Looking at surface water flow records

Confusion may arise from the way in which stream and river flows values are recorded and over the units used, especially in terms of the time period that relates to the flow value. The graph represents the flow of a stream as measured continuously at a gauging station.

During the 24-hour day represented by the shaded section, the minimum flow was 0.2 cumecs and the maximum flow was 0.8 cumec (cumec is an abbreviation of cubic metres per second).

The total daily flow is represented by the shaded area on the graph, which in this case is 0.48 cumec-days. This value is easier to understand if it is expressed as 41 472 m3/d by multiplying by the number of seconds in a day.

The shaded area under the curve also provides the average daily flow, which is the arithmetic mean. The value in this instance is 0.48 cumec or 41 472 m3/d.

During the late morning, a spot gauging was taken by current-meter and this produced an instantaneous flow value of 0.35 cumec.

This Handy Hint is based on information in my book Field Hydrogeology.

Copyright © 2004 by Rick Brassington

Eur Geol Eur Ing Professor F.C. Brassington BSc MSc CGeol FGS CEng MICE FCIWEM