SMALL DAMS PETITS BARRAGES

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Some type of surfacing should be placed on top of the crest for protecting against damage by wave splash and spray, rainfall, wind, frost and traffic when the crest is used as a roadway. The usual treatment for small dams consists of placing a layer of gravelly material or selected fine rock at least 10 cm thick. In the south part of Brazil it is usual to use a granular material with some cohesion, to protect the small dam crests against erosion at a low cost. This material is composed by a blend of gneiss and limestone granular material with some percentage of bituminous shale, grading in such a way to form an adequate and appropriate material, used in the construction of rural roads, as can be seen in Fig. 5.15. This material has been used successfully for the crest protection of small dam crest and berms, in which the bituminous shale cause the gluing of the particles together, implicating in a good cohesion and avoiding erosion during rainy season, and also the developing of cracks during the dry season. Figure 5.15 – Constructing a rural road using a granular material composed by gneiss, limestone and bituminous shale. 5.11.5 Traffic Safety Requirements When the crest of a dam is used as a highway, cable or beam-type guardrails are usually constructed along both shoulders of the crest. In other cases the crest can be lined with guard posts at 8 m interval or, on very minor structures, by boulders placed at intervals along the crest. If little or no traffic will use the crest, special treatment may not be necessary. 5.12 CONSTRUCTION TECHNIQUES FOR THE FOUNDATION AND THE FILL The foundation can cause problems in the event of a strong earthquake when it contains materials that are likely to present a significant decrease in strength in relation with strong development of pore pressures (phenomenon of liquefaction of saturated loose sands) or high distortion (soft clays), as pointed out by the French Guidelines on Small Dams. As a general rule, these materials also pose problems in “static” design of the dam and may have been replaced or treated within the dam area. In this case it is to check the influence of whatever 84
material has been left in place or has not been treated beyond the dam’s upstream and downstream toes. In the case of sandy layers, classic treatment consists in building a mesh of vertical drains (to drain overpressures generated by the earthquake) or in improving the ground by densifying it. For the fill, modifications may be necessary to deal with any internal problems and strains that may occur. Generally, a probable consequence of a strong earthquake is the appearance of concentrated leakage through the dam. Such modifications concern zoning of the fill, resistance of the materials to retrogressive erosion, and design of the crest. The following precautions are worth mentioning: � Avoid fine, cohesion less and uniform soil in saturated zones; � Provide a chimney drain or enlarge it in the case of homogeneous fills; � Design transition zones that are as wide as possible; � Be specially prudent with the thickness of filters; � Place a layer of sand upstream from the core to plug any cracks that may be caused by an earthquake; � Build the dam or its core with materials offering good resistance to internal erosion (plastic clays, sandy gravel with fines of a very continuous grading). In addition, as recommended by the French Guidelines, if the design earthquake intensity is very strong, it may be wise to increase freeboard and crest width. 5.13 REFERENCES [1] CHINCOLD (1979) – Dam Construction by the Chinese People, The Chinese National Committee on Large Dams;. [2] SHERARD, J.L., DUNNIGAN, L.P. (1985) – “Filters and Leakage Control in Embankment Dams”, Proc. Symposium on Seepage and Leakage from Dams, ASCE. [3] Bureau of Reclamation (1987) – Design of Small Dams, United States Department of the Interior, A Water Resources Technical Publication; [4] LEWIS, B. (2002) – Farm Dams – Planning, Construction and Maintenance, National Library of Australia Cataloguing; [5] CEMAGREF (2002) – Small Dams – Guidelines for Design, Construction and Monitoring, French Committee on Large Dams; [6] DURAND JM, ROYET P, MÉRIAUX P (2002) – Technique des Petits Barrages en Afrique Sahélienne et Équatoriale, Cemagref Editions. [7] SMEC (2006) – Draft Guidelines for Managing Small Dams, SMEC Australia Pty Ltd, Guide developed on behalf of The Republic of Uganda. [8] JSIDRE (2006) – The Guidelines for Designing of Agricultural Land Improvement Projects, “Tameike Small Dams”, Japanese Society of Irrigation, Drainage and Reclamation Engineering, February 2006. 85
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SMALL DAMS Design, Surveillance and
