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The flow velocity is measured in verticals at distances w~i~ w_i , i=1,m from a reference point on the river bank. The water depth at vertical i is denoted by d~i~ d_i and the average flow velocity in that vertical by , see the underneath figure.

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Discharge computation

The discharge q~i~ q_i in section i-1 to i is computed from:

• Mean-section method:
  
• Mid-section method:
  
  for i= 1,n+1, with:
  d~o~ d_o = d~nd_n+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~ h_Q is computed from:

• if |h~1~ h₁ - h~2~ h₂ | < 0.05 by: h~Q~ h_Q = 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~ v_p 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~ v_i = v~vv_v,i~ _i . sin a~i~a_i
• v~i~ v_i =

where:

v~i~ v_i = point velocity in vertical i
v~v v_v,i~ _i = combined boat and stream velocity
a~i~ a_i = angle between current meter and section line
v~b v_b,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~ d_i = flow depth at vertical i
wd = current meter depth

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