SMALL DAMS PETITS BARRAGES

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downstream and bank to bank) can be taken. In the following figure are presented two different types of benchmark used in earthfill dams. Fig. 6.7 – Two types of benchmarks installed at the downstream slope. For small dams, the most common (and very often unique) measurement is settlement, which in general changes very little after a few years. It is important to start the settlement measurements as soon as the last layers of fill are compacted. The survey targets sealed into the dam body are positioned on the crest of the fill or near it and also along the downstream berm. Measurement of the relative internal displacement of the foundation and earthfill using a vertical device with several places that measure the settlement each 5 m, for instance, it is usually more recommended for medium and large dams, and it is not usual to small dams. 6.4.2 Guidelines on Dam Monitoring Recommended Types and Amount of Instruments The monitoring of small dams usually have to reduce to a minimum the cost with the instruments to be installed, but installing them where it is really important and essential to the dam supervision safety. In order to have a good quality system and with a minimum of instruments, in the following paragraphs are presented some recommendations about the type and number of devices to be installed, for dams with PIC (Potential Impact Classification) class 3 and with 100 to 300 m in length. For “Normal Geology” it means when it is enough to monitor only one foundation layer with piezometers, for instance the contact soil-rock, and “Special Geology” when it is convenient to instrument two different levels at the foundation, as a consequence of the existence of different horizontal layers and pervious materials at the foundation. Table 6.3 – Recommended types and amount of instruments for small earthfill or rockfill dams (PHC = 3) Instrument Location Normal Geology Special Geology (Parameter) Piezometer (uplift water Right abutment 2 5 Central section 3 to 5 6 to 8 102
pressure) Left abutment 2 5 Weir gauge (seepage water) Right abutment - 1 Central section 2 2 Left abutment - 1 Bench marks Crest Lc/50 Lc/20 (Displacements) Berm (eventual) Lb/50 Lb/20 (*) Obs. Lc and Lb correspond to the length of the crest and the downstream berm in meters. It is important to point out that the total amount of instruments recommended in this table is the minimum, and in the case of dams with foundations deserving special attention, with an intricate geology incorporating faults and folds directly under the dam, it is important to install some more instruments. Considering that for small dams there are usually small support for their monitoring maintenance it is recommended to install standpipe piezometers, if possible, which normally present a performance compatible with that of the dam itself. These instruments can be successfully installed in soils with a permeability coefficient higher or equal to 10 -6 cm/s, as already discussed. It is also important to install one or more weir gauge to monitor the leakage. Recommendations for Piezometer Measurements In the location of the piezometers at the dam foundation, impervious core or horizontal filter, the following recommendations are important to be attended: � To install foundation piezometers upstream and downstream of the grout curtain or the cutoff trench, in order to calculate its performance; � Perform the installation of a piezometer at the upstream drain blanket, in order to know the water head at the drainage system; � In dams with PHC = 3 install some piezometers at the central core, near the axis of the dam, to evaluate the maximum pore pressures and the phreatic line location; � If the geological investigations showed a fault crossing the foundation from upstream to downstream it is very important to install some foundation piezometers along this fault, which usually implies in a preferential seepage way. In the following sketch and expressions are presented the location of a grout curtain or the cutoff trench at the foundation of an earthfill dam, and how it is possible to calculate its efficiency considering the water head drop. 103
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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
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Condition Effect on safety 13. Dama
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Fig. 3.2 - Massive dam break overto
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and suffusion or internal instabili
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downstream part of the embankment m
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small dam impounding a lot of water
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Whenever the Supervising Authority
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emergency management organizations
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c) The decommissioning plan should
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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 and 84: Fig. 5.14 - Hongshiyan homogenous d
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: Water Level Sounder - Details of th
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
Page 135 and 136: Embankment dams that have properly
Page 137 and 138: and minimize erosion. Design of sui
Page 139 and 140: [20] SMEC- “Draft Guidelines for
Page 141 and 142: present visual information. It must
Page 143 and 144: Fig. 8.1 - Three small dams in casc
Page 145 and 146: Social Disruption low (rural area)
Page 147 and 148: Fig. 8.4 - Flood water level after
Page 149: 8.9 REFERENCES [1] BURREC (1994) -
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SMALL DAMS PETITS BARRAGES

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