The basic concepts in fluvial geomorphology are Equilibrium, Regime Theory and Channel Geometry, Geomorphic Thresholds and Scale. Equilibrium state is one in which the input of mass and energy to a specific system equals the outputs from the same system. In fluvial geomorphology it is this equilibrium state that the stream channels tend to achieve
Regime theory is grounded on the propensity of a stream system to obtain an equilibrium state under constant environmental conditions. The Regime Theory has a set of empirical equations relating channel shape to discharge, bank resistance and sediment load. It laid the foundation for a large body of work in Fluvial Geomorphology poring on the geometric properties of equilibrium alluvial channels and their adjustments to discharge and sediment transport regimes.
Many of the concepts in fluvial geomorphology can be traced to European origins; however, "Classical" American geomorphology as expressed by W.M. Davis has its roots in the Surveys of the Western United States conducted by the U.S. Geological and Geographical Survey following the Civil War. The leading figures in this period of exploration were John Wesley Powell, Gore Karl Gilbert, and Clarence E. Dutton. Others of note during this time frame were Ferdinand V. Hayden, Lt. George N.
Wheeler, and Archibald R. Marvine. As the west was being explored and the landforms analyzed, these individuals formulated several key ideas about geomorphology.
Clarence Dutton made contributions by creating an awareness of isostatic adjustments and descriptions of landforms. lie also discussed the "Great Denudation," a period of extensive erosion which he felt created the Colorado Plateau. His writings also
contained several references to the idea of parallel retreat of slopes. This concept is based upon a belief that hillsides maintain their angle of slope and form as erosion occurs.
The first fluvial geomorphic model was the fluvial geographical cycle or the cycle of erosion, developed by William Morris Davis between 1884 and 1899. The cycle was inspired by theories of evolution, and was depicted as a sequence by which a river would cut a valley more and more deeply, but then erosion of side valleys would eventually flatten out the terrain again, now at a lower elevation. The cycle could be started over by uplift of the terrain. The model is today considered too much of a simplification to be especially useful in practice.
The Geographical Cycle, as envisioned by Davis, starts with the rapid uplifting of a plain and the beginning of fluvial erosion. Erosion of this initial stage soon produces the second stage, youth. This stage is characterized by low relief and poor drainage with road flat water divides. As the erosion process continues, relief increases until the mature stage is reached. At this time, narrow ridges form water divides and very little flat terrain remains. Additional erosion leads to the old age stage in which relief in slight and low flat plains art dominant. The "almost featureless" plain resulting from the Geographical Cycle was termed a peneplain by Davis. Among suggested examples of peneplains are the Rocky Mountain Peneplain in the Colorado