* falling in mountainous areas infiltrated the earth's surface and later appeared in the lowlands as streams and springs. In spite of the inaccurate theories proposed in ancient times, it is only fair to state that practical application of various try-orotogic principles was often carried out with considerable success. For example, about 4000 s.c. u du- was constructed across the Nile to permit reclamation of previously barren lands for agricultural production. Several thousand years later a canal to convey fresh water from Cairo io Suez was built. Mesopotamian towns were protected uguinrt floods by high earthen walls. The Greek and Roman aqueducts and early Chinese irrigation and flood control works were also significant projects. Near the end of the fifteenth century the trend toward a more scientific approach to hydrology based on the observation of hydrologic phenomena became evident. Leonardo da Vinci and Bernard Palissy independe-ntly reached an accurate under- standing of the water cycle. They apparently bised theii theories more on our"*iion than on purely philosophical reasoning. Nevertheless, until the seventeenth century it seems evident that little if any effort was directed toward obtaining quantitative measurements of hydrologic variables. The advent of what might be called the "modern" science of hydrology is usually considered to begin with the studies of such pioneers as Perrault, Mariotte, and Halley in the seventeenth century.r'a Perrault obtained measurements of rainfall in the Seine River drainage basin over a period of 3 years. Using these and measurements of runoff, and knowing,the drainage area size, he showeJ that rainfall was adequate in quantity to account for river flows. He also made measurements of evaporati,on and capillarity. Mariotte gauged the velocity of flow of the River Seine. Recorded veloc- ities were translated into terms of dischirge by introducing measurements of the river cross section' The English astronomer Halley measured the rate of evaporation of the Mediterranean Sea and concluded that the amount of water evaporated was sufficient to account for the outflow of rivers tributary to the sea. Measurements such as these, although crude, permitted reliable conclusions to be drawn reggrding the hydrologic phenomena being studied. brth numerous advances in hydraulic theory zometer, the Pitot tube, Bernoulli's theorem, ples.8 perimental hydrology flourished. Significant ydrology and in the measurement of surface water. Such significant contributions as Hagen-Poiseuille's capillary flow equation, Darcy's law of flow in porous media, und th" Dupuit-Thiem well formula were evolved'e-lr The beginning of systematic stream guoling can also be traced to this period' Although the basis for modern hydrology wui tirrr established in the nine- ,) 1.4 THE HYDROLOGIC BUDGET 5 1.3 teenth century, much of the effort was empirical in nature. The fundamentals of physical hydtotogy had not yet been well established or widely recognized. In the early years of tle twJntieth ""niury the inadequacies of many earlier empirical formula- tions became well known. As a result, interested governmental agencies began to develop their own programs of hydrologic research' From about 1930 to 1950, rational analysis began to ieplace empiricism.3 Sherman's unit hydrograph, Horton's infiltration theory, und Th"it's nonequilibrium -approach to well hydraulics are out- standing examples of the great progress made'r2-'o Since 1930 a theoreiical approach to hydrologic problems has largely replaced less sophisticated methods of ttre past. Advances in scientific knowledge permit a better understanding ofthe physicai basis ofhydrologic relations, and the advent and ' continued developnient of high-speed digital computers have made possible, in both a practical and an economic iense, extensive mathematical manipulations that would - have been overwhelming in the past. For a more compiehensivi historical treatment, the reader is referred to the works of Meinzer, Jonls, Biswas, and their co-workers'1'2'4'5'15 THE HYDROLOGIC CYCLE The hydrologic cycle is a continuous process by which water is transported from the oceans to the atmosphere to the landind back to the sea. Many subcycles exist' The evaporation of inlan-d water and its subsequent precipitation over land before return- ingio the ocean is one example. The driving force for the global water transport system is provided by the sun, which furnishes the energy required for evaporation' Note that the water quality also changes during passage through the cycle; for example, sea water is converted to fresh water through evaporation' The complete water cycle is global in nature. world water problems require studies on regional, national, internitional, continental, and global scales.16 Practical significance of the fact that the total supply of fresh water available to the earth is limited and very small compared with ihe salt water content of the oceans has received little attention. Thus waters flowing in one country cannot be available at the same time for use in other regions of the world. Raymond L' Nace of the u's' Geological Survey has aptly sta=ted thatoowater resources are a global problem with local roots."tu Mtdern hydrologists are obligated to cope with problems requiring definition in varying scales of oider of magnitude difference. In addition, developing techniques to contiol weather must receive careful attention, since climatological changes in one area can profoundly affect the hydrology and therefore the water resources of other regions. THE HYDROLOGIC BUDGET Because the total quantity of water available to the earth is finite and indestructible, the global hydrolojic ,yrt"* may be looked upon as closed. Open hydrologic subsys- tems are abundantlhowever, and these are usually the type analyzed' For any system' ' a water budget can be developed to account for the hydrologic components' 1 . 4 CHAPTER 1 INTRODUCTION Figures I'I,I.2, and 1.3 show a hydrologic budget for the coterminous United States, a conceptualized hydrologic cycle, and the distribution of a precipitation input, respectively. These figures illustrate the components of the water cycle with which a hydrologist is concerned. In a practical sense, some hydrologic region is dealt with and a budget for that region is established. Such regions may be topographically defined (watersheds and river basins are examples), politically specified (e.g- couniy or city limits), or chosen on some other grounds. Watersheds or drainagi tasins are the easiest to deal with since they sharply define surface water boundaries. These topo- graphically determined areas are drained by a river/stream or system of connecting rivers/streams such that all outflow is discharged through a single outlet. Unfortu- nately, it is often necessary to deal with regions that are not well suited to tracking hydrologic components. For these areas, the hydrologist will find hydrologic budgeting somewhat of a challenge. The primary input in a hydrologic budget is precipitation. Figures 1.1-1.3 illustrate this. Some of the precipitation (e.g., rain, snow, hail) may be intercepted by trees, grass, other vegetation, and structural objects and will eventually return to the , atmosphere by evaporation. Once precipitation reaches the ground, some ofit may fill depressions (become depression storage), part may penetrale the ground (infiltraie) to replenish soil moisture and groundwater reservoirs, and some may become surface runoff-that is, flow over the earth's surface to a defined channel such as a stream. Figure 1'3 shows the disposition ofinfiltration, depression storage, and surface runoff. and vegetation I '1.' Consumptive use 100 bgd bgd = billion gallons per day *r-d{i; Figure 1.1 Hydrologic budget of cotermirious united States. (U.S. Geological survey.)
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