What is drainage?
Drainage is the way water flows over the land through a system of rivers and streams. Rainwater collects in highlands and flows downhill, joining together to form larger rivers until it finally reaches the sea. The whole network of a main river and the smaller streams that join it is called a drainage system or river system.
Key idea
Water always flows from a high place (the source) to a low place (the mouth). Gravity pulls it downhill until it reaches a lake or the sea.
Parts of a river
- Source — where a river begins, usually in the highlands.
- Tributary — a smaller river or stream that joins a larger one.
- Confluence — the point where two rivers meet.
- Meander — a bend or loop in a river as it crosses flatter land.
- Mouth — where the river ends and empties into a sea or lake, sometimes forming a delta.
Example
The Rajang River in Sarawak is the longest river in Malaysia. The Pahang River is the longest in Peninsular Malaysia. Both begin in highlands and flow down to the South China Sea.
Why rivers are important
Rivers give people water for drinking, farming and industry. Their valleys have fertile soil for crops such as rice. Rivers are also used for transport, fishing and, where they flow fast, for producing hydroelectric power. Many early towns grew up beside rivers because water was easy to reach.
Remember
- A river flows from its source (high land) to its mouth (the sea).
- A tributary joins the main river; the meeting point is the confluence.
- The Rajang is Malaysia's longest river; the Pahang is the longest in the peninsula.