Equilibrium‐conditions in debris‐laden streams

The work of streams is highly important in several fields of geology. Streams remove rock‐debris from the sites of weathering and transport it to flood‐plains, lakes, and ocean, where it is deposited to form new rocks. And during this erosion, transportation, and deposition, streams carve out and build up land‐forms, such as mountains, valleys, and plains. Because of these multifold results of stream‐activity, geologists have long been interested in the processes of stream‐work. Fifty‐six years ago, Gilbert formulated the major principles of stream‐work and land‐sculpture in a paper (G. K. Gilbert, Report on the geology of the Henry Mountains, U.S. Geog. and Geol. Sur. of the Rocky Mountain Region, pp. 99–150, 1877) which still, from the geological viewpoint, stands as the classic of the subject. The essence of Gilbert s ideas is the concept of graded streams—the concept that, either by cutting down their beds or by building them up with sediment, streams tend always to make for themselves channels and slopes that, over a period of years, will transport exactly the load of sediment delivered into them from above.