1.UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION DESIGN OFSMALL DAMS A Water Resources Technical PublicationFirst Edition, 1960 Second Edition, 1973 Revised Reprint, 1977Third Edition, 1987

2. As the Nations principal conservation agency, the Department of theInterior has responsibility for most of our nationally owned publiclands and natural resources. This includes fostering the wisest use ofour land and water resources, protecting our fish and wildlife, preserv-ing the environmental and cultural values of our national parks andhistorical places, and providing for the enjoyment of life through out-door recreation. The Department assesses our energy and mineralresources and works to assure that their development is in the bestinterests of all our people. The Department also has a major respon-sibility for American Indian reservation communities and for peoplewho live in Island Territories under U.S. Administration. For sale by the U.S. Government Printing OtTice Superintendent of Documenta, Mail Stop: SSOP. Washington, DC 20402-9323 3. IIIMission of the Bureau of ReclamationThe Bureau of Reclamationof the U.S. Departmentof the Interior isresponsible for the developmentand consarvationof the Nationswater resources in the Western United States. The Bureaus original purpose to provide for the reclamation of aridand semiarid lands in the West today covers a wide range of interre-la ted functions. These include providing municipal and industrial watersupplies; hydroelectric power generation;irrigation water for agricul-ture; water quality improvement; flood control;river navigation;riverregulationand control; fish and wildlife enhancement; outdoorrecrea-tion; and research on water-related design, construe tion, materials,atmospheric management,and wind and solar power.Bureau programsmost frequentlyare the result of close cooperationwith the U.S. Congress, other Federal agencies, States, local govern-men ts, academicinstitutions,water-user organizations,and otherconcernedgroups. 4. Preface to the Third EditionThe second edition of Design of Small Dams has siderations, has been revised to include a discus-been very popular throughout the world; it has been sion on the management of fish and wildlifepublished in a number of different languages andresources at, completed project,s, in addition to newused extensively in the United Stat,es. Since the design considerations. An expanded section onsecond edition was published in 1974, there havewater quality implications to dam design and opbeen significantrevisions in the approaches and erat,ion is also included.procedures related to the design of dams. BecauseChapter 3, Flood Hydrology Studies, has beenof these revisions and the continued demand for thiscomplet,ely revised, including incorporating t,he pre-manual, it was decided that, this new third edition vious appendix A, EsGmatingRainfallRunoffbe prepared and published.from Soil and Cover Data, int,o the chapt,er. Ref-The purpose of this third edition has beenerence to t,he Soil Conservation Services curvechanged in scope and intent from that of the second number approach for assigning infiltration losses,edition. The title Design of Small Dams has beenthe triangular unit-hydrographapproach, and allretained even though some of the information in discussions and plates providing guidance for es-the third edition relates to large dams. Many of thetimatingprobable maximumprecipitationhavetheoretical concepts presented can be applied tobeen eliminated. These topics have been replacedlarge or small structures; however, it is recom-by a treatment of infiltrationlosses as actually apmended that the procedures and methods presentedplied by the Bureau of Reclamation, expanded con-be used only as guidelines. When preparing the de-sideration and guidance relative t,o the developmentsign of large or complicated structures, especially of unit, hydrographs using the dimensionless uni-those located where they create a high hazard, thegraph and S-graph approaches, and specific ref-owner should rely on experienced dam engineers, erence to theNat,ional WeatherServicesexperienced consultants, or refer to more detailedHydrometeorologicalReport series as the basis forreferences. developing probable maximum precipitation esti- Some of the chapters and appendixes have beenmates for the contiguous United Statues.revised extensively, while others reflect only minor Chapter 5, Foundationand Const,ruction Ma-revisions. Chapter 1, Plan Formulation, has beenterials, has been updated t,o incorporate currentcondensed to briefly cover only the basic conceptsstandards in foundation and construction mat,erialsof plan formulation. The authors of this chapterinvestigations. A reservoir studies section has beenconcluded that a detailed discussion of plan for- added to the section on scope of investigations. Themulation was not appropriate because the primarysections on soil and rock classification have beenfocus of this manual is on design, not project plan-updated to reflect current standards, and a new sec-ning. Also, a discussion of plan formulation,par- tion on engineering geophysics has been added toticularly with an emphasis on Federal plansummarize the capabilities of these methods. Theformulat,ion requirements, would not be of interest sections on subsurface explorations and samplingto a majority of dam designers. The chapter thushave been revised extensively to represent, new tech-provides a brief discussion of the steps of plan for- nology. The logging of explorations has also beenmulation and some of the fundamental tests for therevised to reflect current standards, and t,he fieldviability of proposed plans.and laboratorytest section has been updated. Chapter 2, Ecological and Environmental Con-Changes in soil mechanics terminologyand soil V 5. vitesting procedures generated by revision of the Bu- modified low Froude number basin as an alternativereaus Earth Manual are reflected in this chapter.to basin 4 design, and modifications in the designThe previous table 8, Average Properties of Soils,criteria for baffled apron spillways to permit theirwhich is now table 5-1, was recompiled to include use for higher unit discharges. Other contemporarylaboratory test results obtained since the last edi-spillway concepts are introduced, although designtion. Figure 5-14, Permeabilityof Soils, was addedcriteria are not included because they are still underto this edition to illustrate ranges of permeabilitydevelopment. Included in this category are laby-measured on compacted soil specimens tested at therinth weirs where large flows must be discharged inBureaus laboratory in Denver. The bibliography a limited space such as a narrow canyon, and thehas been updated to include selected sources of in- use of air slots (aerators) in spillways where thereformation for foundation and construction mate- is high potential for cavitation damage. Plunge-poolrials investigation.design criteria have been somewhat improved by theChapter 6, EarthfillDams, has been revised to addition of several references to recent research.update terminology and reflect design philosophy, The suggested method for calculating the dischargeprocedures, and standards that have evolved since under radial gates has been revised to reflect1974. The major change is greater emphasis on in- up-to-date criteria developed by the U.S. Armyternal filtering and drainage to control seepage andCorps of Engineers, Waterways ExperimentSta-internal erosion within embankmentdams. New tion. The section on siphon spillways has beenfigures have been added that show current dam em- omitted from this edition because they are seldombankments that have been designed and con-used as fibw control structures for dams. The bib-structed by the Bureau of Reclamation.Other liography has been revised by the removal of ref-illustrations have been replaced or revised to reflecterences that were hard to obtain and by the additioncurrent thinking and technology. Liberal referenceof many new references that reflect the currentis made to design standards that have been devel- state-of-the-art.oped as guides for Bureau engineers.Chapter 12, Operation and Maintenance,nowChapter 7, Rockfill Dams, required only minor includes additional topics, clarification, and morerevisions; however, the Bureau does not have ex-detail. The new topics added are Changes in Op-tensive experience with the design and construction erating Plan, which addresses modification to aof rockfill dams. Design and constructionproce- structure to add additional storage or to change thedures for rockfill dams have changed over the lastpurpose of allocation of storage; Emergency Pre-two or three decades and continue to do so. The paredness Plan, which addresses instructions to anchapter gives a good general background for the operator during emergency situations; and Damdesign of rockfilldams; however, the designer Operators Training, which outlines the require-should also refer to the literature on the subject. ments for the training of operators to assure thatChapter 8, Concrete Gravity Dams, now in- operation and maintenance of a facility are per-cludes additional topics, clarification,and more de-formed in an accurate and responsible manner.tail. This chapter has also been revised to address Chapter 13 is a new chapter dealing with damconcerns for concrete dams of any height. Sectionssafety. Although dam safety is always an underlyingon material properties and foundation considera-consideration in the design, construction,opera-tions have also been added. More complete discus- tion, and monitoring of a dam, the passage of leg-sions are now included for forces acting on the dam,islation on Safety of Dams has placed addit,ionalrequirements for stability, and stress and stabilityemphasis on dam safety; and the inclusion of aanalyses. Discussions addressing the analysis ofchapter on this subject was believed to be impor-cracked dams have been clarified and expanded totant. This chapter presents procedures and refer-include analysis during an earthquake. Also, a gen- ences to other procedures for the evaluation anderal iterative approach for cracked dam analysis, analyses of dam safety issues for both new and ex-applicable for static and dynamic conditions, is nowisting dam structures.included. The appendix designations have been revised.The Spillways and Outlet Works chapters, 9The previous appendix A is now part of chapter 3,and 10, respectively, now include two new hydraulic and the original appendix H, Sedimentation,isdesigns for energy dissipators. These designs are a now appendix A. A new appendix H, Operation 6. viiand Maintenance, presents a checklist for Oper-have been added.ation and Maintenance inspections. The intent of this third edition is to expand dis- Appendix D, Soil Mechanics Nomenclature, cussion of concepts for design of small to large damswas updated to reflect current terminology in use and to update the different approaches and pro-from ASTM Designation D-653, Standard Defi-cedures being employed in the current state-of-the-nitions of Terms