Difference between revisions of "Current meter"

From FIThydrowiki
Jump to navigation Jump to search
 
(32 intermediate revisions by 2 users not shown)
Line 1: Line 1:
NOTE: fix equations
 
 
 
=Quick summary=
 
=Quick summary=
[[file:adcp_example_units.png|thumb|250px|Figure 1:]]
+
[[file:current_meter_types.png|thumb|250px|Figure 1: Current meter: a) mechanic, b) electromagnetic, c) acoustic (Sources: SEBA hydrométrie, OTT, Sontek).]]
[[file:adcp_qboat.png|thumb|250px|Figure 2: ]]
+
[[file:current_meter_section.png|thumb|250px|Figure 2: Flow cross-section with the verticals (in red) and the  points (black dots) for velocity measurement with the current meter]]
[[file:adcp_wse.png|thumb|250px|Figure 3: ]]
+
[[file:current_meter_operator.png|thumb|250px|Figure 3: Operator in the downstream migration channel performing measurements with a current meter.]]
[[file:adcp_workflow.png|thumb|250px|Figure 4: ]]
 
[[file:adcp_output.png|thumb|250px|Figure 5: ]]
 
  
Developed by: Various Companies
+
Developed by:  
  
 
Date:  
 
Date:  
Line 14: Line 10:
 
Type: [[:Category:Devices|Device]]
 
Type: [[:Category:Devices|Device]]
  
Suitable for the following [[::Category:Measures|measures]]:
 
  
 
=Introduction=
 
=Introduction=
The first devices to measure flow velocities appeared during the 1780s with the first mechanical current meter which counts the rotations of a propeller and links it to the flow velocity (by proportionality principle).  
+
The first devices to measure flow velocities appeared during the 1780s, with the first mechanical current meter which counts the rotations of a propeller and links it to the flow velocity (by proportionality principle).  
  
Today there are 3 different techniques to assess the flow velocity: mechanically, electromagnetically, and acoustically (Figure 73). The acoustic current meters using the Doppler Effect are not presented here, as these tools (ADCP, ADV, etc.) are presented separately.  
+
Today there are 3 different techniques to assess the flow velocity: mechanically, electromagnetically, and acoustically (Figure 1). The acoustic current meters using the Doppler Effect are not presented here, as these tools (e.g ADCP, ADV) are presented separately.  
  
 
=Application=
 
=Application=
For a mechanical flow meter, the rotation of the propeller produces an electrical impulse detected and recorded by a counter connected to the current meter.  
+
In a mechanical flow meter, the rotation of the propeller produces an electrical impulse detected and recorded by a counter connected to the current meter.  
 
The electromagnetic flow meter uses the Faraday law. The sensor creates a magnetic field between two electrodes located at the end of the probe. The flow velocity is deduced from the measurement of the electromagnetic force generated by the passage of water through the magnetic field.  
 
The electromagnetic flow meter uses the Faraday law. The sensor creates a magnetic field between two electrodes located at the end of the probe. The flow velocity is deduced from the measurement of the electromagnetic force generated by the passage of water through the magnetic field.  
  
 
The measurement conditions of discharge through flow velocity fields are regulated by the European standard NF EN ISO 748.
 
The measurement conditions of discharge through flow velocity fields are regulated by the European standard NF EN ISO 748.
The velocities are measured along a cross section at verticals. The number of verticals (n) depends on the width of the channel:
+
The velocities are measured along a cross section at verticals. The number of verticals (n) depends on the width of the channel (w):
*Width of channel < 0,5 m, n = 5 or 6
+
* W < 0.5 m, n = 5 or 6
*Width of channel > 0,5 m and < 1 m, n = 6 or 7
+
* W > 0.5 m and < 1 m, n = 6 or 7
*Width of channel > 1 m and < 3 m, n = 7 or 12
+
* W > 1 m and < 3 m,   n = 7 or 12
*Width of channel > 3 m and < 5 m, n = 13 to 16
+
* W > 3 m and < 5 m,   n = 13 to 16
*Width of channel > 5 m, n ≥ 22
+
* W > 5 m,   n ≥ 22
  
One method among others to measure the mean velocity on each vertical is to measure the velocity in one or several measurement points at different water levels on the vertical. The number of measurements points for each vertical depends on the water level. For example, only one point is needed for water level <20 cm at 60% of the water level. If there are only 2 measurement points, they should be at 20 and 80% of the water level, and the mean velocity corresponds to the average of the two measured velocities. In the following example, 6 measurements were selected (Figure 74). The example is linked to the velocity profile inside a downstream migration channel, which is not logarithmic.
+
One method among others to measure the mean velocity on each vertical is to measure the velocity in one or several measurement points at different water levels on the vertical. The number of measurements points for each vertical depends on the water level. For example, only one point is needed for water level <20 cm at 60% of the water level. If there are only 2 measurement points, they should be at 20 and 80% of the flow depth, and the mean velocity corresponds to the average of the two measured velocities. In the following example, 6 measurements were selected (Figure 2). The example is linked to the velocity profile inside a downstream migration channel, which is not logarithmic.
  
