Cambridge IGCSE Geography

## Rivers and drainage basins A **drainage basin** is the area of land that a river and its tributaries drain. Rain that falls anywhere in the basin ends up, one way or another, in the same main river. The edge of the basin is the **watershed**, a line of high ground (often a ridge) beyond which water drains into a different river. | Term | Meaning | |---|---| | Source | The place where the river begins, usually in hills or mountains, often a spring or a lake | | Mouth | The place where the river meets the sea, a lake or a larger river | | Tributary | A smaller river that flows into a larger one | | Confluence | The point where two rivers meet | | Channel | The bed and banks that contain the river's water | | Watershed | The boundary between one drainage basin and the next | | Wetted perimeter | The length of the bed and banks that is in contact with the water, measured across the channel | | Discharge | The volume of water passing a point in a given time, in cubic metres per second (cumecs) | | Velocity | The speed of the water, in metres per second | **Discharge** is calculated from the size of the channel and the speed of the water: $$ \text{discharge} = \text{cross-sectional area} \times \text{velocity} $$ The cross-sectional area is the width multiplied by the average depth, so a channel 8 m wide and 1.5 m deep (average) has an area of $8 \times 1.5 = 12\,\mathrm{m^2}$. If the water moves at $0.5\,\mathrm{m\,s^{-1}}$, the discharge is $12 \times 0.5 =…