and Symbols Relating to Soil and art of planning, design, construction, operation, andRock Mechanics, and from USBR 3900, Standardevaluation processes. The text is not intended inDefinitions of Terms and Symbols Relating to Soil any way to encourage assumption of undue respon-Mechanics. The latter reference is from the Bu-sibility on the part of unqualified personnel, butreaus recently revised Earth Manual, volume 2, rather to point out the importance of specializedTest Designations.training. Engineers who do not have specialized Appendix E, Construction of Embankments, training in dam engineering should seek advicehas been revised to emphasize and more fully de-from experienced consultants.scribe construction control philosophy and proce-This manual was prepared by personnel of thedures. Several photographsof more modernBureau of Reclamation, U.S. Department of the In-equipment and construction techniques have been terior, Denver, Colorado, under the direction ofadded. The Rapid Method of Compaction Con- Darrell Webber, Assistant Commissioner, Engi-trol has been eliminated; the reader is now referred neering and Research, with contributionsfrom theto the Bureaus Earth Manual for that procedure.staff of other Assistant Commissioners.Neil Par-Terminologyhas been updated to that currently rett, Chief, Division of Dam and Waterway Design,used within the Bureau of Reclamation.established a three-man team to coordinate the as- A discussion on concrete erosion has been added, sembly of this new edition: Harold K. Blair, Chair-and the discussion on abnormal set of concrete hasman, Head, Design Section No. 2 of the Concretebeen expanded in appendix F, Concrete in Con-Dams Branch; Thomas N. McDaniel, Design Man-struction. The design of concrete mixes has been ager, EmbankmentDams Branch; and Ronald D.revised and includes revisions to tables, forms, andMohr, General Engineer, Document Systems Man-the steps involved in concrete mix design.agement Branch. Numerous engineers, technicians,Appendix G, Sample Specifications,has beenand support personnel participated with this teamupdated to include guide specifications currently in the preparation of this third edition and theirused by the Bureau of Reclamation.efforts are greatly appreciated. Special recognitionThroughout the third edition, figures and illus-to the many authors, both current and past, istrations have been revised and many new figures appropriate:Current Author(s) Past Author(s) Chapter 1W.C. Dunkin, C.W. Huntley A.F. Johnson Chapter 2J.C. Hokenstrom E.A. Seamen, L.W. Davidson Chapter 3A.G. Cudworth, Jr.D.L. Miller, R.A. Clark, S. Schamach Chapter4 T.N. McDaniel, H.K. Blair H.G. Arthur Chapter5 S.R. Bartlett, R.C. Hatcher J.W. Hilf Chapter6 T.N. McDaniel H.G. Arthur Chapter7 T.N. McDaniel R.W. Bock, L.W. Davidson Chapter8 H.L. Boggs, C.C. Hennig A.T. Lewis, J.S. Conrad, E.L. Watson, L.M. Christiansen Chapter 9H.K. Blair, T.J. RhoneC.J. Hoffman Chapter 10 H.K. Blair, T.J. RhoneC.J. Hoffman Chapter 11 T.N. McDaniel, H.K. Blair E.R. Lewandowski Chapter 12 W.P. Gersch, L.J. Yocom H.G. Arthur Chapter 13 H.J. Warren, D.G. Achterberg,D.J. Trieste Appendix A R.I. Strand, E.L. Pemberton R.I. Strand 7. *.*VIII Current Author(s)Past Author(s) Appendix BR.I. Strand, T.J. RhoneC.J. Hoffman, J.M. Lara, R.I. Strand Appendix CR.A. Simonds, H.K. Blair P.K. Bock, C.J. Hoffman Appendix DR.A. Young J.W. Hilf Appendix ET.N. McDanielJ.W. Hilf Appendix FJ.L. HartJ.E. Backstrom, L.C. Porter,E.L. Ore, G.B. Wallace Appendix GJ.L. Hart, R. Wright,R.E. Fink, N.F. Larkins,R.H. Restad, T.N. McDanielE.R. Lewandowski Appendix HW.P. Gersch, L.J. Yocom Preparation of the manuscript for publicationsional references to proprietary materials or prod-was performed by the personnel of the Planningucts in this publication. These references are notand Editing Section, Document Systems Manage- to be construed in any way as an endorsement be-ment Branch, A. J. Huber, Branch Chief. cause the Bureau does not endorse proprietary The Bureau of Reclamation expresses apprecia-products or processes of manufacturers or the ser-tion to the organizations who have permitted thevices of commercial firms.use of their material in this text. There are occa- 8. Preface to the Second EditionThe first edition of Design of Small Dams wasdiscussion of the slurry trench method of cutoffpublished to serve primarily as a guide to safe prac-construction, earthquake considerations, soil-tices for those concerned with the design of small cement design criteria, additional design details,dams in public works programs in the Unitedand a more extensive reference list. The discussionStates. Its publication was warmly received and, inof rockfill dam design has been considerably ex-the intervening years since then, it has been widely panded in chapter VII to reflect the recent interestused in the United States, reprinted numerousin rockfill dams and the growth of available infor-times, and translated into many foreign languages, mation on this subject. Baffled spillway design pro-including Korean, Spanish, Japanese, and Chinese.cedures have been incorporated in chapter IX, and Since publication of the first edition of Design additional information on tunneling has been pre-of Small Dams, a large body of new literature has sented in chapter X. Appendix A includes new in-become available to dam designers, and many newformation on the estimation of rainfall runoff fromdesign procedures used at the Bureau of Recla- soil cover data, and an expanded discussion of flowmation have been changed to reflect more.modernin natural channels is contained in appendix B. Ap-techniques. As the number of changes in design pendix C includes new tables for the design of bothtechniques increased, it became apparent that theirreinforced concrete pressure pipe and cast-in-placeincorporation in a second edition would be bene- conduits, and appendix E has a more complete dis-ficial to those individuals and agencies concerned cussion of the rapid method of compaction control.with small dams. Appendix G has been expanded to include speci- The purpose of the second edition remains es- fications concerning air and water pollution, andsentially the same as for the first edition. Many of each specification has been updated to reflect cur-the design procedures proposed in the first editionrent Bureau requirements. A new appendix on res-remain virtually unchanged. However, a number of ervoir sedimentation is presented in appendix H,new procedures have been developed by the Bureau which outlines current procedures used to estimateand are currently in use. To make this new infor-the rate of sedimentation and the period of timemation available generally, it is included in the sec- before sediment will interfere with the useful func-ond edition. The increased concern of the Bureau tions of the reservoir. A convenient list of conver-of Reclamation with environmental problems is re-sion factors is presented in appendix I to facilitateflected by the inclusion of chapter II, Ecologicalthe increased utilization of metric units. Many mi-and Environmental Considerations. This chapternor changes have been made throughout the text tooutlines some of the practical measures which mayreflect current design and construction techniques.be t.aken to reduce the environmental and ecologicalIt is intended that this book will provide the de-impact of a project. Chapter III has been extensivelysigner with an important source of information.revisedto include current methods of design flood However, this text is not intended in any way tocomputation and to incorporate new graphical data. encourage the assumption of undue responsibility Chapter V has been revised to reflect the avail-on the part of unqualified personnel, and the useability of current information concerning founda-or application of the methods and data containedtion design and to include supplemental foundation herein is strictly the responsibility of the personinvestigation procedures. Chapter VI contains ad-utilizing the material. Designs should reflect theditional material on the design of earth dams, a actual site conditions and should not merely be pat-ix 9. Xterned after a successful design used at anotherrecognition is given to H. G. Arthur, Director oflocation. Design and Construction, for his overall guidance Periodically, the names of Bureau of Reclamation in preparation of the text and to Dr. J. W. Hilf,projects and features are changed by acts of Con- Chief of the Division of Design, for his technicalgress, Federal agencies, etc., and therefore thereadvice.may be a few inconsistencies in the project and fea- The second edition of the text was coordinated,ture names referred to in the text. edited, and much supplemental technical informa- Some recent changes include the following: tion provided by L. W. Davidson, Civil Engineer,Earth Dams Section. Detailed editorial guidance,Cachuma Dam to Bradbury Dam final review, and preparation of the manuscript forWasco Reservoir to Clear Lake publication was performed by W. E. Foote of t,heSoap Park Reservoir to Milly K. Goodwin LakeTechnical Services Branch.Missouri River Basin Project to Pick-SloanThe Bureau of Reclamationagain expressesMissouri Basin Program. grateful appreciation to those organizations whichhave permitted the use of material from their pub- There are occasional references to proprietary lications, especially the National Oceanic and At-materials or products in this publication. Thesemospheric Administration, U.S. Departmentofmust not be construed in any way as an endorse- Commerce, for material used in chapter III; the Soilment since the Bureau cannot endorse proprietaryConservationService, U.S. Department of Agri-products or processes of manufacturers or the ser-culture, whose material was used in appendix A; thevices of commercial firms for advertising, publicity, U.S. Geological Survey of the Departmentof thesales, or other purposes. Interior, who supplied material used in chapter V, The second edition was prepared by the engineers and the Corps of Engineers, U.S. Departmentofof the Bureau of Reclamation, U.S. Department ofthe Army, whose report on slurry trench construc-the Interior, at its Engineering and Research Centertion was used in the preparation of chapter VI. Ac-in Denver, Colo. A number of engineers and tech-knowledgmentsto other organizationswhichnicians participated in the preparation of the sec- furnished lesser amounts of material are givenond edition and in its critical review, and the efforts throughout the text.of these persons are greatly appreciated. Special 10. Preface to the First EditionThis book presents instructions,standards, andearthfill dams because they are the most commonprocedures for use in the design of small dams. Ittype. For the purpose of this book, small dams in-is intended to serve primarily as a guide to safe clude those structureswithheights abovepractices for those concerned with the design ofstreambed not exceeding 50 feet except for concretesmall dams in public works programs in the United dams on pervious foundations. For