SMALL DAMS

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S mall concrete dams Watertightness is provided by a reinforced concrete face extended into the foundation by a grout curtain. At the facing/rock interface, there is an inspection gallery. For such a small dam, it would have been perfectly feasible to eliminate this gallery, possibly by building gentler slopes. A symmetrical cross-section is well suited to sites with mediocre foundations as the forces transferred to the foundation are lower. It is of special interest in areas of high seismic activity as the dynamic stresses, in particular tensile stresses, are approximately one tenth of those with a conventional gravity dam design. The search for an economical solution for the upstream watertight structure makes this kind of design attractive, even for small dams. 134 Fig. 7 - Typical cross-section of MYKONOS 1 dam with a symmetrical cross-section BARRAGE TYPE <strong>DAMS</strong> FOREWORD Barrage type dams take a special place among small dams. They are intended to create reservoirs of generally limited capacity and to regulate often high flows in rivers. They are required in many cases: hydroelectric power generation, navigation, or any other project requiring creation of a reservoir.
Chapter V Some of these barrages, although limited in height, discharge high flows (exceeding 1000 m 3 /s), which means they must be considered as large dams and suitable design rules must be applied; the details of their design are outside the scope of this volume. DIMENSIONING PRINCIPLES Once the reservoir water level has been set and the design flood determined, the necessary flow section must be dimensioned. The level of the invert is chosen in such a way as to avoid disturbing bedloads, which are often considerable in the rivers in question. In general, an elevation close to the river bottom is chosen. Once the reservoir water level and the invert elevation are established, the barrage's length must be calculated. This can be done using the De Marchi empirical formula concerning flows over sills and narrow sections. Q = L.h v 2g (H a - h v ) where: Q : flow in m 3 /s : contraction factor (around 0.9) L : barrage opening in metres h v : height of water level above the sill 300 metres downstream from the barrage H a : head above the sill 100 metres upstream from the barrage. Total opening is distributed among a certain number of sluices of a width calculated according to the type of gate used. In modern barrages, the choice is essentially between tilting gates (see figure 8 below, p. 137) for relatively small closure surfaces of the order of 3 metres height for 20 metres width, or radial gates with arms articulated on the downstream side (see figure 9 below, p. 137) when the arms work in compression, or on the upstream side when the arms work in tension. This type of gate can be used to close off sluices up to 15 metres in height and 20 to 25 metres in width. Then comes dimensioning of the concrete structure consisting of piers and their foundation slabs and of the invert. A barrage type structure functions like a gravity dam and the actions involved are: !"pressure of water on the gates transferred via the arms to the trunnions, as well as pressure on the cutwater; !" dead weight of the structure; !" uplift; !" ground reaction. Using these various actions, stability is studied as explained previously under the heading Stability Analysis (see p. 122). Foundation slab dimensions must enable a distribution of forces such that stresses are less than the ground's bearing capacity. Very often, this type of dam is built in alluvial valleys, so a check must be made that there is no risk of flow around the structure or of piping. 135
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FRENCH COMMITTEE ON LARGE DAMS COMI
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PHOTOGRAPH REFERENCES Cover: CACG,
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M E M B E R S O F T H E R E A D I N
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TABLE OF CONTENTS Foreword - What n
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Table of contents FILL DAM DESIGN..
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Table of contents Chap. VII - Life
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W hat need for guidelines for small
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W hat need for guidelines for small
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C hoice of site and type of dam TOP
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C hoice of site and type of dam AVA
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C hoice of site and type of dam CON
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P reliminary determination of desig
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G eological and geotechnical studie
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F ill dams GEOTECHNICAL STUDIES 68
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F ill dams For fill, the wetter the
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F ill dams 72 If the latter is unal
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F ill dams As concerns freeboard R,
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F ill dams Wave height h (m) Thickn
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F ill dams In the case of a widely
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F ill dams Fig. 3 - Sloped granular
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F ill dams It is therefore necessar
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F ill dams The selected profile sho
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F ill dams 86 Case of compressible
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F ill dams In present practice, the
Page 89 and 90: F ill dams MONITORING SYSTEM 1 The
Page 91 and 92: F ill dams The most common measurem
Page 93 and 94: F ill dams 94 When H 2 V > 30, the
Page 95 and 96: F ill dams DESIGN OF THE FREE OVERF
Page 97 and 98: F ill dams 98 In the case of very w
Page 99 and 100: F ill dams TENDERING AND DAM CONSTR
Page 101 and 102: F ill dams In the case of a rock fo
Page 103 and 104: F ill dams However, when the materi
Page 105 and 106: F ill dams All of the inspections m
Page 107 and 108: F ill dams SPECIFIC FEATURES OF VER
Page 109 and 110: F ill dams !"engineering costs. The
Page 111 and 112: ▲ 1 - Compacting clay in the cut-
Page 113 and 114: ▲ 7 - Scarification after passage
Page 115 and 116: ▲ 12 - Rip-rap on a dam built for
Page 117 and 118: ▼ 20 - Overspill part of a side i
Page 119 and 120: C H A P T E R V Small concrete dams
Page 121 and 122: Chapter V Arch dams Arch dams trans
Page 123 and 124: Chapter V Masonry dams are no longe
Page 125 and 126: Chapter V Finally, the slope of the
Page 127 and 128: Chapter V FOUNDATION TREATMENT Hydr
Page 129 and 130: Chapter V and account will be taken
Page 131 and 132: Chapter V Thrust of ice This force
Page 133 and 134: Chapter V The commonly accepted cri
Page 135 and 136: Chapter V MONITORING SYSTEMS The ge
Page 137 and 138: Chapter V The typical cross-section
Page 139: Chapter V LOUBERRIA DAM Louberria d
Page 143 and 144: Chapter V Fig. 8 - Dam with a tilti
Page 145 and 146: Chapter V BIBLIOGRAPHY 1 - Ministè
Page 147 and 148: M anagement of water quality EUTROP
Page 149 and 150: M anagement of water quality !"the
Page 151 and 152: M anagement of water quality Proces
Page 153 and 154: M anagement of water quality 148 Al
Page 155 and 156: M anagement of water quality While
Page 157 and 158: M anagement of water quality It con
Page 159 and 160: M anagement of water quality It sho
Page 161 and 162: M anagement of water quality These
Page 163 and 164: 4. Grégoire (A.), 1987- Caractéri
Page 165 and 166: L ife of the dam SPECIAL FEATURES O
Page 167 and 168: L ife of the dam GENERAL SURVEILLAN
Page 169 and 170: L ife of the dam ORGANISATION OF SU
Page 171 and 172: L ife of the dam During such period
Page 173 and 174: L ife of the dam MAINTENANCE 168 Th
Page 175 and 176: L ife of the dam BIBLIOGRAPHY 1 - C
Page 177 and 178: C onclusion FLOOD DATA It is fairly
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SMALL DAMS

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