Booklet 7 - Flow Measurement Methods in Open Channels

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−inadequate approachthe converging section of the flume is too short to adequately correct major distortions of theapproach and distribution velocity. The reader can refer to section 2.1.10 which discussesinstallation conditions, for an understanding of rules that regulate the approach.−poor measurement technique in submerged flow conditionsoften, due to a lack of knowledge, a user is unaware of how to recognize or gauge a channelthat is operating in submerged flow conditions and takes flow measurements at only onelocation, instead of at both measuring points, which this situation requires.−obstructions in the throat section of the flume2.1.9. Selection criteriait is important to ensure that nothing is blocking flow in the throat of the flume, particularly inthe case of small flumes. Where this occurs, liquid is forced to move over the obstacle, whichincreases the water level at the measuring point.As indicated in section 1.7 of this document, installation of a Parshall flume is the preferred type of flumewhere the daily flow is 1,800 m 3 and over.Because there are a number of different Parshall flume dimensions available to measure the range ofanticipated flows, other criteria should be considered when selecting a flume, such as:−−−−−−discharge: it is important to select the correct size of flume to ensure that free flow conditions are presentat the maximum discharge, and to consider installation constraints;loss of head: for any one flow, the degree to which the water level rises, due to introducing different sizesof flumes;the sensitivity required to detect and measure fluctuations in water level, where there are very littlevariations in flow;the desired precision;the overall work that is required to install flumes of different sizes;the costs associated with installation of flumes of different sizes.2.1.10. Installation detailsThe Parshall flume must be located in a straight section of the flow (8) .When installing a flume, it is important to ensure that none of the flume’s original physical features aredamaged (see Table 5).The crest (DR), which is the bottom of the converging section of the flume, must be higher than the bottom ofthe channel in which it is placed. This elevation must be equal to the difference between the water depth in thePage 44 of 223Booklet 7 - Flow Measurement Methods in Open Channels
channel at maximum flow (H c ), before the flume is installed, and the anticipated water depth at the measuringpoint h 2 (DR = H c - h 2 ) during minimum submerged flow conditions. The crest of the flume that is introducedmust be connected to the crest of the converging section by an inverted slope section that has a 1:4 ratio(vertical:horizontal) (see Figure 6).The length of the approach section must be equivalent to at least twenty times the diameter of the waterdelivery pipe.In the approach section, the slope should be less than 1 %. It is important to ensure that a steep slope does notproduce a hydraulic jump in the converging section of the flume, as shown in Figure 7. It should not create toogreat a velocity, which will slow down the rise in water depth in the converging section.The minimum width of the approach channel should be consistent with dimension “D” of Table 2 and themaximum width should not exceed dimension “P” in the same table (more than 10 m). It is important to avoidintroducing a water delivery pipe into the converging section of the flume, as shown in Figure 8.At the outlet of the flume, there should be enough slope to allow water to discharge quickly. The slope shouldbe approximately 2 %.After the diverging section, there should be no pronounced curve that can restrict flow and cause a submergedflow.In the converging section, the stilling well conduit should be located within the middle two-thirds (2/3) sectionof the length of the wall and at a right angle with the wall. The crest of these conduits, that is, their bottom,must be below the level of the crest of the converging section, as shown in Figure 6, and level with the flumewall.Booklet 7 - Flow Measurement Methods in Open Channels Page 45 of 223
Page 1: Centre d’expertise en analyse env
Page 5: FOREWORDThis Sampling Guide for Env
Page 8 and 9: 4.4. Area/velocity method..........
Page 10 and 11: LIST OF ILLUSTRATIONSFigure 1 - Wei
Page 13 and 14: 1. GENERAL1.1. Definition of flowra
Page 15 and 16: Note: If effluents have different d
Page 17 and 18: This equation shows that water dept
Page 19 and 20: Sizes vary according to the type an
Page 21 and 22: FIGURE 1 - WEIR COMPONENTSFlow is d
Page 23 and 24: 1.10. Reference measurementIf a mea
Page 25 and 26: FIGURE 2 - PALMER-BOWLUS - FLUME CH
Page 27 and 28: TABLE 1 - DIMENSIONS FOR PALMER-BOW
Page 29 and 30: 1.12. Choosing a measurement method
Page 31 and 32: FIGURE 4 - FLUME - FLUME AND FLOW C
Page 33 and 34: TABLE 3 - CHART FOR COMPARING THE M
Page 35 and 36: TABLE 4 - DIMENSIONS FOR STILLING W
Page 37 and 38: 2. DESCRIPTION OF FLUMESThe section
Page 39 and 40: 2.1.2. Operating principleA Parshal
Page 41 and 42: TABLE 5 - PARSHALL FLUME - STANDARD