the latter struc-States. The book will serve this purpose in three tures, the maximum height is further limited toways: (1) It will provide engineers with informationdams whose maximum net heads (headwater to tail-and data necessary for the proper design of small water) do not exceed 20 feet. The text is not in-dams, (2) it will provide specialized and highly tech-tended to cover dams of such large volumes thatnical knowledge concerning the design of smallsignificant economies can be obtained by utilizingdams in a form that can be used readily by engineersthe more precise methods of design usually reservedwho do not specialize in this field, and (3) it willfor large dams. In recognition of the limited engi-simplify design procedures for small earthfill dams.neering costs justified for small dams, emphasis isAn earlier publication, Low Dams which wasplaced on efficiency and relatively inexpensive pro-prepared in 1938 by the National Resources Com- cedures to determine the necessary design data.mittee,, presented much useful information on the Simplified design methods are given to avoid thedesign of small dams. In the 20 years that have complex procedures and special investigationsre-elapsed since the printing of that book, however, quired for large dams or for unusual conditions. Ad-there have been many technical advances in theequate but not unduly conservative factors of safetydesign of dams, and the need for a new work in- are used in the simplified design methods.corporating the latest design techniques has become Small dams are properly considered to be asso-increasingly evident. It is believed that this book,ciated with small streams and drainage areas of lim-Design of Small Dams, will fill that need. Theited extent. For these situations or for those innew book retains much of the format of Low which spillway capacity is obtainable at relativelyDams and some of the material from the earlier low cost, a sufficient approximation of the inflowpublication has been incorporated in the new one, design flood discharge may be determined by pro-but most of the text is wholly new. cedures given in this- text. For important projects,Although this text is related almost exclusivelyparticularly where the spillway cost is a major itemto the design of small dams and appurtenant struc-of project cost and thus may have an importanttures, it is important that the designer be familiarbearing on project feasibility, more exact and com-with the purposes of the project, the considerationsplex studies which are beyond the scope of this textinfluencing its justification, and the manner of ar-may be justified.riving at the size and type of structure to be built. This text is addressed to the designer of the struc-For these reasons, an outline discussion of a desir-ture and does not include in its scope the field ofable project investigationhas been included inconstruction practices or methods. However, as thechapter I.integrity of the design requires adherence to lim-Only the more common types of small dams nowiting specifications for materials and to the practicebeing constructed are discussed. These include con- of good workmanship in construction,appendixescrete gravity, earthfill (rolled-type),and rockfill are included on Constructionof Embankments,dams. Emphasis is placed on the design of rolledConcrete in Construction, and Sample Speci- xi 11. xiifications. More detailed specifications will be re-or in its critical review, and the efforts of all of thesequired to ensure proper construction of any specificare gratefully acknowledged. Special recognition isdam.given to 0. L. Rice, Chief of the Dams Branch, for This text is not intended in any way to encouragehis guidance and counsel, especially in determiningassumption of undue responsibility on the part of the scope and treatment of the text.unqualified personnel, but rather to point out the The text was coordinated and edited by H. G.importance of specialized training and to stimulate Arthur, Supervisor, Design Unit, Earth Dams Sec-wider use of technically trained and experiencedtion, and final review and preparation of the man-consultants.uscript for the printer was by E. H. Larson, Head, This text should be of service to all concernedManuals and Technical Records Section.with the planning of small water storage projects, The Bureau of Reclamation expresses gratefulbut in no way does it relieve any agency or personappreciation to those organizations which have per-using it of the responsibility for safe and adequatemitted the use of material from their publications,design. The stated limitationsof the design pro-especially the Soil Conservation Service, U.S. De-cedures should be heeded. partment of Agriculture, whose material was used This book was prepared by the engineers of the in appendix A; and the Corps of Engineers, U.S.Bureau of Reclamation, U.S. Department of the In- Department of the Army, whose Technical Manualterior, at Denver, Colo., under the direction ofTM 5-545 was freely used in the preparation of partGrant Bloodgood, Assistant Commissioner and D of chapter V. Acknowledgmentsto other organ-Chief Engineer, and L. G. Puls, Chief Designing izations furnishing a lesser amount of material areEngineer. More than 30 engineers and many tech- given throughout the text.nicians participated in the preparation of the book 12. SectionCONTENTSPagePrefaces .. ... ... ... .... .. .... .. ... ... ... ... ... .. ... ... ... .. .... .. ... ... ... .. ... ... ... .. .... .. .... .. ... ... ... .. .... .. ... ... ... ... .....................................CHAPTER 1. PLAN FORMULATIONGeneral ... ... .... .. .... .. .... .. ... ... ... ... ... .. .... .. ... ... ... .. .... .. ... .. .... .. .... .. ... ... ... .. .... .. ... .. .... .. .... .. .... .........................................1CHAPTER2. ECOLOGICAL AND ENVIRONMENTAL CONSIDERATIONSA. INTRODUCTION2.1.Planning ... .. .... .. .... .. .... .. .... .. ... .. .... .. .... .. ... ... ... .. .... .. .... .. ... ... ... .. .... .. ... ... ... .. .... .. .... .. ... ... ... ...........................3B. GENERAL ENVIRONMENTALISSUES2.2.Requirements .. .... .. .... ... ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... .... .. .... .. .... .. .... .. .... ... .... .. .... .. .... .. .... .. 42.3.Categories of resources ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... ... ... .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... . 4C. FISH AND WILDLIFE CONSIDERATIONS2.4.General ... .. .... ... ... ... ... ... .... .. .... .. .... ... ... ... ... ... ... ... ... ... ... ... .... .. .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... .. .... ... ... ... 42.5.Ecological and environmental considerations for fish . .... ... ... .. .... ... ... ... .... .. .... .. .... ... ... ... ... ... ... ... .... .. 42.6.Ecological and environmental considerations for wildlife . .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... .. .... .. .8D. WATER QUALITY2.7.General . .. .... ... .... .. .... .. .... .. .... ... ... ... ... ... ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... ... ... ... ... ... ... ... .. 14(a) Water quality analysis .. .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... .. .... ... ... ... .... .. .... .. .... .. .... ... ... ... .... .. .... .. .. 14(b) Effects of design and operating criteria .. ... .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... .... .. .... .. .... .. .... .. ...16(c) Design considerations ... ....*....................................................................................... .. ... ... ... ... ... 17E. ARCHEOLOGICAL AND HISTORICAL CONSIDERATIONS2.8.Requirements ... .. .... .. .... .. .... .. .... .. .... ... ... .. .... ... ... ... ... ... ... ... ... ... ... ... ... ... .... .. .... .. .... .. .... ... ... ... ... ... ... ... ... ... ... . 18F. RECREATION CONSIDERATIONS2.9.Planning for recreation facilities . ... ... ... ... .... .. ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... .... .. .... .. .... .. .... .. 19G. BIBLIOGRAPHY2.10. Bibliography ... .. .... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .... .. .... .. .... .. .... .. .... .. .... .. .... .. .... ... ... ... ... ... ... ... ... ... 21CHAPTER 3. FLOOD HYDROLOGYSTUDIES 3.1. Purpose and scope.................................................................................................................................23 3.2. Background ............................................................................................................................................ 23 ...XIII 13. xivDESIGN OF SMALL DAMSSection Page (a) PMF hydrograph ....................................................................................................................... 23 (b) Specific-frequency flood hydrograph ...................................................................................... 233.3.Basic hydrologic and meteorologic data.. ...........................................................................................233.4.Hydrologic data ..................................................................................................................................... 23 (a) Recorded streamflow data ........................................................................................................23 (b) Peak discharge data .................................................................................................................. 243.5.Meteorologic data.. ................................................................................................................................243.6.Field reconnaissance of drainage basins for flood hydrology studies.. ..........................................24 (a) Drainage network ......................................................................................................................24 (b) Soil and geologic conditions.. ................................................................................................... 25 (c) Vegetative cover ......................................................................................................................... 25 (d) Land use ..................................................................................................................................... 25 (e) Significant nearby basins.. ........................................................................................................ 253.7.Field reconnaissance report.. ............................................................................................................... 263.8.Development of probable maximum storms.. .................................................................................... 26 (a) Hydrometeorological reports 51 and 52 .................................................................................. 26 (b) Regionalized procedures west of the Continental Divide ....................................................273.9.Flood runoff from rainfall .................................................................................................................... 