Rivers

Most ancient civilizations grew along the banks of rivers. Even today, millions of people all over the world live on the banks of rivers and depend on them for their survival. All of us have seen a river - large or small, either flowing through our town, or somewhere else. Rivers are nothing more than surface water flowing down from a higher altitude to a lower altitude due to the pull of gravity. One river might have its source in a glacier, another in a spring or a lake. Rivers carry dissolved minerals, organic compounds, small grains of sand, gravel, and other material as they flow downstream.

Rivers begin as small streams, which grow wider as smaller streams and rivers join them along their course across theland. Eventually they flow into seas or oceans. Most rivers With the exception of the Nile, flow towards the Equator. The flow in most rivers is not uniform, which means that sometimes there are floods and sometimes no water flows in them. Flood control projects attempt to reduce the variation in flow. Unfortunately most of the world's major rivers are heavily polluted, but two of the world's largest river systems-the Amazon, that drains a vast area of South America and the Congo in sub-Saharan Africa- remain relatively healthy.

This is because both have few industries and a small human population in their watersheds. The Nile, 6695 km long, and the Amazon 6437 km long, are the world's two longest rivers. Sometimes, measurements of their lengths can vary according to the criteria used for measurement. An Arab philosopher and physician Avicenna suggested, nearly 1000 years ago, that landscapes changed largely as a result of the action of running water. His views were largely ignored until the 16th century.

The longest river in Asia is the Yangtze, which is 5472 km long. The world's highest waterfall are the Angel Falls in Venezuela, 979 m high, over 780 m of which is an uninterrupted drop. India has a large number of rivers that are lifelines for the millions living along their banks. These rivers can be categorized into four groups: Rivers that flow down from the Himalayas and are supplied by melting snow and glaciers. This is why these are perennial, that is, they never dry up during the year The Deccan Plateau rivers, which depend on rainfall for their water, The coastal rivers, especially those on the west coast, which are short and do not retain water throughout the year, The rivers in the inland drainage basin of west Rajasthan, which depend on the rains. These rivers normally drain towards silt lakes or flow into the sand.