Stream gauging techniques - RiverFlow 2018 · 2018-09-13 · STREAM GAUGING TECHNIQUES Presentation based on the WMO Manual on streamgauging (2010), Volume II Chapter 2, with additional

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STREAM GAUGING TECHNIQUES

Presentation based on the WMO Manual on streamgauging

(2010), Volume II Chapter 2, with additional material

provided by Alexandre HAUET (EDF DTG Grenoble, France)

IAHR WMO IAHS Training ‐ ‐ Course on Stream Gauging

Lyon -- September 2-4, 2018

World Meteorological Organization -- Working together in weather, climate and water

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Sunday, September 02, 2018

STREAM GAUGING… WHAT FOR ?? Different needs :

Knowing the discharge of a river at a given place and a given time:

• Check environmental regulation (ecological instream flow) / Punctual studies

• Discharge measurement by field hydrologist

Knowing the discharge of a river continuously (and in real-time):

• Use of a rating curve :– Measurement of the water stage at a station, continuously and in real time

– Establishment of a stage-discharge relationship (rating curve), based on gaugings

– Computation of the discharge from the measured stage

IAHR / WMO / IAHS International Streamgauging course

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RIVERS ARE COMPLEX Complexity at the spatial scale:

Complexity at the time scale

Upstream

Downstream

17m


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RIVERS ARE COMPLEX Interaction with the environment:

No instrument for measuring directly the discharge continuously

rating curve

Not a unique gauging methods :

Different methods / Field hydrologist toolbox

How the Mississippi

has changed course…


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LET SPEAK THE SAME LANGUAGE Hydraulic description of a river cross-section:


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LET SPEAK THE SAME LANGUAGE Hydraulic description of a river cross-section:

Geometric characteristics

Bathymetry

Water

depth

Wetted

area

River width


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LET SPEAK THE SAME LANGUAGE Hydraulic description of a river:


Cinematic characteristics

Bathymetry

Water

depth

Wetted

area

Flow

velocity

River width


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LET SPEAK THE SAME LANGUAGE Hydraulic description of a river:


Cinematic characteristics

Bathymetry

Water

depth

Wetted

area

Flow

velocity

River width

Discharge : Q = wetted area * mean velocity

[m3/s] [m2] [m/s]

Volume per unit time


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LET SPEAK THE SAME LANGUAGE Discharge is :

a characteristic quantity of the state of the river and the basin

a characteristic quantity for

• water resource management

• drinking water

• irrigation

• hydroelectricity / cooling of power plants

• quantifying flood risk

• …

Rivers.. It’s not only a matter if discharge

Sediment transport, biology, ecology, pollution, fishing…

But it is out of the scope of this course !

Jiang Zi GjiangDesman of Pyrénées

Mékong


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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)

Precalibrated measuring structures (course of Roberto Ranzi)

Indirect determination of flood peak (course of Jérôme Le Coz)

WMO reference documents :

WMO Manual on Streamgauging (2010)

WMO Guide to Hydrological Practices, Volume I


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PRELIMINARY OPERATIONS BEFORE GAUGING Prior site visits, especially for new sites

Make sure that the whole stream discharge is measured

Secondary branch during flood, for example

Find the right gauging site

Not necessary at the exact location of the stage gauge, but not too far !

Depending on the gauging method used

Depending on the river morphology / vegetation…

Allowing to work safely !!

Find the right gauging method

To make the best discharge measurement safely

Keep a constant discharge during the measurement

Adapt the gauging method to the dynamics of the flow

• Avoid more than 10% of discharge variation during the gauging

Monitor the stage variation during the gauging• Computation of mean gauge height H

Have equipment well maintained and in working order…

Course “Assessment of the performance of flow measurement instruments” on Wednesday

… And trained staff knowing how to use it!!


𝐻 =σ𝑡 ℎ𝑡𝑞𝑡

𝑄

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VOLUMETRIC METHOD

Q = Volume per unit time

Measuring the time (t) to fill of a container of known capacity (Vol)

Q = V / t

Equipment required

calibrated container and stop-watch

Only applicable to small discharges…

Q < 10 L/s

..but it is the most accurate method of measuring such flows !


