SonTek – a Xylem brand
FlowTracker2 User’s Manual (January 2019)
71
This method is used by the U.S. Geological Survey (USGS), the primary U.S.
government agency responsible for river discharge monitoring.
Equation 5:1 - Mid-Section Method
=
+
+
Edge Open water Open Water
where, is the average velocity in the vertical or at the station,
d is the water depth measured at the station,
b is the location of the station.
The application of the Mid-Section equation within a measurement section is graphically
shown in Figure 5:2. The principle of the Mid-Section method is highlighted in the figure
below where the panel width (W
2)
is calculated based on the station locations (L
2
) with
the station as the center of the panel.
Figure 5:2 - Mid-Section Method
There are few special cases to consider when applying the Mid-Section method in
calculating of total discharge.
a) Edges
i). Edge can be either the Left Bank or Right Bank,
ii). Edge calculations are handled differently from stations in open water with
reference to the first component of Equation 5:1,
iii). The mean velocity at the edge is scaled from the adjacent station by a user
defined correction factor (CF),
iv). Edge water depth of zero will result in zero flow for the edge calculation.
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