Runoff is
seen as an output from a catchment. Unlike other hydrological processes, we can
measure the runoff reliably by determining the streamflow. The discharge may be
measured directly, but to enable continuous monitoring, two-step procedure is
preferred.
The water
surface elevation, namely stage is the first data we need. We may either
measure it manually using staff gauges, or automatically by using float-gauge
recorder and bubble gauge. The output from stage measurement is stage
hydrograph.
Next, we
need to determine the flow velocity. This can be accomplished by using current
meters. There are two types of current meters, namely vertical and horizontal
axis meters. A current meter needs to be calibrated prior to measurement, and
it is usually done using a towing tank.
The stream
discharge can be calculated using area-velocity method. The cross section of
stream is divided into strips by verticals, and the average velocity for each
of them is determined with the aid of current meters. Then, we can calculate
the segmental discharge for each strip, and eventually the total discharge for
the cross section.
With stage and discharge data, we may develop a stage-discharge relationship for a stream. This relationship allows us to obtain continuous streamflow data without spending too much time and cost.
The following show the information related to streamflow measurement. Watch the video above for full details.
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