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TRACER DILUTION METHOD

Based on the mass conservation Determining the degree of dilution by the flowing water of an added tracer solution

Tracers used : salt conductivity or Fluorescent tracers (Uranine, Rhodamine) fluorescence Requirements for the tracer :

• dissolves readily in the stream’s water at ordinary temperatures;• absent in the water of the stream (or present only in negligible quantities);• not decomposed in the stream’s water and not retained or absorbed by sediment, plants or

organisms;• concentration can be measured accurately by simple methods; • harmless to humans, animals and vegetation in the concentration it assumes in the stream.

2 injections methods : Slug injection and Constant rate injection


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Principle of the slug injection method

Injection of a known mass M of tracer

Tracer is dilute onto a cloud

Mass conservation 𝑀 = 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑙𝑜𝑢𝑑 𝑉 ∗ 𝑚𝑒𝑎𝑛 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑙𝑜𝑢𝑑 𝐶

When mixing length is reached, V = 𝑠𝑡𝑟𝑒𝑎𝑚 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒 𝑄 ∗ 𝑑𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑙𝑜𝑢𝑑 𝑡

𝑀 = 𝑉 ∗ 𝐶 = Q ∗ t ∗ C Q =𝑀

𝑡∗𝐶=

𝑀

𝑑𝑡(𝐶𝑡−𝐶0)

t

C

C0

𝑀

𝑀 = 𝑉 ∗ 𝐶

𝑀 = Q ∗ t ∗ C


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Principle of the constant rate injection method

Injection of a tracer of concentration c1 at a constant discharge of q during a long time• Container equipped with a Marriott vessel

Tracer is dilute onto the river discharge Q

When mixing length is reached, concentration is homogeneous on the cross-section C2

Mass conservation 𝑐1𝑞 = 𝐶2(Q + 𝑞). As q ≪ 𝑄, Q = 𝑞𝑐1

𝐶2

t

C

C2


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TRACER DILUTION METHOD Recommendations / limitations

Adequate mixing of the tracer with the stream water in a short length of channel

Adapted for turbulent streams • Mountainous streams, bends or abrupt constrictions

• Supercritical flows

• Flood flow (if not too much suspended sediments)

• If cross-sectional area cannot be accurately measured or is changing during the measurement.

• Fish passage

Slug injection : fast method• Adapted for unsteady flow measurement

Not adapted for :• Fluvial flow with long mixing length

• High sediment concentration flows– Adsorption and masking

• Avoid large dead-water zones


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IAHR / WMO / IAHS International Streamgauging coursePrehistoric first dilution gauging

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VELOCITY-AREA METHOD USING CURRENT METERS

Q = Cross sectional area X Average velocity

Measure cross sectional area• Streambed bathymetry• Sufficient sampling to catch the shape of the wetted area


Bathymetry

Water

depth

Wetted

area

Flow

velocity

River width

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Q = Cross sectional area X Average velocity

Measure cross sectional area• Streambed bathymetry• Sufficient bathymetric sampling to catch the shape of the wetted area

Determine average velocity over the cross-section• Stream velocity varies through the stream profile• Sufficient sampling to determine the average velocity


Velocity contour :

Low vel. High vel.

energy lost due to friction

along the stream channel

lowest velocity close to the

bottom and the banks

highest velocity

at the top and the

middle

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Selection of the gauging cross-section

A stream reach as simple as possible

• subcritical flow

• uniform reach upstream and downstream / No singularity (bridge, weir, dam, gorges…)

• A cross section perpendicular to the flow

General recommendations:

• velocities at all points are parallel to one another and at right angles to the cross-section

• curves of distribution of velocity in the section are regular in the vertical and horizontal planes;

• velocities greater than 0.150 m/s; depth of flow greater than 0.3 m;

• regular and stable streambed;

• no aquatic growth, minimal formation of slush or frazil ice


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Selection of the gauging cross-section

Small modifications of the cross section are possible

• Small dikes to concentrate the flow

• Removing stones from the bed

• …

Stream modification must be limited and reversible

• Not disturbing the fishes (spawning areas)


