Stages of Valley Development:

The development of stream valleys takes place in a orderly fashion. A valley passes through three stages during its evolution. The three stages are (i) Youth Stage, (ii) Mature Stage, and (iii) Old Stage.

(1). Youth or Early Stage:

A stream is said to be in the youth stage when it cuts its valley downward to establish graded condition with its base level.

1. Position: The youth stage is commonly found in mountainous regins from where a stream starts its journey.
2. Erosion: Down-cutting is dominant.
3. Valley: Narrow V-shaped valley.
4. Longitudinal Profile: Longitudinal profile is ungraded. The gradient is steep and water falls and rapid are common.
5. Valley Floor: The stream occupies most of the width of the valley floor as a result there is little or no flood plain.
6. Stream Pattern: The stream course is angular and without meanders. Tributaries are short and few.

(2). Mature Stage:

A stream is said to be in a mature stage when downward erosion diminishes and lateral erosion dominates.

1. Position: Mature stage is found in the plains lying adjacent to the mountain region.
2. Erosion: Downcutting is slight and sidecutting becomes dominant.
3. Valley: Broad and trough shaped.
4. Longitudinal Floor: The stream swings in meanders. The flood plains are narrow and sandbars are present.
5. Stream Pattern: The stream moves in meanders. The tributaries are many.

(3). Old Stages:

In the old stage of valley development, the flood plan of a stream becomes several times wider then its meander belt.

1. Position: The old stage is fond near the mouth of streams.
2. Erosion: In the old stage, the stream ceases to enlarge the flood plains. The man work of a stream is to rework the unconsolidated sediment of the flood plain.
3. Valley: Valleys become wide and open with low boundaries which may be indistinct.
4. Longitudinal Profile: The gradient become very lo. The stream approaches base level it aggrades strongly.
5. valley Floor: Ox Bow lakes are very common. Natural levees are very are also present, which are accompanies by back swamps and yazoo tributaries. The meander belt is narrower than the valley floor.
6. Stream Pattern: The stream pattern is meandering with oxbow lakes. The tributaries are few and large.

From the above discussion it is assumed that the base level of a stream remains constant as a river progresses from youth to old stage. On many occasions, however, the land is uplifted. The effect of uplifting on a mature stream is to abandon lateral erosion and revert to downcutting. Such rivers are said to be “rejuvenated”. Mature streams readjust to uplift by cutting a new flood plain at a level below the old one. This produces step-like features in the river valley which are called “river terraces”.