Universitā degli studi di Roma “Tor Vergata” - ART - TORVERGATA ...

more conservative, but for the rough bed channel the second one is more conservative for a
factor about 2 - 3.
Rougher the bed, quicker the tracer concentration moves towards the bed and from the
variable parameter model the best location for the dosage is slightly closer at the surface (Fig.
2.2.5).
1994).
Fig. 2.2.5: Concentration profiles downstream from a steady transverse sources (from Rutherford,
The vertical diffusion can be estimated experimentally dosing continuously a
conservative tracer with a transverse system and the mixing problem solution for an unbounded
channel is:
c =
b
m
4πe
y
xu
x
⎡ u x ( y − yo
)
exp⎢−
⎢⎣
4ey
x
2
⎤
⎥
⎥⎦
Eq. 2.2-29
where m is the tracer mass dosed [g]; b is the water width [m] and yo is the distance from the
channel bottom location of the tracer source [m].
A plot of
b
m
e 4π
y x xu
vs.
1 allows to estimate ey for each x provide ux, b and m. ey
x
value estimated in this way is 10-20% higher then the true value, but if it is used in the constant
mixing model this overestimation is cancelled out.
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