The lifeblood of Egyptian civilization was/is the Nile River. The Nile originates in Sub-Sharan Africa. There are multiple sources but the accepted main source is Lake Victoria which is the border between Kenya, Uganda and Tanzania. From the source to the mouth it is approximately 4,130 miles long making it the longest river in the world. Because at its sources there are seasonal rains there are seasonal floods on the Nile. If it was a very wet year at the sources the floods would be excessive and would ruin the crops. If the rains were sparse at the sources there would be drought. But if it was a normal year the floods would moisten the land and the new silt would rejuvenate the soil. The pictures below are a Nilometer for measuring the depth of the Nile. All of the various temples along the Nile had a Nilometer. Based on the measurements the Pharaoh and later rulers would decide whether to tax the farmers. They taxed when the rains were within the normal range but not if there was drought or overly flooded fields.