ABSTRACT
Even in the most arid parts of the world extensive human settlement is occasionally possible along the banks of major rivers which import water surpluses from better-watered regions. The Nile and the Colorado are two such rivers whose waters have permitted the desert to bloom. Yet their histories are very different. Along the Nile there is a history of traditional irrigation development going back at least 6,000 years. This irrigation, which has been continuous since that time, has given rise to some of the greatest civilisations of the ancient world. Even today irrigated agriculture in Egypt alone supports almost 50 million people. The story is very different along the Colorado, for here irrigation by white Americans is only about 100 years old, and all major developments have taken place in the twentieth century. The Colorado can claim to be the river on which modern dryland irrigation systems were first developed, and in the Hoover Dam it has one of the USA’s most potent symbols of human conquest of the environment.
