River Stages and Delta Formation

1. RIVER STAGES & DELTA FORMATION
ENGR. MD. SHAMIM AHMED
LECTURER
DEPT. OF CIVIL ENGINEERING
SOUTHERN UNIVERSITY BANGLADESH

2. FLUVIAL CYCLE
The entire journey of river starts from initial or youth stage up to old stage complete one
cycle of process is called ‘Fluvial cycle’.
The River’s Journey
For any river system it is developed from the starting point where it originate up to the
end point where it reaches the ocean. The entire journey of river can be clearly
distinguished into different stages. The stages of river are mainly divided into three
stages, they are –
 Youth or Initial Stage
 Mature Stage
 Old Stage

3. Youth or Initial Stage
 River has a small amount of water but it travels very quickly down the steep mountain
slope.
 The flowing water is found to cause appreciable erosion of the valley and tributaries
gradually developed.
 This erosion (wearing away) occurs in 4 ways.
4 Processes of River Erosion -
• Hydraulic Action – The force of the moving water wears away the banks and
bed of the river.
• Abrasion – Small stones carried by the river wear away at the banks and bed of
the river.
• Attrition – The small stones in the river are worn down and broken up as they hit
off each other.
• Solution – Rocks and soil are dissolved by acids in the water.

4. Mature Stage
 In this stage the long profiles of rivers are found to have obtained equilibrium streams and a
drainage system.
 The power of erosion of the river is also much reduced and balance with its transporting
capacity.
 Transportation occurs in 4 ways.
River Transportation -
• Rolling – The large stones are rolled
along the bed of the river.
• Bouncing – The smaller pebbles are
bounced along the bed of the river.
• Suspension – Light material like sand and
silt are carried along (floating) in the water.
• Solution – Dissolved materials are carried
along by the river.

5. Landforms of the Mature Stage
In the Mature Stage the river begins to slow down, and so it begins to deposit some of its load.
It creates the following features.
1. Wide river valley
2. Meanders
3. Flood plain
Wider River Valley
In the mature stage the river moves from side to side and the valley becomes wide and flat.
Meanders
Meanders are bends or curves along the river. They are formed by erosion and deposition.
Erosion occurs on one side of the river while deposition occurs on the opposite side.
Flood Plain
A flood plain is the flat area of land on either side of the river.

6. Fig. Wider valley in the mature stage of the river. Fig. Development of meander.

7. Old Stage
In this stage the river is carrying lots of sand and silt. It is now flowing over flat land and so it
is moving slowly. Therefore it begins to drop off its load. This is called deposition.
DELTAS
Deltas are defined as alluvial deposits of roughly triangular shape that are deposited by major
rivers at their mouths i.e. where they enter sea .
As the river enters the sea it drops off all the remaining material it is carrying. This material
builds up to form new land. The river is forced to break up into smaller channels called
distributaries.

8. Old Stage
In this stage the river is carrying lots of sand and silt. It is now flowing over flat land and so it
is moving slowly. Therefore it begins to drop off its load. This is called deposition.
DELTAS
Deltas are defined as alluvial deposits of roughly triangular shape that are deposited by major
rivers at their mouths i.e. where they enter sea .
As the river enters the sea it drops off all the
remaining material it is carrying. This material
builds up to form new land. The river is forced
to break up into smaller channels called
distributaries.

9. THANK YOU