ABSTRACT
For much of history, hydrology was merely one component of the science of hydraulics, and more specifically, of hydraulic construction projects. Since the main objective of this book is to describe and explain the processes of the water cycle, it seems relevant to review the origin of the first rational explanations of the water cycle. However, because the modern history of hydrology is well documented (Bonnin, 1984; Malissard, 2002; Nordon, 1991a; Nordon, 1991b; Purple, 2000), in this chapter we will limit our discussion to the earliest theories about the hydrological cycle. It is almost impossible to specify the precise date that marked the beginning of the science of hydrology. However, we can make a start by noting that since Ancient times, populations have established themselves along the banks of waterways such as the Tigris and Euphrates rivers of Mesopotamia, the Nile River of Egypt, the Indus in India, and the Yellow River of China. Although an understanding of the water cycle may not have been a priority for ancient civilizations, there is no doubt that they possessed a certain degree of empirical knowledge, as is evidenced by various hydraulic constructions such as dams, dikes and irrigation canals, some of which are still in use today.