28 (a) Basic unit hydrograph theory.. ................................................................................................28 (b) Unit hydrograph lag time ......................................................................................................... 29 (c) Temporal distribution of unit runoff.. ....................................................................................33 (d) Development of synthetic unit hydrographs.. ........................................................................ 34 (e) Infiltration and other losses..................................................................................................... 39 (f) Base flow and interflow ............................................................................................................ 42 (g) Design-flood hydrographs ......................................................................................................... 513.10. Flood runoff from snowmelt ................................................................................................................ 523.11. Envelope curves of prior flood discharges ......................................................................................... 533.12. Estimates of frequency of occurrence of floods ................................................................................ 543.13. Flood hydrology reports ....................................................................................................................... 563.14. Bibliography ...........................................................................................................................................57CHAPTER4. SELECTIONOF TYPE OF DAMA. CLASSIFICATION OF TYPES4.1.General ................................................................................................................................................... 594.2.Classification according to use ............................................................................................................594.3.Classification by hydraulic design ...................................................................................................... 594.4.Classification by materials ................................................................................................................... 594.5.Earthfill dams ........................................................................................................................................ 604.6.Rockfill dams ......................................................................................................................................... 614.7.Concrete gravity dams ..........................................................................................................................624.8.Concrete arch dams .............................................................................................................................. 634.9.Concrete buttress dams.. ...................................................................................................................... 644.10. Other types.. ........................................................................................................................................... 64B. PHYSICAL FACTORS GOVERNING SELECTION OF TYPE4.11. General ................................................................................................................................................... 644.12. Topography ............................................................................................................................................ 644.13. Geology and foundation conditions ....................................................................................................65(a) Rock foundations .......................................................................................................................65(b) Gravel foundations .................................................................................................................... 65 14. CONTENTS xvSection Page (c) Silt or fine sand foundations.. ..................................................................................................65 (d) Clay foundations ........................................................................................................................ 65 (e) Nonuniformfoundations.. ......................................................................................................... 654.14. Materials available ................................................................................................................................ 654.15. Hydrology ...............................................................................................................................................664.16. Spillway ..................................................................................................................................................664.17. Earthquake.. ........................................................................................................................................... 66C. LEGAL, ECONOMIC,AND ESTHETIC CONSIDERATIONS4.18. Statutory restrictions ............................................................................................................................664.19. Purpose and benefit-cost relation.. .....................................................................................................674.20. Appearance.. ........................................................................................................................................... 67CHAPTER5. FOUNDATIONSAND CONSTRUCTION MATERIALSA. SCOPE OF INVESTIGATIONS5.1.General ...................................................................................................................................................695.2.Foundations.. .......................................................................................................................................... 695.3.Embankment soils.. ............................................................................................................................... 715.4.Riprap and rockfill.. .............................................................................................................................. 745.5.Concrete aggregate ................................................................................................................................745.6.Reservoir studies ...................................................................................................................................76 (a) General.. ......................................................................................................................................76 (b) Reservoir maps.. .........................................................................................................................76 (c) Investigation methods ............................................................................................................... 776. COLLECTION AND PRESENTATION OF DATA5.7.General ...................................................................................................................................................785.8.Presentation of data ............................................................................................................................. 78C. SOURCES OF INFORMATION5.9.Topographic maps ................................................................................................................................. 795.10. Geologic maps ........................................................................................................................................ 805.11. Agricultural soil maps ........................................................................................................................... 815.12. Remote sensing.. ....................................................................................................................................82D. SOIL CLASSIFICATION5.13. General ...................................................................................................................................................865.14. Soil components .................................................................................................................................... 87 (a) Size .............................................................................................................................................. 87 (b) Gradation.. ..................................................................................................................................87 (c) Angularity ...................................................................................................................................88 (d) Shape ........................................................................................................................................... 885.15. Soil moisture .......................................................................................................................................... 885.16. Properties of soil components .............................................................................................................88 (a) Gravel and sand ......................................................................................................................... 88 (b) Silt and clay ............................................................................................................................... 90 (c) Organic material ........................................................................................................................ 94 15. xvi DESIGN OF SMALL DAMSSectic vzPage5.17. Unified soil classification system.. ......................................................................................................94 (a) General.. ......................................................................................................................................94 (b) Field classification .....................................................................................................................945.18. Engineering characteristics of soil groups.. ....................................................................................... 95 (a) General.. ......................................................................................................................................95 (b) Shear strength.. .......................................................................................................................... 95 (c) Permeability ................................................................................................................................ 95E. ROCK CLASSIFICATIONAND DESCRIPTION OF PHYSICAL PROPERTIES OF ROCK5.19. General ................................................................................................................................................... 