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EQUIPMENT Different supports depending on the accessibility of the river

Wading rod :

• Section fully accessible by foot, distance across the section measured with a tape

Gauging truck

• Retractable arm mounted on a truck

• sounding weights

Cableways

• Carrier cable permanently stretched across a section

• Equipped with a sounding weight or a cable car


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MECHANICAL CURRENT METERS Velocity by counting revolutions of rotor during a short-time period

𝑉𝑓𝑙𝑜𝑤 = 𝑓 𝑉𝑟𝑜𝑡𝑜𝑟 current meter calibration

Two types of current meter rotors

cup type with a vertical shaft (Price AA)

propeller type with a horizontal shaft (Ott C2)

Contact to generate an electric pulse for indicating the revolutions of the rotor

Can measure from 0.05 to 5 m/s, depending on the rotor type

Mind measuring the component of velocity normal to the cross-section

Advantages :

Mechanical : one can see when it is not working properly… or not

Drawbacks :

Need care and periodic verification of the moving parts

Susceptible to vegetationIAHR / WMO / IAHS International Streamgauging course

• Larger section

• Lower velocity

component

• Same discharge

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ELECTROMAGNETIC CURRENT METERS

Principle :

Water (conductor) moving through a magnetic field produce an electric current (Faraday principle)

Velocity of the water is proportional to the electric current produced

Velocity range :

0 to 6 m/s; accuracy of 2% +/- 2cm/s

Advantages :

Can measure low velocities

No moving part less maintenance

Can measure with vegetation

Drawbacks :

Susceptible to electrical interference


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ACOUSTIC CURRENT METERS Principle

Transmit acoustic signals into a water column with a frequency f

Signal is backscattered by particles moving in the water

Doppler effect change of frequency of the backscatter signals f’

Computation of radial velocity on each beam

Computation of flow velocity

Velocity range

-0,2 m/s à 2,4 m/s; accuracy : 1% ± 0.25 cm/s

Advantages :

No moving part less maintenance

Measurement of 2D or 3D velocity components (Vx, Vy, Vz) and backward flow

Can measure very low velocities (2 cm/s)

Drawback :

Susceptible to vegetation

𝑉 cos𝛼 =𝑓 − 𝑓′

𝑓


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Measurement protocol

Temporal sampling of the velocity

• Streams : turbulent flow average turbulent velocities

• Exposure time of at least 30s to get average velocity– And at least 100 rotations for a mechanical current meter

– Optimal exposure time should be evaluated for each measurement (increase exposure time when velocity

decrease)

• Standard Iso748 :


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Measurement protocol : measuring the stream bathymetry

Spatial sampling of the cross section bathymetry at n verticals

• depth of each vertical di

Spatial sampling of the cross section velocity distribution at the n verticals

• Velocity distribution method

• Reduced point method

• Integration method

depth-averaged velocity of each vertcal Vi


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VELOCITY-AREA METHOD USING CURRENT METERS Measurement protocol : computing depth-averaged velocity at vertical i

Velocity distribution method

• Important number of velocity measurement along each vertical between surface and bed


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Velocity distribution method

• Important number of velocity measurement along each vertical between surface and bed

• Interpolation between measured velocity

• Extrapolation to the bed and the surface (log- or power-law)

• 𝑉𝑖 =0𝑑𝑖 𝑉𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑

𝑑𝑖

•


number and spacing of the points are

chosen as to define accurately the

velocity distribution in each vertical with

a difference in readings between two

adjacent points of not more than 20 %

with respect to the higher value

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Reduced point method

• 1 to 6 velocity measurements per vertical– At a relative depth below the free surface

• Computation of Vi with algebraic formula– 1 pt method : 𝑉𝑖 = 𝑉0.6𝑑𝑖– 2 pts method : 𝑉𝑖 = 0.5 (𝑉0.2𝑑𝑖 + 𝑉0.8𝑑𝑖)

