River discharge is the volume of water flowing through a river channel. This is the total volume of water flowing through a channel at any given point and is measured in **cubic metres per second (cumecs)**.

Discharge is calculated as follows:

**cross sectional area of a river or stream x mean velocity of water**

- Describe
**three**relationships shown on the diagram above e.g. as discharge increases, velocity increases

**WETTED PERIMETER**

The wetted perimeter of a river refers to that part of the channel that is in contact with water. It represents the **friction** that slows down the river velocity.

The longer the wetted perimeter, the more friction between channel and water.

**HYDRAULIC RADIUS**

The hydraulic radius is a measure of efficiency in a river channel. It is calculated by comparing the wetted perimeter with the cross-sectional area of the channel.

*Hydraulic radius = cross-sectional area / wetted perimeter*

The higher the hydraulic radius, the more efficient the river.

## ACTIVITIES

- Make simple sketches of the diagram above
- Read 107 - 109 (Core Book): Discharge, stream flow and channel shape.
- Make detailed notes under the different headings.