98 (a) Definition and types ..................................................................................................................98 (b) Mineral identification............................................................................................................... 98 (c) Common rock-forming minerals .............................................................................................. 995.20. Igneous rocks ......................................................................................................................................... 100 (a) General ........................................................................................................................................ 100 (b) Classification.. ............................................................................................................................101 (c) Primary structural features.. .................................................................................................... 1015.21. Sedimentary rocks.. ............................................................................................................................... 102 (a) General ........................................................................................................................................ 102 (b) Characteristics ...........................................................................................................................103 (c) Primary structural features ...................................................................................................... 1035.22. Metamorphicrocks ...............................................................................................................................105 (a) General ........................................................................................................................................ 105 (b) Classification ..............................................................................................................................1055.23. Rock classification ................................................................................................................................ 107 (a) Unit names and identification ................................................................................................. 108 (b) Descriptors and descriptive criteria for physical characteristics.. ...................................... 111F. SURFACE EXPLORATIONS5.24. General ................................................................................................................................................... 1135.25. Fluvial-lacustrine soils .......................................................................................................................... 113 (a) Definition ....................................................................................................................................113 (b) Outwash deposits ....................................................................................................................... 113 (c) Flood plain deposits.. ................................................................................................................. 114 (d) Lacustrine deposits .................................................................................................................... 1165.26. Glacial deposits.. .................................................................................................................................... 116 (a) General ........................................................................................................................................ 116 (b) Glacial till.. ................................................................................................................................. 116 (c) Glacial outwash .......................................................................................................................... 1165.27. Aeolian deposits.. ...................................................................................................................................1195.28. Residual soils .........................................................................................................................................119G. GEOPHYSICAL EXPLORATIONMETHODS5.29. General ................................................................................................................................................... 1215.30. Surface geophysical techniques ...........................................................................................................122 (a) Seismic refraction surveys ........................................................................................................123 (b) Seismic reflection surveys ........................................................................................................123 (c) Shear-wave surveys ....................................................................................................................124 (d) Surface waves .............................................................................................................................125 (e) Vibration surveys .......................................................................................................................125 (f) Electrical-resistivity profiling surveys ....................................................................................126 16. CONTENTSxviiSe& 3nPage(g)Electrical-resistivitysoundings ................................................................................................127(h)Electrical-resistivity, dipole-dipole surveying ........................................................................127(i)Electromagnetic-conductivity profiling surveys.. ...................................................................128(j)Electromagnetic-conductivity sounding surveys.. ..................................................................128(k)Ground-probing radar ...............................................................................................................128(1)Self-potentialsurveying.. ..........................................................................................................128H. SUBSURFACE EXPLORATORY METHODS5.31. Accessible exploratory methods ..........................................................................................................129 (a) Test pits ......................................................................................................................................130 (b) Large-diameter borings.. ...........................................................................................................130 (c) Trenches ...................................................................................................................................... 130 (d) Tunnels ....................................................................................................................................... 1315.32. Nonaccessible exploratory methods.. .................................................................................................. 132 (a) Cone-penetrometer testing.. ..................................................................................................... 132 (b) Standard penetration testing.. .................................................................................................132 (c) Auger drilling.. ............................................................................................................................ 133 (d) Rotary drilling.. ..........................................................................................................................140 (e) Core drilling.. ..............................................................................................................................148I. SAMPLING METHODS5.33. General ................................................................................................................................................... 1505.34. Disturbed samples (hand-sampling methods) ................................................................................... 151 (a) Accessible test pits, trenches, and large-diameter borings ..................................................151 (b) Stockpiles and windrows .......................................................................................................... 151 (c) Hand-auger borings ................................................................................................................... 151 (d) Concrete aggregate sources ......................................................................................................151 (e) Riprap sources ............................................................................................................................1525.35. Disturbed samples (mechanical sampling methods) ........................................................................153 (a) Power auger drills.. ....................................................................................................................153 (b) Reverse-circulationdrills.. ........................................................................................................ 1555.36. Protection and preparation of disturbed samples for shipping.. .................................................... 1555.37. Undisturbed hand-sampling methods.. ............................................................................................... 155 (a) Procedures for obtaining hand-cut samples.. .........................................................................155 (b) Protection and shipping preparation for hand-cut undisturbed samples.. ........................1555.38. Undisturbed mechanical sampling methods.. ....................................................................................155 (a) Soft, saturated cohesive or noncohesive soils.. ...................................................................... 156 (b) Soft to moderately firm cohesive soils ................................................................................... 158 (c) Medium to hard soils and shales.. ...........................................................................................1595.39. Rock coring methods ............................................................................................................................160J. LOGGINGEXPLORATIONS5.40. Identificationof holes ........................................................................................................................... 1615.41. Log forms ...............................................................................................................................................1625.42. Information on log forms ..................................................................................................................... 164(a) Drilling notes column ................................................................................................................ 