How the Egyptians predict the Nile floods?

Agriculture in ancient Egypt depended upon the flooding of the Nile River. The rich silt from the Nile’s annual flood regularly renewed the fertility of Egyptians farmland.

The floodwater irrigated the fields and the depth of the inundation determined how much land could be cultivated. Around 3000 BC Egyptian scholars invent a device called the nilometer to predict the extent of the flood. The nilometer is used to determine the depth of the Nile at a given point and time, allowing scholars to predict whether or not the flood will supply a sufficient amount of water for the crops.

The purpose of the measurement of the Nile flood in earlier times was to facilitate the prediction of famine or prosperity and the determination of how labor would be allocated during the summer months.

The nilometer also helps determine if a flood has the potential to put nearby cities in danger. When the river was not flooding, Egyptians dug channels in the riverbanks. These were used to move water away from the river. The channels would feed into large ponds that acted as reservoirs.
How the Egyptians predict the Nile floods?