ABSTRACT
The amount of water within a river or stream is of great interest to hydrologists. It represents the endproduct of all the other processes in the hydrological cycle and is where the largest amount of effort has gone into analysis of historical records. The methods of analysis are covered in Chapter 6; this chapter deals with the mechanisms that lead to water entering the stream: the runoff mechanisms. Runoff is a loose term that covers the movement of water to a channelised stream, after it has reached the ground as precipitation. The movement can occur either on or below the surface and at differing velocities. Once the water reaches a stream it moves towards the oceans in a channelised form, the process referred to as streamflow or riverflow. Streamflow is expressed as discharge: the volume of water over a defined time period. The SI units for
discharge are m3/s (cumecs). A continuous record of streamflow is called a hydrograph (see Figure 5.1). Although we think of this as continuous measurement it is normally either an averaged flow over a time period or a series of samples (e.g. hourly records).