165(b) Center column.. .......................................................................................................................... 170(c) Classification and physical conditions column.. .................................................................... 1705.43. Description of soils ............................................................................................................................... 1715.44. Description of rock cores .....................................................................................................................172(a) Objectives of geologic logging ................................................................................................... 173(b) Data required for geologic logs of drill holes ......................................................................... 173 17. . ..XVIII DESIGN OF SMALL DAMSSectionPageK. FIELD AND LABORATORY TESTS5.45. General ................................................................................................................................................... 1755.46. Field permeability tests ........................................................................................................................ 175(a) General ........................................................................................................................................175(b) Open-end tests ...........................................................................................................................176(c) Packer tests ................................................................................................................................ 1775.47. Inplace unit weight tests (sand replacement method). .................................................................... 1785.48, Vane shear test.. ....................................................................................................................................1795.49. Laboratory tests on soils ......................................................................................................................179(a) Gradation ....................................................................................................................................179(b) Moisture content .......................................................................................................................181(c) Atterberg limits .......................................................................................................................... 181(d) Specific gravity ...........................................................................................................................183(e) Laboratory compaction ............................................................................................................. 183(f) Relative density .......................................................................................................................... 1835.50. Laboratory tests on riprap and concrete aggregate ..........................................................................185(a) Specific gravity and absorption ............................................................................................... 185(b) Abrasion.. .................................................................................................................................... 185(c) Soundness ................................................................................................................................... 185L. BIBLIOGRAPHY5.51. Biliography .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... .... .. .... ... .... .. .......................186CHAPTER6. EARTHFILL DAMSA. INTRODUCTION6.1.Origin and development .......................................................................................................................1876.2.Scope of discussion ............................................................................................................................... 1876.3.Selection of type of earthfill dam .......................................................................................................188 (a) General ........................................................................................................................................ 188 (b) Diaphragm type ......................................................................................................................... 189 (c) Homogeneous type.. ................................................................................................................... 189 (d) Zoned embankment type .......................................................................................................... 192B. DESIGN PRINCIPLES6.4.Design data ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... ... .... .................... 1926.5.Design criteria . .... ... ... ... .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ... ....192C. FOUNDATION DESIGN6.6.General ................................................................................................................................................... 1936.7.Rock foundations.. .................................................................................................................................1946.8.Methods of treating rock foundations.. .............................................................................................. 1946.9.Sand and gravel foundations ............................................................................................................... 202(a) General.. ......................................................................................................................................202(b) Amount of underseepage .......................................................................................................... 203(c) Seepage forces ............................................................................................................................ 2046.10. Methods of treating sand and gravel foundations ............................................................................205(a) General ........................................................................................................................................205 18. CONTENTSxixSectiaPage (b) Cutoff trenches .......................................................................................................................... 206 (c) Partial cutoff trenches .............................................................................................................. 206 (d) Sheet piling cutoffs ................................................................................................................... 207 (e) Cement-bound and jet-grouted curtain cutoffs ..................................................................... 208 (f) Slurry trench cutoffs .................................................................................................................209 (g) Grouting.. ....................................................................................................................................212 (h) Upstream blankets .................................................................................................................... 212 (i) Downstream embankment zones for pervious foundations.. ............................................... 215 (j) Toe drains and drainage trenches.. ......................................................................................... 219 (k) Pressure-relief wells .................................................................................................................. 2206.11.Designs for sand and gravel foundations.. .........................................................................................224 (a) General.. ...................................................................................................................................... 224 (b) Case 1: Exposed pervious foundations (shallow depth) ....................................................... 225 (c) Case 1: Exposed pervious foundations (intermediate depth) .............................................. 225 (d) Case 1: Exposed pervious foundations (great depth) ........................................................... 227 (e) Case 2: Covered pervious foundations ....................................................................................228 (f) Summary of pervious foundation treatments ........................................................................ 2286.12.Methods of treating silt and clay foundations.. ................................................................................ 229 (a) General ........................................................................................................................................ 229 (b) Saturated foundations ...............................................................................................................231 (c) Relatively dry foundations.. ......................................................................................................2326.13.Designs for silt and clay foundations.. ...............................................................................................234 (a) Saturated foundations.. .............................................................................................................234 (b) Relatively dry foundations ....................................................................................................... 234 D. EMBANKMENTS6.14.Fundamental considerations ................................................................................................................2396.15.Pore water pressure .............................................................................................................................. 2406.16.Seepage through embankments ...........................................................................................................2416.17.Stability analyses ..................................................................................................................................2436.18.Embankment design .............................................................................................................................244(a) Use of materials from structural excavation ..........................................................................244(b) Embankmentslopes, general ................................................................................................... 245(c) Diaphragm type .......................................................................................................................... 