Hydrological Services – HydroTablet
25-Feb-15 Issue 1.00
Page 20 of 22
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Appendix C Discharge Calculation Methods
In both methods the mean water velocity in each vertical is calculated by using the weighting
table shown in Appendix A. For example, if 3 water velocities are measured in a single
vertical, they would be measured at depths of 0.2D, 0.6D and 0.8D. The mean velocity of this
vertical would therefore be :
V
mean
= (V
0.2D
x 0.25) + (V
0.6D
x 0.50) + (V
0.8D
x 0.25)
The following sketch shows a typical discharge with depth measurements d0, d1, d2, d3, …
taken at each vertical (note d0 is the depth at the bank, usually zero, but may be non zero) – and
the distance between the verticals b0, b1, b2, b3,…..calculated from the distance from the
reference point - and the mean water velocity v1, v2, v3, …. calculated for each vertical.
These measurements are then used to calculate the discharge using either the Mean Section
method or the Mid Section method.
*** PLEASE NOTE ***
Each method will yield slightly different results, as described on the following pages.
