What data is collected?
To understand the amount of water in our rivers, lakes, estuaries, or channels we measure:
- stream level
- storage level
- streamflow
- directly measured flow
You will also find parameters such as:
- mean daily flow, an old manual method.
- depth below water surface, accompanying water quality samples.
Understanding Surface Water Parameters
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Streamflow, or discharge, is the volume of water moving down a stream or river per unit of time, commonly expressed in megalitres per day (ML/d).
Because stream discharge cannot be measured directly, it must be computed from variables that can be measured directly, such as stream depth, stream width, and streamflow velocity. This is generally done by multiplying the cross-sectional area of water in the stream channel by the average velocity of the water in that cross section.
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Stream water level is the elevation of water surface at a particular time and date, measured relative to a specified datum.
We use sensors such as bubblers, shaft encoders, pressure sensors or radar to relate pressure to known heights in the stream bed. Gauge boards are used to verify the sensor data.
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Storage Water level is the elevation of water surface in a water storage at a particular time and date, measured relative to a specified datum, typically the Australian Height Datum (AHD).
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Where permanent flow meters or acoustic doppler technology measure and record streamflow directly in near real time, we call the parameter 'directly measured flow'. This measurement type is used where conditions make a stage-discharge rating table impractical, such as in pipes or waterways with tidal influence. This data has high precision and may help determine the direction of water movement in estuaries.
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Mean daily flow is the name given to an old technique, where a site is visited in person each day to manually read the gauge board and relate river height to a stage discharge relationship to calculate streamflow or discharge. You will find any of our long-term historic sites have this data in early years and then move to more modern technology. This manual process is less accurate than our more modern techniques.
If you are looking at streamflow don't forget to click all available parameters to see the full flow record.
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Depth below water surface is used to indicate the depth at which a water quality measurement is taken to give context for analysis. It is especially useful when measurements are taken at different depths. Since water quality often changes within the stream profile this can help interpretation and give meaning to what you are seeing.
Reviewed 28 August 2024