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UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION DESIGN OF SMALL DAMS A Water Resources Technical Publication First Edition, 1960 Second Edition, 1973 Revised Reprint, 1977 Third Edition, 1987 As the Nation’s principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserv- ing the environmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major responsibility for American Indian reservation communities and for people who 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 III Mission of the Bureau of Reclamation The Bureau of Reclamation of the U.S. Department of the Interior is responsible for the development and consarvation of the Nations water resources in the Western United States. The Bureau’s original purpose “to provide for the reclamation of arid and semiarid lands in the West” today covers a wide range of interre- la ted functions. These include providing municipal and industrial water supplies; hydroelectric power generation; irrigation water for agricul- ture; water quality improvement; flood control; river navigation; river regulation and control; fish and wildlife enhancement; outdoor recreation; and research on water-related design, construe tion, materials, atmospheric management, and wind and solar power. Bureau programs most frequently are the result of close cooperation with the U.S. Congress, other Federal agencies, States, local govern- men ts, academic institutions, water-user organizations, and other concerned groups. Preface to the Third Edition The 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 wildlif’e published in a number of different languages and resources at, completed project,s, in addition to new used extensively in the United Stat,es. Since the design considerations. An expanded section on second edition was published in 1974, there have water quality implications to dam design and op been significant revisions in the approaches and erat,ion is also included. procedures related to the design of dams. Because Chapter 3, “Flood Hydrology Studies,” has been of these revisions and the continued demand for this complet,ely revised, including incorporating t,he pre- manual, it was decided that, this new third edition vious appendix A, “EsGmating Rainfall Runoff’ be prepared and published. from Soil and Cover Data,” int,o the chapt,er. Ref- The purpose of this third edition has been erence to t,he Soil Conservation Services’ curve changed in scope and intent from that of the second number approach for assigning infiltration losses, edition. The title Design of Small Dams has been the triangular unit-hydrograph approach, and all retained even though some of the information in discussions and plates providing guidance for es- the third edition relates to large dams. Many of the timating probable maximum precipitation have theoretical concepts presented can be applied to been eliminated. These topics have been replaced large or small structures; however, it is recom- by a treatment of infiltration losses as actually ap mended that the procedures and methods presented plied by the Bureau of Reclamation, expanded con- be used only as guidelines. When preparing the de- sideration and guidance relative t,o the development sign of large or complicated structures, especially of unit, hydrographs using the dimensionless uni- those located where they create a high hazard, the graph and S-graph approaches, and specific ref- owner should rely on experienced dam engineers, erence to the Nat,ional Weather Service’s experienced consultants, or refer to more detailed Hydrometeorological Report series as the basis for references. developing probable maximum precipitation esti- Some of the chapters and appendixes have been mates for the contiguous United Statues. revised extensively, while others reflect only minor Chapter 5, “Foundation and Const,ruction Ma- revisions. Chapter 1, “Plan Formulation,” has been terials,” has been updated t,o incorporate current condensed to briefly cover only the basic concepts standards in foundation and construction mat,erials of plan formulation. The authors of this chapter investigations. A reservoir studies section has been concluded that a detailed discussion of plan for- added to the section on scope of investigations. The mulation was not appropriate because the primary sections on soil and rock classification have been focus 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 to ticularly with an emphasis on Federal plan summarize the capabilities of these methods. The formulat,ion requirements, would not be of interest sections on subsurface explorations and sampling to a majority of dam designers. The chapter thus have been revised extensively to represent, new tech- provides a brief discussion of the steps of plan for- nology. The logging of explorations has also been mulation and some of the fundamental tests for the revised to reflect current standards, and t,he field viability of proposed plans. and laboratory test section has been updated. Chapter 2, “Ecological