Le transport de l'eau à grande distance

Long-distance water supply systems

Ingénieur à la SOGREAH, Grenoble.

Résumé

This article is in two parts : a historical review and an exposé on present water conveying problems. In the historical part, while the authors mention major achievements at various periods, they have mainly set out to give fuller details of some of the principal "conquests" of hydraulic engineering down the ages. This is a very old branch of engineering indeed : over 5000 years ago all the houses at Mohenjo Daro on the river Indus had running water and sewerage ; most of them had washrooms, bathrooms and lavatories, and there were publics baths in the town. The main examples of old long-distance water supply systems mentioned by the authors are the following : (i) Long-distance aqueducts with free gravity flow, e.g. the Niniveh canal in the seventh century B.C., Greek aqueducts from the fifth century B.C. onwards and Roman aqueducts from the third century B.C. onwards ; (ii) Pipelines under pressure, e.g. the bronze Pergamon water supply pipeline (Greece) in the third century B.C., siphons in the Lyons aqueduct in Roman Gaul and lead pipes, all in the last few centuries B.C. and the first few A.D.; (iii) Water supplies delivered by pumping plant under pressure and a large-diameter (east-iron pipe at Versailles, France in the seventeenth century. The authors end their historical review with two examples which can be considered precursors of modern practice : (i) The Pia aqueduct in Rome (1870) in which 27 km of gravity-fed pipe under pressure replaced a 65 km long freeflowing aqueduct ; (ii) The pump-fed Coolgardie and Kalgoorlie pipeline in Australia (1903), which is 565 km long and delivers water from the 100 ft up to the 410 ft level via eight successive booster stations. After this historical review, the authors observe that in spite of the much-improved means at their disposal, modern hydraulicians still basically rely on water-conveying methods centuries or even a few thousand years old, such as the following for example : (i) Use of natural streams, rivers, etc.; (ii) Open canals; (iii) Covered canals and freely flowing ducts (iv) Pipes under pressure. The authors discuss the merits and disadvantages of these methods and then those of various water-conveying duct materials ; finally, they determine with the aid of an example the effect of such factors as power cost, interest rates and discharge on water conveying costs. The authors conclude that, with high flows, it may be more economical to convey water over a distance of several hundred kilometres than to distill sea water ; consequently, any choice between a long-distance supply system and distillation plant should be based on a very thorough economic study.