Possibly the nile, but seeing as I didn't do any research... this is an educated guess.
The Euphrates River
Because they help prevent Flooding
Floodplain is important because it helps reduce flooding and recharges our drinking water supply.
Because when it rain and flooding it really absorbed by the ground,
the Mesopotamians viewed it as a yearly, unpredictable disaster; while the Egyptians viewed it as a very predictable event that they could use to their advantage because of the silt that the floods left behind.
It is predictable because scientists use many helpful devices to measure it.
The 'miracle' of the Nile is a statement that points to the annual flooding and the silt that it brings and deposits from the upper Nile to the lower Nile delta. This is considered a 'miracle' because it is very predictable and nondestructive unlike most river floods.
Probably because of their yearly, somewhat predictable flooding, which caused great amounts of rich soil to be laid on the surrounding plains, and allowing agricultural resources to support a large population.
because they got silt and farming was there only help and this is not very specific
because they got silt and farming was there only help and this is not very specific
The Aswan dams are important because they prevent flooding of low lying land each year, and distribute water more equally for irrigation.
because
It was important because if the Egyptians knew when the floods came, they would know when to plant things