Where a streambed is rough the stream flows more slowly because of?

When a streambed is rough, the irregularities and obstacles such as rocks and vegetation create turbulence in the water flow. This turbulence increases friction between the water and the streambed, which slows down the overall velocity of the stream. Additionally, the rough surface disrupts the smooth flow of water, causing it to lose energy as it navigates around these obstacles. Consequently, the combination of increased friction and turbulence results in a slower flow rate in rough streambeds.