Braided channels.  A river actively engaged in aggrading its valley with coarse waste builds a flood plain of comparatively steep gradient and often flows down it in a fairly direct course and through a network of braided channels.  From time to time a channel becomes choked with waste, and the water no longer finding room in it breaks out and cuts and builds itself a new way which reunites down valley with the other channels.  Thus there becomes established a network of ever-changing channels inclosing low islands of sand and gravel.

Terraces.  While aggrading streams thus tend to shift their channels, degrading streams, on the contrary, become more and more deeply intrenched in their valleys.  It often occurs that a stream, after having built a flood plain, ceases to aggrade its bed because of a lessened load or for other reasons, such as an uplift of the region, and begins instead to degrade it.  It leaves the original flood plain out of reach of even the highest floods.  When again it reaches grade at a lower level it produces a new flood plain by lateral erosion in the older deposits, remnants of which stand as terraces on one or both sides of the valley.  In this way a valley may be lined with a succession of terraces at different levels, each level representing an abandoned flood plain.

Meanders.  Valleys aggraded with fine waste form well-nigh level plains over which streams wind from side to side of a direct course in symmetric bends known as meanders, from the name of a winding river of Asia Minor.  The giant Mississippi has developed meanders with a radius of one and one half miles, but a little creek may display on its meadow as perfect curves only a rod or so in radius.  On the flood plain of either river or creek we may find examples of the successive stages in the development of the meander, from its beginning in the slight initial bend sufficient to deflect the current against the outer side.  Eroding here and depositing on the inner side of the bend, it gradually reaches first the open bend whose width and length are not far from equal, and later that of the horseshoe meander whose diameter transverse to the course of the stream is much greater than that parallel with it.  Little by little the neck of land projecting into the bend is narrowed, until at last it is cut through and a “cut-off” is established.  The old channel is now silted up at both ends and becomes a crescentic lagoon, or oxbow lake, which fills gradually to an arc-shaped shallow depression.

Flood plains characteristic of mature rivers.  On reaching grade a stream planes a flat floor for its continually widening valley.  Ever cutting on the outer bank of its curves, it deposits on the inner bank scroll-like flood-plain patches.  For a while the valley bluffs do not give its growing meanders room to develop to their normal size, but as planation goes on, the bluffs are driven back to the full width of the meander belt and still later to a width which gives room for broad stretches of flood plain on either side.