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The annual Nile flood.
Because the Nile River did not flood in Nubia as much as it did in Egypt
To measure anything - one use was to record the annual Nile flood levels.
The fertile parts of Egypt (present and past) are all along the Nile River.
The Fertile Crescent, located between the Tigris and Euphrates rivers. It is located in south-west Asia, also known as Ancient Mesopotamia.
The silt brought down during the annual flood of the Nile.
As they knew when it would happen, they ensured they were ready to take full advantage when the flood waters receded leaving the very fertile soil.
The sudden flood of the river Nile irrigated the land and provided excellent fishing for the duration of the flood, also sweeping in new, more fertile soil and minerals from other places. The flood would typically last from June to September in our calendar.
Farmers on the River Nile benefitted from the river's annual flood. The flood irrigated and fertilized the land along the Nile, making it possible for them to grow and harvest crops.
The fertile land on the flood plains produce good grass.
Because the torrent of water would carry sediment, as does any flood, and this would be deposited when the Nile overflowed its banks.
The rivers carry silt and sediment, which they get from the mountains due to soil erosion. (the rivers flow extremely fast due to a steep slope) Due to less gradient of slope in the N.Plains, the rivers flow more sluggishly and are not able to carry the silt anymore. So, they deposit these minerals on their banks (forming flood plains if they flood) causing the land to become fertile.
The rivers carry silt and sediment, which they get from the mountains due to soil erosion. (the rivers flow extremely fast due to a steep slope) Due to less gradient of slope in the N.Plains, the rivers flow more sluggishly and are not able to carry the silt anymore. So, they deposit these minerals on their banks (forming flood plains if they flood) causing the land to become fertile.
Headwater is not normally known for fertile ground.
Mesopotamia's soil was fertile because of flood rains and overflowing rivers.
The envirometal threat is that it can flood the farms etc around it therefore making the ground saturated and therefore it can't be fertile!
Khenmu, and the god of the flood of the Nile itself was Hapi.