Methods of Measuring the Flow of Water in Open Channels 2.3. Velocity-area methods are based on the principle of the continuity of fluid flow. If you are interested in obtaining a more accurate stream discharge measurement, the velocity-area method might be your method of choice. These methods are used for instantaneous measurement of streamflow and to establish the stage-discharge relationship (Harmel et al. . This is an average measure. | 10 Sunday, September 02, 2018 STREAM GAUGING METHODS 3 classical methods for stream gauging: Volumetric method Tracer dilution method (slug and constant-rate injections) Velocity-area method (current meter and ADCP) Other ways for measuring stream discharge : Non-intrusive methods (course of Ichiro Fujita) Index-velocity method (course of Jérôme Le Coz) Measuring Stream Discharge Using the USGS Midsection Method . As the term implies, the flow is the product of the average velocity in the cross-section and the cross-sectional area of flow. The product of these two measurements gives discharge in volume per unit time: Q = V*A 31.25 m/s x 36 m2 = 45 m /s Equipment. DOI: 10.1061/(ASCE)HY.1943 . Some methods are better suited for low fl ows while others can handle a wide range of fl ows. on Hydroscience and Engineering (ICHE -2006),Sep 10 -Sep 13,Philadelphia,USA 1 Irrigation canal discharge measurement by using commercial digital video camera W. C. Huang 1 and M. C. Lee 2 and J. M. Leu 3 and C. J. Lai 4 and H. C. Chan 5 ABSTRACT This study present the image measurement techniques on the surface velocity field and water stage. This depends on measuring the average velocity of flow and the cross-sectional area of the channel and calculating the flow from: Q (m 3 /s) = A (m 2) x V (m/s) The metric unit m 3 /s is referred to as the cumec. Direct discharge determinations (mass per unit time) in the field are rare the electromagnetic discharge method and the tracer dilution method. Most years the U.S. Geological Survey (USGS) makes over 50,000 stream discharge measurements. Some methods measure fl ow directly, while others may measure velocities that are used in specifi c equations to calculate fl ow. AREA VELOCITY METHOD This method measures the volume of water passing a selected stream cross section in a certain time interval. Streamflow Measurement Streamflow measurement techniques can be broadly classified into two categories as (i) direct determination and (ii) indirect determination. Farina et al. water flow using a simple traditional method. 1967. • If the computed T c is < 0.1 hour, use 0.1 hour. by taking just a few velocity measurements and using a known relationship between those velocities and . Discharge Q = A V. We measure cross-sectional area A using the tagline method, and velocity V using the oat and/or owmeter methods. Area Velocity Method, (ii) the Slope Area Method, (iii) the Weir Method and (iv) the Volumetric Method. Measurement of peak discharge by the slope-area method, by Tate Dahymple and M.A. Discharge measurement made from a footbridge with a 10-ft wading rod. discharge based on USGS and ISO methods. by the velocity measuring points which are the closest to the wall. Measurement of the mean flow velocity (commonly by doppler or electromagnetic field) over a determined cross-sectional area (the . stop-watch. the considered point to a reference vel~ity measured dt"the rod, yard or . 4.2 Discharge Measurement using Current Meters 4.2.1 General . . You need: tape measure . Using the depth and width measurements for calculating the area and the velocity measurements, the discharge is computed by the ADCP using discharge = area x velocity, similar to the conventional current-meter method. Velocity-Area Method Discharge = (Mean water velocity) x (Cross-section area of water) or 19.1.1 Embody Float Method One of the simplest ways of measuring velocity and discharge in a stream is to use a floating Figure 2: River cross-section and illustration of the compartments. Wu, Yu, Wei, Liang, and Zeng ( 2018 ) conducted a series of experiments to reveal the overtopping process of non-cohesive and cohesive levees in a U-bend flume in which the levee breaching . 4.1.1MEASUREMENT OF RIVER FLOWS There are several methods for measuring river flows - the long-established and time-tested velocity-area method, structural (use of weir, notch) and dilution techniques and recent innovations such as the moving boat method, ultrasonic, and electromagnetic methods. Diagram showing velocity measurement locations at 0.2 (20%), 0.6 (60%) and 0.8 (80%) depth within a channel, and how these are measured using a wading rod and current meter (Nolan and Shields, 2000). The indirect measurement of discharge, derived using the velocity-area method, presents errors, and thus, uncertainty. m/s).. 