– 3 pts method : 𝑉𝑖 = 0.25 (𝑉0.2𝑑𝑖 + 2 𝑉0.6𝑑𝑖 + 𝑉0.8𝑑𝑖)

– 5 pts method : 𝑉𝑖 = 0.1 (𝑉𝑠𝑢𝑟𝑓𝑎𝑐𝑒 + 3 𝑉0.2𝑑𝑖 + 3 𝑉0.6𝑑𝑖 + 2 𝑉0.8𝑑𝑖 + 𝑉𝑏𝑒𝑑)

– 6 pts method : 𝑉𝑖 = 0.1 (𝑉𝑠𝑢𝑟𝑓𝑎𝑐𝑒 + 2 𝑉0.2𝑑𝑖 + 2 𝑉0.4𝑑𝑖 + 2 𝑉0.6𝑑𝑖 + 2 𝑉0.8𝑑𝑖 + 𝑉𝑏𝑒𝑑)

– Surface velocity method : 𝑉𝑖 = 0.85 ∗ 𝑉𝑠𝑢𝑟𝑓𝑎𝑐𝑒

• Example with 2 pts method :


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Integration method using mechanical current meters

• current meter is lowered and raised through the entire depth at each vertical at a uniform rate.

• average number of revolutions per second is determined depth-averaged velocity

• the speed at which the meter is lowered < 5% of the flow velocity and between 0.04 and 0.10 m/s

• two complete cycles are made in each vertical

– if the results differ by more than 10 per cent, the measurement is repeated.

• restriction of use :

– depth > 1 m

– velocities > 1 m/s

• the integration method should not be used with a vertical axis current meter


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COMPUTATION OF DISCHARGE WITH CURRENT METERS Mid-section method

A cross-section with n verticals i of known depth di and depth-averaged velocity Vi


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The relative location of each vertical bi is measured


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For vertical i, a subsection is defined with :

• A width Wi of (bi+1-bi-1)/2; a depth of di, a mean velocity of Vi

• The discharge qi of the subsection centered on i is 𝑞𝑖 = 𝑊𝑖 ∗ 𝑑𝑖 ∗ 𝑉𝑖


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For vertical i, a subsection is defined with :

• A width Wi of (bi+1-bi-1)/2; a depth of di, a mean velocity of Vi

• The discharge qi of the subsection centered on i is 𝑞𝑖 = 𝑊𝑖 ∗ 𝑑𝑖 ∗ 𝑉𝑖

Total discharge is the sum of the qi : 𝑸 = σ𝒒𝒊• With an interpolation of the velocity between the banks and the first and last verticals


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COMPUTATION OF DISCHARGE WITH CURRENT METERS About the sampling

Enough verticals to have a good sampling of the bed bathymetry

Enough verticals and points per vertical to have a good sampling of the velocity

… but not too long to be in a steady flow..

find a compromise between sampling and duration


Some Rules of thumb :

No general rules !

Try to detail areas with strong gradients of bathymetry or velocity, especially if they contribute

significantly to the total flow

The interval between any two verticals should not be greater than 1/20 of the total width

The discharge of any subsection should not be more than 10% of the total discharge.

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STREAM GAUGING WITH AN ADCP

ADCP : Acoustic Doppler Current Profiler

Ultrasonic measurement (300 à 3000 kHz)

Sonar principle to measure the river bathymetry wetted area

Doppler shift to measure flow velocity

Profiler :

• ADCP mounted on a float, generally pointing down

• Sending an ultrasonic acoustic wave in the water

• Backscatter by particles in suspension in the water

• Analyze of the Doppler shift between the transmitted and the backscatter signals


Q

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HOW AN ADCP MEASURES THE WATER DEPTH

Sonar principle :

Peak of retuned intensity when the echo hit the river bed


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HOW AN ADCP MEASURES THE WATER VELOCITY

Let postulate that the ADCP is not moving

ADCP transmits an ultrasonic pulse in the water

Pulse is backscattered by particles in the water

ADCP received backscattered echo

Analysis of Doppler shift between transmitted and

backscattered pulses velocity of the particles

Basic hypothesis: particles are advected by the water

velocity of the particle = velocity of the water


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BACKSCATTERED PARTICLES

Maximum backscatter for

d=0,4mm if F=1200kHz

d=0,2mm if F=2400kHz

zooplankton and small particles


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Doppler shift radial velocity