To do the measurements, the operator needs to be equipped with waders and to be in the stream (Figure 75).
+
To do the measurements, the operator needs to be equipped with waders and to be in the stream (Figure 3).
  
 
By the method of mean section, the mean velocity between the banks and the closer verticals can be calculated. The mean velocity on each vertical is calculated that way, in the case of 6 measurement points:
 
By the method of mean section, the mean velocity between the banks and the closer verticals can be calculated. The mean velocity on each vertical is calculated that way, in the case of 6 measurement points:
  
V_(mean section)=0.1(V_s+2V_0.8+2V_0.6+2V_0.4+2V_0.2+V_pf)
+
<math>V_{mean section}=0.1(V_s+2V_{0.8}+2V_{0.6}+2V_{0.4}+2V_{0.2}>+V_{pf})</math>
  
 
Then a mean velocity is calculated for each flow section between the verticals and the closer bank; by making an average for the sections without including the banks, and by applying the following formula:  
 
Then a mean velocity is calculated for each flow section between the verticals and the closer bank; by making an average for the sections without including the banks, and by applying the following formula:  
  
V_(mean section)=m/(m+1)*V_(mean closer vertical)
+
<math>V_{mean section}=\frac{m}{(m+1)}*V_{mean closer vertical}</math>
  
where m is a parameter depicting the characteristics of the river bed or of the wall. m is generally comprised between 5 and 7 but can be equal to 10 if the walls are really smooth. If m=4 the river bed and the walls are rough.  
+
where m is a parameter depicting the characteristics of the river bed or of the wall. m is generally comprised between 5 and 7, but can be equal to 10 if the walls are really smooth. If the river bed and the walls are rough, m=4.  
  
 
The discharge per section can be calculated according to standard EN ISO 748:2007:  
 
The discharge per section can be calculated according to standard EN ISO 748:2007:  
  
Q_section=V_(mean section)*H_(water mean)*L_flow
+
<math>Q_{section}=V_{mean section}*H_{water mean}*W</math>
  
Where Hwater mean is the mean water level and Lflow is the width of the channel.
+
where <math>H_{water mean}</math> is the mean water level and <math>W</math> is the width of the channel.
  
In order to have the total discharge, all discharges per section have to be added.  
+
The total discharge is the sum of all the discharges per section.  
  
The most recent devices have the possibility to directly treat the data and give the discharge on the cross section.
+
The most recent devices have the possibility to directly treat the data and provide the total discharge.
 +
 
 +
=Relevant mitigation measures and test cases=
 +
{{Suitable measures for Current meter}}
  
 
=Other information=
 
=Other information=
The total costs for the geophone and accelerometer sensors amount to approx. 885-1'330 €. The costs for the field computer, the analog-digital-converter, and the 3G modem are approx. 5'300-6'200 €. The total costs for the Teledyne RiverPro 1200 kHz, Teledyne Q-boat and DGPS from Hemisphere Atlas link amount to approx. 22’000 €, 21’200 € and 3’340 € respectively. The costs of shipping, VAT, some mounting apparatus and long-range radio modem are excluded. For current costs of the equipment, we recommend to ask the corresponding supplier. Note that Q-boat can also house Sontek RiverSurveyor M9. Furthermore, a rugged laptop for field use is recommended.
+
Several companies commercialize these technologies.
 +
 
 +
At the French Test Cases an electromagnetic flow meter Marsh McBirney, FLO-MATE 2000 was used.
  
 
=Relevant literature=
 
=Relevant literature=
*Mueller, D.S., Wagner, C.R., Rehmel, M.S., Oberg, K.A., Rainville, F. (2013). Measuring discharge with acoustic Doppler current profilers from a moving boat (ver. 2.0, December 2013), U.S. Geological Survey Techniques and Methods, book 3, chap. http://dx.doi.org/10.3133/tm3A22.
 
 
*Simpson, M.R. (2002). Discharge measurements using a broadband acoustic Doppler current profiler. Open-file Report 2001-1, https://doi.org/10.3133/ofr011.
 
 
<b>Links to the suppliers of equipment:</b>
 
 
*Teledyne Marine, ADCP RiverPro: http://www.teledynemarine.com/riverpro-adcp?ProductLineID=13
 
 
*Teledyne Marine, Q-Boat: http://www.teledynemarine.com/Lists/Downloads/Q-Boat_1800_Datasheet.pdf
 
 
*Hemisphere Atlas DPS: https://hemispheregnss.com/Atlas/atlaslinke284a2-gnss-smart-antenna-1226
 
 
*Sontek ADCP M9: https://www.sontek.com/riversurveyor-s5-m9
 
 
<b>Software for ADCP data analysis:</b>
 
 
*Velocity Mapping Toolbox: https://hydroacoustics.usgs.gov/movingboat/VMT/VMT.shtml
 
  
*Q-GIS: https://qgis.org/en/site/
+
*Aurélien Despax, 2016, Incertitude des mesures de débit des cours d’eau au courantomètre, Amélioration desméthodes analytiques et apports des essais interlaboratoires, Ingénierie de l’environnement, UniversitéGrenoble Alpes, 2016
  
*ARC-GIS: https://www.esri.com/en-us/arcgis/about-arcgis/overview
+
*Manon Dewitte, Dominique Courret, Fatma Lemkecher, Laurent David, 2019, Presentation of Las Rives Test Case, FIThydro
  
 
=Contact information=
 
=Contact information=

Latest revision as of 16:08, 10 April 2020

Quick summary

Figure 1: Current meter: a) mechanic, b) electromagnetic, c) acoustic (Sources: SEBA hydrométrie, OTT, Sontek).
Figure 2: Flow cross-section with the verticals (in red) and the points (black dots) for velocity measurement with the current meter
Figure 3: Operator in the downstream migration channel performing measurements with a current meter.