1. The velocity head rod (VHR) is a fast and inexpensive method of measuring velocity in a stream. With the cross-section of the river being known, the discharge can be calculated using the relation: Q = AV… (3.16) where, Q = discharge, cfs. Using the formula Q = volume/time , you find that Q = 2 gallons / (.5 min) = 4 gpm 44 pages. 2009). Strict standard procedures, however, are followed in measuring these parameters as described in the paper. Velocity-area methods. (Source: www.montana.edu). Application of the index velocity method for computing continuous records of discharge has become increasingly common, especially since the introduction of low-cost acoustic Doppler velocity meters (ADVMs) in 1997. Stream cross-section A. establish a reference line perpendicular to the stream, either using an existing object (bridge) or clothesline strung between two tent stakes B. at regular intervals along this line . If a current meter is not available, a rough estimate of velocity can be made by measuring the time required for a weighted float to travel a fixed distance along the stream. fl ow. Velocity-area methods are based on the principle of the continuity of fluid flow. This Paper. One emerging technology is large-scale particle image velocimetry (LSPIV). 36 Full PDFs related to this paper. Flow measuring structures (weirs, flume…etc) 2. 1967. area of the channel. Q = AV where Q is stream discharge (volume/time), A is cross-sectional area, and V is flow velocity You need: tape measure watch or stop-watch Stream Gauging: Necessity; Selection of gauging sites; Methods of discharge measurement; Area-Velocity method; Venturi flume; Chemical method; weir method; Measurement of velocity; Floats Surface float, Sub-surface float or Double float, Twin float, Velocity rod or Rod float; Pitot tube; Current meter; Working of current meter; rating of current meter; Measurement of area of flow . If the pitot tube is to be used to measure the velocity of a liquid in a pipe, then we must adopt some method to know the static pressure head H. For instance, we may use a pitot tube and a vertical piezometer tube and measure the difference of the liquid levels in the two tubes. Thus the water discharge of a tap (faucet) can be measured with a measuring jug and a stopwatch. Stream discharge can be measured using (1) volumetric gauging, (2) float gauging, (3) current metering, (4) dilution gauging (constant injection or gulp methods), (5) structural methods, and (6) slope-area methods. 11. A brief discussion of these methods follows. rock or very cohesive . The amount of water passing a point on the stream channel during a given time is a function of velocity and cross-sectional area of the flowing water. Full PDF Package Download Full PDF Package. Float method 36 Full PDFs related to this paper. The velocity in this case is determined at site by direct measurement of the velocity in place of theoretical calculation from bed slope etc. Full PDF Package Download Full PDF Package. CFS = Area x Velocity CFS = 4.86 x 2.2. Figure 1a and 1b showing stream velocity distribution. New technologies have been developed for open-channel discharge measurement due to concerns about costs, accuracy, and safety of traditional methods. Methods of measuring irrigation flow rate can be grouped into three basic categories—direct, velocity-area, and constricted flow. Velocity-area methods. Slope area methods For flow measuring structures the discharge Q is a function of the water-surface elevation measured at specified location Q=f(H) Area Velocity Method - Calculation of discharge Figure (4.14) shows the cross section of a river in which N-1 verticals are drawn. 2. 1. Abstract: - Stream discharge can be measured using several methodswhich can be influenced by the natural , streaming characteristics of the river. Assume you get 30 seconds. The total discharge is calculated be the method of mid-sections as follows: VELOCITY/AREA METHOD. When flow velocities and the velocity coefficient are known, the area of the river cross section is needed to calculate the discharge with the velocity-area method (e.g. Compare your estimates 13. 