246(d) Homogeneous type .....................................................................................................................249(e) Zoned embankments ..................................................................................................................2496.19.Seismic design.. ......................................................................................................................................253 E. EMBANKMENT DETAILS6.20.Crest design ............................................................................................................................................253(a) General ........................................................................................................................................253(b) Width ..........................................................................................................................................253(c) Drainage ...................................................................................................................................... 253(d) Camber ........................................................................................................................................ 253(e) Surfacing.. ................................................................................................................................... 255(f) Safety requirements ................................................................................................................... 255(g) Zoning .......................................................................................................................................... 255(h) Typical crest details ..................................................................................................................2556.21.Freeboard ................................................................................................................................................ 2556.22.Upstream slope protection ...................................................................................................................258(a) General ........................................................................................................................................258(b) Selecting the type of protection .................................................... . ......................................... 258 19. xxDESIGN OF SMALL DAMSSection Page (c) Dumped rock riprap ..................................................................................................................260 (d) Hand-placed rock riprap.. .........................................................................................................262 (e) Concrete paving.. ........................................................................................................................ 262 (f) Soil-cement .................................................................................................................................2636.23. Downstream slope protection.. ............................................................................................................2656.24. Surface drainage.. .................................................................................................................................. 2666.25. Flared slopes at abutments.. ................................................................................................................ 267F. DESIGN EXAMPLES OF SMALL EARTHFILL DAMS6.26. General ................................................................................................................................................... 2676.27. Maximum sections ................................................................................................................................ 268(a) Amarillo Regulating Reservoir.. ............................................................................................... 268(b) Cawker City Dike ...................................................................................................................... 268(c) Big Sandy Dike .......................................................................................................................... 268(d) Carpinteria Reservoir Dike ...................................................................................................... 268(e) Carter Lake Dam No. 3.. ..........................................................................................................270(f) Crane Prairie Dam.. ................................................................................................................... 270(g) Crescent Lake Dam.. ................................................................................................................. 270(h) Dickinson Dam.. ........................................................................................................................270(i) Dry Falls Dam ............................................................................................................................272(j) Fruitgrowers Dam ...................................................................................................................... 272(k) Howard Prairie Dam.. ...............................................................................................................272(1) Lion Lake Dikes ......................................................................................................................... 272(m) Lovewell Dam ...........................................................................................................................272(n) Eklutna Dam.. ............................................................................................................................272(0) Lower Two Medicine Dam .......................................................................................................272(p) Olympus Dam ............................................................................................................................274(q) Picacho North Dam ..................................................................................................................274(r) Picacho South Dam.. ................................................................................................................. 274(s) Pishkun Dikes ............................................................................................................................276(t) Lubbock Regulating Reservoir .................................................................................................276(u) Shadow Mountain Dam.. ..........................................................................................................276(v) Soda Lake Dike .......................................................................................................................... 276(w) Stubblefield Dam ...................................................................................................................... 276(x) Tiber Dike .................................................................................................................................. 276(y) Sheep Creek Barrier Dam.. ......................................................................................................276(z) Wasco Dam ................................................................................................................................. 276(aa) Ute Dam Dike ..........................................................................................................................276(bb) San Justo Dike ........................................................................................................................278(cc) Calamus Dam ...........................................................................................................................278G. BIBLIOGRAPHY6.28. Bibliography. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ................... 283CHAPTER7. ROCKFILL DAMSA. GENERAL7.1.Origin and usage.. ..................................................................................................................................2877.2.Definition and types of rockfill dams ................................................................................................ 287 20. CONTENTS xxiSectionPageB. FOUNDATION DESIGN7.3.Foundation requirements and treatment ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... .... ... ... ... .... 2897.4.Membrane cutoffs ... .... ... ... ... .... .. .... .. .... ... .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... ... ... ... .... ... ... ... .... ... .......... 289C. EMBANKMENT DESIGN7.5.Selection of rock materials .. ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... ... ... ... .... ... ... ... .... ... .... ... ... ... .... ... ..2917.6.Embankment sections . .. .... .. .... ... .... .. .... ... .... .. .... .. .... ... .... ... ... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ... .... .. ..... .. .. 2927.7.Placement of rockfill materials . .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... ... .... .. .... ... .... ... .... .. .... ... .... ... . 2977.8.Seismic design .. .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ... .... ... .... .. .... ................. 299D. MEMBRANE DESIGN7.9.Impervious central core.. ...................................................................................................................... 3007.10. Reinforced concrete.. .............................................................................................................................3007.11. Asphaltic concrete.. ............................................................................................................................... 3027.12. Steel ........................................................................................................................................................ 3077.13. Timber planking.. .................................................................................................................................. 308E. BIBLIOGRAPHY7.14. Bibliography. ... .... ... .... .. .... ... ... ... .... ... ... ... .... .. .... ... ... ... .... ... ... ... .... .. ..... .. .... ... .... .. .... ... .... ... .... .................... 312CHAPTER8. CONCRETE GRAVITYDAMSA. INTRODUCTION8.1.Origin and development .. .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... ... .... .. .... ... .... ... .... .. .... ... .... .. .... . 3158.2.Scope of discussion .... ... ... ... .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... .... .. .... ... .... .. .... ... .... ... .... .. .... ....... 315B. CONCRETE PROPERTIES8.3.Strength ..................................................................................................................................................3158.4.Elastic properties ..................................................................................................................................3168.5.Thermal properties ............................................................................................................................... 3168.6.Average properties ................................................................................................................................. 