and Environmental Con- Changes in soil mechanics terminology and soil V vi testing procedures generated by revision of the Bu- modified low Froude number basin as an alternative reau’s Earth Manual are reflected in this chapter. to basin 4 design, and modifications in the design The previous table 8, “Average Properties of Soils,” criteria for baffled apron spillways to permit their which is now table 5-1, was recompiled to include use for higher unit discharges. Other contemporary laboratory test results obtained since the last edi- spillway concepts are introduced, although design tion. Figure 5-14, “Permeability of Soils,” was added criteria are not included because they are still under to this edition to illustrate ranges of permeability development. Included in this category are laby- measured on compacted soil specimens tested at the rinth weirs where large flows must be discharged in Bureau’s laboratory in Denver. The bibliography a limited space such as a narrow canyon, and the has been updated to include selected sources of in- use of air slots (aerators) in spillways where there formation for foundation and construction mate- is high potential for cavitation damage. Plunge-pool rials investigation. design criteria have been somewhat improved by the Chapter 6, “Earthfill Dams,” has been revised to addition of several references to recent research. update terminology and reflect design philosophy, The suggested method for calculating the discharge procedures, and standards that have evolved since under radial gates has been revised to reflect 1974. The major change is greater emphasis on in- up-to-date criteria developed by the U.S. Army ternal filtering and drainage to control seepage and Corps of Engineers, Waterways Experiment Sta- internal erosion within embankment dams. New tion. The section on siphon spillways has been figures have been added that show current dam em- omitted from this edition because they are seldom bankments 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 reflect erences that were hard to obtain and by the addition current thinking and technology. Liberal reference of many new references that reflect the current is made to design standards that have been devel- state-of-the-art. oped as guides for Bureau engineers. Chapter 12, “Operation and Maintenance,” now Chapter 7, “Rockfill Dams,” required only minor includes additional topics, clarification, and more revisions; 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 a of rockfill dams. Design and construction proce- structure to add additional storage or to change the dures for rockfill dams have changed over the last purpose of allocation of storage; “Emergency Pre- two or three decades and continue to do so. The paredness Plan,” which addresses instructions to an chapter gives a good general background for the operator during emergency situations; and “Dam design of rockfill dams; 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 that Chapter 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 dam concerns for concrete dams of any height. Sections safety. Although dam safety is always an underlying on 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,ional requirements for stability, and stress and stability emphasis on dam safety; and the inclusion of a analyses. Discussions addressing the analysis of chapter on this subject was believed to be impor- cracked dams have been clarified and expanded to tant. This chapter presents procedures and refer- include analysis during an earthquake. Also, a gen- ences to other procedures for the evaluation and eral iterative approach for cracked dam analysis, analyses of dam safety issues for both new and ex- applicable for static and dynamic conditions, is now isting dam structures. included. The appendix designations have been revised. The “Spillways” and “Outlet Works” chapters, 9 The previous appendix A is now part of chapter 3, and 10, respectively, now include two new hydraulic and the original appendix H, “Sedimentation,” is designs for energy dissipators. These designs are a now appendix A. A new appendix H, “Operation vii and 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 dams was 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, and Rock Mechanics,” and from USBR 3900, “Standard evaluation processes. The text is not intended in Definitions 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, but reau’s recently revised Earth Manual, volume 2, rather to point out the importance of specialized “Test Designations.” training. Engineers who do not have specialized Appendix E, “Construction of Embankments,” training in dam engineering should seek advice has been revised to emphasize and more fully de- from experienced consultants. scribe construction control philosophy and proce- This manual was prepared by personnel of the dures. Several photographs of more modern Bureau of Reclamation, U.S. Department of the In- equipment and construction techniques have been terior, Denver, Colorado, under the direction of added. The “Rapid Method