Final answer:
The shape of a river in a flat area is typically wider with slower flow and more sedimentation, forming features like deltas or estuaries, while in the mountains, the river is narrow and fast-flowing, creating steep valleys and sharp geological features due to higher erosion rates.
Step-by-step explanation:
The shape of a river differs significantly between flat areas and mountainous regions due to the processes of erosion and deposition. In the mountains, rivers often begin as narrow, fast-flowing streams with clear, cold, and nutrient-low source water. The steep gradients result in high flow rates that can carve deep, v-shaped valleys and sharp features into the landscape.
As the river travels downhill and reaches flatter areas, the gradient decreases, and the water flow slows down, causing the river to widen and sediment to deposit, which can lead to the formation of broader, meander-filled river channels and features such as deltas or estuaries.
When a river reaches the ocean or a lake, it slows down dramatically, leading to the deposition of silt and the formation of deltas if the silt content is high and there is minimal wave action. In contrast, high wave action or low silt content results in estuarine areas. The local landscape and relief also significantly influence the river's shape, with flat regions causing more sedimentation due to the slower water flow compared to the steeper, more erosive conditions of the mountains.