ABSTRACT
Measuring the amount of water flowing in a stream or river requires consideration of both the velocity and the cross-sectional area in the channel. Velocity varies considerably within a channel and the cross-sectional area may vary with time depending on the nature of the stream bed. Continuous ‘measurement’ of streamflow produces a hydrograph (a time series of flows); although this is most commonly achieved through estimating flow using a stage vs discharge relationship (a rating curve), rather than with direct measurement. Stage (stream height) is measured continuously and velocity and cross-sectional area assumed to follow a fixed relationship. Maintaining accurate records of streamflow requires good knowledge of when cross-sectional area may change; e.g. during a flood event when the river bed could degrade through erosion or aggrade through sediment deposition. When it is not possible to measure streamflow directly there are estimation techniques which include dilution gauging (measuring the dilution of a solute in a stream) and geomorphological techniques (measuring bed roughness and the slope of the streambed.