of Compaction Con- Darrell Webber, Assistant Commissioner, Engi- trol” has been eliminated; the reader is now referred neering and Research, with contributions from the to the Bureau’s Earth Manual for that procedure. staff of other Assistant Commissioners. Neil Par- Terminology has 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 has man, Head, Design Section No. 2 of the Concrete been expanded in appendix F, “Concrete in Con- Dams Branch; Thomas N. McDaniel, Design Man- struction.” The design of concrete mixes has been ager, Embankment Dams Branch; and Ronald D. revised and includes revisions to tables, forms, and Mohr, General Engineer, Document Systems Man- the steps involved in concrete mix design. agement Branch. Numerous engineers, technicians, Appendix G, “Sample Specifications,” has been and support personnel participated with this team updated to include guide specifications currently in the preparation of this third edition and their used by the Bureau of Reclamation. efforts are greatly appreciated. Special recognition Throughout the third edition, figures and illus- to the many authors, both current and past, is trations have been revised and many new figures appropriate: Current Author(s) Past Author(s) Chapter 1 W.C. Dunkin, C.W. Huntley A.F. Johnson Chapter 2 J.C. Hokenstrom E.A. Seamen, L.W. Davidson Chapter 3 A.G. Cudworth, Jr. D.L. Miller, R.A. Clark, S. Schamach Chapter 4 T.N. McDaniel, H.K. Blair H.G. Arthur Chapter 5 S.R. Bartlett, R.C. Hatcher J.W. Hilf Chapter 6 T.N. McDaniel H.G. Arthur Chapter 7 T.N. McDaniel R.W. Bock, L.W. Davidson Chapter 8 H.L. Boggs, C.C. Hennig A.T. Lewis, J.S. Conrad, E.L. Watson, L.M. Christiansen Chapter 9 H.K. Blair, T.J. Rhone C.J. Hoffman Chapter 10 H.K. Blair, T.J. Rhone C.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 *.* VIII Current Author(s) Past Author(s) Appendix B R.I. Strand, T.J. Rhone C.J. Hoffman, J.M. Lara, R.I. Strand Appendix C R.A. Simonds, H.K. Blair P.K. Bock, C.J. Hoffman Appendix D R.A. Young J.W. Hilf Appendix E T.N. McDaniel J.W. Hilf Appendix F J.L. Hart J.E. Backstrom, L.C. Porter, E.L. Ore, G.B. Wallace Appendix G J.L. Hart, R. Wright, R.E. Fink, N.F. Larkins, R.H. Restad, T.N. McDaniel E.R. Lewandowski Appendix H W.P. Gersch, L.J. Yocom Preparation of the manuscript for publication sional references to proprietary materials or prod- was performed by the personnel of the Planning ucts in this publication. These references are not and 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 the vices of commercial firms. use of their material in this text. There are occa- Preface to the Second Edition The first edition of “Design of Small Dams” was discussion of the slurry trench method of cutoff published 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 United and a more extensive reference list. The discussion States. Its publication was warmly received and, in of rockfill dam design has been considerably ex- the intervening years since then, it has been widely panded in chapter VII to reflect the recent interest used in the United States, reprinted numerous in 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 new formation on the estimation of rainfall runoff from design procedures used at the Bureau of Recla- soil cover data, and an expanded discussion of flow mation have been changed to reflect more.modern in 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 both techniques increased, it became apparent that their reinforced concrete pressure pipe and cast-in-place incorporation 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, and sentially the same as for the first edition. Many of each specification has been updated to reflect cur- the design procedures proposed in the first edition rent 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 estimate and are currently in use. To make this new infor- the rate of sedimentation and the period of time mation 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 facilitate flected by the inclusion of chapter II, “Ecological the increased utilization of metric units. Many mi- and Environmental Considerations.” This chapter nor changes have been made throughout the text to outlines some of the practical measures which may reflect current design and construction techniques. be t.aken to reduce the environmental and ecological It is intended that this book will provide the de- impact of a project. Chapter III has been extensively signer with an important source of information. revised’to include current methods of design flood However, this text is not intended in any way to computation 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 use ability of current information concerning founda- or application of the methods and data contained tion design and to include supplemental foundation herein is strictly the responsibility of the person investigation procedures. Chapter VI contains ad- utilizing the material. Designs should reflect the ditional material on the design of earth dams, a actual site conditions and should not merely be pat- ix