Component of velocity in the beam axis

V cos α = C ∆f / f0 with ∆f = f1 − f0

f0 : frequency of the transmitted pulse

f1 : frequency of the backscattered pulse

C : speed of the sound. C depends on the water temperature it is crucial to measure

accurately the water temperature


ADCP

transducer

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V cos α = C ∆f / f0 with ∆f = f1 − f0

f0 : frequency of the transmitted pulse

f1 : frequency of the backscattered pulse

C : speed of the sound. C depends on the water temperature de l’eau it is crutial to

measure accurately the water temperature


ADCP

transducer

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How measuring 3D velocity components (North / East / Vertical components)

Geometric configuration :

2, 3, 4 divergent beams

Measurement of radial velocity on each beam

trigonometric calculation to obtain 3D velocity

• under the assumption that the velocity is homogeneous on the 3 beams


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Stationary ADCP

Measurement of the radial velocity on each beam


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Stationary ADCP



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Stationary ADCP



Beam A Beam B

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Stationary ADCP

Plan view : in the plan of the beams 3-4


1

2

34

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Stationary ADCP



Beam 4 Beam 3

Vwater

Vwater

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Stationary ADCP



Beam 4 Beam 3

V3-4 V3-4

VzVz

• Vwater = V3-4+ Vz

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Stationary ADCP



Beam 4 Beam 3

VzVz

V3-4V3-4


• On Beam 3:

• V3 = V3-4 *sin + Vz*cos

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Stationary ADCP


Beam 4 Beam 3

VzVz

V3-4 V3-4


• On Beam 3:


• On Beam 4 :

•V4 = -V3-4 *sin + Vz*cos


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Stationary ADCP


Beam 4 Beam 3

VzVz

V3-4 V3-4


• On Beam 3:


• On Beam 4 :


V3-4= (V3-V4)/(2*sin )

Vz=(V3+V4)/(2*cos )


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Stationary ADCP


1

2

34

y


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Stationary ADCP


Beam 1 Beam 2

VzVz

V1-2 V1-2


• On Beam 1:


• On Beam 2 :


V1-2= (V1-V2)/(2*sin )

Vz=(V1+V2)/(2*cos )


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Stationary ADCP

Plan view:

• With Beams 1 and 2, one can compute V1-2 and Vz

• With Beams 3 and 4, one can compute V3-4 and Vz

• One can compute 3 components of Vwater

2 measurements of Vz

Difference between those measurements « error velocity »

If strong error velocity, no homogeneity invalidated measurement

1

2

34


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ADCP = Profiler :

Ability to measure a profile of the water currents throughout the water column

“range-gating” the backscattered signal in time :

• ADCP assigns discrete sections of the echo record to distinct sections of the water column depth

cells or bins

• ADCP assigns separate measurements of the three components of water currents to different depth

cells and generates a water-current profile


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UNMEASURED AREAS

ADCP measurement range:

↘ when frequency ↗ :

• TRDI StreamPro 2400 kHz : 6m maxi

• TRDI RioGrande 600 kHz : 60m maxi

↘ when sediment load ↗

Close to the ADCP:

Transducer depth

Distance (time) the emitted sound travels while internal electronics prepare for data

reception and the transducers stop vibrating from the transmission and become quiescent

enough to accurately record the backscattered acoustic energy

Flow disturbance:

• Hydraulic of the flow around the ADCP


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UNMEASURED AREAS

Close to the river bed

« side-lobes » hit the river bed before the main lobe

Shortest distance


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UNMEASURED AREAS



Side-lobe blanking

d = P (1 − cos )

6% for = 20◦

14% for = 30◦

α


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UNMEASURED AREAS



Side-lobe blanking

d = P (1 − cos )

6% for = 20◦

14% for = 30◦

Mesured, but filtered


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UNMEASURED AREAS

Bad bins / bad ensembles

error velocity > threshold

correlation < threshold


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MEASUREMENT OF THE ADCP DISPLACEMENT

