[Infographics]

Measuring surface runoff:

Stream gauge

Read:

http://quebec.hwr.arizona.edu/classes/hwr201/infographics/2016-3-8-stream-gauge/fs2011-3001.pdf

https://www.usgs.gov/special-topic/water-science-school/science/how-streamflow-measured

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Types of river gauges.

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Staff gauge. It is a simple ruler installed permanently in the stream bed. This type of stream gauge is often installed together with automatic gauges, and is used for periodic checking of automatic measurements.

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Stream gauge for automatic reading of water level. A pipe connects the river with measuring instruments inside the building. The building may also house a computer and transmitting devices to send data to a server for real-time applications.

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Stream gauge for automatic reading of water level. A pipe connects the river with measuring instruments inside the building. The building may also house a computer and transmitting devices to send data to a server for real-time applications.

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Stream gauge for automatic reading of water level. A pipe connects the river with measuring instruments inside the building. The building may also house a computer and transmitting devices to send data to a server for real-time applications.

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Stream gauge for automatic reading of water level. A pipe connects the river with measuring instruments inside the building. The building may also house a computer and transmitting devices to send data to a server for real-time applications.

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Example of stream gauge.

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Example of stream gauge.

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Example of stream gauge.

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Example of stream gauge.

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Example of stream gauge.

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USGS stream gauges in the US. Colors code stream level for easy visual inspection of data.

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Water level data plotted as a function of time is called “hydrograph”. Hydrographs are produced using stream gauges.

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Stream flow forecast based on previous stream gauge measurements. Such data are used in forecasting floods in real time.

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Simple method for measuring flow in a stream. Floaters are dropped at start line and the time to the end line is measured. From the measured time and the distance between the lines the velocity of the floaters is computed, and then the average velocity of the water (this requires a correction factor that may or may not be known).

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Simple method for measuring flow in a stream. Floaters are dropped at start line and the time to the end line is measured. From the measured time and the distance between the lines the velocity of the floaters is computed, and then the average velocity of the water (this requires a correction factor).

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The weir method that is useful where a weir structure is present. The idea here is to look at the shape of the water flowing through the weir (in a way similar to flow in a pipe or in a garden hose).

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This is similar to the floater method, but the velocity and flow are measured with a flow meter rather than with a floater and stop watch. Velocity can be measured at different depths and then averaged over those depths. This will give a better measure of flow rate than that from the floaters method.

Rating curves

Rating curve is a function that relates water level (stage) to flow rate (discharge). Water level is easy to measure. Flow rate is not. The rating curve is established once, from simultaneous measurements of stage and water level at a few times. After that, only water level is measured, and flow rate is computed using the rating curve. That’s how most stream gauges work. See example on the next page.

Note: rating curves can be plotted in two different ways – with stage on the horizontal axis or with flow rate on the horizontal axis.

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Example of time series of water stages and calculated flow rates.