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The flow velocity is measured in verticals at distances w~i~ wi , i=1,m from a reference point on the river bank. The water depth at vertical i is denoted by d~i~ di and the average flow velocity in that vertical by , see the underneath figure.
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Discharge computation
The discharge q~i~ qi in section i-1 to i is computed from:
- Mean-section method:
- Mid-section method:
for i= 1,n+1, with:
d~o~ do = d~ndn+1~ 1 = 0
The total discharge then follows from:
If the water levels at the beginning and at the end of the measurements are denoted by h~1~ h1 and h~2~ h2 respectively, then the representative water level h~Q~ hQ is computed from:
- if |h~1~ h1 - h~2~ h2 | < 0.05 by: h~Q~ hQ = ½ (h~1~ h1 + h~2~ h2 )
- if |h~1~ h1 - h~2~ h2 | ³0.05 by:
To estimate the average velocity in a vertical in the cross-section from point measurements v~p~ vp at p * flow depth, following methods are available in hymos: (iso748 and iso/tr7178):
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Following methods are distinguished to compute the stream velocity in vertical i :
- v~i~ vi = v~vvv,i~ i . sin a~i~ai
- v~i~ vi =
where:
v~i~ vi = point velocity in vertical i
v~v vv,i~ i = combined boat and stream velocity
a~i~ ai = angle between current meter and section line
v~b vb,i~ i = boat velocity at vertical i
The stream velocity is measured at a constant depth wd below the water surface. This velocity is transformed into the average velocity in the vertical by assuming a power law velocity profile:
with:
= average stream velocity in vertical i
c = power of power law velocity profile (5 £c £7)
d~i~ di = flow depth at vertical i
wd = current meter depth
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