How can the shape of a river stream bed affect the rivers speed and its power to cause erosion?

A wider and shallower river stream bed tends to slow down the river's speed as frictional forces increase with more contact with the bed. This can reduce the river's power to cause erosion. Conversely, a narrower and steeper stream bed can increase the river's speed, which enhances its erosive power by allowing it to carry more sediment and erode the riverbanks more effectively.