2.2 About the methods Discharge measuring methods Table 1 summarizes the discharge measuring methods (see also Herschy 1978). Choice of method to use will be determined by the volume of water to be measured, the degree of accuracy desired, whether the installation is permanent or temporary, and the financial investment required. IV CONTENTS Measurement of discharge Continued. It is intended as a learning and reference tool for anyone responsible for . The dipping bar (Tauchstab) can be The Gravitational, Dilution, and the Velocity Area methods are more commonly 4.8 indirect method-٧ - Make use of the relation between the discharge and the flow discharge and the depths at specified locations. (Mid-section Method) Q VdA A n Q Vi di w i i 1 Estimation of streamflow - Velocity-area method • Measure V (current meter) at 0.2 and 0.8 of depth • Average V and multiply by A (area = width * depth) • Sum up across stream to get total Q = S (Vi Ai) Vi V0.2 V0.8 2 n Q Vi DiWi i 1 Measurement Distance Width, Depth, Mean Area, d w Discharge . Method # 5. particular area. Float method Inexpensive and simple. Figure 1a is a cross -sectional view with contours indicating how velocity varies from top to bottom and across the stream channel. The velocity field is estimated by choosing a number m of verticals, distributed across the river, where vertical velocity profile is sampled by a current-meter at n i different . •If the velocity at 0.8 depth is greater than the velocity at 0.2 depth or if the velocity at 0.2 depth is twice the velocity at 0.8 depth then the velocity profile is considered abnormal and the NEMS Open Channel Flow Measurement, Date of Issue: June 2013 Page | iii Definitions ADCP Abbreviation for Acoustic Doppler Current Profiler.An instrument that uses acoustic signalling to measure velocity, depth and boat speed. Considering geh total area to be divided info N-1 segments. Direct determination of stream discharge: (a) Area-velocity methods, (b) dilution techniques, (c) electromagnetic method, and (d) ultrasonic method. Stream Discharge using the Float Method. Benson. The most accurate method is to measure the cross- sectional area of the stream and then, using a current meter, determine the average velocity in the cross-section. A short summary of this paper. Determination of discharge (usually symbolized as Q ) thus requires two measurements: the velocity of moving water (V, e.g., in m/s) and the cross-sectional area of the water in the channel (A, e.g, in m2). A where: 3Q = discharge (m /s) v = flow velocity (m/s) A = flow area 2(m ) Most streams do not have a nice flow area (like in a pipe), but have an irregular shape . The velocity averaged over the vertical at each section is known. •Velocities should decrease closer to bottom due to friction. The velocity head rod (VHR) is a fast and inexpensive method of measuring velocity in a stream. After the ADVM is selected, installed, and configured, the stage-area rating and the index velocity rating must be developed. Measurement of peak discharge at culverts by indirect methods, by G.L. Area-Velocity Method. Using a channel width of 10 feet and an average depth of 0.8 feet and the discharge calculation becomes 10 ft x 0.8 ft x 0.9 ft/sec = 7.2 cubic ft/sec (cfs). The conventional approach to measuring stream flow is the current meter method, based on determining the mean discharge using the velocity and the cross sectional area. Strict standard procedures, however, are followed in measuring these parameters as described in the paper. The method of making discharge measurements at a cross section requires determination of the mean velocity in each of the selected verticals. 14. Using a channel width of 10 feet and an average depth of 0.8 feet and the discharge calculation becomes 10 ft x 0.8 ft x 0.9 ft/sec = 7.2 cubic ft/sec (cfs). The choice of method depends on the characteristics of the stream and on the application. m 3 /second, also called cumecs), A is the cross-sectional area of the stream (e.g. m 2), and V is the average velocity (e.g. %) . This Paper. CFS = 10.69 (Cubic Feet per Second) or CFS x 448.83 = 4,797.99 GPM (converted CFS to GPM) Measurement of peak discharge at width contractions by indirect methods, by H.F. Matthai. This PowerPoint presentation describes how stream discharge should be measured when wading and using the velocity-area method. These methods are used for instantaneous measurement of streamflow and to establish the stage-discharge relationship (Harmel et al. Five depth measurements are typical but more is better, especially in larger streams. Comparison of methods Summary of discharge measurements at 01402000 Millstone River at Blackwells Mills, NJ on May 10, 2006 during field training exercise [* velocity too slow to measure] Cross section Flowtracker Pygmy meter Floatation Method Culvert Computation Percent Difference Ideal cross section 1.04 1.06 1.00 - 4 - 6% Presently (2011), the index velocity method is being used to compute discharge records for approximately 470 gaging stations operated and maintained by the U.S. Geological Survey. Equipment. I. The slope-areamethod can be used with reasonable accuracy in open channels having stable bound aries, bed and sides (e.g. Hydrometry — Measurement of liquid flow in open channels — Velocity area methods using point velocity measurements SKU: iso_072754_176230 Published by ISO Publication Year 2021 5 Edition 42 pages Model CMCsp current meter counter with direct velocity reading, in-built Bluetooth module for Average your cross-sectional