Page 43 and 44: TABLE 6 - PARSHALL FLUME - RECOMMEN
Page 45: 2.1.7. PrecisionThe margin for erro
Page 49 and 50: FIGURE 8 - PARSHALL FLUME - JUNCTIO
Page 51 and 52: FIGURE 9 - PARSHALL FLUME - EFFECTS
Page 53 and 54: 2.1.12. Discharge equation in a sub
Page 55 and 56: FIGURE 11 - LOSS OF HEAD - PARSHALL
Page 57 and 58: To monitor the total rise, follow t
Page 59 and 60: A Palmer-Bowlus flume, as experimen
Page 61 and 62: FIGURE 13 - SHAPE OF A PALMER-BOWLU
Page 63 and 64: TABLE 10 - PALMER-BOWLUS FLUME - ST
Page 65 and 66: Because some manufacturers do not a
Page 67 and 68: −use of the depth/flow table2.2.1
Page 69 and 70: For temporary systems, a simple ver
Page 71 and 72: Q is the flowrate in liters or US g
Page 73 and 74: FIGURE 15 - SHAPE OF LEOPOLD-LAGCO
Page 75 and 76: 2.3.7. Measurement capacity of a fl
Page 77 and 78: 2.3.11. Installation specifications
Page 79 and 80: 2.4.2. Operating principleCutthroat
Page 81 and 82: TABLE 14 - CUTTHROAT FLUME - STANDA
Page 83 and 84: TABLE 15 - CUTTHROAT FLUME - RECOMM
Page 85 and 86: TABLE 16 - CUTTHROAT FLUME - VALUES
Page 87 and 88: TABLE 18 - CUTTHROAT FLUME - DISCHA
Page 89 and 90: Since a number of other cutthroat f
Page 91 and 92: where:Q is the flowrate in cubic me
Page 93 and 94: Example: To measure a 0.6 m 3 (21 C
Page 95 and 96: It consists of two sections: approa
Page 97 and 98:
FIGURE 18 - H FLUME - PHYSICAL CHAR
Page 99 and 100:
Although this type of flume can be
Page 101 and 102:
TABLE 21 - H FLUME - STANDARD DIMEN
Page 103 and 104:
TABLE 23 - H FLUME - RECOMMENDED MI
Page 105 and 106:
CoefficientsandexponentsTABLE 24 -
Page 107 and 108:
−erosion at the outlet of the flu
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2.5.13. Flume modificationTo obtain
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Example:For a rectangular weir wher
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−−−−−−−the presence o
Page 115 and 116:
TABLE 25 - WEIR CALIBRATION - VOLUM
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FIGURE 20 - RECTANGULAR WEIR WITHOU
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TABLE 26 - RECTANGULAR WEIR WITHOUT
Page 121 and 122:
Inadequate approach velocityThe app
Page 123 and 124:
FIGURE 21 - RECTANGULAR WEIR WITH C
Page 125 and 126:
The Kindsvater-Carter equation take
Page 127 and 128:
3.3.5. PrecisionIn free flow condit
Page 129 and 130:
TABLE 28 - RECTANGULAR WEIR WITH CO
Page 131 and 132:
FIGURE 22 - TRAPEZOIDAL WEIR (CIPOL
Page 133 and 134:
TABLE 29 - TRAPEZOIDAL WEIR (CIPOLL
Page 135 and 136:
Length of contractionsIf side contr
Page 137 and 138:
In addition to the information prov
Page 139 and 140:
The discharge equation resulting fr
Page 141 and 142:
3.6. Combined weirTo obtain a preci
Page 143 and 144:
In addition to the information prov
Page 145 and 146:
3.6.5. PrecisionIn free flow condit
Page 147 and 148:
FIGURE 25 -COMPOUND WEIR - PHYSICAL
Page 149 and 150:
TABLE 32 - COMPOUND WEIR - MEASUREM
Page 151 and 152:
4.1.1.2 Characteristics of tracersT
Page 153 and 154:
S gis the specific weight of the tr
Page 155 and 156:
4.1.2.1.4 Disadvantages of the meth
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When selecting a sampling point, it
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4.1.2.2.8 Detection and measurement
Page 161 and 162:
Dyes are well suited to flow measur
Page 163 and 164:
4.1.2.3.8 Detection and measurement
Page 165 and 166:
4.1.2.4.3 Preparation of radioactiv
Page 167 and 168:
4.1.2.4.9 Preliminary testsBefore c
Page 169 and 170:
4.1.3.1.3 Advantages of the method
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Testing procedures are as follows:T
Page 173 and 174:
Use the following formula to determ
Page 175 and 176:
The discharge equation is therefore
Page 177 and 178:
• Choosing a tracerExamine the di
Page 179 and 180:
Sampling must be carried out during
Page 181 and 182:
−−contamination of sampling con
Page 183 and 184:
Instantaneous injections1 2 3 4 5nP
Page 185 and 186:
tracer is lost due to splashing, by
Page 187 and 188:
The concentration of tracers is usu
Page 189 and 190:
4.1.3.3.7 Causes of errorThe princi
Page 191 and 192:
4.2.4. DisadvantagesThe principal d
Page 193 and 194:
−If the dimensions cannot be meas
Page 195 and 196:
4.3.7. DisadvantagesFlow measuremen
Page 197 and 198:
4.3.8.2 Calculation of pumping time
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4.3.8.4 Number of testsWhen a pumpi
Page 201 and 202:
−−−−−requires a number of
Page 203 and 204:
4.4.9. Flow areaMeasurement of the
Page 205 and 206:
Velocity measurements should be tak
Page 207 and 208:
considering only the source of erro
Page 209 and 210:
There are also other causes of bias
Page 211 and 212:
12. GRANT, D. M., ISCO Open Channel
Page 213:
36. INTERNATIONAL STANDARD ORGANISA
Page 216 and 217:
CHANDRA, U., Aoki, P. E., Ramos e S
Page 218 and 219:
HAMMER, Mark J., Water and Waste-Wa
Page 220 and 221:
Resources Instrumentation, June 4-6
Page 222 and 223:
REPLOGLE, John A., Meyers, Lloyd E.
Page 224 and 225:
TRIESTE, Douglas J., Evaluation of
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Booklet 7 - Flow Measurement Methods in Open Channels

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