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FOREWORD The ICOLD - International
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ACKNOWLEDGEMENT The Ad Hoc Committe
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FOREWORD ACKNOWLEDGEMENT SUMMARY TA
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5.5.5 Compaction in confined areas
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7.2.1 Introduction 7.2.2 Spillway c
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1. SMALL DAMS DEFINITION AND CLASSI
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2 Fig. 1.2 - Relationship H . V wit
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1.3 REFERENCES [1] French Committe
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2.3 ZONED EARTHFILL DAMS In arid pa
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sloping core guarantees water impou
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Fig. 2.11 - Hlinky Concrete Gravity
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Fig. 2.13 - Photograph of Neusberg
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The gabion dam as the gabion retain
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Some inflatable dams are operated b
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3.1 INTRODUCTION 3. SAFETY OF SMALL
Page 33 and 34: Condition Effect on safety 13. Dama
Page 35 and 36: Fig. 3.2 - Massive dam break overto
Page 37 and 38: and suffusion or internal instabili
Page 39 and 40: downstream part of the embankment m
Page 41 and 42: small dam impounding a lot of water
Page 43 and 44: Whenever the Supervising Authority
Page 45 and 46: emergency management organizations
Page 47 and 48: c) The decommissioning plan should
Page 49 and 50: 5.1 INTRODUCTION 5. FEATURES OF THE
Page 51 and 52: 5.2 DESIGN FLOODS Inadequate flood
Page 53 and 54: downstream slope will show seepage
Page 55 and 56: Fig. 5.2 - Design Freeboard 5.4.3 F
Page 57 and 58: 2 U f Fe S 1400 D Where Uf is the d
Page 59 and 60: Maximum compaction is obtained at c
Page 61 and 62: characteristic must be determined.
Page 63 and 64: 5.6.1 Foundation Watertightness The
Page 65 and 66: � A continuous vertical chimney d
Page 67 and 68: Thickness of pervious layer Thick D
Page 69 and 70: t 5.7.1.4 Practical Considerations
Page 71 and 72: It is generally accepted that cohes
Page 73 and 74: � Simple Bishop (1955) � Spence
Page 75 and 76: � The elements for surface draina
Page 77 and 78: The supporting layer for the rip-ra
Page 79 and 80: For very small reservoirs (fetch of
Page 81 and 82: The junction of the downstream slop
Page 83: Fig. 5.14 - Hongshiyan homogenous d
Page 87 and 88: The homogeneous dam is recommended
Page 89 and 90: [3] OL and OH soils are not recomme
Page 91 and 92: part (core) lies in the zone (Fig.
Page 93 and 94: 6. GUIDELINES ON SURVEILLANCE OF SM
Page 95 and 96: cases the owner may retain the serv
Page 97 and 98: Surface displacement on an embankme
Page 99 and 100: Fig. 6.1 - Leakage measurement usin
Page 101 and 102: Water Level Sounder - Details of th
Page 103 and 104: pressure) Left abutment 2 5 Weir ga
Page 105 and 106: Fig. 6.9 - Recommended standpipe pi
Page 107 and 108: the others weir gauges need to be i
Page 109 and 110: � Earthquakes sensible at the dam
Page 111 and 112: APPENDIX INSPECTION CHECKLIST FOR S
Page 113 and 114: Exposed reinforcement � The condu
Page 115 and 116: These spillways can be lined or unl
Page 117 and 118: flowing water. Flowing water with h
Page 119 and 120: Fig. 7.3 - Installation of the arti
Page 121 and 122: Fig. 7.7 - Dam overtopping protecti
Page 123 and 124: complete construction was in 2001,
Page 125 and 126: In some cases, the downstream face
Page 127 and 128: Tube-a-manchettes injection system
Page 129 and 130: 7.3.5 Slope Protection Measures 7.3
Page 131 and 132: Pipe Rehabilitation SLIPLINING MODI
Page 133 and 134: Conditions Pros Cons Comments types
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Embankment dams that have properly
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and minimize erosion. Design of sui
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[20] SMEC- “Draft Guidelines for
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present visual information. It must
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Fig. 8.1 - Three small dams in casc
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Social Disruption low (rural area)
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Fig. 8.4 - Flood water level after
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8.9 REFERENCES [1] BURREC (1994) -
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SMALL DAMS PETITS BARRAGES

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