316 (a) Basic considerations .................................................................................................................. 316 (b) Criteria ........................................................................................................................................ 316C. FORCES ACTING ON THE DAM8.7.General ...................................................................................................................................................3178.8.External water pressure .......................................................................................................................318 (a) Basic considerations .................................................................................................................. 318 (b) Criteria ........................................................................................................................................ 3188.9.Temperature ...........................................................................................................................................318(a) Basic considerations ..................................................................................................................318(b) Criteria.. ......................................................................................................................................3208.10. Internal water pressures ......................................................................................................................320(a) Basic considerations ..................................................................................................................320 ---(b) Criteria .... ... .... .. .... .. .... ... ... ... .... .. .... ... ... ... .... .. .... .. .... ... ... ... .... .. .... ... .... ... .... .. .... ... .... .. .... ................. 321 21. xxiiDESIGN OF SMALLDAMSSectionPage8.11. Dead load ................................................................................................................................................ 321(a) Basic considerations.. ................................................................................................................321(b) Criteria ........................................................................................................................................3218.12. Ice ............................................................................................................................................................ 321(a) Basic considerations ..................................................................................................................321(b) Criteria.. ......................................................................................................................................3218.13. Silt pressure ...........................................................................................................................................322(a) Basic considerations.. ................................................................................................................322(b) Criteria ........................................................................................................................................3228.14. Earthquake.. ........................................................................................................................................... 322(a) Basic considerations ..................................................................................................................322(b) Criteria.. ......................................................................................................................................3258.15. Load combinations ................................................................................................................................ 326(a) Basic considerations.. ................................................................................................................326(b) Criteria.. ......................................................................................................................................326D. FOUNDATIONCONSIDERATIONS8.16. Deformation modulus ...........................................................................................................................326 (a) Basic considerations.. ................................................................................................................ 326 (b) Criteria.. ...................................................................................................................................... 3278.17. Shear strength.. ..................................................................................................................................... 327 (a) Basic considerations.. ................................................................................................................ 327 (b) Criteria.. ...................................................................................................................................... 3288.18. Foundation configuration.. ................................................................................................................... 328 (a) Basic considerations .................................................................................................................. 328 (b) Criteria.. ...................................................................................................................................... 328E. REQUIREMENTS FOR STABILITY8.19. Safety factors.. ....................................................................................................................................... 328 (a) Basic considerations .................................................................................................................. 328 (b) Criteria.. ...................................................................................................................................... 328F. STRESS AND STABILITY ANALYSES8.20. Sliding stability ..................................................................................................................................... 329(a) Basic considerations .................................................................................................................. 329(b) Criteria.. ............................................................. .;. ...................................................................... 3308.21. Internal stresses-untrackedsections ............................................................................................... 330(a) Basic considerations .................................................................................................................. 330(b) Criteria.. ...................................................................................................................................... 3318.22. Internal stresses and sliding stability-crackedsections ................................................................331(a) Basic considerations .................................................................................................................. 331(b) Static method of analysis.. ....................................................................................................... 331(c) Pseudostatic method of analysis ..............................................................................................332(d) General iterative method of analysis.. .................................................................................... 334(e) Criteria ........................................................................................................................................ 334G. ADDITIONALTOPICS8.23. Dams on pervious foundations ............................................................................................................ 3348.24. Details of layout and design ................................................................................................................ 335 (a) Nonoverflow sections ................................................................................................................335 22. . CONTENTSXXIIISection Page(b) Overflow sections.. .....................................................................................................................335(c) Contraction joints.. ....................................................................................................................335H. COMPUTER METHODS8.25. General .. .. .... ... .... .. .... ... .... .. .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ........................... 336I. BIBLIOGRAPHY8.26. Bibliography .. .... ... ... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... .. .... ... .... .. .... ... ... ... .... ... .... ... .... .. ..................... 336CHAPTER9. SPILLWAYSA. GENERAL9.1.Function .................................................................................................................................................. 3399.2.Selection of inflow design flood .......................................................................................................... 339 (a) General considerations ..............................................................................................................339 (b) Inflow design flood hydrographs .............................................................................................3409.3.Relation of surcharge storage to spillway capacity .......................................................................... 3419.4.Flood routing ......................................................................................................................................... 3419.5.Selection of spillway size and type ..................................................................................................... 344 (a) General considerations ..............................................................................................................344 (b) Combined service and auxiliary spillways.. ............................................................................345 (c) Emergency spillways .................................................................................................................. 346B. SERVICE SPILLWAYS9.6.Selection of spillway layout ................................................................................................................. 3479.7.Spillway components ............................................................................................................................ 35: (a) Control structure ....................................................................................................................... (b) Discharge channel ..................................................................................................................... 351 (c) Terminal structure.. ......................................................................