

Difference between revisions of "How to measure stream flow rate"

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==Flow ==
==Flow ==
Flow is the total volume of a fluid that flows past a fixed point in a river or stream over time. It is comparable to the speed at which a volume of fluid travels. Volumetric flow rates can be measured in various units such as:
*cubic feet/sec (cfs)
*cubic feet/sec (cfs)

Revision as of 20:51, 10 December 2009

Engr115 Page in Progress
Warning: Possibly Inaccurate Content




  • liters/sec
  • cubic feet/sec (cfs)
  • gallons/min (gpm)
  • cubic meters/sec

This page focuses on using hand methods to find the flow of streams and small rivers but can also be used to find the flow through pipes, sewage systems, and household appliances. People use flow data for Microhydro systems, waste-water information, settling rates, water table statistics, etc. To find the flow of larger water bodies such as dams or major rivers, meters are used. Meters are described briefly in this page. [1]

Measuring Flow

There are numerous ways to measure flow rate which include:

Bucket method

The Bucket method is a simple way to measure the flow rate using household items. It requires a stopwatch, a large bucket, and two to three people.

  1. Measure the volume of the bucket or container.
  3. With the stopwatch, time how long it takes the waterfall to fill the bucket with water. It is important to start the stopwatch simultaneously with the bucket being filled and to stop the stopwatch when the bucket fills therefore more than one person is needed here. Also note that the bucket should not be filled by holding it below the surface of the stream because it is not the true flow rate.
  4. Record the time it takes to fill the bucket.
  5. Repeat steps two and three about six or seven times and take the average. It is also a good idea to do a few trial runs before recording any data so that one can get a feel for the timing and measurements required.

Here is an example using data found for the flow rate of the Jolly Giant Creek on Humboldt State Universitygrounds:

Trial Number Time (seconds) Bucket Volume (gallons)
1 13.2 5
2 14 5
3 14.5 5
4 13 5
5 13.4 5
6 13.1 5

Using this data, the volumetric flow rate (Q) is equal to the volume of the bucket (v) divided by the average time (t).
so t=13.5 seconds
and v= 5 gallons

Q=5 gallons/ 13.5 seconds
The flow rate Q= 0.37 gallons per second
or 22.2 gallons per minute

Float method

Finding the flow rate using a float and meter stick.


  2. Using a meter stick, or some other means of measurement, measure the depth of the stream at equal intervals along the width of the stream. This method is similar to hand calculating a Riemann sumfor the width of the river.
  6. Repeat step five 5-6 times and determine the average time taken for the float to travel the stream.
  8. The velocity found in step 7 must be multiplied by a friction correction factor. Since the top of a stream flows faster than the bottom due to friction against the stream bed, the friction correction factor evens out the flow. For rough or rocky bottoms, multiply the velocity by 0.8. For smooth, muddy, sandy, or smooth bedrock conditions, multiply the velocity by a correction factor of 0.9. [3]


An example of a v-notch weir

Weirs are small dams that can be used in measuring flow rate for small to medium sized streams (a few meters or wider). They allow overflow of the stream to pour over the top of the weir, creating a waterfall, as seen in figure 4. Weirs increase the change in elevation making the streamflow more consistent which makes flow rate measurements more precise. However, it is very important that all the water in the stream be directed into the weir for it to accurately represent the stream flow. It is also important to keep sediment from building up behind the weir. Sharp crested weirs work best. [4] There are many different types of weirs which include broad crested weirs, sharp crested weirs, combination weirs, V-notch weirs and minimum energy loss weirs. [5]



Further reading


  1. Source of Information -
  2. Source of Information -
  3. Source of Information -
  4. Source of information -
  5. Source of information -
  6. Source of information -
  7. Source of information -
  8. Source of information -
  9. Source of information -

Beth's Comments

  • L1 - Check out C-12. Can you bring in an image to draw the reader into the first screen?
  • Does Lonny want you to discuss WHY we are interested in stream flow rates? For Appropedia... there might be interest for microhydro installations. Also, your page seems to focus on flow rate for smaller water bodies (streams) and not rivers. If my interpretation is correct, you could state this information at the beginning of your page.
  • Review Ben's peer review comments for additional questions to answer. I had similar questions.
  • Your table of contents seems straight forward. There is high tech equipment available for flow measurements, but it is not so appropriate tech oriented. See if Lonny wants you to cover other methods.
  • I would avoid headings that are questions. Instead, use statements.
  • read through all the editing codes.
  • See W-1 - avoid "get rid of"
  • Be sure to cite the source of your data
  • Refer to tables, using Table numbers. (C5)
  • Check for spelling errors... I saw a float when I think you meant flow. ... meadium....
  • Use this reference, as it explains the standard protocol Be sure to check the float method in this reference, as I think your description of the float method does not agree
  • I think you should provide an example for the float method as well. Your example idea is very helpful and clarifies the instructions.
  • Check that you are using correct conventions (e.g. C3,C5,C6,C8,C9)
  • Vortex meter is not so relevant to stream flow measurement. Can you clarify how a current meter and a pygmy meter are different?
  • Can you include an example calculation for a weir?
  • See the reference for how to use a flow meter.
  • Appears that Monica is doing most of the editing?