a canyon, gorge or vale
a flood plain
flood plain
A wide river valley is called a vale. In Scotland, a wide and flat river valley is also called a strath.
Mississippi River
An estuary.
The River Mersey is between 12 metres and 20 metres wide, depending on which point it's measured as it flows through Stockport.
Ganges River is 200-400 miles wide
A small, secluded, and often wooded valley is known as a dell or in Scotland as a glen. A wide, flat valley through which a river runs is known in Scotland as a strath. (from https://en.wikipedia.org/wiki/Valley)
whether they are deep or wide, slow or fast flowing, shallow or steep gradient, a river flows in a channel
Congaree River is a short but wide river in South Carolina in the United States.It flows for only 47 miles (78 km).
that's easy its the st. johns river it go through northern Florida
a dale
From atop the mountain, I could see the entire valley below.
In the lower course of a river. At this point the river has enough energy to erode away the sides of the valley (interlocking spurs) resulting in a "u" shaped valley (instead of "v" shaped as is typical with the upper course of a river.