Question

Why is the speed of the rivers fast in the mountains and slow at the mouths?

Answer 1

mountains have a steep terrain, which help in the quick flow of water in river. but at the mouth, the terrain is flat. so water flow is low.

Answer 2

The speed of the river is fast in the mountain because in mountainous region the river experiences its youth stage. It is formed by number of small streams and it run on an irregular gradient thus having a fast flow. Whereas the river becomes slow at the mouth because the gradient of the river becomes less steep and erosion takes place in the plain areas. The sediments get collected on the river bed and the water gets heavy ultimately resulting into a slow and steady water flow.