areas (A): Using the average area and corrected velocity, you can now compute discharge, Q. Slope-hydraulic Radius-Area Method Measurement of water surface slope, cross-sectional area, and wetted perimeter over a length of uniform section channel are used to calculate the flow rate, by using a resistant equation such as the Manning formula. Tables Table 14-1 Computation of discharge using velocity head rod 14-5 (VHR) measurements Table 14-2 Data for computing discharge from slope-area 14-9 measurements, example 14-1 Table 14-3 Hydraulic parameters for starting cross section 14-18 M-1, example 14-4 Table 14-4 Stage discharge for section M-1 with meander 14-19 Turn in your write-up no later than 1 week after your lab period. Use a marked rod, a yard or meter stick to measure the depth at regular intervals across the stream. 12 pages. Measurement of Velocity: The current meter measures velocity at a point. Tracer-dilution methods can vary considerably in accuracy, from +/- 1% to over 30%, depending upon the equipment used, experience of the personnel, and the accuracy of the measuring equipment. Measurement of velocity Continued. Measuring Stream Discharge Using the USGS Midsection Method . It is suitable for use under somewhat special conditions when direct measure ment of discharge by more accurate methods, such as the velocity-areamethod, Is not possible. Click here to purchase the full version from the ANSI store. V = Average velocity, ft./sec. • Runoff measuring devices Direct Discharge Methods Weirs Orifices Flumes Velocity - Area Methods Float method Current meter. 1965. Flow-measurement equipment required includes: (1) current meter or flowmeter, (2) top-setting wading rod (marked in tenths of a foot), and (3) tape measure or tagline (marked in tenths of a foot) (4) waders, (5) data sheet, (6) also bring a clipboard, notebook, and a . The index velocity method can be used at locations where stage-discharge methods are used, but it is especially appropriate when more than one specific discharge can be measured for a specific stage. The velocity-area method is the most common method of estimating river flow. Smoothing River Discharge Time Series Computed Using the Velocity-Area Method . 7) Work out the measurements to obtain total discharge Q. Current velocity may be measured using various types of meters and devices. Measuring Flowrate (volumetric) • How do you measure (volumetric) flowrate? where Q is stream discharge (volume/time), A is cross-sectional area, and V is flow velocity. Discharge, or the volume of water flowing in a stream over a set interval of time, can be determined with the equation: Q = AV, where Q is discharge (volume/unit time-e.g. See example below: Float-Area Method If my float measurements gave me an average surface velocity of 2.2 ft/s (feet per second), then I can calculate the CFS discharge by using the discharge formula below. Analyze your data for flow and velocity for the two methods 12. Conf. The method chosen to measure site discharge or stream fl ow depends on a variety of factors including: • With a bucket and a stopwatch! Because m 3 /s is a large unit, smaller flows are measured in litres per second (l/s). Area of Cross-Section and Velocity as Observed at Bridge Site: The area of cross-section is measured by taking a series of levels of the river at H.F.L. Velocity-area method using the dipping bar or "Tauchstab nach Jens" The principle of this method is the same as for the current-meter. DOI: 10.1061/(ASCE)HY.1943 . of these discharge measurements are performed using the velocity-area method; it consists in integrating flow velocities and depths through the cross-section [1]. The 7th Int. The velocity-area method for the determination of discharge in open channels consists of measurements of stream velocity, depth of flow and distance across the channel between observation verticals. Over 75 percent of those measurements are made by wading streams and using the velocity-area method. The velocity-area method is the most common method of estimating river flow. Float-Area Method The amount of water passing a point on the stream channel during a given time is a function of velocity and cross-sectional area of the flowing water. A = Area of water section, ft 2. After the ADVM is selected, installed, and configured, the stage-area rating and the index velocity rating must be developed. Hauet et al., 2008). The velocity is measured at one or more points in each vertical by current meter and an average velocity determined in each vertical. For measuring the discharge of a river we need a different method and the most common is the 'area-velocity' method. 