graded stream

A river or stream seeks comfort over its own bed. It scours its channel, wears down obstacles, carries sand grains and boulders drawn from its outback, runs its course with the sheer weight of its will. By erosion and deposition a river modifies the slope of its bed until its rate of flow can transport its load efficiently. A river or stream that reaches such equilibrium is called a graded stream. A graded stream is a somewhat theoretical stream—explained by fluid mechanics, felt as mystery. Flow is never perfectly even; interruptions and changes abound. Some stretches of the same stream may flow at grade, while others do not. Flood, drought, rock that resists, sandbars that succumb—flowing water constantly responds to variables. Thus, equilibrium is a dynamic rather than steady balance of energy and resistance—gravity as a fluid medium, reading the land it traverses.

Ellen Meloy