When at the beginning of summer in East Africa, where the source of the Nile is located, the mountain snows begin to melt, the water level in the river rises and the flood begins. The Nile slows down its already calm course and floods the low banks, turning them into real swamps for several months. In stagnant water, suspended particles gradually settle down, and when the river returns to its channel, the banks are covered with a new layer of fertile silt. In the southern regions of Egypt, the rise of water begins in mid-July, and above all - 8-10 m above the usual level! - the water rises in August - September and stays high until mid-November. During a flood, the water rises slowly, its level rising by several centimeters a day, so that people have time to leave, taking their property and livestock. The main difficulty in processing the most fertile flooded "lower fields" is due to the fact that after the decline in water, moisture is distributed unevenly - high-lying areas lose it too quickly, while coastal fields, on the contrary, become swampy, because water stands on them almost all year round. And the Egyptians came up with a very simple device that allowed them to adjust the amount of water in the fields at their discretion. In much the same way as children build earthen dams on streams in the spring, the Egyptians began to build walls of densely beaten earth, covered with clay, on the flood banks of the river, so that water would not seep through them. From a bird's eye view, the Nile Valley looked like a notebook sheet lined in a box. During the spill, water fell into the "cells" - pools, and people could dispose of it as needed - hold it for a long time in high places or, conversely, break through the earthen wall and drain excess water. Gradually, individual structures were linked into long chains that stretched along the Nile for tens of kilometers.
The dark land in the Nile Valley was so different from the rocky and clay soil of the neighboring plateaus that the Egyptians called their country "Kemet" - "Black". The river itself brought extraordinary land, millimeter by millimeter laying a fertile layer on the stone foundation of the banks. The water in the Nile is muddy because it contains many tiny particles of various origins - there are also grains of rocks picked up by the river where it flows along a rocky bed, and plant remains brought by tributaries from coastal tropical forests.