2.2.7 discharge velocity : The ratio of the volume rate of flow {integral of the axial component of local velocities with respect to the cross-sectional area) to the area of the measuring cross-section. Stream Discharge Measurement Using a Large-Scale Particle Image Velocimetry (LSPIV) Prototype. ISO 3354:2008 specifies a method for the determination of the volume flow-rate in a closed conduit by means of the velocity-area method using propeller-type current-meters under the following conditions: a) the velocity distribution is regular; b) the fluid is water which is clean or considered to be clean; c) the conduit is full; d) the flow is steady. ISO 1088:2007 is intended to be applied to velocity-area methods that involve measurement of point velocities at a relatively small number of discrete depths and transverse positions in the flow cross-section, as described in ISO 748. For example, velocity area method requires condition, which produces a stable depth discharge relationship, and the use of flume and weir is restricted to small rivers where there the provision for sufficient head and constriction in the river is acceptable. If the computed T c is > 10 hours, peak discharge should be estimated using the NEH-4 procedures which are automated in the TR-20 computer program. Calculation of mean velocity and discharge using water surface velocity in small streams . Streamflow, or discharge, is defined as the volumetric rate of flow of water (volume per unit time) in an open channel Streamflow in the USGS is usually expressed in English dimensions of cubic feet per second (ft3/s) or CFS. It can be applied to velocity-area discharge measurements that use a velocity meter to measure point velocities at multiple vertical sections in a channel cross section. described two methods for estimating the discharge in an open channel, which represent valid alternatives to the Velocity-Area method. 2009). If the cross section area A is known and the mean velocity of the stream flow V determined, the discharge Q is . A short summary of this paper. Stream water velocity is typically measured using a current meter. Flow-measurement equipment required includes: (1) current meter or flowmeter, (2) top-setting wading rod (marked in tenths of a foot), and (3) tape measure or tagline (marked in tenths of a foot) (4) waders, (5) data sheet, (6) also bring a clipboard, notebook, and a . Use the guidelines for laboratory write-ups to help you structure and present the results. The rod can be made using a 3-6 ft long, two-inch wide, very thin, piece of wood. Current-meter measurements Continued. It can be applied to velocity-area discharge measurements that use a velocity meter to measure point velocities at multiple vertical sections in a channel cross section. Q = AV. •The use of 0.6 and 0.2/0.8 methods assume the velocity profile is logarithmic. The rod can be made using a 3-6 ft long, two-inch wide, very thin, piece of wood. Previous article. LSPIV is capable of measuring surface velocity by analyzing recorded images of particles added to the stream surface. Pa£e Three-point method_____-----_--- 41 Runoff Portion of precipitation that makes its way towards streams, lakes or oceans as surface or subsurface flow Factors affecting runoff Climatic factors Apparatus and procedures are described in more detail in Welch (1948) and Buchanan and Sommers (1973). The index velocity method can be used at locations where stage-discharge methods are used, but it is especially appropriate when more than one specific discharge can be measured for a specific stage. Quality Assurance Practices for the Mitigation of Systematic Discharge Measurement Errors: pdf--2015.05: Minimum requirements for documenting stage-area and index-velocity ratings for computation of streamflow records using the index velocity method: pdf--2014.09 A rating table is used to convert number of pulses to velocity. The total uncertainty in the computed discharge is a combination of the uncertainties in the measured components. Float method As the term implies, the flow is the product of the average velocity in the cross-section and the cross-sectional area of flow. PDF Published 2021-09-29 Issue Vol 16 (2021) Section . Different tools exist for contactless river area measurements of a cross section. Stream Discharge Measurement Using a Large-Scale Particle Image Velocimetry (LSPIV) Prototype. Mean velocity of the stream is often taken as 0.8 to 0.9 of the average surface velocity. Measurement of fluid flow in closed conduits — Velocity area method using Pitot static tubes Mesurage du débit des fluides dans les conduites fermées — Méthode d'exploration du champ des vitesses au moyen de tubes de Pitot doubles This is a preview of "ISO 3966:2008". The two methods have certain limitations and are not applicable in all the circumstances. Calculation of mean velocity and discharge using water surface velocity in small streams . 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