The ADCP moves across the river cross-section

It measures the section area (m²)

It measures the velocity distribution (m/s)

The displacement of the ADCP must be measured

Vwater/bed = Vwater/aDcp + VaDcp/bed

Discharge (m3/s)


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MEASUREMENT OF THE ADCP DISPLACEMENT Bottom Tracking:

Based on the Doppler-shift

Measures the Doppler shift of the acoustic pulses reflected from the

streambed

Assuming the streambed is not moving, the measured Doppler shift is

directly related to the velocity of the boat

Bottom-tracking pulses are sent before the water measurement pulses

GPS:

Supplementary equipment


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DISCHARGE COMPUTATION To compute the discharge :

only the angle between the water-velocity and the boat velocity vectors is needed.

where

T is the total time for which data were collected;

D is the total depth;

Vf is the mean water-velocity vector;

Vb is the mean boat-velocity vector;

θ is the angle between the water-velocity vector

and the boat-tracking vector;

dz is the vertical differential depth; and

dt is differential time.


| 65


DISCHARGE COMPUTATION With Bottom Tracking, the ADCP :

measures the water velocity in the beams reference system

Measures it’s displacement in the beams reference system

Same reference system: direct computation

• Compass of the ADCP not used for the discharge computation


| 66


DISCHARGE COMPUTATION With GPS, the ADCP

Measures the water velocity in the beams reference system

Measures it’s displacement in a geographical reference system (North / East)

Need to link the 2 coordinates systems:

• Compass of ADCP used to orient the beams on the magnetic North

• Magnetic declination to find the True North

Prefer Bottom Tracking positioning except :

If the quality of the BT is bad (aquatic vegetation, for example)

If the bed of the river moves (bed load)

• we'll discuss it again later


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UNMEASURED DISCHARGE Areas without measured velocity

Top and bottom blankings

Close to the banks

Missing cells or ensembles

Estimation of the unmeasured areas

Unmeasured areas must be as small as possible

Importance of the choice of the measurement section !


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UNMEASURED DISCHARGE

Invalid cells:

interpolation from neighboring cells

Invalid ensembles:

interpolation from neighboring ensembles


| 69


UNMEASURED DISCHARGE Top and bottom blankings

Extrapolation of vertical velocity profiles

At the top:

• Fitted Power law

• Linear slope

• Constant

Fond :

• Fitted Power law

• « No slip » power law

Power

Power

ADCP measurements

Power

Linear slope Constant

No slip


| 70


UNMEASURED DISCHARGE Select the best extrapolation:

Fitted on the measured velocities

Software « Qrev » of the USGS

Measure carefully the transducer depth

Depends on the instrument, the float, etc…


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UNMEASURED DISCHARGE

Extrapolation of the discharge close to the banks

𝑸𝒃𝒂𝒏𝒌 = 𝑪. 𝑽𝒎. 𝑳. 𝒅𝒎

C bank coefficient (triangle : 0,35, rectangle : 0,91)

Vm closest measured velocity (average on n shore ensembles)

dm closest measured velocity depth

L distance to the bank

River bed River bedIAHR / WMO / IAHS International Streamgauging course

| 72


UNMEASURED DISCHARGE Give it some attention…or not !

Depends on the relative weight of each components of computed discharge

Key point for uncertainty estimation

• Qmeasured / Qtotal > 80% uncertainty ≈ 5-10%

• Qmeasured / Qtotal > 60% uncertainty ≈ 10-15%; give attention to the computed discharge

• Qmeasured / Qtotal < 50% … find an other measurement site (if possible)

ADCP is well adapted for subcritical, quite deep (> 0.6 m) flows


| 73


MOVING BED PROBLEM Bottom-tracking assumes that the bed is not moving

If bedload, the bed moves:

The moving bed bias introduces an apparent upstream boat velocity, which reduces the

calculated downstream water velocity and the corresponding discharge will be biased low.

