A riverbed is the ground at the bottom of a river where the water flows. Just as your bed is the surface you lie on at night, a riverbed is the surface the river “lies” on as it moves through the landscape.

When you wade into a stream, your feet touch the riverbed. It might be covered with smooth pebbles, rough rocks, sand, or mud. During a drought, when water levels drop, more of the riverbed becomes visible. Sometimes rivers dry up completely in summer, leaving the entire riverbed exposed until rain returns.

The shape and material of a riverbed matter greatly. A rocky riverbed creates rapids and waterfalls as water tumbles over obstacles. A sandy or muddy riverbed allows calmer, smoother flow. Over thousands of years, rivers gradually carve deeper into their riverbeds, which is how canyons form. The Grand Canyon started as a river slowly cutting down through rock, deepening its bed inch by inch, century after century.

Scientists study riverbeds to understand how rivers behave and change. Farmers and engineers pay attention to riverbeds when building bridges or managing water flow. If you've ever built a stream in a sandbox, watching water carve its own path and carry away sand, you've seen how rivers shape their beds in miniature.