THE THREE STAGES OF A RIVER


From  Living  Library

 

There are three stages of a river :

A river rises in high ground ( its source ). It then flows down a slope ( its course ) until it reaches the sea ( its mouth ).

The youthful stage :

Youthful rivers are usually small in size.

Fast - flowing rivers usually erode more powerfully than slow flowing rivers.

The mature stage :

By the time the rivers has reached the mature stage the river will have received the waters of many tributaries.

So the river will have increased in size. As these larger rivers sweep quickly along they transport large loads of materials

with them.

How rivers transport materials :

A rivers old age :

Why old rivers deposit their loads :

Rivers slow down when they enter almost-flat plains of old age. Slow moving rivers cannot carry large loads as fast flowing rivers can. So the old rivers deposit their loads. The loads of old rivers consist of light particles such as mud and grains of sand.

This material is called alluvium. It is deposited along the river bed.

 

Flood plains :

These are almost flat plains which border old rivers and are sometimes flooded by the river. They are covered in fertile alluvial soils which are deposited by the river.

The Formation :
Unable to carry all of its load the river deposits some of it on its bed. This raises the level of water so that it almost reaches the tops of the river banks. In times of heavy rainfall the river water may rise still further overflowing its banks and flooding the nearby plains.

Examples occur in the lower stages of the Suir, Barrow and Nore.

Ox-Bow lakes :

These are horse-shoe lakes found near old rivers.
Here are 3 steps to an Ox-Bow lake.
1. Meanders can become so big that only a narrow neck of land
separates their outer banks.
2. Eventually - in times of flood when the river flows more
quickly - the water cuts through the neck of the land.
3. Levee deposits later seal off both ends of the abandoned meander which becomes an Ox-Bow lake.

.....

 

by Claire Sullivan Sixth Class 1999/2000
Part of SIP Project
Sources: Waterford Corporation
Living Library