ABSTRACT
In many cases, the flow is two-dimensional, that is to say the velocity component in the third dimension is zero. Typical examples are flow over a weir of uniform shape or under a rectangular sluice gate, each spanning the full channel width. The omission of the third dimension considerably simplifies the diagrammatic representation of the stream
lines and it is often convenient to space the lines an equal distance apart in the zone of uniform flow. If the velocity at one point in the diagram is known, the velocity at any other point may be determined from a knowledge of the spacing. Nevertheless stream lines tend to be employed more for qualitative than quantitative purposes.
