Hydrological Services – HydroTablet
25-Feb-15 Issue 1.00 Page 21 of 22 ©Hydrological Services P/L
HS reserve the right to modify this document at any time
Mean Section Method (From Australian Standard AS3778.3.1 ISO 748)
The cross section is regarded as being made up of a number of segments, each bounded by
two adjacent verticals as shown in the following diagram.
The discharge of each segment is calculated as :
Discharge = Mean velocity x Mean depth x Width
of Segment of Segment of Segment of Segment
q
(0-1)
= (v1 x Bank Factor) x (d0+d1)/2 x b0
q
(1-2)
= (v1 + v2)/2 x (d1+d2)/2 x b1
q
(2-3)
= (v2 + v3)/2 x (d2+d3)/2 x b2 etc…
where
Mean velocity = sum of mean velocity of / 2
of Segment bounding verticals
= (v1 + v2) / 2
Mean depth = sum of depth of / 2
of Segment bounding verticals
= (d1 + d2) / 2 (Note d0 = Depth at Water Edge)
The total discharge is obtained by adding the discharge from each segment.
q
(total)
= q
(0-1)
+ q
(1-2)
+ q
(2-3)
+ ………
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