Detection and the Prevention of Leaks from Dams

PREFACE 1 GENERAL CONSIDERATIONS 1.1 Introduction: Understanding leakage and seepage in relation to dam safety 1.2 Leakage and seepage 1.3 Mechanisms of failure 1.4 Nature and objectives of the studies on dam leakage 1.5 Risk analysis 1.6 Typical features of geological formations 1.7 Available techniques 2 WATER BALANCE, LEAKAGE LAWAND PIEZOMETRY 2.1 Water balance of a reservoir 2.2 Effects related to the water level at the reservoir 2.3 Piezometric studies 3 PERMEABILITY TESTS IN BOREHOLES 3.1 Generalities 3.2 Gilg-Gavard tests 3.3 Lugeon test 3.4 Lefranc test 3.5 Method based upon the induction of a vertical ascending flow through pumping 3.6 Test for the determination of the effective porosity 3.7 Estimation of the transmissibility from the level recovery after pumping 4 GEOPHYSICAL TECHNIQUES 4.1 Generalities 4.2 Surface prospecting geological methods 4.3 Geophysical well-logging 5 NATURAL TRACERS OFWATER: (A) TEMPERATURE, ELECTRICAL CONDUCTIVITY AND CHEMICAL COMPOSITION 5.1 Introduction 5.2 Water temperature 5.3 Electrical conductivity 5.4 Chemical composition of water 6 NATURAL TRACERS OFWATER: (B) STABLE ISOTOPES, TRITIUM AND CARBON ISOTOPES 6.1 Basic concepts 6.2 Stable isotopes of water 6.3 Tritium 6.4 Carbon-13 6.5 Carbon-14 7 ARTIFICIAL TRACERS 7.1 Introduction 7.2 Suspended solids 7.3 Ionic tracers 7.4 Gaseous fluoro-compounds 7.5 Fluorescent tracers 7.6 Artificial radioactive tracers 8 LOCALISATION AND MEASUREMENT OF FLOWS IN BOREHOLES 8.1 Introduction 8.2 Appropriate tracers 8.3 Filtration velocity 8.4 Point dilution technique for the measurement of horizontal groundwater flow 8.5 Method based on the labelling of the entire water column 8.6 Measurement of vertical flows 9 INTERCONNECTION EXPERIMENTS 9.1 Introduction 9.2 Theoretical considerations 9.2.4 The longitudinal dispersion coefficient 242 9.3 Guidelines for conducting interconnection experiments 9.4 Case studies 10 TESTS INSIDE THE RESERVOIR 10.1 Introduction 10.2 Use of float drogues 10.3 Tracing of the reservoir water 10.4 Free migration of the tracer cloud 10.5 Method of filter tubes 10.6 Labelling of the infiltration zone (adsorbed tracer) 10.7 Direct measurement of infiltration 11 GENERAL STRATEGY OF STUDIES 11.2 Preconstruction studies 11.3 Studies during the first filling of a reservoir 11.4 Leakage investigation after its appearance 11.5 Relation of reservoir with local aquifers 12 CASE STUDIES 12.1 Introduction 12.2 Arquillo de San Blas dam, Spain 12.3 Lake Managua, Nicaragua 12.4 Sabaneta reservoir, Dominican Republic 12.5 Lake Laja, Chile 12.6 The Colbún reservoir, Chile.