3.1 Measurement of discharge
Ming Yong River itself does not have a stream gauging station, hence the
discharge was manually measured and calculated (Figure S2). Flow
velocity and water depth were measured during each sampling event using
the float method (Figure S2a) and meter rule (Figure S2b) respectively.
The cross-sectional area of the channel was measured in February 2014,
September 2015, November 2016, and April 2017 (Figure S2c) because of
danger when conducting measurements during the high-flow summer. To
calculate the cross-sectional area, the width of the river channel under
bankful conditions was first measured using a tape measure. The width
was divided into 20 transacts and the height of the tape measure to the
riverbed was measured at each transact. The cross-sectional area was
thus obtained by the sum of all transacts (height*width of transact).
Discharge was then calculated using the following formula:
Q = A*V
where Q is water discharge (in m3/s), A is the
cross-sectional area of the river channel (in m2), and
V is the flow velocity (in m/s).