SMALL DAMS PETITS BARRAGES

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For dams with 5 to 15 m height, the following crest width are then recommended. Table 5.18 – Crest width recommended for small dams – Bureau of Reclamation/87 [3] Dam Height (m) Crest Width (m) 5 4 10 5 15 6 Many successful small dams have been constructed with crest less than 6 m wide. No dam should have a crest width of less than 3 m, because this is the minimum needed for an access road to permit maintenance works. The French Guidelines for Small Dams observed that for zoned dams their width also depend on the number of zones at the crest. The following minimum widths are proposed, depending on their safety parameter H V 2 : Table 5.19 – Minimum crest widths proposed for small dams (French Guidelines) [5] Parameter H V 2 < 100 100 to 300 > 300 L minimum 3 m 4 m 5 m Lewis, 2002 [4] observed that the crest width increases as the height of the dam increases, and presents the following empirical formula for crest width: Crest width (m) = H 0,5 + 1 Where H is the height of the crest above the bed stream. Table 5.16 presents the Australian recommended top width for dams of various heights based on the above formula. Table 5.20 – Crest width recommended for small dams (Lewis, 2002) Dam Height Crest Width (m) (m) 4 3.00 5 3.25 6 3.50 7 3.65 8 3.85 9 4.00 In China, at the Hongshiyan homogenous dam, 12 m maximum height, in Hubei Province, a crest width 5 m had been used, as can be seen in Fig. 5.14. 82
Fig. 5.14 – Hongshiyan homogenous dam in China For ease of construction with power equipment, the minimum width should be 4.0 m. 5.11.2 Drainage Surface drainage of the crest should be provided by a crown of at least 8 cm, or by sloping the crest to drain toward the upstream slope. The latter is preferred, unless the downstream slope is protected against erosion. In such a way the crest should be drained with a slope toward the reservoir (3% to 4% inclination). 5.11.3 Allowance for Settlement Settlement in small dams is due to consolidation or saturation. Consolidation is the process of squeezing out the pore water by the weight of the embankment itself. Consolidation settlement can be settlement of the embankment or the foundation, and need special care when there are collapsible soils at the abutments, which usually occur in regions with tropical weather. The collapsible soils suffer sudden settlement when the soil layer, usually located at the abutments, are saturated during the reservoir filling period. In general, most consolidation settlement takes place during construction, particularly with coarse grained (silty and sandy) materials. Consolidation settlement will continue for an appreciable time after construction when materials, such as highly plastic clays, are used. This is particularly evident when the materials are wet during construction. Under these conditions, consolidation settlement of up to 5% can be expected. Poorly compacted soils may exhibit a sudden settlement when saturation occurs in response to seepage flow. This may lead to settlement of the soil below the seepage line. The joint between the settlement soil and the overlying unsettled soil is a common location of tunnel failure in dispersive soils. There is no simple method of predicting the amount of saturation settlement, for this type of soils. Settlement includes consolidation of both the fill materials and the foundation materials due to the weight of the dam and the increase moisture caused by the storage of water. Settlement by consolidation depends on the properties of the materials in the embankment and foundation and on the method and speed of construction. The design height of earth dams should be increased by an amount equal to the estimates settlement. 5.11.4 Surfacing 83
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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
Page 31 and 32: 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: The junction of the downstream slop
Page 85 and 86: material has been left in place or
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
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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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