SMALL DAMS

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Chapter II !" taking into account the statistical distribution of the affinity ratio (passage from average runoff to peak discharge); !"the probability approach to instantaneous flow in order to obtain an overall design hydrograph. This model makes no hypothesis on the equation of rainfall probability. The simple exponential decay function for rainfall relative to the recurrence interval is not imposed. Thanks to the progressive passage from the flow equation to the rainfall equation, the model avoids the over-estimation of the discharges of intermediate recurrence intervals (50 to 500 years). Although not very realistic, the single-frequency hydrographs obtained are easy to use in calculation of flood attenuation. The AGREGEE model and the GRADEX method give similar results in estimation of extreme floods (1000 years to 10 000 years). THE PMP - PMF METHOD 1 This method is very rarely used in France. It is based on knowledge of the Probable Maximum Precipitation (PMP) in the catchment area and a rainfall - runoff model to calculate Probable Maximum Flood (PMF). It results in a design hydrograph. The PMP is defined as the highest theoretical precipitation that is physically probable for a specific geographic location, over a defined period of time. Its estimation is based on observed rainfall data and on maximising the meteorological parameters linked to precipitation: humidity, temperature, pressure of saturating vapour in the air, wind speed, convection, etc. Such calculation requires the skills of a meteorologist. In order to facilitate the calculation, some countries have published regional PMP estimates. 29 THE SHYPRE MODEL: SIMULATION OF FLOOD SCENARIOS 2 Cemagref 3 has developed a model for simulating flood scenarios called the SHYPRE model. This approach is based on gaining maximum value from temporal information about rainfall episodes in order to generate flood hydrographs with realistic shapes. By coupling a stochastic model for simulation of hourly rainfall and a simple model for transforming rainfall into discharge, the method generates a collection of flood hydrographs over a very long period. 1. See Bibliography, references 4 and 8, p. 36. 2. See Bibliography, references 2, 3 and 10, p. 36. 3. The french agricultural and environmental research institute – http://www.cemagref.fr
P reliminary determination of design flood In this way, with no prior assumptions concerning the law of probability, the frequency distribution, from routine to exceptional, can be constructed empirically. This goes for both peak flows and for average flows and threshold discharges of various durations. Such floods are available to calculate hydraulic transients, including attenuation in a reservoir and modelling a flood plain. In this method, the stochastic model of rainfall not only complies with temporal information, it also gives an original approach to infinite rainfall behaviour. Processing some 50 rainfall gauging stations along the French Mediterranean coastline has given an idea of regional trends simply through the characteristics of daily rainfall and has opened up the possibility of building a spatial regional model. The method has proven to be more stable than simple statistics, which depend heavily on sampling, and the model helps to evaluate the impact of anthropic effects. EMPIRICAL FORMULAS AND REGIONAL FORMULAS These methods of estimating flow are extremely succinct and under no circumstance may be a substitute for a complete hydrological study. 30 THE FRANCOU-RODIER ENVELOPE CURVE 1 From observations of maximum floods over the last 2 centuries in 1400 catchment areas throughout the world with surface areas in the 10 - 2.10 6 sq.km range, FRANCOU and RODIER established an envelope curve formulated as follows: 1- k/10 Q/Qo = (S/So) • Q is the peak discharge of the flood (m 3 /s) for an area of the catchment S (km 2 ). • Qo = 10 6 and So = 10 8 . • k is a regional parameter. It varies in France in the 5.5 bracket (Mediterranean zone) to 3.5 (oceanic zone in the north of France). At a global scale, the highest k values (and thus in proportion the highest flow) are close to 6 like in Texas, New-Mexico and in some of the Pacific areas affected by typhoons (Korea, Japan, Philippines, …). On the opposite, the large African tropical streams are quite well characterised by an exponent k value close to 2 (it is the case for the Niger and Senegal rivers). Concerning an envelope of observed maximum floods, these estimates of discharge are not affected by the frequency of appearance. The authors, however, consider that a good part of the floods correspond to a recurrence period of around 100 years. 1. See Bibliography, reference 6, p. 36.
Page 1 and 2: FRENCH COMMITTEE ON LARGE DAMS COMI
Page 3 and 4: PHOTOGRAPH REFERENCES Cover: CACG,
Page 5 and 6: M E M B E R S O F T H E R E A D I N
Page 7 and 8: TABLE OF CONTENTS Foreword - What n
Page 9 and 10: Table of contents FILL DAM DESIGN..
Page 11 and 12: Table of contents Chap. VII - Life
Page 13 and 14: W hat need for guidelines for small
Page 15 and 16: W hat need for guidelines for small
Page 17 and 18: C hoice of site and type of dam TOP
Page 19 and 20: C hoice of site and type of dam AVA
Page 21 and 22: C hoice of site and type of dam CON
Page 23 and 24: P reliminary determination of desig
Page 27: P reliminary determination of desig
Page 37 and 38: G eological and geotechnical studie
Page 67 and 68: F ill dams GEOTECHNICAL STUDIES 68
Page 69 and 70: F ill dams For fill, the wetter the
Page 71 and 72: F ill dams 72 If the latter is unal
Page 73 and 74: F ill dams As concerns freeboard R,
Page 75 and 76: F ill dams Wave height h (m) Thickn
Page 77 and 78: 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
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F ill dams MONITORING SYSTEM 1 The
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F ill dams The most common measurem
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F ill dams 94 When H 2 V > 30, the
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F ill dams DESIGN OF THE FREE OVERF
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F ill dams 98 In the case of very w
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F ill dams TENDERING AND DAM CONSTR
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F ill dams In the case of a rock fo
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F ill dams However, when the materi
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F ill dams All of the inspections m
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F ill dams SPECIFIC FEATURES OF VER
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F ill dams !"engineering costs. The
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▲ 1 - Compacting clay in the cut-
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▲ 7 - Scarification after passage
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▲ 12 - Rip-rap on a dam built for
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▼ 20 - Overspill part of a side i
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C H A P T E R V Small concrete dams
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Chapter V Arch dams Arch dams trans
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Chapter V Masonry dams are no longe
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Chapter V Finally, the slope of the
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Chapter V FOUNDATION TREATMENT Hydr
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Chapter V and account will be taken
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Chapter V Thrust of ice This force
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Chapter V The commonly accepted cri
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Chapter V MONITORING SYSTEMS The ge
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Chapter V The typical cross-section
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Chapter V LOUBERRIA DAM Louberria d
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Chapter V Some of these barrages, a
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Chapter V Fig. 8 - Dam with a tilti
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Chapter V BIBLIOGRAPHY 1 - Ministè
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M anagement of water quality EUTROP
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M anagement of water quality !"the
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M anagement of water quality Proces
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M anagement of water quality 148 Al
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M anagement of water quality While
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M anagement of water quality It con
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M anagement of water quality It sho
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M anagement of water quality These
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4. Grégoire (A.), 1987- Caractéri
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L ife of the dam SPECIAL FEATURES O
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L ife of the dam GENERAL SURVEILLAN
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L ife of the dam ORGANISATION OF SU
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L ife of the dam During such period
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L ife of the dam MAINTENANCE 168 Th
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L ife of the dam BIBLIOGRAPHY 1 - C
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C onclusion FLOOD DATA It is fairly
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