I. Overview
1 Application scope
1.1 The weir or flume for flow measurement in open channel consists of a water measuring weir or flume and a stage-discharge conversion instrument (secondary instrument). The water measuring weir or flume device includes upstream and downstream approach sections, weir body and stage observation facilities. The secondary instrument displays instantaneous flow rate or accumulated water volume besides completing the stage-discharge conversion.
1.2 The symbols adopted are shown in Table 1 in Annex 2, and the symbols not listed in Table 1 are shown in figures and relevant provisions.
1.3 To limit the flow state, it is generally required that water flowing through the weir or flume is in a free flow state, that is, the downstream stage of the water measuring weir or flume is lower than a certain limited stage, and at this moment the upstream stage of the weir or flume has a single value relation with the flow rate. Specific instructions may be provided in this regulation if submerged flow measurements are carried out in a certain measuring weir or flume is required in a submerged-flow state.
1.4 Common measuring weirs or flumes and measured discharge range included in this regulation are as follows:
1.4.1 The sharp-crested weirs are divided into three main types: triangular-notched weirs, rectangular-notched weirs and equal-width weirs. The measured discharge range of triangular-notched sharp-crested weirs is 0.2×10-3~1.8 m3/s; that of rectangular-notched sharp-crested weirs: 1.4×10-3~49 m3/s; and that of equal-width sharp-crested weirs: 0.8×10-3~77 m3/s.
1.4.2 Broad-crested weirs are divided into two main types: rectangular broad-crested weirs and round-rim broad-crested weirs. The measured discharge range of rectangular wide-crested weirs is 8×10-3~65m3/s, that of round-rim broad-crested weirs 8×10-3~820 m3/s.
1.4.3 Triangular-profile weir, with the measured discharge range of 3×10-3~1300m3/s.
1.4.4 Flat V-shaped weir, with measured discharge range of 14×10-3~630m3/s.
1.4.5 Parshall flume, with the measured discharge range of 0.1×10-3~93m3/s.
1.4.6 Cutthroat flume, with the measured discharge range of 0.7×10-3~3.0m3/s.
2 Working principle
If the measuring weirs or flumes are set in the open channel and the stage is measured according to the specified position, the flow rate discharged through the weirs and flumes has a single value relation with the stage. According to the corresponding discharge equation or empirical relationship, the measured stage value may be converted into the discharge value.
II Technical requirements
(i) Sharp-crested weirs
3 Sharp-crested weir is a water measuring structure which is installed in an open channel perpendicular to the flow direction (it has a certain shape of notch and can be processed into a sharp-crested weir body with a weir opening), and that its nappe surface is fully developed as the flow passes over. The flow equation for the three types are as follows:
3.1 Flow equation of triangular-notched sharp-crested weir (Figure 1)
I. Overview
II Technical requirements
(i) Sharp-crested weirs
(ii) Broad-crested weir
(iii) Triangular-profile weir
(iv) Flat V-shaped weir
(v) Parshall flume
(vi) Cutthroat flume
(vii) Stage-discharge conversion and display
III Verification conditions, items and methods
(i) Verification by open channel flow standardizing device and flowmeter standardizing device
(ii) On-site verification
(iii) Analysis of verification results
IV Treatment of results and verification period
Annex 1 On-site comparison test
Annex 2 Relevant parameters and symbols
Annex 3 Format of the back of the verification certificate
