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AS 3778.4.6:2022
[Current]Measurement of water flow in open channels, Part 4.6: Measurement using flow gauging structures — Flat-V weirs (ISO 4377:2012, IDT)
AS 3778.4.6:2022 identically adopts ISO 4377:2012, which specifies the methods of measurement of flow in rivers and artificial channels under steady or slowly varying conditions using flat-V weirs.
Published: 10/06/2022
Pages: 60
Table of contents
Cited references
Content history
Table of contents
Header
About this publication
Preface
Foreword
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols
5 Characteristics of flat-V weirs
6 Installation
6.1 Selection of site
6.1.1
6.1.2
6.1.3
6.1.4
6.2 Installation conditions
6.2.1 General requirements
6.2.2 Approach channel
6.2.2.1
6.2.2.2
6.2.2.3
6.2.2.4
6.2.2.5
6.2.2.6
6.2.2.7
6.3 Weir structure
6.3.1
6.3.2
6.3.3
6.3.4
6.4 Downstream conditions
7 Maintenance
8 Measurement of head(s)
8.1 General
8.2 Stilling (gauge) wells
8.2.1
8.2.2
8.2.3
8.2.4
8.2.5
8.2.6
8.2.7
8.2.8
8.2.9
8.3 Zero setting
8.3.1
8.3.2
8.3.3
8.3.4
8.4 Location of head measurement sections
8.4.1
8.4.2
8.4.3
8.4.4
9 Discharge relationships
9.1 Equations of discharge
9.1.1
9.1.2
9.2 Effective heads
9.3 Shape factors
9.4 Coefficient of velocity
9.4.1
9.4.2
9.5 Conditions for modular/drowned flow
9.6 Drowned flow reduction factor
9.6.1
9.6.2
9.6.3
9.7 Limits of application
9.7.1
9.7.2
9.7.3
10 Computation of discharge
10.1 General
10.2 Successive approximation method
10.2.1 Computation using individual head measurements
10.2.2 Computation of modular stage-discharge function
10.3 Coefficient of velocity method
10.3.1 Modular flow conditions
10.3.2 Drowned flow conditions
10.4 Accuracy
10.4.1
10.4.2
11 Uncertainties in flow determination
11.1 General
11.1.1
11.1.2
11.1.3
11.1.4
11.1.5
11.2 Combining uncertainties
11.3 Uncertainty in the discharge coefficient u*(CDe)68 for the flat-V weir
11.4 Uncertainty in the drowned flow reduction factor u*(Cdr)
11.5 Uncertainty in the effective head
11.6 Uncertainty budget
11.7 Variation of uncertainty with flow and uncertainty in mean daily flow and the daily flow volume
11.7.1 Uncertainty curve
11.7.2 Uncertainty in the daily mean flow
11.7.3 Uncertainty in the daily flow volume
12 Examples
12.1 Example 1 — Computation of modular flow at low discharge
12.1.1 Data
12.1.2 Solution by successive approximation method (see 10.2)
12.1.3 Solution by coefficient of velocity method (see 10.3)
12.2 Example 1 — Uncertainty in computed discharge
12.2.1 Uncertainty in the discharge coefficient
12.2.2 Uncertainty in drowned flow reduction factor
12.2.3 Uncertainty in the horizontal; component of the weir crest gradient
12.2.4 Uncertainty in the effective total head
12.2.5 Overall uncertainty
12.3 Example 2 — Computation of drowned flow at high discharge
12.3.1 Data
12.3.2 Solution using successive approximation method (see 10.2)
12.3.3 Solution using the coefficient of velocity method (see 10.3)
12.4 Example 2 — Uncertainty in computed discharge
12.4.1 Uncertainty in the discharge coefficient
12.4.2 Uncertainty in the horizontal; component of the weir crest gradient
12.4.3 Uncertainty in the effective total head
12.4.4 Uncertainty in the separation pocket (crest tapping) head
12.4.5 Uncertainty in drowned flow reduction factor
12.4.6 Overall uncertainty for non-modular flow example
Annex A
A.1
A.2
A.3
A.4
A.5
Annex B
B.1 General
B.2 Confidence limits and coverage factors
B.3 Random and systematic error
B.4 Measurement standards
B.5 Evaluation of Type-A uncertainty
B.6 Evaluation of Type-B uncertainty
B.6.1 General
B.6.2 Triangular distribution
B.6.3 Rectangular distribution
B.6.4 Normal probability distribution
B.6.5 Bimodal probability distribution
B.7 Combined uncertainty value, uc
Annex C
Bibliography
Cited references in this standard