A riverbed is a channel with a river at the bottom of a valley. During the normal flow period, river water is contained in and flows along the riverbed. However, during a flood, the river overflows the riverbed and flows onto the floodplain. The riverbed can bend subject to lateral erosion; hence, it continually changes its course. Common landscape features in a riverbed are potholes (deep pools), deep rock grooves, thresholds, cascades (waterfalls), shoals, channel sand bars and river islands.