Moving bed error

Solution: integration of a GPS to measure the velocity of the ADCP :


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MOVING BED PROBLEM If you don’t have a GPS… you can correct the moving bed error !

Stationary moving bed analysis (SMBA)

• Keep the ADCP at a fixed location during 5 minute minimum

• Moving bed BT course goes upstream, travelling an upstream distance D

• Moving bed velocity = D / duration of the test

• Repeat the analysis for different location across the section

Computation of the averaged moving bed velocity over the cross section

D


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MOVING BED PROBLEM If you don’t have a GPS… you can correct the moving bed error !

Loop analysis:

• Round trip across the section

• Departure and arrival exactly at the same location

• Moving bed BT course distorted upstream– Distance D between departure and arrival

• Moving bed velocity = D / duration of the test– Averaged moving bed over the cross-section

• The compass must be well calibrated !

Moving bed corrections are included in the ADCP

softwares


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MOST USED INSTRUMENTS


| 77


MOST USED INSTRUMENTS TRDI StreamPro

2400 kHz / maximum depth: 6 m

For shallow and slow flows

TRDI RioPro

1200kHz for the 4 velocity beams

600kHz for the vertical bathymetric beam

Maximul depth : 25m

Automatic adaptation of the cells size

SonTek S5 and M9

1 vertical bathymetric beam at 0.5 Mhz

4 velocity beams at 3.0Mhz

4 velocity beams at 1.0Mhz

Automatic adaptation of the cells size and of the frequency


| 78


ADCP: EXAMPLES OF DEPLOYMENT Floats

Remote controlled boats

Attached to a holder


| 79


ADCP: RULES OF THUMB1. Before the measurement:

Choose the right measurement section

ADCP system tests and compass calibration

Put the ADCP in the river (check the measured temperature)

2. Evaluation of the cross-section: round trip without recording

Is the section OK for and ADCP gauging ?

3. Measurement of the moving bed: Stationary or Loop analysis

No Moving Bed use BT

Moving Bed use GPS / correct moving bed using SMBA or Loop if no GPS

4. Gauging (finally !)

Go slow and smooth, over a straight transect

Do not get too close to the banks: keep at least two valid cells

Repeat at least 4 transects (WMO)

• France : at least 6 reciprocal transects

• USGS : at least 2 reciprocal transects and a combined duration of all transects of at least 720 s


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ADCP: SOFTWARES TRDI : WinRiver II

For collecting and postprocessing data

SonTek : RiverSurveyor Live

For collecting and postprocessing data

USGS’s Qrev

For quality analysis and postprocessing


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ADCP: SOFTWARES USGS’s Qrev

Quality Analysis / Quality Control

• Green OK / Yellow take care / Red problem


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ADCP: SOFTWARES USGS’s Qrev

Quality Analysis / Quality Control

• Green OK / Yellow take care / Red problem

Estimation of the uncertainty


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STREAM GAUGING METHODS What should you remember?

No single solution: a toolbox of methods for the field hydrologist

Volumetric method very small discharges (< 10L/s)

Dilution method supercritical, very turbulent flows

Velocity-area using current meters subcritical shallow flows

Velocity-area using ADCP subcritical deeper flows

Choice of the method to use depends on :

• River hydraulic

• The site configuration

• Hazardousness, accessibility of the gauging site

• Material available:– Different prices : mechanical current meter = ; ADCP = 30 k€

• …


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STREAM GAUGING METHODS What should you remember?

No single solution: a toolbox of methods for the field hydrologist

Volumetric method very small discharges (< 10L/s)

Dilution method supercritical, very turbulent flows

Velocity-area using current meters subcritical shallow flows

Velocity-area using ADCP subcritical deeper flows

Choice of the method to use depends on :

• River hydraulic

• The site configuration

• Hazardousness, accessibility of the gauging site

• Material available:– Different prices : mechanical current meter = ; ADCP = 30 k€

• …


Documents

Stream gauging techniques - RiverFlow 2018 · 2018-09-13 · STREAM GAUGING TECHNIQUES Presentation based on the WMO Manual on streamgauging (2010), Volume II Chapter 2, with additional