Developed by:

Date:

Type: Device


Introduction

The first devices to measure flow velocities appeared during the 1780s, with the first mechanical current meter which counts the rotations of a propeller and links it to the flow velocity (by proportionality principle).

Today there are 3 different techniques to assess the flow velocity: mechanically, electromagnetically, and acoustically (Figure 1). The acoustic current meters using the Doppler Effect are not presented here, as these tools (e.g ADCP, ADV) are presented separately.

Application

In a mechanical flow meter, the rotation of the propeller produces an electrical impulse detected and recorded by a counter connected to the current meter. The electromagnetic flow meter uses the Faraday law. The sensor creates a magnetic field between two electrodes located at the end of the probe. The flow velocity is deduced from the measurement of the electromagnetic force generated by the passage of water through the magnetic field.

The measurement conditions of discharge through flow velocity fields are regulated by the European standard NF EN ISO 748. The velocities are measured along a cross section at verticals. The number of verticals (n) depends on the width of the channel (w):

  • W < 0.5 m, n = 5 or 6
  • W > 0.5 m and < 1 m, n = 6 or 7
  • W > 1 m and < 3 m, n = 7 or 12
  • W > 3 m and < 5 m, n = 13 to 16
  • W > 5 m, n ≥ 22

One method among others to measure the mean velocity on each vertical is to measure the velocity in one or several measurement points at different water levels on the vertical. The number of measurements points for each vertical depends on the water level. For example, only one point is needed for water level <20 cm at 60% of the water level. If there are only 2 measurement points, they should be at 20 and 80% of the flow depth, and the mean velocity corresponds to the average of the two measured velocities. In the following example, 6 measurements were selected (Figure 2). The example is linked to the velocity profile inside a downstream migration channel, which is not logarithmic.

To do the measurements, the operator needs to be equipped with waders and to be in the stream (Figure 3).

By the method of mean section, the mean velocity between the banks and the closer verticals can be calculated. The mean velocity on each vertical is calculated that way, in the case of 6 measurement points:

Then a mean velocity is calculated for each flow section between the verticals and the closer bank; by making an average for the sections without including the banks, and by applying the following formula:

where m is a parameter depicting the characteristics of the river bed or of the wall. m is generally comprised between 5 and 7, but can be equal to 10 if the walls are really smooth. If the river bed and the walls are rough, m=4.

The discharge per section can be calculated according to standard EN ISO 748:2007:

where is the mean water level and is the width of the channel.

The total discharge is the sum of all the discharges per section.

The most recent devices have the possibility to directly treat the data and provide the total discharge.

Relevant mitigation measures and test cases

Relevant measures
Baffle fishways
Bottom-type intakes (Coanda screen, Lepine water intake, etc)
Bypass combined with other solutions
Complete or partial migration barrier removal
Construction of a 'river-in-the-river'
Construction of off-channel habitats
Fish guidance structures with narrow bar spacing
Fish lifts, screws, locks, and others
Fish refuge under hydropeaking conditions
Fishways for eels and lampreys
Mitigating rapid, short-term variations in flow (hydro-peaking operations)
Mitigating reduced annual flow and low flow measures
Mitigating reduced flood peaks, magnitudes, and frequency
Nature-like fishways
Operational measures (turbine operations, spillway passage)
Other types of fine screens
Placement of dead wood and debris
Placement of spawning gravel in the river
Placement of stones in the river
Pool-type fishways
Sensory, behavioural barriers (electricity, light, sound, air-water curtains)
Skimming walls (fixed or floating)
Vertical slot fishways
Relevant test cases Applied in test case?
Altheim test case -
Altusried test case -
Anundsjö test case Yes
Bragado test case Yes
Freudenau test case -
Gotein test case Yes
Guma and Vadocondes test cases Yes
Günz test case Yes
Las Rives test case Yes
Schiffmühle test case Yes
Trois Villes test case Yes

Other information

Several companies commercialize these technologies.

At the French Test Cases an electromagnetic flow meter Marsh McBirney, FLO-MATE 2000 was used.

Relevant literature

  • Aurélien Despax, 2016, Incertitude des mesures de débit des cours d’eau au courantomètre, Amélioration desméthodes analytiques et apports des essais interlaboratoires, Ingénierie de l’environnement, UniversitéGrenoble Alpes, 2016
  • Manon Dewitte, Dominique Courret, Fatma Lemkecher, Laurent David, 2019, Presentation of Las Rives Test Case, FIThydro

Contact information