Booklet 7 - Flow Measurement Methods in Open Channels

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1.8. Flow metering systemA flow metering system usually consists of two components: a primary device, as defined earlier, and asecondary device (or flowmeter).1.8.1. The secondary deviceTo obtain a flow measurement using the primary device, a second device called a “secondary device”must be installed. A secondary device can be simple or more sophisticated.The simplest device is a point-specific level reading indicator, such as a float. Depth is converted toflow using the depth/flow table that corresponds to the primary device in use. More sophisticatedinstruments can measure depth, perform a depth/flow conversion, continuously monitor values andeven transmit them over distances.1.9. Units of measurementThe most common units of measurement are:gal US /d : US gallons per daygal US /min : US gallons per minutegal UK /d : imperial gallons per daygal UK /min : imperial gallons per minutem 3 /d : cubic meters per dayft 3 /s : cubic feet per secondl/min : liters per minuteThe following units are also used occasionally:Mgal US /d : millions of US gallons per daygal US /h : US gallons per hourgal US /s : US gallons per secondMgal UK /d : millions of imperial gallons per daygal UK /h : imperial gallons per hourgal UK /s : imperial gallons per secondm 3 /h : cubic meters per hourm 3 /min : cubic meters per minutel/h : liters per hourl/s : liters per secondUnits/day are used occasionally to express hourly flow.Example:The flow for an 8 to 9 hour period is 42,000 m 3 /d. To obtain the absolute hourlyvolume, divide this figure by 24. 42,000 m 3 /d therefore becomes 1,750 m 3 /h.For the purpose of this document, except in very specific instances, metric units of measurement havebeen used.Page 20 of 223Booklet 7 - Flow Measurement Methods in Open Channels
1.10. Reference measurementIf a measuring device is installed in an open channel, a reference measurement technique must be used.A reference measurement is usually a ruler in meters or feet, that is permanently placed at themeasuring point and is used to:−−−calibrate the secondary device (flowmeter);take a point-specific flow reading;quickly and easily check and compare the flowmeter value to the reference value.The reference value is always considered the true value.1.11. Measuring point1.11.1. LocationThe location of a measuring point to gauge the discharge of liquid must be determined on the basis ofthe following considerations:−−−−−there must be a minimum number of measuring points, considering the costs to build and maintainthem;the measuring point must allow measurement of the continuous flowrate of the total liquiddischarge;the primary device must allow minimum, medium and maximum flows to be measured;no branching off should be made downstream from the measuring chamber;the site must be accessible all year long.1.11.2. Measuring chamberThe physical characteristics of a chamber must enable personnel to carry out the measurements,maintenance and testing necessary to ensure the quality of measurements. The chamber must meetspecific requirements:−−−−−−−−depending on the flowrates present and the primary device installed, the chamber must be largeenough to allow the primary device to be inspected and the secondary device to be inserted. Theremust also be enough room available to install a temporary or permanent automatic sampler;it must have a lighting and heating system that meet the requirements of this type of structure;it must have a remotely-controlled ventilation system;if the chamber is located deeper than 6 m, it must have a safety landing;the chamber’s access hole must be at least 915 mm in diameter;the access cover must be at least 750 mm in diameter to allow access for personnel and equipment;a ladder must be permanently installed to provide access inside the manhole;safety standards governing construction and access to enclosed locations must be respected.Booklet 7 - Flow Measurement Methods in Open Channels Page 21 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: FIGURE 1 - WEIR COMPONENTSFlow is d
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 and 46: 2.1.7. PrecisionThe margin for erro
Page 47 and 48: channel at maximum flow (H c ), bef
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
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2.3.7. Measurement capacity of a fl
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2.3.11. Installation specifications
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2.4.2. Operating principleCutthroat
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TABLE 14 - CUTTHROAT FLUME - STANDA
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TABLE 15 - CUTTHROAT FLUME - RECOMM
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TABLE 16 - CUTTHROAT FLUME - VALUES
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TABLE 18 - CUTTHROAT FLUME - DISCHA
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Since a number of other cutthroat f
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where:Q is the flowrate in cubic me
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Example: To measure a 0.6 m 3 (21 C
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It consists of two sections: approa
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FIGURE 18 - H FLUME - PHYSICAL CHAR
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Although this type of flume can be
Page 101 and 102:
TABLE 21 - H FLUME - STANDARD DIMEN
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TABLE 23 - H FLUME - RECOMMENDED MI
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CoefficientsandexponentsTABLE 24 -
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−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
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TABLE 25 - WEIR CALIBRATION - VOLUM
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FIGURE 20 - RECTANGULAR WEIR WITHOU
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TABLE 26 - RECTANGULAR WEIR WITHOUT
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Inadequate approach velocityThe app
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FIGURE 21 - RECTANGULAR WEIR WITH C
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The Kindsvater-Carter equation take
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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
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Length of contractionsIf side contr
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In addition to the information prov
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The discharge equation resulting fr
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3.6. Combined weirTo obtain a preci
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In addition to the information prov
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3.6.5. PrecisionIn free flow condit
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FIGURE 25 -COMPOUND WEIR - PHYSICAL
Page 149 and 150:
TABLE 32 - COMPOUND WEIR - MEASUREM
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4.1.1.2 Characteristics of tracersT
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S gis the specific weight of the tr
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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
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Dyes are well suited to flow measur
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4.1.2.3.8 Detection and measurement
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4.1.2.4.3 Preparation of radioactiv
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4.1.2.4.9 Preliminary testsBefore c
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4.1.3.1.3 Advantages of the method
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Testing procedures are as follows:T
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Use the following formula to determ
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The discharge equation is therefore
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• Choosing a tracerExamine the di
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Sampling must be carried out during
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−−contamination of sampling con
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Instantaneous injections1 2 3 4 5nP
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tracer is lost due to splashing, by
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The concentration of tracers is usu
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4.1.3.3.7 Causes of errorThe princi
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4.2.4. DisadvantagesThe principal d
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−If the dimensions cannot be meas
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4.3.7. DisadvantagesFlow measuremen
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4.3.8.2 Calculation of pumping time
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4.3.8.4 Number of testsWhen a pumpi
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−−−−−requires a number of
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4.4.9. Flow areaMeasurement of the
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Velocity measurements should be tak
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considering only the source of erro
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There are also other causes of bias
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12. GRANT, D. M., ISCO Open Channel
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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
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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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