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