SMALL DAMS

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Chapter III Brief preliminary calculations will be done on each site to determine the main geometrical characteristics: !" depth-area curve, depth-volume curve (dam and reservoir); !" for one or several values of storage: height, crest length and volume of the dam (where necessary for each type of dam envisaged at this stage), flooded surface area, ratio of storage to dam volume. When carrying out these studies, measurements of lengths and surface areas from available topographical documents will be used as well as calculations of volumes through incorporation of depth-area curves. The use of specific computer programs on PCs helps in these calculations and makes it possible to print out comparative charts with graphs. A preliminary cost estimate for the dam according to one or several dimensioning hypotheses is generally carried out in order to compare sites and/or seek out an economic optimum. This is done by applying ratios or benchmark costs taken from the designer's previous experience with dams of the same type, using data bases specific to each engineering firm complemented by a calculation of the same ratios for the recorded cost of dams of the same type (after discounting all of those prices). It is then possible to rank the sites selected after this first sort, according to criteria that will vary in nature and priority according to the nature of the project, and which must be chosen by the designer. Dam selection according to the principles set out above is in particular applicable for the various alternatives for a single site. It can in fact be necessary to study several possibilities for storage and/or layout unless there is only one clearly localised topographical narrowing at the site. 49 GEOLOGICAL SURFACE STUDY Objective After the stage of dam site identification, a visual examination by a geologist with experience in dams is vital before the studies are continued. This only takes a day or even half a day. The site tour is intended to determine the broad lines of the site geology before any heavier site investigation techniques are implemented. It has many purposes: !"to situate the site in the local and regional geological context; !" to detect any prohibitory geological conditions that might be immediately visible; !" to orient the rest of the studies, and in particular define and set out later site investigations; !" possibly to refine the dam layout, taking into account geomorphological or other details.
G eological and geotechnical studies 50 Methodology of the geological surface study Before the site tour, the geologist refers to existing geological maps (1/50 000, or if none 1/80 000) which essentially enable him to place the site in its local geological lithostratigraphic and structural context. In some cases, this preliminary examination alone can result in a strong presumption that the geology is unfavourable (for example karstic formations). Prior knowledge of the geological context is vital as it enables examination of the site to be oriented towards a search for certain types of indications using previous experience with similar contexts. Depending on the region concerned by the site in question, locating major regional tectonic structures can be of great importance in the rest of the studies and can sometimes explain the special behaviour of some foundations. The methods used in this kind of site investigation will vary according to the size of the dam under study and the geological context. They will consist at least in touring the dam site and all or part of the reservoir basin while noting any possible observation, and can be complemented by geological mapping at a suitable scale, surveying lithostratigraphic cross-sections with sampling, examination of aerial photographs and in some cases examination of satellite images. The result of this first site investigation is a preliminary assessment (sometimes called prefeasibility) on the wisdom of undertaking more detailed studies. In this stage sites can be classified in the following categories: !" favourable sites, when no prohibitory condition has been revealed; !" unfavourable sites, where problems appear that would be hard to solve and/or would have an economic impact out of proportion with the advantages to be procured by dam construction; !" doubtful sites, that can be divided up between those where no surface observation is possible because of outcropping conditions and those where uncertainties persist as to the interpretation and/or gaps in those observations. Investigations in continuous pits dug out with a mechanical shovel are then necessary to rank the site in one of the two preceding categories. It is useful to record the observations made during this phase of study and the conclusions drawn from them on a summary sheet like the one given hereafter and proposed by B. COUTURIER 1 . In addition to filling in the data required in this sheet, sketching a rapid geological profile on the spot along the proposed dam axis is an opportunity for the geologist to express his vision of the site after these preliminary investigations. The geological cross-section should distinguish between observed facts, interpolation, and pure intuition, and will be more precise when outcropping conditions are good. 1. See Bibliography, reference 3, p. 66.
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Page 7 and 8: TABLE OF CONTENTS Foreword - What n
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Page 11 and 12: Table of contents Chap. VII - Life
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Page 85 and 86: F ill dams 86 Case of compressible
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Page 93 and 94: F ill dams 94 When H 2 V > 30, the
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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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SMALL DAMS

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