Egypt is (and was) one of the most arid areas in the world. The River Nile in Egypt received 90% of its water during a 100-day flood period every year, as noted by Herodotus, in The Histories, [2, 92], where he states:
. . . . the water begins to rise at the summer solstice, continues to do so for a hundred days, and then falls again at the end of that period, so that it remains low throughout the winter until the summer solstice comes round again in the following year.
The floodwaters of the Nile come as a result of the rainy season in Ethiopia, which erodes the silt of the Ethiopian highlands, and carries it towards Egypt along the Blue Nile and other tributaries. No appreciable amount of water comes to Egypt via the White Nile, which starts from Central Africa.
The Ancient Egyptians managed their limited water resources efficiently, and became the best dry-weather agrarians in the world. Ancient Egypt was renowned worldwide for its dry-weather irrigation and farming techniques. Diodorus spoke of the efficient Egyptian farming system,
. . .being from their infancy brought up to agricultural pursuits, they far excelled the husband-men of other countries, and had become acquainted with the capabilities of the land, the mode of irrigation, the exact season for sowing and reaping, as well as all the most useful secrets connected with the harvest, which they had derived from their ancestors, and had improved by their own experience.
Several entities were formed along the Nile Valley to manage the gushing floodwaters by observing, recording, and regulating the water flow to the whole Nile Valley. As a consequence, a highly organized communal irrigation system was developed and used since time immemorial.
The limited available water resources in Ancient Egypt were managed most efficiently by utilizing organized methods of water conservation and diversion. According to Strabo, the Egyptian communal irrigation system was so admirably managed,
. . .that art contrived sometimes to supply what nature denied, and, by means of canals and embankments, there was little difference in the quantity of land irrigated, whether the flood was deficient or abundant.
The Ancient Egyptians made precise observations of the increase of the Nile elevation during the inundation season. Nilometers, devices used for measuring the gradual rise and fall of the Nile, were constructed in various parts of Egypt, and water surface fluctuations were recorded and reported. The elevations at the Nilometers throughout Egypt were all tied to a single common datum. Regulating the flow amounts and duration was controlled by knowledgeable officials, using sluice gate(s) to control the flow of water to a determined height and duration. Diodorus, in I. [19. 5-6], affirms:
. . .at flood-time it might not form stagnant pools over the land to its detriment, but that the flood-water might be let upon the countryside, in a gentle flow as it might be needed, through gates which they [Egyptians] had built.
The water of the inundation was managed differently in various districts. This depended on many factors, such as the relative heights/elevations of the adjoining lands, and what the crops they happened to be cultivating at the time, etc.
The Ancient Egyptian waterworks and land reclamation projects were huge—even by our present-day standards of projects that use heavy equipment. Here are a few examples:
For more information about the Ancient Egyptian water pumps and other lifting devices, etc, refer to: