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SAA AS 3778.3.3

2001 Edition, March 12, 2001

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MEASUREMENT OF WATER FLOW IN OPEN CHANNELS PART 3.3: VELOCITY-AREA METHODS - MEASUREMENT BY SLOPE-AREA METHOD



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SAME AS ISO 1070
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Description / Abstract:

This International Standard specifies a method of determining liquid flow in open channels from observations of the surface slope and cross-sectional area of the channel. It is suitable for use under somewhat special conditions when direct measurement of discharge by more accurate methods, such as the velocity-area method, is not possible.

The slope-area method can be used with reasonable accuracy in open channels having stable boundaries, bed and sides (e.g. rock or very cohesive clay), in lined channels and in channels with relatively coarse material. It may also be used in alluvial channels, including channels with overbank flow or non-uniform channel cross-sections, but in these cases the method is subject to large uncertainties owing to the selection of the rugosity coefficient (such as Manning's coefficient n or Chezy's coefficient ().

Generally the method may be used to determine discharge

a) at the time of determining gauge heights from a series of gauges;

b) for a peak flow that left marks on a series of gauges or where peak stages were recorded by a series of gauges;

c) for a peak flow that left high-water marks along the stream banks.

This method is not suitable for use in very large channels, channels with very flat surface slopes and high sediment load or channels having significant curvature.

Although the accuracy of the results given by the slope-area method is less than that of the results given by the velocity-area method, the slope-area method is sometimes the only method that can be used for determining the extreme high-stage end of rating curves in cases where the magnitude of floods is such that other methods of measuring discharge cannot be used.