The techniques of construction of canals with weirs and locks were devel-
oped in very early times, too, so that already Senostris II and his grandson
Amenemhet III of the Twelfth Dynasty (1991–1786 ) were able to lower
the water table of Lake Qarun in Faiyum so as to be able to carry out land
reclamation measures in the oasis. Until the second half of the nineteenth
century basin irrigation remained the prevalent form of irrigation in Egypt.
As a rule it allowed only one harvest annually; however, the noxious salts
were washed out of the soils regularly. Moreover, the fields received annually
fresh layers of Nile silt containing numerous nutrients, which were of great
importance for the crops planted and at the same time improved the soil
structure. The sedimentation that took place annually is estimated at 19–21
tons/ha on average (Anhoury 1941: 503).