The river valley becomes flat in its lower course due to the levels of erosion occurring in the river itself. In the upper course, the river's energy is used for vertical erosion(downward erosion) in order to get to sea level. That's why you see steep V-shaped valleys or Gorges being formed. However, in the lower course when the river is at sea level, a lot of this erosion becomes lateral(horizontal) which is why you see rivers becoming a lot wider in the lower course. Therefore, because the river is no longer eroding downwards there's no longer a difference in height between it and its valley, so the river valley becomes flat.
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.
UPPER COURSE: -v shapped valley -gorge -waterfall MIDDLE COURSE: -wider v shapped valley LOWER COURSE: -rapids -plunge pool
A river usually flows quickly in the upper course, as it is at a higher elevation - mountains streams, waterfalls, etc. In the lower course, it will slow down as the lower elevation means the slope is more horizontal. It is here that the river may start to meander across the valley floor, forming bends, oxbow lakes, and a flood plain.
As a river continues its journey towards the sea, the valley cross section continues to become wider and flatter with an extensive floodplain either side of the channel. The river erodes laterally and deposition also becomes important. By the time it reaches the lower course the river is wider and deeper and may contain a large amount of suspended sediment.
the pebbles will be in the lower course of a riverthe pebbles will be in the lower course of a river
It is very steep at the top and narrow but. At the bottom it isn't steep.
la salle
the genesee river follows a meandering course...take a look what the river looks like on google image.
middle course, upper course, lower course...
v shaped valley
The mouth of the River Tees is at the North Sea. The lower course of the River Tees goes through Redcar near Middlesbrough.
Yangzi River.