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Measurements for
water
A.M.J. Coenders
Waterbalans: Discharge streamflow
Discharge & Streamflow measurements
-Point velocity & velocity area method
∫ ∑ ∆⋅≈⋅=A n
ii AudAuQ
{ }8.06.02.03/1 uuuu ++=
{ }8.06.02.0 24/1 uuuu +⋅+=
• Three point measurement (measured away from the water surface):
or
Figure 5.3: Influence number of points in the verticalFigure 5.4: Influence number of verticals in the cross-section
Pendulum
AuCF NN ⋅⋅⋅⋅= 22/1 ρ
tan Nbody
F
Gϕ =
bodyϕ
G
bodytcoefficienu ϕtan2
⋅=
hence
Cub propellor
Cub and propeller current meter
Wading
Cable way
Bridge support
U = K x B x vwater x L
Electromagnetic streamflow
Electromagnetic streamflow measurements (pipe flow)
**
U LQ K
B=
Schematic view of electromagnetic gauge with coil installed below channel bed
c
vFF sd ⋅=
Fd is the Doppler shift frequencyFs is the frequency of the sound under stagnant conditionv is the relative velocity between the sound source and the sound receiver [m/s]c is the speed of sound [m/s]
Acoustic Doppler Current ProfilerADCP
The principles of doppler
c
vFF sd ⋅⋅= 2
Ac
vFF sd cos2 ⋅⋅⋅=
in water:
Transmitting and receiving:
Component parallel to flow:
detected frequency increases for objects moving toward the observer
Pro’s: -continuous -almost complete vertical-velocity in 3-dimensionsCons:-Deep water-Expensive, trained personnel
ADCP
Floats:
Floats:Scheldt fieldwork, tidal movement
Integrating rising bubble technique
Dwv
w r
L DT
vv= =
w rq v D v L= =
rQ v A=
•Integrating rising •bubble technique
L
L
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