A river with a steep gradient that has very few tributaries and flows quickly. Its channels erode deeper rather than wider. A river with a gradient that is less steep than those of youthful rivers and flows more slowly. A mature river is fed by many tributaries and has more discharge than a youthful river. The features found in the youthful stage of a river are all formed by the are bends or curves which are found in the mature stage (middle course) of a river.